Pathophysiology of hyponatremia after transsphenoidal pituitary surgery

Incidence of postoperative hyponatremia after endoscopic endonasal pituitary transposition for skull base pathologies

PURPOSE

Pituitary transposition is a novel surgical approach to access the retroinfundibular space and interpeduncular cistern. Few studies have evaluated post-surgical outcomes, including incidence of hyponatremia, following pituitary transposition.

METHODS

This is a retrospective study including 72 patients who underwent endoscopic endonasal surgery involving pituitary transposition for non-pituitary derived tumors over a decade at the University of Pittsburgh Medical Center. Anterior pituitary deficiencies and replacement therapy, tumor pathology and pre-operative serum sodium (Na) were recorded. Na was assessed at postoperative day 1, 3, 5, 7, and 10. Anatomical/surgical parameters included sellar height, sellar access angle to approach the tumor, and cranial extension of the tumor above the sellar floor (B) compared to the height of the gland (A) (B/A). T-test (normally distributed variables) and Wilcoxon rank-sum test (not-normally distributed) were applied for mean comparison. Logistic regression analyzed correlations between anatomical/surgical parameters and postoperative hyponatremia.

RESULTS

55.6% of patients developed post-operative transient hyponatremia. Two patients (5%) developed severe hyponatremia (sodium level < 120 mmol/L). Eleven (15.3%) patients required desmopressin replacement immediately post-operatively, and 2 other patients needed desmopressin after discharge and after sodium nadir developed. Hyponatremia was inversely associated with sellar access angle (p = 0.02) and the tumor cranial extension above the sellar floor showing a trend towards significance (p = 0.09).

CONCLUSION

More than half of patients who had pituitary transposition developed transient hyponatremia. Hyponatremia was more common in those with narrower sellar access angle and smaller cranial extension of the tumor above the sellar floor. Anatomical/surgical parameters may allow risk-stratification for post-operative hyponatremia following pituitary transposition.

Copeptin and the syndrome of inappropriate antidiuresis (SIAD) after pituitary transsphenoidal surgery

OBJECTIVE

This study evaluates the predictive value of copeptin for syndrome of inappropriate antidiuresis (SIAD) postpituitary transsphenoidal surgery (TSS).

DESIGN

Data from 133 consecutive patients undergoing TSS (November 2017-October 2022) at Oxford University Hospitals NHS trust are presented in this retrospective study.

METHODS

Logistic regression (LR) and receiver operating characteristic (ROC) curves were performed to evaluate the diagnostic utility of copeptin. The Mann-Whitney U test was used to compare copeptin levels between the SIAD and no SIAD groups.

RESULTS

Fourteen patients (10.8%) developed SIAD. Copeptin was available in 121, 53 and 87 patients for Days 1, 241 and 8 post-TSS, respectively. LR for Day 1 copeptin to predict SIAD gave an odds ratio (OR) of 1.0 (95%CI 42 0.84-1.20, p = .99), area under-ROC curve (AUC) was 0.49; Day 2 copeptin OR was 0.65 (95%CI 0.39-1.19, 43 p = .77), AUC was 0.57 LR for Day 1 sodium to predict SIAD gave an odds ratio (OR) of 1.0 (95%CI 0.85-1.21, p = .99), AUC was 0.50.

CONCLUSIONS

In conclusion, our data provide no evidence for copeptin as a predictive marker for post-TSS SIAD.

Development and validation of a nomogram for assessment postoperative sodium disturbance in PAs patients: a retrospective cohort study

Background

Pituitary adenomas (PAs) are neuroendocrine tumors located in the sellar region. Surgery, being the primary treatment option for most PAs, is known to cause disruptions in sodium metabolism.

Objective

To develop and validate a nomogram for assessment the incidence of postoperative sodium disturbance (SD) in patients with PAs.

Methods

In this retrospective study, 208 patients with PAs who underwent resection surgery between 2013 and 2020 were included. Various demographic characteristics, clinical features and laboratory data were analyzed as potential predictors of postoperative sodium disturbance (SD). LASSO regression were used to identify independent preoperative variables associated with SD. Logistic regression was employed to calculate odds ratios (ORs) and 95% confidence intervals (CIs). A nomogram was constructed to visualize these results and evaluated using metrics such as the area under the curve (AUC) for discrimination, the Hosmer-Lemeshow test for calibration and decision curve for usefulness assessment.

Results

The incidence of SD was 44.23% (92 cases out of 208). Six preoperative factors, including sex, types of PAs, phosphocreatine kinase (CK), serum iron (Fe), free fatty acids (NEFA) and mean corpuscular volume (MCV), were identified for constructing a predictive nomogram. The nomogram showed high accuracy, with AUC values of 0.851 (95% CI [0.799-0.923]) and 0.771 (95% CI [0.681-0.861]) in the training and validation datasets, respectively. Calibration assessment and decision curve analysis confirmed its good agreement and clinical utility.

Conclusion

A practical and effective nomogram for predicting SD after PAs surgery is presented in this study.

Fluid Restriction Reduces Delayed Hyponatremia and Hospital Readmissions After Transsphenoidal Surgery

CONTEXT

Postoperative hyponatremia leads to prolonged hospital length of stay and readmission within 30 days.

OBJECTIVE

To assess 3 strategies for reducing rates of postoperative hyponatremia and analyze risk factors for hyponatremia.

DESIGN

Two retrospective analyses and 1 prospective study.

SETTING

Tertiary referral hospital.

PATIENTS

Patients undergoing transsphenoidal surgery for pituitary adenomas and other sellar and parasellar pathologies.

INTERVENTION(S)

Phase 1: no intervention. Phase 2: postoperative day (POD) 7 sodium testing and patient education. Phase 3: fluid restriction to 1 L/day on discharge in addition to phase 2 interventions.

MAIN OUTCOME MEASURES

Rates of early and delayed hyponatremia and readmissions. Secondary outcomes were risk factors for hyponatremia and readmission costs.

RESULTS

In phase 1, 296 patients underwent transsphenoidal surgery. Twenty percent developed early and 28% delayed hyponatremia. Thirty-eight percent underwent POD 7 sodium testing. Readmission rates were 15% overall and 4.3% for hyponatremia. In phase 2 (n = 316), 22% developed early and 25% delayed hyponatremia. Eighty-nine percent complied with POD 7 sodium testing. Readmissions were unchanged although severity of hyponatremia was reduced by 60%. In phase 3 (n = 110), delayed hyponatremia was reduced 2-fold [12.7%, relative risk (RR) = 0.52] and readmissions 3-fold [4.6%, RR = 0.30 (0.12-0.73)]; readmissions for hyponatremia were markedly reduced. Hyponatremia readmission increased costs by 30%.

CONCLUSIONS

Restricting fluid to 1 L/day on discharge decreases rates of delayed hyponatremia and readmissions by 50%. Standardized patient education and POD 7 sodium testing decreases severity of hyponatremia but does not impact readmission rates. These protocols should be considered standard practice for patients undergoing transsphenoidal surgery.

Predictors of Delayed Hyponatraemia After Surgery for Pituitary Tumour

Delayed hyponatraemia(DH) is a common complication following trans-sphenoidal surgery(TSS) for pituitary tumour. We evaluated the prevalence of DH following TSS, and assessed the factors associated with DH, including early post-operative diabetes insipidus(EPDI). This retrospective study included 100 TSS for pituitary tumours in 98 patients, over a period of 26 months. Subjects were divided into two groups: those who developed hyponatraemia and those who did not develop hyponatraemia, during post-operative days 4 to 14. The clinical characteristics and peri-operative parameters were compared between the two groups, to identify factors predicting DH. The mean age of the patients was 42.0±13.6 years, 58 (59%) were females and 61 (61%) had functional tumours. Thirty-six patients(36%) developed DH following TSS of whom majority(58%) were diagnosed on post-operative days 7 and 8; only 8/36 (22%) were symptomatic. Syndrome of inappropriate antidiuretic hormone secretion(SIADH) was found to be the most common aetiology of DH. On logistic regression analysis, intra-operative cerebrospinal fluid(CSF) leak (OR 5.0; 95% CI 1.9-13.8; p=0.002), EPDI (OR 3.4; 95% CI 1.3-9.2; p=0.015) and peri-operative steroid use (OR 3.6; 95% CI 1.3-9.8; p=0.014) were found to be significantly associated with DH. In conclusion, EPDI, intra-operative CSF leak and peri-operative steroid use were significant predictors of DH. EPDI predicts moderate to severe hyponatraemia with 80% specificity but has low sensitivity(47%). As most patients have asymptomatic hyponatraemia, serum sodium measurement on POD 7 to 10 would be helpful to identify DH in patients at increased risk.

Machine learning models predict delayed hyponatremia post-transsphenoidal surgery using clinically available features

PURPOSE

Delayed hyponatremia (DHN), a unique complication, is the leading cause of unexpected readmission after pituitary surgery. Therefore, this study aimed to develop tools for predicting postoperative DHN in patients undergoing endoscopic transsphenoidal surgery (eTSS) for pituitary neuroendocrine tumors (PitNETs).

METHODS

This was a single-center, retrospective study involving 193 patients with PitNETs who underwent eTSS. The objective variable was DHN, defined as serum sodium levels < 135 mmol/L at ≥ 1 time between post operative days 3 and 9. We trained four machine learning models to predict this objective variable using the clinical variables available preoperatively and on the first postoperative day. The clinical variables included patient characteristics, pituitary-related hormone levels, blood test results, radiological findings, and postoperative complications.

RESULTS

The random forest (RF) model demonstrated the highest (0.759 ± 0.039) area under the curve of the receiver operating characteristic curve (ROC-AUC), followed by the support vector machine (0.747 ± 0.034), the light gradient boosting machine (LGBM: 0.738 ± 0.026), and the logistic regression (0.710 ± 0.028). The highest accuracy (0.746 ± 0.029) was observed in the LGBM model. The best-performing RF model was based on 24 features, nine of which were clinically available preoperatively.

CONCLUSIONS

The proposed machine learning models with pre- and post-resection features predicted DHN after the resection of PitNETs.

Delayed postoperative hyponatremia in patients with acromegaly: incidence and predictive factors

PURPOSE

Delayed postoperative hyponatremia (DPH) is a unique complication of transsphenoidal surgery (TSS) in pituitary tumors. Growth hormone (GH) enhances renal sodium reabsorption; however, the association between postoperative GH reduction and DPH in acromegaly is unclear. This study was performed to clarify the incidence of and the predictive factors for DPH in patients with acromegaly who underwent TSS.

METHODS

Ninety-four patients with active acromegaly were examined retrospectively. During the postoperative course, patients with serum sodium levels ≤ 134 mEq/L were classified into the DPH group. We compared basic clinical characteristics, tumor characteristics, and preoperative and postoperative examination findings between the DPH and non-DPH groups.

RESULTS

DPH occurred in 39 patients (41.5%), and the lowest serum sodium levels were generally observed during postoperative days (PODs) 7-9. They needed a 3-day longer hospital stay than those without DPH. The DPH group had lower preoperative body weight and body mass index. In addition, a transient increase in body weight during PODs 5-7 occurred with a transient decrease in urinary volume in the DPH group. Preoperative and postoperative GH and insulin-like growth factor-1 levels did not differ between the two groups.

CONCLUSION

The findings suggested that lower preoperative weight and a postoperative transient gain in body weight are associated with an increased risk of DPH in acromegaly patients undergoing transsphenoidal surgery.

The Potential of Self-Assessment and Associated Factors for Delayed Symptomatic Hyponatremia Following Transsphenoidal Surgery: A Single Center Experience

(1) Background: We identified screening parameters and associated factors for delayed, symptomatic hyponatremia (DSH) following inpatient discharge after transsphenoidal surgery (TSS). (2) Methods: In this prospective, monocentric study, 108 patients who underwent TSS for pituitary pathologies were included, provided with a questionnaire and instructed to document urine specific gravity, fluid intake/urine output, body weight and clinical symptoms for every of five days following discharge from hospital. (3) Results: The overall incidence of DSH within 14 days following discharge from the hospital was 14.8% (n = 9). Symptomatic patients presented on average 8.6 days after surgery. Mild DSH was present in 3.3% of the patients, moderate in 1.6% and severe hyponatremia in 9.8% of patients. Female sex (p = 0.02) and lower BMI (p = 0.02), as well as nausea (66.7%; p < 0.01) and emesis (33.3%; p < 0.05), were associated with DSH. A significant weight delta between morning and afternoon weight two days before the event of DSH between both groups (1.26 kg (n = 5) vs. 0.79 kg (n = 52), p < 0.05) was detected. (4) Conclusions: Handing out a symptom questionnaire at discharge seems to be an easy and feasible tool for the detection of DSH after hospital discharge.

Disorders of Salt and Water Balance After Pituitary Surgery

Transsphenoidal surgery is the first-line treatment for many clinically significant pituitary tumors and sellar lesions. Although complication rates are low when performed at high-volume centers, disorders of salt and water balance are relatively common postoperatively. Both, or either, central diabetes insipidus (recently renamed arginine vasopressin deficiency - AVP-D), caused by a deficiency in production and/or secretion of arginine vasopressin, and hyponatremia, most commonly secondary to the syndrome of inappropriate antidiuresis, may occur. These conditions can extend hospital stay and increase the risk of readmission. This article discusses common presentations of salt and water balance disorders following pituitary surgery, the pathophysiology of these conditions, and their diagnosis and management.

Multidisciplinary Postoperative Care Pathway to Reduce Readmissions following Endoscopic Transsphenoidal Pituitary Surgery: Improving Quality of Patient Care

Background  Thirty-day unplanned readmission following endoscopic transsphenoidal pituitary surgery (ETPS) occurs in up to 14% of patients. Delayed hyponatremia is one of the most common causes, accounting for 30% of readmissions and often occurs within 1 week of surgery. The authors' prior retrospective review identified endocrinology follow-up as protective factor. Objectives  Implementation of a multidisciplinary postoperative care (POC) pathway: (1) to reduce 30-day hospital readmissions following ETPS and (2) improve inpatient and outpatient coordination of care with endocrinologist. Methods  This study is a single institution temporal cohort study of patients prior to (control cohort) and after implementation of the POC pathway (intervention cohort). The POC pathway utilized postdischarge 1 to 1.5 L/d fluid restriction, postoperative days 5 to 7 serum sodium, and endocrinology follow-up within 1 week of discharge to stratify patients into tiered hyponatremia regimens. Results  A total of 542 patients were included in the study, 409 (75%) in the control cohort and 133 (25%) in the intervention cohort. All-cause readmission was significantly reduced following implementation of the POC pathway (14 vs. 6%, p  = 0.015). Coordination with endocrinologist significantly increased in the inpatient (96 vs. 83%, p  < 0.001) and outpatient (77 vs. 68%, p  = 0.042) settings. Patients who were not in the POC pathway had the highest risk of readmission (odds ratio: 2.5; 95% confidence interval: 1.1-5.5). Conclusion  A multidisciplinary POC pathway incorporating endocrinologist in conjunction with postdischarge weight-based fluid restriction and postoperative serum sodium levels can safely be used to reduce 30-day readmissions following ETPS.

Impact of surgical factors on delayed hyponatremia in patients with nonfunctioning pituitary adenoma after endonasal endoscopic transsphenoidal procedure

PURPOSE

Delayed hyponatremia can occur after pituitary surgery, resulting in prolonged hospitalization. However, the influence of surgical factors after such a procedure has not been well established. The impact of surgery and related factors on delayed hyponatremia was investigated.

METHODS

This was a retrospective analysis of 137 consecutive patients who underwent transsphenoidal surgery for a nonfunctioning pituitary adenoma between 2008 and 2019. Preoperative (demographics, comorbidities), intraoperative (resection extent, operation time, blood loss volume, cerebrospinal fluid leak, tumor consistency), and postoperative [hematoma, meningitis, diabetes insipidus (DI), hormonal assessment] data were collected, with statistical analysis of each factor performed.

RESULTS

Among the 137 patients, delayed hyponatremia occurred in 31 (22.6%). Multivariate analysis revealed that those with hypertension had a significantly higher likelihood of avoiding delayed hyponatremia (p = 0.004). Although no correlations of direct surgical factors with delayed hyponatremia were found, multivariate analysis of indirect surgical factors showed that presence of a firm tumor, transient DI, and meningitis were significantly associated with delayed hyponatremia (p = 0.014, 0.001, and 0.047, respectively). There was also a significant association of severe hyponatremia with appearance of symptoms (p = 0.002).

CONCLUSION

There was a tendency for hypertension to be associated with delayed hyponatremia avoidance, with indirect surgical factors including tumor consistency, transient DI, and meningitis found to have an influence on delayed hyponatremia. It was concluded that attention should be given to non-hypertensive patients with a firm tumor, transient DI, or meningitis after pituitary surgery, as delayed hyponatremia may occur.

Postoperative complications after endoscope-assisted transsphenoidal surgery for pituitary adenomas: a case series, systematic review, and meta-analysis of the literature

PURPOSE

Endoscope-assisted transsphenoidal surgery over the last few years has led to more radical excision of pituitary adenomas (PAs) with a low complication rate. Systematic registration of complications by experienced surgical teams could help to improve this technique while ameliorating the patients' quality of life.

MATERIALS AND METHODS

One hundred ten endoscopic procedures were performed in 94 patients with PAs (37 functional) by the same neurosurgical team of a tertiary center during the period 2014-2019. Post-surgical complications were analyzed and compared with data published during the last 5 years in the PubMed and Cochrane databases by performing a systematic review and meta-analysis of the literature.

RESULTS

The overall complication rate in our series was 23.4%. Diabetes insipidus (DI) and intraoperative cerebrospinal fluid (CSF) leakage were the commonest complications (12.8%), followed by postoperative hypopituitarism (9.2%) and hematoma (8.5%) during the follow-up of 2.15 ± 1.4 years. Syndrome of inappropriate antidiuretic hormone secretion, meningitis, deep vein thrombosis, and hyposmia were rare (< 3%). Postoperative hypopituitarism was significantly associated with incidence of hematoma. No statistically significant association was found between PAs Hardy and Knosp scale grading or between patients' characteristics with the occurrence of postoperative complications. Our meta-analysis including nine studies found no significant differences comparing the complications of endoscopic versus microscopic surgery.

CONCLUSION

The endoscopic approach is safe when performed by experienced surgical teams. CSF leakage and DI were the commonest complications in our series; however, confirmation by larger studies is required. Meta-analysis showed no statistically significant differences in complication rates comparing endoscopic versus microscopic surgery.

Identifying risk factors for postoperative diabetes insipidus in more than 2500 patients undergoing transsphenoidal surgery: a single-institution experience

OBJECTIVE

Diabetes insipidus (DI) following transsphenoidal surgery can adversely impact quality of life and be difficult to manage. This study sought to characterize pre- and perioperative risk factors that may predispose patients to DI after pituitary surgery.

METHODS

A retrospective review of patients treated at a single institution from 2007 to 2019 was conducted. DI was defined as postoperative sodium > 145 mEq/L and urine output > 300 ml/hr and/or postoperative desmopressin (ddAVP) use. DI was further characterized as transient or permanent. Uni- and multivariate analyses were performed to determine variables associated with postoperative DI.

RESULTS

The authors identified 2529 patients who underwent transsphenoidal surgery at their institution. Overall, DI was observed in 270 (10.7%) of the 2529 patients, with 114 (4.5%) having permanent DI and 156 (6.2%) with transient symptoms. By pathology type, DI occurred in 31 (46.3%) of 67 craniopharyngiomas, 10 (14.3%) of 70 apoplexies, 46 (14.3%) of 322 Rathke's cleft cysts, 77 (7.7%) of 1004 nonfunctioning pituitary adenomas (NFPAs), and 62 (7.6%) of 811 functioning pituitary adenomas (FPAs). Final lesion pathology significantly affected DI rates (p < 0.001). Multivariate analysis across pathologies showed that younger age (odds ratio [OR] 0.97, p < 0.001), intraoperative CSF encounter (OR 2.74, p < 0.001), craniopharyngioma diagnosis (OR 8.22, p = 0.007), and postoperative hyponatremia (OR 1.50, p = 0.049) increased the risk of DI. Because surgery for each pathology created specific risk factors for DI, the analysis was then limited to the 1815 pituitary adenomas (PAs) in the series, comprising 1004 NFPAs and 811 FPAs. For PAs, younger age (PA: OR 0.97, p < 0.001; NFPA: OR 0.97, p < 0.001; FPA: OR 0.97, p = 0.028) and intraoperative CSF encounter (PA: OR 2.99, p < 0.001; NFPA: OR 2.93, p < 0.001; FPA: OR 3.06, p < 0.001) increased DI rates in multivariate analysis. Among all PAs, patients with DI experienced peak sodium levels later than those without DI (postoperative day 11 vs 2). Increasing tumor diameter increased the risk of DI in FPAs (OR 1.52, p = 0.008), but not in NFPAs (p = 0.564).

CONCLUSIONS

In more than 2500 patients treated at a single institution, intraoperative CSF encounter, craniopharyngioma diagnosis, and young age all increased the risk of postoperative DI. Patients with postoperative hyponatremia exhibited higher rates of DI, suggesting possible bi- or triphasic patterns to DI. Greater vigilance should be maintained in patients meeting these criteria following transsphenoidal surgery to ensure early recognition and treatment of DI.

Incidence and risk factors of delayed postoperative hyponatremia after endoscopic endonasal surgery for Rathke’s cleft cyst: A single-center study

Backgroud

Delayed postoperative hyponatremia (DPH) is common for sellar lesions. However, the true prevalence and associated factors of DPH after endoscopic endonasal surgery (EES) for Rathke’s cleft cyst (RCC) have not been studied in a large patient cohort.

Methods

A retrospective analysis was conducted over 6 years at our institution, and patients with RCC treated by EES were enrolled according to our inclusion criteria. Patient demographics, clinical characteristics, images, and surgical procedures were documented. Serum sodium was routinely measured before surgery, on postoperative day 1, and every 2 days thereafter until discharge. For patients with DPH, electrolyte, hematocrit, serum protein levels, and plasma and urinary osmolality were daily measured to explore potential etiology.

Results

Of the 149 eligible patients, 25 (16.8%) developed DPH, which was similar to other sellar lesions, except craniopharyngioma, in the same period in our institution. Significant risk factors suggested by univariate analysis were cyst location, requirement of postoperative hydrocortisone therapy, postoperative meningitis, intraoperative cerebrospinal fluid (CSF) leakage, and subtotal resection (STR) of the cyst wall (all p &lt; 0.05). In addition, other supplementary 11 cases of suprasellar RCC with different surgical strategies (aggressive resection) and relevant factors were enrolled into multivariate analysis. Suprasellar location [odds ratio (OR) 8.387, 95% confidence interval (CI) 1.014–69.365, p = 0.049], requirement of postoperative hydrocortisone therapy (OR 4.208, 95%CI 1.246–14.209, p = 0.021), and intraoperative CSF leakage (OR 6.631, 95%CI 1.728–25.440, p = 0.006) were found to be the independent predictors of DPH.

Conclusion

DPH is a common complication after EES for RCC. Suprasellar location, requirement of postoperative hydrocortisone therapy, and intraoperative CSF leakage are the most reliable risk factors. Cortisol deficiency and syndrome of inappropriate antidiuretic hormone (SIADH) are considered as the main etiologies of DPH in RCC. Conservative excision of the cyst wall may reduce DPH occurrence.

Complication Rates after Endoscopic Transsphenoidal Surgery for ACTH-Secreting Pituitary Adenomas: A Comparative Analysis with GH and Nonfunctioning Adenomas

Objectives Some complications have been more frequently reported after surgery for adrenocorticotropin hormone (ACTH)-secreting pituitary adenomas. We compared complication rates in patients with ACTH-secreting pituitary adenomas with those in patients with growth hormone secreting pituitary adenomas (growth hormone [GH] group) and nonfunctioning adenomas (nonfunctioning group).

Design A comparative three-group analysis was performed for all patients who had endoscopic transsphenoidal surgery for pituitary adenomas at our center between January 2011 and May 2019. Variables included demographics, preoperative clinical and radiological characteristics, and postoperative radiological and endocrinological outcomes. Complications were divided into four categories: endocrinological, neurosurgical, medical, and ENT (ear–nose–throat)-related complications. Univariate and multivariate statistical analysis were performed.

Results A total of 111 patients with pituitary adenomas and a mean age of 53.7 years were included (25 ACTH, 35 GH, and 51 nonfunctioning adenomas). Overall, 28 patients had microadenomas (25.2%) and 83 had macroadenomas (74.8%). Univariate statistical analysis for complications between groups showed no differences in neurosurgical and medical complications. Transient diabetes insipidus and postsurgical bacterial sinusitis were the only variables more frequently seen in the ACTH group (p = 0.01 and 0.04, respectively). Multivariate analysis for transient diabetes insipidus showed no differences between groups (p = 0.58).

Conclusion Complication rates were similar in all three adenoma groups, particularly concerning major infections, thrombotic events, postoperative cerebrospinal fluid (CSF) leak, and transient diabetes insipidus. Transient diabetes insipidus was related with adenoma size and intraoperative CSF leak. Despite postoperative bacterial sinusitis was statistically higher in the ACTH group, this data should be interpreted with caution given the low number of patients with this complication.

The management and outcome of hyponatraemia following transsphenoidal surgery: a retrospective observational study

Purpose

Hyponatraemia is a common complication following transsphenoidal surgery. However, there is sparse data on its optimal management and impact on clinical outcomes. The aim of this study was to evaluate the management and outcome of hyponatraemia following transsphenoidal surgery.

Methods

A prospectively maintained database was searched over a 4-year period between January 2016 and December 2019, to identify all patients undergoing transsphenoidal surgery. A retrospective case-note review was performed to extract data on hyponatraemia management and outcome.

Results

Hyponatraemia occurred in 162 patients (162/670; 24.2%) with a median age of 56 years. Female gender and younger age were associated with hyponatraemia, with mean nadir sodium being 128.6 mmol/L on postoperative day 7. Hyponatraemic patients had longer hospital stay than normonatraemic group with nadir sodium being inversely associated with length of stay (p < 0.001). In patients with serum sodium ≤ 132 mmol/L, syndrome of inappropriate antidiuretic hormone secretion (SIADH) was the commonest cause (80/111; 72%). Among 76 patients treated with fluid restriction as a monotherapy, 25 patients (25/76; 32.9%) did not achieve a rise in sodium after 3 days of treatment. Readmission with hyponatraemia occurred in 11 cases (11/162; 6.8%) at a median interval of 9 days after operation.

Conclusion

Hyponatraemia is a relatively common occurrence following transsphenoidal surgery, is associated with longer hospital stay and risk of readmission and the effectiveness of fluid restriction is limited. These findings highlight the need for further studies to better identify and treat high-risk patients, including the use of arginine vasopressin receptor antagonists.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-022-05134-9.

Predicting the Need for Desmopressin Treatment During Inpatient and After Discharge Following Endoscopic Sellar Surgery

Introduction

Postoperative diabetes insipidus (DI) is a common complication following endoscopic sellar surgery. However, the requirement of desmopressin treatment for patients with DI are heterogenous. Although the predictors of postoperative DI have been reported, whether these patients required desmopressin treatment remained uninvestigated. Predicting the need of desmopressin can benefit clinical decision making more directly than predicting the occurence of postoperative DI. This study aimed to identify variables that predict the need for desmopressin treatment following sellar surgery.

Methods

Patients undergoing endoscopic sellar surgery between 2016 and 2019 were retrospectively reviewed. Twenty-three variables, characterized as potential predictors for requiring desmopressin treatment, were analyzed. To assess the capability to generalize the identified predictors, external validation with receiver operating characteristic (ROC) analysis was performed using a second series from 2019 to 2020.

Results

Postoperative DI occurred in 40 of 159 included patients. Twelve patients required inpatient desmopressin treatment and 20 patients needed desmopressin prescription after discharge. The potential predictors of requiring any desmopressin use included higher peak sodium (Na) level (p = 0.007), lower minimum Na level (p = 0.043), and higher peak urine output (p = 0.006), but these were not supported by external validation. The predictors of requiring desmopressin after discharge included higher peak Na (p = 0.040) and minimum Na levels (p = 0.048), which were supported by external ROC validation showing areas under curve of 0.787, 0.611, and 0.898 for peak Na (p = 0.036), minimum Na (p = 0.460), and peak Na – minimum Na levels (p < 0.001), respectively. A criterion of peak Na ≥ 150 mmol/L or peak Na – minimum Na ≥ 10 predicted the need of desmopressin prescription after discharge. A postoperative management algorithm was proposed.

Conclusion

The required treatments for patients with postoperative DI following endoscopic sellar surgery are heterogenous. Elevated peak Na and large peak Na—minimum Na levels in the perioperative period predicted requiring desmopressin after hospital discharge. Patients with peak Na <150 mmol/L and peak Na—minimum Na <10 can be safely discharged without desmopressin prescription.

The management of acute and chronic hyponatraemia

Hyponatraemia is the most common electrolyte abnormality encountered in clinical practice; despite this, the work-up and management of hyponatraemia remain suboptimal and varies among different specialist groups. The majority of data comparing hyponatraemia treatments have been observational, up until recently. The past two years have seen the publication of several randomised control trials investigating hyponatraemia treatments, both for chronic and acute hyponatraemia. In this article, we aim to provide a background to the physiology, cause and impact of hyponatraemia and summarise the most recent data on treatments for acute and chronic hyponatraemia, highlighting their efficacy, tolerability and adverse effects.

Radiographic pituitary stalk disruption: A rare sequela of secondary empty sella syndrome

Background:

This two-patient case series describes a rare sequela of postoperative empty sella syndrome (ESS) following transsphenoidal resection of pituitary macroadenomas. This is characterized by progressive hormone dysfunction, diabetes insipidus (DI), and associated MRI evidence of pituitary stalk disruption.

Case Description:

This phenomenon was retrospectively evaluated in a review of 2000 pituitary tumor resections performed by a single neurosurgeon (KOL). Chart review was retrospectively conducted to gather data on demographics, pituitary hormone status, tumor characteristics, and management. We identified 2 (0.1%) cases of progressive pituitary endocrine dysfunction occurring in the postoperative period associated with MRI evidence of pituitary stalk disruption within 6 weeks of discharge from the hospital. This was felt to be caused by the rapid descent of the residual normal pituitary gland down to the floor of the postoperative empty sella, causing relatively swift stalk stretching. Both patients developed DI, and one patient demonstrated increased pituitary hormone dysfunction.

Conclusion:

This phenomenon is a rare manifestation of postoperative ESS, secondary to surgical resection of a pituitary macroadenoma. We discuss the associated potential risk factors and strategies for avoidance in these two cases. Routine instillation of intrasellar fat in patients at risk is felt to be protective.

Routine postoperative fluid restriction to prevent syndrome of inappropriate antidiuretic hormone secretion after transsphenoidal resection of pituitary adenoma

OBJECTIVE

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a common problem during the postoperative course after pituitary surgery. Although treatment of this condition is well characterized, prevention strategies are less studied and reported. The authors sought to characterize outcomes and predictive factors of SIADH after implementation of routine postoperative fluid restriction for patients undergoing endoscopic transsphenoidal surgery for pituitary adenoma.

METHODS

In March 2018, routine postoperative fluid restriction to 1000 ml/day for 7 days was instituted for all patients who underwent surgery for pituitary adenoma. These patients were compared with patients who underwent surgery for pituitary adenoma between March 2016 and March 2018, prior to implementation of routine fluid restriction. Patients with preoperative history of diabetes insipidus (DI) or concern for postsurgical DI were excluded. Patients were followed by neuroendocrinologists and neurosurgeons, and sodium levels were checked between 7 and 10 days postoperatively. SIADH was defined by a serum sodium level less than 136 mmol/L, with or without symptoms within 10 days after surgery. Thirty-day readmission was recorded and reviewed to determine underlying reasons.

RESULTS

In total, 82 patients in the fluid-unrestricted cohort and 135 patients in the fluid-restricted cohort were analyzed. The patients in the fluid-restricted cohort had a significantly lower rate of postoperative SIADH than patients in the fluid-unrestricted cohort (5% vs 15%, adjusted OR [95% CI] 0.1 [0.0-0.6], p = 0.01). Higher BMI was associated with lower rate of postoperative SIADH (adjusted OR [95%] 0.9 [0.9-1.0], p = 0.03), whereas female sex was associated with higher rate of SIADH (adjusted OR [95% CI] 3.1 [1.1-9.8], p = 0.03). There was no difference in the 30-day readmission rates between patients in the fluid-unrestricted and fluid-restricted cohorts (4% vs 7%, adjusted OR [95% CI] 0.5 [0-5.1], p = 0.56). Thirty-day readmission was more likely for patients with history of hypertension (adjusted OR [95% CI] 5.7 [1.3-26.3], p = 0.02) and less likely for White patients (adjusted OR [95% CI] 0.3 [0.1-0.9], p = 0.04).

CONCLUSIONS

Routine fluid restriction reduced the rate of SIADH in patients who underwent surgery for pituitary adenoma but was not associated with reduction in 30-day readmission rate.

30-Day Readmissions and Coordination of Care Following Endoscopic Transsphenoidal Pituitary Surgery: Experience with 409 Patients

Objective The study aimed to (1) quantify readmission rates and common causes of readmission following endoscopic transsphenoidal pituitary surgery (ETPS); (2) identify risk factors that may predict readmission within 30 days; (3) assess postoperative care coordination with endocrinology follow-up; and (4) identify patients for whom targeted interventions may reduce 30-day readmissions.

Methods Retrospective quality improvement review of patients with pituitary adenoma who underwent ETPS from December 2010 to 2018 at a single tertiary care center.

Results A total of 409 patients were included in the study, of which 57 (13.9%) were readmitted within 30 days. Hyponatremia was the most common cause of readmission (4.2%) followed by pain/headache (3.9%), cerebrospinal fluid leak (3.4%), epistaxis (2.7%), hypernatremia (1.2%), and adrenal insufficiency (1.2%). Patients with hyponatremia were readmitted significantly earlier than other causes (4.3 ± 2.2 vs. 10.6 ± 10.9 days from discharge, p = 0.032). Readmitted patients had significantly less frequent outpatient follow-up with an endocrinologist than the nonreadmitted cohort (56.1 vs. 70.5%, p = 0.031). Patients who had outpatient follow-up with an endocrinologist were at lower risk of readmission compared with those without (odds ratio: 0.46; 95% confidence interval: 0.24–0.88).

Conclusion Delayed hyponatremia is one of the most common causes of 30-day readmission following ETPS. Postoperative follow-up with an endocrinologist may reduce risk of 30-day readmission following ETPS.

Implications for Clinical Practice A multidisciplinary team incorporating otolaryngologist, neurosurgeons, and endocrinologist may identify patients at risk of 30-day readmissions. Protocols checking serum sodium within 1 week of surgery in conjunction with endocrinologist to tailor fluid restriction may reduce readmissions from delayed hyponatremia.

Postoperative diabetes insipidus: how to define and grade this complication?

PURPOSE

Although transient diabetes insipidus (DI) is the most common complication of pituitary surgery, there is no consensus on its definition. Polyuria is the most overt symptoms of DI, but can also reflect several physiological adaptive mechanisms in the postoperative phase. These may be difficult to distinguish from and might coincide with DI. The difficulty to distinguish DI from other causes of postoperative polyuria might explain the high variation in incidence rates. This limits interpretation of outcomes, in particular complication rates between centers, and may lead to unnecessary treatment. Aim of this review is to determine a pathophysiologically sound and practical definition of DI for uniform outcome evaluations and treatment recommendations.

METHODS

This study incorporates actual data and the experience of our center and combines this with a review of literature on pathophysiological mechanisms and definitions used in clinical studies reporting of postoperative DI.

RESULTS

The occurrence of excessive thirst and/or hyperosmolality or hypernatremia are the best indicators to discriminate between pathophysiological symptoms and signs of DI and other causes. Urine osmolality distinguishes DI from osmotic diuresis.

CONCLUSIONS

To improve reliability and comparability we propose the following definition for postoperative DI: polyuria (urine production > 300 ml/hour for 3 h) accompanied by a urine specific gravity (USG) < 1.005, and at least one of the following symptoms: excessive thirst, serum osmolality > 300 mosmol/kg, or serum sodium > 145 mmol/L. To prevent unnecessary treatment with desmopressin, we present an algorithm for the diagnosis and treatment of postoperative DI.

Diabetes insipidus secondary to sellar/parasellar lesions

Diabetes insipidus (DI) is a well-recognised transient or permanent complication following transsphenoidal surgery for pituitary adenomas or other sellar/parasellar lesions. However, data regarding the prevalence of pre-operative DI in sellar/parasellar lesions other than pituitary adenomas are scarce. We systematically reviewed the existing data for defining the prevalence of DI before any treatment in adult patients with sellar/parasellar lesions, excluding pituitary adenomas and metastatic lesions. In total, 646 patients with sellar/parasellar lesions presenting with DI at diagnosis were identified. The most common pathologies of sellar/parasellar lesions presenting with DI at diagnosis were lymphocytic hypophysitis (26.5%), craniopharyngiomas (23.4%), Langerhans's cell histiocytosis (18.9%) and Rathke's cleft cyst (12.7%), accounting for the vast majority (more than 80%) of these lesions. Overall, DI at diagnosis was found in 23.4% of all patients with sellar/parasellar lesions, albeit with a wide range from 10.6% to 76.7%, depending on the nature of the pathology. The highest prevalence of DI was found in less commonly encountered lesions namely germ-cell tumours (76.7%), abscesses (55.4%) and neurosarcoidosis (54.5%), each accounting for less than 3% of all sellar/parasellar lesions. Most DI cases (68.8%) were associated with anterior pituitary hormonal deficiencies, in contrast to pituitary adenomas that rarely present with DI. The enlargement and enhancement of the pituitary stalk were the most common findings on magnetic resonance imaging besides the loss of the high signal of the posterior pituitary on T1-weighted images. Resolution of DI spontaneously or following systemic and surgical management occurred in 22.4% of cases. Post-operative DI, not evident before surgery, was found in 27.8% of non-adenomatous sellar/parasellar lesions, and was transient in 11.6% of them. Besides distinctive imaging features and symptoms, early recognition of DI in such lesions is important because it directs the diagnosis towards a non-adenomatous sellar/parasellar tumour and the early initiation of appropriate treatment.

An Effective and Practical Fluid Restriction Protocol to Decrease the Risk of Hyponatremia and Readmissions After Transsphenoidal Surgery

BACKGROUND

Delayed hyponatremia is a common complication following transsphenoidal surgery (TSS) of pituitary lesions, which leads to significant patient morbidity, as well as increased hospital costs associated with readmission.

OBJECTIVE

To report the effects of fluid restriction, during a postoperative period of 4 d, to decrease rates and readmissions for hyponatremia in a cohort of patients undergoing TSS.

METHODS

Because of our observed postoperative rates of hyponatremia, we implemented 1000-mL fluid restriction limited to postoperative days (POD) 4 to 8 in consecutive patients undergoing surgery at our center between March 2018 and January 2019. Patients were monitored for the development of hyponatremia and readmissions. We compared outcomes with those of patients who had undergone TSS prior to fluid restriction.

RESULTS

Data from 57 patients who underwent TSS following implementation of fluid restriction were compared to prior patients who underwent TSS without restriction. The rate of hyponatremia in patients (n = 57) prior to fluid restriction was 12.3%. Following implementation of fluid restriction, we had zero cases of hyponatremia or readmissions. We found body mass index to be inversely related to the risk of hyponatremia and readmissions. Furthermore, male gender, follicle stimulating hormone and/or luteinizing hormone staining on pathology, and administration of preoperative and intraoperative glucocorticoids were associated with decreased risk of hyponatremia readmissions.

CONCLUSION

The implementation of 1000-mL fluid restriction between POD 4 and 8 is a highly successful and simple approach to decrease the risk of delayed hyponatremia after TSS.

Delayed Hyponatremia after Transsphenoidal Surgery for Pituitary Adenomas: A Single Institutional Experience

Background

Hyponatremia is a common complication after transsphenoidal surgery (TSS) for pituitary adenomas. This study retrospectively reviewed various clinical factors of pituitary adenoma patients who underwent TSS and aimed to identify possible risk factors of postoperative hyponatremia.

Methods

Total 1,343 patients who underwent TSS for their pituitary adenomas in a single institution were enrolled to this study. We identified and analyzed 93 patients (6.9%) with postoperative hyponatremia and compared them with other 1,250 patients in a control group. Patients' age, sex, tumor extent based on the modified Hardy classification, tumor size and hormonal type of the tumors were analyzed in comparison between two groups. The results of pre- and post-operative combined pituitary function test and their comparison were analyzed to elucidate a possible association between postoperative hyponatremia and hypopituitarism.

Results

The onset of postoperative hyponatremia was 7.8 days after surgery (range: postoperative day 3–13). The initial level of serum sodium (Na) level at the start of treatment was 123.5 mmol/L (range: 114–131 mmol/L) and the duration of treatment was 2.7 days (range: 1–9 days). Female predominance was evident in the hyponatremia group (77.4% vs. 61.4%, p=0.02). Preoperative hypopituitarism (58.5% vs. 71.5%, p=0.007) and postoperative hypocortisolism (33.7% vs. 23.4%, p=0.029) were related to postoperative hyponatremia. Other pre- and post-operative clinical factors were not associated with postoperative hyponatremia.

Conclusion

Postoperative hyponatremia is a common complication after TSS and is potentially fatal. Female patients were more likely to develop delayed hyponatremia. We demonstrated possible associations of delayed postoperative hyponatremia with preoperative and postoperative pituitary functions, but the mechanism behind it should be further investigated.

[Central diabetes insipidus after resection of sellar-suprasellar tumors: prevalence and predictors of manifestation]

Central diabetes insipidus is a neuroendocrine disorder caused by disturbances in antidiuretic hormone release. The last one is responsible for fluid and electrolyte balance regulation. The most common cause of diabetes insipidus is resection of sellar-suprasellar tumors followed by damage to hypothalamic nuclei responsible for antidiuretic hormone release, disruption of antidiuretic hormone transportation from hypothalamus or its release by neurohypophysis. According to various data, postoperative diabetes insipidus occurs in 13-30% of cases. The highest risk of diabetes insipidus is observed after resection of craniopharyngioma, Rathke's cleft cyst and ACTH-releasing pituitary microadenoma. This review is devoted to prevalence and predictors of diabetes insipidus after resection of sellar-suprasellar tumors.

Delayed Postoperative Hyponatremia Following Endoscopic Transsphenoidal Surgery for Non-Adenomatous Parasellar Tumors

Little is known about delayed postoperative hyponatremia (DPH) accompanied with transsphenoidal surgery for non-adenomatous skull base tumors (NASBTs). Consecutive data on 30 patients with parasellar NASBT was retrospectively reviewed with detailed analyses on perioperative serial sodium levels. Serological DPH (sodium ≤ 135 mmol/L) was observed in eight (27%), with four (13%) of them being symptomatic. DPH developed on postoperative day 7-12 where the mean sodium levels were 134 mmol/L (a mean of 7 mmol/L drop from the baseline) in asymptomatic and 125 mmol/L (a mean of 17.5 mmol/L drop from the baseline) in symptomatic DPH. Serological DPH was accompanied with "weight loss and hemoconcentration (cerebral salt wasting type)" in four (50%), "weight gain and hemodilution (syndrome of inappropriate antidiuretic hormone secretion type)" in three (38%), and no significant weight change in one. Intraoperative extradural retraction of the pituitary gland was the only significant factor for serological DPH (p = 0.035; odds ratio, 12.25 (95% confidence interval, 1.27-118.36)). DPH should be recognized as one of the significant postsurgical complications associated with TSS for NASBTs. Although the underlying mechanism is still controversial, intraoperative extradural compression of the pituitary gland and subsequent dysregulation of the hypothalamo-hypophyseal axis may be responsible.

Feasibility of machine learning based predictive modelling of postoperative hyponatremia after pituitary surgery

PURPOSE

Hyponatremia after pituitary surgery is a frequent finding with potential severe complications and the most common cause for readmission. Several studies have found parameters associated with postoperative hyponatremia, but no reliable specific predictor was described yet. This pilot study evaluates the feasibility of machine learning (ML) algorithms to predict postoperative hyponatremia after resection of pituitary lesions.

METHODS

Retrospective screening of a prospective registry of patients who underwent transsphenoidal surgery for pituitary lesions. Hyponatremia within 30 days after surgery was the primary outcome. Several pre- and intraoperative clinical, procedural and laboratory features were selected to train different ML algorithms. Trained models were compared using common performance metrics. Final model was internally validated on the testing dataset.

RESULTS

From 207 patients included in the study, 44 (22%) showed a hyponatremia within 30 days postoperatively. Hyponatremic measurements peaked directly postoperatively (day 0-1) and around day 7. Bootstrapped performance metrics of different trained ML-models showed largest area under the receiver operating characteristic curve (AUROC) for the boosted generalized linear model (67.1%), followed by the Naïve Bayes classifier (64.6%). The discriminative capability of the final model was assessed by predicting on unseen dataset. Large AUROC (84.3%; 67.0-96.4), sensitivity (81.8%) and specificity (77.5%) with an overall accuracy of 78.4% (66.7-88.2) was reached.

CONCLUSION

Our trained ML-model was able to learn the complex risk factor interactions and showed a high discriminative capability on unseen patient data. In conclusion, ML-methods can predict postoperative hyponatremia and thus potentially reduce morbidity and improve patient safety.

Surgical Outcomes Following Repeat Transsphenoidal Surgery for Nonfunctional Pituitary Adenomas: A Retrospective Comparative Study

BACKGROUND

Endonasal transsphenoidal surgery (ETSS) remains the preferred treatment for recurrent or residual nonfunctional pituitary adenomas (NFPAs). However, surgical complications and outcomes with repeat ETSS are unclear.

OBJECTIVE

To compare outcomes from primary and repeat ETSS in patients with NFPAs.

METHODS

Retrospective review of ETSS for NFPAs at USC University Hospital and LAC + USC Medical Center between 2000 and 2015. Patients with ≥3-mo follow-up data were included. Patients were categorized as primary or repeat ETSS. Patient and tumor characteristics were compared preoperatively, and postoperative outcomes were analyzed.

RESULTS

Two hundred sixty-eight patients (89%) met the inclusion criteria (primary ETSS = 211 and repeat ETSS = 57) with a mean follow-up time of 38 mo (range 3-235 mo). Both groups had similar demographics, endocrine function, and tumor characteristics. Surgical complication rates were similar and no mortalities were observed. Repeat ETSS patients had a higher rate of new postoperative panhypopituitarism (primary ETSS: 0.5% vs repeat ETSS: 7.1%, P = .011), lower rates of gross total resection (GTR; primary ETSS: 59.2% vs repeat ETSS: 26.3%, P = .001), and greater rates of postoperative radiosurgery (36.8% vs 24.2%, P = .009). At 2-yr follow-up, progression-free survival on MRI was similar in both groups (primary ETSS: 97.9% vs repeat ETSS: 95.4%, log-rank test P = .807).

CONCLUSION

At experienced tertiary pituitary centers, repeat ETSS for NFPAs was associated with a similar incidence of surgical complications as primary ETSS. However, repeat ETSS carried a higher rate for worsening endocrine dysfunction and a lower rate of GTR.

Diabetes insipidus and syndrome of inappropriate antidiuresis (SIADH) after pituitary surgery: incidence and risk factors

Electrolyte disorders are relatively frequent and potentially serious complications after pituitary surgery. Both DI (diabetes insipidus) and SIADH (syndrome of inappropriate antidiuresis) can complicate and prolong hospital and intensive care unit stay, and the latter may even be preventable. We aim to assess the incidence of both electrolyte disorders and their risk factors. From a prospective registry of patients who underwent endoscopic transnasal transsphenoidal surgery (TSS) for pituitary adenoma, patients with postoperative DI and SIADH were identified. Univariable and multivariable statistics were carried out to identify factors independently associated with the occurrence of either DI or SIADH. A total of 174 patients were included, of which 73 (42%) were female. Mean age was 54 years (range 20-88). During postoperative hospital stay, 13 (7.5%) patients presenting with DI and 11 (6.3%) with SIADH were identified. Patients who developed DI after surgery had significantly longer hospital stays (p = 0.022), as did those who developed SIADH (p = 0.002). Four (2.3%) patients were discharged with a diagnosis of persistent DI, and 2 (1.1%) with the diagnosis of SIADH. At the last follow-up, 5 (2.9%) patients presented with persistent DI, while none of the patients suffered from SIADH. Younger age (odds ratio (OR) 0.97, 95% confidence interval (CI) 0.94-1.01, p = 0.166) and pituitary apoplexy (OR 2.69, 95% CI 0.53-10.65, p = 0.184) were weakly associated with the occurrence of DI. We identified younger age (OR 0.96, 95% CI 0.92-0.99, p = 0.045) and lower preoperative serum sodium (OR 0.83, 95% CI 0.71-0.95, p = 0.008) as independent risk factors for SIADH. Although we found a weak association among age, pituitary apoplexy, and the occurrence of DI, no independent predictor was identified for DI. For postoperative SIADH however, lower age and preoperative serum sodium were identified as significant predictors. None of these findings were sufficiently supported by preexisting literature. Both electrolyte disorders are exquisitely hard to predict preoperatively, and further research into their early detection and prevention is warranted.

Tolvaptan Versus Fluid Restriction in the Treatment of Hyponatremia Resulting from SIADH Following Pituitary Surgery

Context

The relevance of hyponatremia has been acknowledged by guidelines from the United States (2013) and Europe (2014). However, treatment recommendations differ due to limited evidence.

Objective

In hyponatremia following pituitary surgery-caused by the syndrome of inappropriate antidiuretic hormone (SIADH) secretion-we compared fluid restriction with the pharmacological increase of water excretion by blocking the vasopressin 2 receptors with tolvaptan at a low and a moderate dose.

Design

Prospective observational study.

Setting

Neurosurgical Department of a University hospital with more than 200 surgical pituitary procedures per year.

Patients

Patients undergoing pituitary surgery and developing serum sodium below 136 mmol/L. The diagnosis of SIADH was established by euvolemia (daily measurement of body weight and fluid balance), inappropriately concentrated urine (specific gravity), and exclusion of adrenocorticotropic and thyroid-stimulating hormone deficiency.

Intervention

Patients were treated with fluid restriction (n = 40) or tolvaptan at 3.75 (n = 38) or 7.5 mg (n = 48).

Main Outcome Measures

Treatment efficacy was assessed by the duration of hyponatremia, sodium nadir, and length of hospitalization. Safety was established by a sodium increment below 10 mmol/L per day and exclusion of side effects.

Results

Treatment with 7.5 mg of tolvaptan resulted in a significant attenuation of hyponatremia and in a significant overcorrection of serum sodium in 30% of patients. The duration of hospitalization did not differ between treatment groups.

Conclusions

Tolvaptan at a moderate dose is more effective than fluid restriction in the treatment of SIADH. Overcorrection of serum sodium may be a side effect of tolvaptan even at low doses.

National trends in hospital readmission following transsphenoidal surgery for pituitary lesions

PURPOSE

Several institutions recently published their experiences with unplanned readmissions rates after transsphenoidal surgery for pituitary lesions. Readmission rates on a national level, however, have not been explored in depth. We investigated nationwide trends in this procedure and associated independent predictors, costs, and causes of 30-day readmission.

METHODS

The Nationwide Readmissions Database was queried to identify patients 18 and older who underwent transsphenoidal surgery for pituitary lesion resection (2010-2015). National trends and statistical variances were calculated based on weighted, clustered, and stratified sample means.

RESULTS

Of the weighted total of 44,759 patients treated over the 6-year period, 4658 (10.4%) were readmitted within 30 days. Readmission rates did not change across the survey period (P = 0.71). Patients readmitted had a higher prevalence of comorbidities than those not readmitted (82.5% vs. 78.4%, respectively, P < 0.001), experienced more postoperative complications (47.2% vs. 31.8%, P < 0.001), and had a longer length of stay (6.59 vs. 4.23 days, P < 0.001) during index admission. The most common causes for readmission were SIADH (17.5%) and other hyponatremia (16.4%). Average total readmission cost was $12,080 with no significant trend across the study period (P = 0.25). Predictors for readmission identified included diabetes mellitus, psychological disorders, renal failure, and experiencing diabetes insipidus during the index admission.

CONCLUSION

Unplanned readmission is an important quality metric. While transsphenoidal pituitary surgery is a relatively safe procedure, 30-day readmission rates and costs have not declined. Future studies on institutional protocols targeting these identified predictors to prevent readmission are necessary to decrease readmission rates on a national scale.

Readmissions after endoscopic skull base surgery: associated risk factors and prevention

BACKGROUND

Unplanned readmissions within 30 days of discharge is a quality measure introduced by the Centers for Medicare Services. This measure has been used to rate hospital quality and also to penalize hospitals for excess readmissions. It has been hypothesized that shorter hospital stays and fewer readmissions are associated with endoscopic skull base procedures. In this study we analyze endoscopic skull base procedures performed at our institution over a 10-year period to identify rates and factors associated with readmissions after endoscopic skull base surgery.

METHODS

A retrospective chart review was performed at a tertiary care academic medical center identifying patients who underwent endoscopic skull base surgery over the past 10 years. Data on patient demographics and tumor variables, as well as patient variables such as body mass index (BMI), revision surgery, history of skull base radiation, medical comorbidities, intraoperative cerebrospinal fluid (CSF) leaks, and postoperative CSF leaks, were recorded.

RESULTS

Eight hundred thirty-three patients were included in our study. Sixty-one patients (7.3%) were readmitted a total of 66 times within 30 days. The most common reasons were as follows: hyponatremia (n = 18); CSF leak (n = 17); epistaxis (n = 3); diabetes insipidus (n = 3); rhinorrhea (n = 3); as well as other reasons. Statistical analysis revealed that the presence of intraoperative CSF leak was the only statistically significant variable associated with increased rate of readmissions within 30 days of discharge (p < 0.001).

CONCLUSION

Presence of intraoperative CSF leak was the only statistically significant variable associated with an increased risk for readmission after surgery. Other tumor and patient variables were not associated with an increased risk of readmission within 30 days.

Readmission after endoscopic transsphenoidal pituitary surgery: analysis of 584 consecutive cases

OBJECTIVE

Hospital readmission is a key component in value-based healthcare models but there are limited data about the 30-day readmission rate after endonasal endoscopic transsphenoidal surgery (EETS) for pituitary adenoma. The objective of this study was to determine the incidence and identify factors associated with 30-day readmission after EETS for pituitary adenoma.

METHODS

The authors analyzed a prospectively acquired database of patients who underwent EETS for pituitary adenoma from 2005 to 2018 at NewYork-Presbyterian Hospital, Weill Cornell Medicine. Clinical, socioeconomic, and radiographic data were reviewed for cases of unplanned readmission within 30 days of surgery and, as a control group, for all other patients in the series who were not readmitted. Statistical significance was determined with an alpha < 0.05 using Pearson's chi-square and Fisher's exact tests for categorical variables and the independent-samples t-test for continuous variables.

RESULTS

Of 584 patients undergoing EETS for pituitary adenoma, 27 (4.6%) had unplanned readmission within 30 days. Most readmissions occurred within the first week after surgery, with a mean time to readmission of 6.6 ± 3.9 days. The majority of readmissions (59%) were for hyponatremia. These patients had a mean sodium level of 120.6 ± 4.6 mEq/L at presentation. Other causes of readmission were epistaxis (11%), spinal headache (11%), sellar hematoma (7.4%), CSF leak (3.7%), nonspecific headache (3.7%), and pulmonary embolism (3.7%). The postoperative length of stay was significantly shorter for patients who were readmitted than for the controls (2.7 ± 1.0 days vs 3.9 ± 3.2 days; p < 0.05). Patients readmitted for hyponatremia had an initial length of stay of 2.6 ± 0.9 days, the shortest of any cause for readmission. The mean BMI was significantly lower for readmitted patients than for the controls (26.4 ± 3.9 kg/m2 vs 29.3 ± 6.1 kg/m2; p < 0.05).

CONCLUSIONS

Readmission after EETS for pituitary adenoma is a relatively rare phenomenon, with delayed hyponatremia being the primary cause. The study results demonstrate that shorter postoperative length of stay and lower BMI were associated with 30-day readmission.

CLINICAL PRACTICE PATTERNS FOR POSTOPERATIVE WATER BALANCE AFTER PITUITARY SURGERY

Objective: Abnormalities of water and sodium balance, including diabetes insipidus and the syndrome of inappropriate antidiuretic hormone (SIADH), are common complications of transsphenoidal surgery. Postoperative practice patterns vary among clinicians, and no consensus guidelines exist to direct their monitoring and management. We aimed to identify and compare practice patterns regarding the evaluation and management to these postoperative complications. Methods: A questionnaire was utilized to capture demographic data and practice habits in the postoperative setting. Respondents were members of the Pituitary Society, an international organization comprised of clinicians and researchers dedicated to the study of pituitary disease. Results: Eighty-six respondents completed at least part of the survey. The geographic distribution of respondents was roughly even between American and non-American practitioners. The majority of respondents practiced at academic institutions (67.4%), worked in multidisciplinary teams (88.4%), and possessed significantly greater than 10 years of clinical experience (71%). Compared to non-American practitioners, American practitioners described a shorter length of stay postoperatively (P<.001) and prescribed more restrictive volume recommendations for postoperative SIADH (P = .0035). Early career clinicians (less than 10 years in practice) checked first postoperative sodium level earlier than later career clinicians (P = .010). Conclusion: Water and sodium dysregulation are common following transsphenoidal surgery, but their management is not well-standardized in clinical practice. We created a questionnaire to define and compare practice patterns. Most respondents practice in academic settings in multidisciplinary teams. The length of clinical experience did not significantly impact practice habits. Practice location influenced length of stay postoperatively and fluid restriction in SIADH. Abbreviations: AVP = arginine vasopressin; DI = diabetes insipidus; LOS = length of stay; SIADH = syndrome of inappropriate antidiuretic hormone.

Efficiency of Single Dose of Tolvaptan Treatment During the Triphasic Episode After Surgery for Craniopharyngioma

Inappropriate antidiuretic hormone syndrome (SIADH) may develop after intracranial surgery. SIADH in the pediatric age group is usually encountered in patients with an intracranial mass both before and after surgery. Fluid restriction is the standard therapy in SIADH. However, a resistant, hyponatremic pattern may be encountered in some cases. Vaptans have been recently introduced for treatment of hyponatremia due to SIADH. There is inadequate data concerning tolvaptan treatment in pediatric patients. We present a 13 year-old female with SIADH of triphasic episode who was transferred to our clinic after surgery for craniopharyngioma. Resistant hyponatremia did not resolve despite fluid restriction and hypertonic saline support. The patient responded rapidly to a single dose of tolvaptan, with no adverse effect, which resulted in successful control of her SIADH.

Delayed postoperative hyponatremia after endoscopic transsphenoidal surgery for pituitary adenoma

BACKGROUND

Hyponatremia generally occurs after transsphenoidal surgery (TSS) in a delayed fashion. Most patients with delayed postoperative hyponatremia (DPH) are asymptomatic or only express non-specific symptoms; consequently, DPH is associated with prolonged hospitalization. No consensus has been reached on which patients are at greatest risk of developing DPH. We reviewed patients with DPH and evaluated predictive factors for DPH.

METHODS

We retrospectively analyzed 107 consecutive patients who underwent endoscopic TSS for pituitary adenoma (January 2010-December 2016). Patients with DPH (hyponatremia group) and without DPH (normonatremia group) were compared according to their nadir sodium levels on postoperative days 3 to 10. We documented the patients' demographics, clinical features, and postoperative physiological characteristics.

RESULTS

Twenty-five (23.4%) patients developed DPH after endoscopic TSS. The patients' mean age was 54 ± 17 years, and 63.6% of the patients were female. The overall prevalence of DPH was 23.4%. The non-parametric χ2 test and the Mann-Whitney U test revealed statistically significant differences in age, use of antihypertensive drugs, nonfunctioning pituitary adenoma, and higher yet normal preoperative thyroid-stimulating hormone level between the hyponatremia and normonatremia groups (P < 0.05). Logistic regression analysis revealed that only older age was a useful independent predictive factor for DPH (odds ratio, 1.05; 95% confidence interval, 1.01-1.08; P = 0.01). The serum sodium levels on postoperative day 2 were significantly lower in the hyponatremia than normonatremia group (P < 0.01) and were negatively correlated with age (r = - 0.25, P < 0.05). The cut-off age for predicting DPH was 55 years. The hospital stay was significantly longer in the hyponatremia than normonatremia group (P < 0.01).

CONCLUSIONS

Age of more than 55 years was an independent predictive factor for DPH even after adjusting for potential confounders. Older age was negatively correlated with the serum sodium level on postoperative day 2. Preventing early decreases in the sodium level could reduce the risk of DPH.

TRIAL REGISTRATION

1707-027.

Strategies to reduce readmissions for hyponatremia after transsphenoidal surgery for pituitary adenomas

PURPOSE

Disorders of water balance, particularly hyponatremia from altered antidiuretic hormone (ADH) secretion, are a common post-operative complication of transsphenoidal surgery (TSS). We present our results from implementation of a 2-week 1.5 liter/daily fluid restriction on readmission rates for hyponatremia.

METHODS

A retrospective chart review was performed on 295 patients that underwent TSS for pituitary adenomas at the University of Colorado, between March 2014 and March 2017. Groups were divided into those before and after the implementation of a two-week, 1.5 liter daily fluid restriction and measurement of a serum sodium level 7 days (+/- 2 days) after discharge. A standard-of-care approach for variable degrees of hyponatremia was also utilized to guide hyponatremia management. Patient demographics, hospital course, post-operative complication rates, and rates of hospital admissions for hyponatremia were then evaluated.

RESULTS

Readmissions for symptomatic hyponatremia within 30 days of TSS occurred in 9 of 118 (7.6%) of patients prior to fluid restriction implementation and in four of 169 (2.4%) of patients in the post-implementation, fluid-restricted group (p-value = 0.04): a 70% reduction in hospitalizations. The two groups were similarly matched for pituitary tumor sub-type, age and gender. None of these factors were predictive for hyponatremia. Importantly, the mild fluid restriction did not result in any hospital readmissions for hypernatremia.

CONCLUSIONS

Mild fluid restriction (to 1.5 liters daily), in addition to a single post-operative serum sodium level, is an effective approach to preventing readmission for hyponatremia after TSS for pituitary adenomas.

Implementation of a Postoperative Outpatient Care Pathway for Delayed Hyponatremia Following Transsphenoidal Surgery

BACKGROUND

After transsphenoidal surgery, delayed hyponatremia (DH) is the leading cause of 30-d unplanned hospital readmissions.

OBJECTIVE

To determine the impact of a DH care pathway on 30-d readmissions after transsphenoidal surgery.

METHODS

Data from before and after DH care pathway implementation were retrospectively reviewed. Patient demographics and clinical characteristics were compared. Readmission causes, clinical pathway failures, sodium trends, and symptoms were evaluated.

RESULTS

Before the DH care pathway implementation, 229 (55%) patients were treated (group 1); afterward, 188 (45%) were treated (group 2). Baseline characteristics were equivalent between groups, except for glucocorticoid supplementation, which was higher in group 2. The incidence of detected DH was significantly lower in group 1 (16/229, 7%) than group 2 (29/188, 15%) (P = .006) likely due to the impact of routine screening in group 2. Ten group 1 patients (4%) were readmitted for hyponatremia and 6 (3%) were managed as outpatients. Eleven group 2 patients (6%) were readmitted and 17 (9%) were managed as outpatients. Readmission rates between groups were similar (P = .49). Patients readmitted with severe hyponatremia experienced symptoms ≥24 h before presentation. The protocol failed to prevent readmission because outpatient management for mild or moderate DH (n = 4) failed, sodium levels precipitously declined after normal screening (n = 3), and severe hyponatremia developed after scheduled screenings were missed (n = 3).

CONCLUSION

Although more DH patients were identified after care pathway implementation, readmission rates were not reduced and clinical outcomes were not changed. Because DH onset timing varies, some patients have highly acute presentation, and most readmitted patients develop symptoms before reaching their sodium nadir, close symptom monitoring may be a reasonable alternative to routine screening.

Diabetes Insipidus after Pituitary Surgery: Incidence after Traditional versus Endoscopic Transsphenoidal Approaches

The endoscopic transnasal approach is gaining increasing popularity as the surgical method of choice for treatment of pituitary lesions. Previous studies have shown advantages such as quicker recovery and fewer cosmetic, dental, and nasal complications. However, no study has compared the rate of diabetes insipidus (DI) between the traditional and endoscopic approaches. This study will examine the incidence of short-and long-term postoperative DI after transnasal pituitary surgery and compare it with the incidence after traditional transseptal surgery. Eighty-one patients underwent transnasal surgery for the management of pituitary lesions. Fifty-five had the traditional sublabial, transseptal, transsphenoidal surgery and 26 patients had the direct transnasal, transsphenoidal endoscopic procedure. The incidence of immediate postoperative DI was 36% in the traditional group and 15% in the endoscopic group. Short-term (>2 weeks) DI that required treatment occurred in 11 patients (20%) in the traditional group and 2 patients (7.6%) in the endoscopic group. Long-term (>6 months) incidence of DI was 7.2% in the traditional group and 3.8% in the endoscopic group. We found a decreased incidence of immediate DI after transnasal endoscopic pituitary surgery as compared with the traditional sublabial transseptal approach. However, the incidence of long-term DI was not significantly different in the two groups.

Postoperative Diabetes Insipidus and Hyponatremia in Children after Transsphenoidal Surgery for Adrenocorticotropin Hormone and Growth Hormone Secreting Adenomas

OBJECTIVES

To define the incidence and risk factors of postoperative sodium alterations in pediatric patients undergoing transsphenoidal surgery (TSS) for adrenocorticotropic hormone and growth hormone secreting pituitary adenomas.

STUDY DESIGN

We retrospectively reviewed 160 patients ≤18 years of age who had TSS for pituitary adenomas at our institution from 1999 to 2017. Variables included daily serum sodium through postoperative day 10, urine specific gravity, and medications administered. We examined associations between sex, repeat surgery, manipulation of the posterior pituitary (PP), tumor invasion into the PP, tumor type and size, cerebrospinal fluid (CSF) leak, lumbar drain insertion, body mass index, puberty, and development of diabetes insipidus (DI) or syndrome of inappropriate antidiuretic hormone secretion (SIADH).

RESULTS

Mean age was 12.9 ± 3.4 years (female = 81). Patients had adrenocorticotropic hormone (150/160) and growth hormone (10/160) producing adenomas. Forty-two (26%) patients developed DI. Among the 37 of 160 who required desmopressin acutely, 13 of 37 required it long term. Risk of long-term need for desmopressin was significantly higher in patients who had CSF leak 9 of 48 (P = .003), lumbar drain 6 of 30 (P = .019), manipulation 11 of 50 (P < .001), or invasion 4 of 15 (P = .022) of the PP. Sixty patients developed hyponatremia, 19 because of SIADH, 39 to hypotonic fluids and 2 to cerebral salt wasting syndrome. Patients with SIADH were placed on fluid restriction; 1 received salt tablets.

CONCLUSIONS

Among 160 children who underwent TSS for pituitary adenomas, the incidence of DI and SIADH after TSS was 26% and 14%, respectively. Combined risk factors for DI and/or SIADH include female sex, manipulation of and/or tumor invasion into the PP, and CSF leak or lumbar drain.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00001595 and NCT00060541.

Management of non-functioning pituitary adenomas: surgery

Non-functional pituitary adenomas (NFPAs) are benign tumors of the pituitary gland that do not over-secrete hormonal products, therefore, they are generally detected through symptoms of mass effect, including headache, vision loss, or hypopituitarism. There are multiple pathological subtypes of NFPAs, such as null cell adenomas, silent gonadotrophs, silent somatotrophs, silent corticotrophs, and silent subtype 3, all of which can be classified based on immunohistochemical studies and electron microscopy. Despite these numerous pathological subtypes, surgical resection remains the first-line treatment for NFPAs. Diagnosis is best made using high resolution MRI brain with and without gadolinium contrast, which is also helpful in determining the extent of invasion of the tumor and recognizing necessary sinonasal anatomy prior to surgery. Additional pre-operative work-up should include full laboratory endocrine evaluation with replacement of hormone deficiencies, and ideally, full neuro-ophthalmologic exam. Although transcranial surgical approaches to the pituitary gland can be performed, the most common approach used is the transnasal transsphenoidal approach with endoscopic or microscopic visualization. This approach avoids retraction of the brain and cranial nerves during tumor removal. Surgery for symptoms caused by mass effect, including headaches and visual loss, are successfully treated with surgical resection, resulting in improvement in pre-operative symptoms as high as 90% in some reports. Although the risk of complications is low, major and minor events, such as permanent hypopituitarism, persistent CSF leak, and carotid artery injury can occur at rates ranging from zero to about 9%.

Transsphenoidal surgery for pituitary tumours: frequency and predictors of delayed hyponatraemia and their relationship to early readmission

OBJECTIVE

A major cause of readmission after transsphenoidal surgery (TSS) is delayed hyponatraemia. The purpose of this study was to identify predictors of hyponatraemia one week post surgery and predictors of 30-day readmissions for hyponatraemia.

DESIGN

A retrospective cohort study including patients who had TSS performed for pituitary lesions.

METHOD

The risk of readmission for hyponatraemia was assessed in consecutive patients between January 2008 and March 2016. The risk of hyponatraemia one week post surgery was assessed in patients admitted for TSS between July 2011 and March 2016.

RESULTS

Of all included patients, 56/522 (10.7%) were readmitted within 30 days. Hyponatraemia was found in 14/56 (25%) of 30-day readmissions. We did not identify any predictive variable for hyponatraemia on readmission. The number of patients with hyponatraemia on the seventh post-operative day was 26/314 (8.3%). The risk of hyponatraemia one week post surgery was increased by an odds ratio of 2.40 (95% CI: 1.06-5.40) in patients with a tumour abutting the optic chiasm and by an odds ratio of 1.16 (1.04-1.31) per mmol/L decrease in sodium levels on the first post-operative day.

CONCLUSIONS

Hyponatraemia occurred in 25% of readmissions; however, we did not identify any predictive variable for readmission with hyponatraemia. One week post surgery, 8.9% had hyponatraemia. Tumours pressing on the optic chiasm as well as a fall in sodium levels on the first post-operative day were associated with an increased risk of hyponatraemia one week post surgery. We suggest that a day 7 serum sodium <130 nmol/L should lead to concern and the provision of patient advice.

Factors Associated with Postoperative Diabetes Insipidus after Pituitary Surgery

BACKGROUND

Determining risk factors for diabetes insipidus (DI) after pituitary surgery is important in improving patient care. Our objective is to determine the factors associated with DI after pituitary surgery.

METHODS

We reviewed records of patients who underwent pituitary surgery from 2011 to 2015 at Philippine General Hospital. Patients with preoperative DI were excluded. Multiple logistic regression analysis was performed and a predictive model was generated. The discrimination abilities of the predictive model and individual variables were assessed using the receiving operator characteristic curve.

RESULTS

A total of 230 patients were included. The rate of postoperative DI was 27.8%. Percent change in serum Na (odds ratio [OR], 1.39; 95% confidence interval [CI], 1.15 to 1.69); preoperative serum Na (OR, 1.19; 95% CI, 1.02 to 1.40); and performance of craniotomy (OR, 5.48; 95% CI, 1.60 to 18.80) remained significantly associated with an increased incidence of postoperative DI, while percent change in urine specific gravity (USG) (OR, 0.53; 95% CI, 0.33 to 0.87) and meningioma on histopathology (OR, 0.05; 95% CI, 0.04 to 0.70) were significantly associated with a decreased incidence. The predictive model generated has good diagnostic accuracy in predicting postoperative DI with an area under curve of 0.83.

CONCLUSION

Greater percent change in serum Na, preoperative serum Na, and performance of craniotomy significantly increased the likelihood of postoperative DI while percent change in USG and meningioma on histopathology were significantly associated with a decreased incidence. The predictive model can be used to generate a scoring system in estimating the risk of postoperative DI.

Validation of an integrative mathematical model of dehydration and rehydration in virtual humans

Water homeostasis is one of the body's most critical tasks. Physical challenges to the body, including exercise and surgery, almost always coordinate with some change in water handling reflecting the changing needs of the body. Vasopressin is the most important hormone that contributes to short‐term water homeostasis. By manipulating vascular tone and regulating water reabsorption in the collecting duct of the kidneys, vasopressin can mediate the retention or loss of fluids quickly. In this study, we validated HumMod, an integrative mathematical model of human physiology, against six different challenges to water homeostasis with special attention to the secretion of vasopressin and maintenance of electrolyte balance. The studies chosen were performed in normal men and women, and represent a broad spectrum of perturbations. HumMod successfully replicated the experimental results, remaining within 1 standard deviation of the experimental means in 138 of 161 measurements. Only three measurements lay outside of the second standard deviation. Observations were made on serum osmolarity, serum vasopressin concentration, serum sodium concentration, urine osmolarity, serum protein concentration, hematocrit, and cumulative water intake following dehydration. This validation suggests that HumMod can be used to understand water homeostasis under a variety of conditions.

Physiologic Mechanisms of Water and Electrolyte Disturbances After Transsphenoidal Pituitary Surgery

BACKGROUND

Disturbances in water and electrolyte homeostasis are common after transsphenoidal surgery. These disorders are variable and unpredictable, increasing patient risk and complicating postsurgical treatment. Clinically, it is generally accepted that damage to the pituitary is the cause, but the mechanisms behind the response variability and underlying pathophysiology remain unknown.

OBJECTIVE

To test the hypothesis that changing the degree of damage to the pituitary stalk produces a spectrum of water and electrolyte disturbance along which all presentations of postsurgical water and electrolyte disturbances can be identified.

METHODS

We used HumMod, a large mathematical model of physiology, to simulate pituitary stalk damage at differing fractions: 20%, 40%, 60%, and 80%. The damaged neurons were modeled to undergo a 5-day countdown to degeneration and release stored antidiuretic hormone as they die, as is proposed to occur.

RESULTS

Lower pituitary damage (20%) resulted in transient polyuria and intermediate damage (40%) was associated with delayed polyuria and diabetes insipidus. Higher levels of damage (60% and 80%) showed a triphasic pattern of diabetes insipidus.

CONCLUSIONS

We postulate that our model provides a plausible mechanistic explanation for some varieties of postsurgical water and electrolyte disturbances, in which increasing damage to the pituitary potentiates the likelihood of a full triphasic response. However, our simulation shows that merely modifying the level of damage does not produce every presentation of water and electrolyte imbalance. This theory suggests that other mechanisms, which are still unclear and not a part of this model, may be responsible for postoperative hyponatremia and require further investigation.