Functional recovery after partial nephrectomy: next generation analysis

Amount of Ipsilateral Parenchymal Volume Preserved Is a Key Determinant of Split Renal Function after Robot-Assisted Partial Nephrectomy

Objective: To identify factors associated with preserved split renal function (SRF) after robot-assisted partial nephrectomy (RAPN). Patients and Methods: The study included patients who underwent RAPN at Nagasaki University Hospital between November 2016 and December 2023. SRF was determined by 99mTc-dimercaptosuccinic acid renal imaging and the estimated glomerular filtration rate, with measurements obtained before and 6 months after surgery. The ipsilateral parenchymal volume (IPV) was measured at the same time. More than 90% SRF after surgery was considered to indicate successful preservation of renal function (the successful group), and ≤90% SRF was considered failure to preserve renal function (the unsuccessful group). The factors most relevant to SRF were sought in univariate and multivariate analyses. Results: Data for a total of 169 patients were analyzed. The median SRF was 32.04 mL/min/1.73 m2 (interquartile range [IQR] 25.95, 38.06) before surgery and 27.33 mL/min/1.73 m2 (IQR 21.64, 34.32) after surgery. The median SRF preservation rate was 88% (IQR 78.4, 97.0), with 94 cases (55.6%) having SRF >90% and 75 cases (44%) having SRF ≤90%. The median IPV on the surgical side was calculated by the software to be 152.2 cm3 (IQR 126.9, 186.6) preoperatively and 127.3 cm3 (IQR 102.9, 161.3) postoperatively, with a median preservation rate of 84.6% (IQR 72.2, 89.7). Univariate analysis showed significant between-group differences in diabetes status, RENAL Nephrometry score, operation time, warm ischemia time, whether or not parenchymal sutures were needed, and the amount of IPV preserved. Only percentage of IPV preserved remained significant in multivariate analysis. Conclusion: The findings of this study suggest that the residual IPV is an important determinant of SRF after RAPN.

Prolonged ischaemia during partial nephrectomy: impact of warm vs cold

OBJECTIVE

To evaluate the impact of prolonged ischaemia during partial nephrectomy (PN), which remains understudied despite its potential clinical relevance.

PATIENTS AND METHODS

Of 1371 patients managed with on-clamp PN (2011-2014), 759 (55%) had imaging and assessment of serum creatinine levels before and after PN within the appropriate timeframes necessary for inclusion. This timeframe was chosen to allow for a robust analysis of both warm and cold ischaemia. Recovery from ischaemia (Recischaemia) was defined as ipsilateral glomerular filtration rate (GFR) preserved, normalized by percentage of parenchymal volume preserved (PPVP), and would be 100% if all nephrons recovered completely from ischaemia. Pearson correlation and multivariable linear regression models were used to assess associations between Recischaemia and ischaemia type and duration.

RESULTS

Of 759 patients, 525 (69%) were managed with warm ischaemia. The median warm/cold ischaemia times were 22 and 30 min, respectively. Overall, the median percent ipsilateral GFR preserved, PPVP and Recischaemia were 79%, 83% and 96%, respectively. Segmented regression analysis demonstrated substantially greater decline in Recischaemia, beginning at approximately 30 min for warm ischaemia, which was not observed for hypothermia. Prolonged ischaemia (defined as >30 min) occurred in 197 patients (26%; 88 warm/109 cold). For limited ischaemia (≤30 min), hypothermia was often used for tumours with increased tumour size and complexity (P < 0.01), while for prolonged ischaemia, the warm/cold subgroups had similar patient and tumour characteristics. For limited ischaemia and prolonged hypothermia, median Recischaemia remained >95%, independent of ischaemia time. Differences in Recischaemia between the warm and cold cohorts became significant only after 30 min (P < 0.05). On multivariable analysis, prolonged warm ischaemia was associated with reduced Recischaemia (P = 0.02), which fell 3.9% for every additional 10 min beyond 30 min.

CONCLUSIONS

Our data suggest that Recischaemia begins to decline significantly after 30 min during PN, although hypothermia was protective. Avoidance of prolonged warm ischaemia should be prioritized in patients with solitary kidneys and/or significant pre-existing chronic kidney disease.

Renal parenchymal volume analysis: Clinical and research applications

Background and Objectives

In most patients, the renal parenchymal volumes in each kidney directly correlate with function and can be used as a proxy to determine split renal function (SRF). This simple principle forms the basis for parenchymal volume analysis (PVA) with semiautomated software, which can be leveraged to predict SRF and new-baseline glomerular filtration rate (NBGFR) following nephrectomy. PVA was originally used to evaluate renal transplantation donors and has replaced nuclear renal scans (NRS) in this domain. PVA has subsequently been explored for the management of patients with kidney cancer for whom difficult decisions about radical versus partial nephrectomy can be influenced by accurate prediction of NBGFR. Our objective is to present a comprehensive review of the applications of PVA in urology including their clinical and research implications.

Methods

Key articles utilizing renal PVA to improve clinical care and facilitate urologic research were reviewed with special emphasis on take-home points of clinical relevance and their contributions to progress in the field.

Results

There have been considerable advances in renal PVA over the past 15 years, which is now established as a reference standard for the prediction of functional outcomes after renal surgery. PVA provides improved accuracy when compared to NRS-based estimates or non-SRF-based algorithms. PVA can be performed in minutes using routine preoperative cross-sectional imaging and can be readily applied at the point of care. Additionally, PVA has important research applications, enabling the precise study of the determinants of functional recovery after partial nephrectomy, which can affect surgical approaches to this procedure.

Conclusions

Despite the wide availability of PVA, primarily for use in renal transplantation, it has not been widely implemented for other urologic purposes at most centres. Our hope is that this narrative review will increase PVA utilization in urology and facilitate further progress in the field.

A Fully Automated Artificial Intelligence-Based Approach to Predict Renal Function After Radical or Partial Nephrectomy

OBJECTIVE

To test if our artificial intelligence (AI)-postoperative glomerular filtration rate (GFR) prediction is as accurate as a validated clinical model. The American Urologic Association recommends estimating postoperative GFR in patients with renal masses and prioritizing partial nephrectomy (PN) when GFR would be <45 ml/minutes/1.73 m2 if radical nephrectomy (RN) was performed. Previously validated models have limited clinical uptake.

METHODS

We included 300 patients undergoing nephrectomy for renal tumors from the KiTS19 challenge. Preoperative GFR was collected just before surgery, and new baseline GFR 3-12 months postoperatively. Split-renal function (SRF) was determined in a fully automated way from preoperative computed tomography, combining our deep learning segmentation model, then using those segmentation masks to estimate postoperative GFR = 1.24 × GFRPre-RN × SRFContralateral for RN and 89% of GFRpreoperative for PN. A clinical model estimated postoperative GFR = 35 + GFRpreoperative x 0.65-18 (if RN)-age x 0.25 + 3 (if tumor>7 cm)-2 (if diabetes). We compared the AI and clinical model GFR estimations to the measured postoperative GFR using correlation coefficients and their ability to predict GFR < 45 using logistic regression.

RESULTS

Median age was 60 years, 41% were female, and 62% had PN. Median tumor size was 4.2 cm, and 92% were malignant. Compared to the measured postoperative GFR, correlation coefficients were 0.75 and 0.77 for the AI and clinical models, respectively. The AI and clinical models performed similarly for predicting GFR < 45 (areas under the curve 0.89 and 0.9, respectively).

CONCLUSION

Our fully automated prediction of new baseline renal function is as accurate as a validated clinical model without needing clinical details, clinician time, or measurements.

Impact of tumor dissecting technique on trifecta achievement in patients requiring extended warm ischemia during robot-assisted partial nephrectomy

PURPOSE

To clarify specific factors associated with surgical outcomes in robot-assisted partial nephrectomy (RAPN) that require extended warm ischemia time (WIT), which may have a negative impact, but cannot always be avoided.

METHODS

We included 1,182 patients who had RAPN performed between January 2016 and December 2022 from a prospectively generated multi-institutional RAPN database, divided into normal WIT (nWIT) (≤ 20 min; 843 patients) and extended WIT (eWIT) (> 20 min; 339 patients) groups. Primary outcome measures were WIT and the Surface-Intermediate-Base (SIB) margin score, which contribute to postoperative trifecta achievement. Results were compared between the two groups using logistic regression.

RESULTS

Patients in the eWIT group had larger tumors, higher RENAL nephrometry scores, and lower SIB scores than those of the nWIT group. The trifecta achievement rate was significantly different between the two groups (nWIT: 70.1 vs. 49.0%, p < 0.001). In the nWIT group, WIT (coefficient: -0.105 [standard error 0.020], p < 0.001) and SIB score (coefficient: -0.107 [0.053], p = 0.045) were significant predictors of trifecta achievement. In the eWIT group, the SIB score (coefficient - 0.216 [0.082], p = 0.008) was significantly associated with trifecta attainment, whereas WIT only showed a trend toward significance. Limitations included a lack of long-term survival, renal function, and chronic complications data.

CONCLUSIONS

For patients with eWIT during RAPN, the tumor dissection technique may be more important than WIT in predicting postoperative outcomes. Further prospective studies are required to confirm our results.

Parenchymal obliteration by renal masses: Functional and oncologic implications

OBJECTIVES

Most renal tumors merely displace nephrons while others can obliterate parenchyma in an invasive manner. Substantial parenchymal volume replacement (PVR) by renal cell carcinoma (RCC) may have oncologic implications; however, studies regarding PVR remain limited. Our objective was to evaluate the oncologic implications associated with PVR using improved methodology including more accurate and objective tools.

PATIENTS/METHODS

A total of 1,222 patients with non-metastatic renal tumors managed with partial nephrectomy (PN) or radical nephrectomy (RN) at Cleveland Clinic (2011-2014) with necessary studies were retrospectively evaluated. Parenchymal volume analysis via semiautomated software was used to estimate split renal function and preoperative parenchymal volumes. Using the contralateral kidney as a control, %PVR was defined: (parenchymal volumecontralateral-parenchymal volumeipsilateral) normalized by parenchymal volumecontralateral x100%. PVR was determined preoperatively and not altered by management. Patients were grouped by degree of PVR: minimal (<5%, N = 566), modest (5%-25%, N = 414), and prominent (≥25%, N = 142). Kaplan-Meier was used to evaluate survival outcomes relative to degree of PVR. Multivariable Cox-regression models evaluated predictors of recurrence-free survival (RFS).

RESULTS

Of 1,122 patients, 801 (71%) were selected for PN and 321 (29%) for RN. Overall, median tumor size was 3.1 cm and 6.8 cm for PN and RN, respectively, and median follow-up was 8.6 years. Median %PVR was 15% (IQR = 6%-29%) for patients selected for RN and negligible for those selected for PN. %PVR correlated inversely with preoperative ipsilateral GFR (r = -0.49, P < 0.01) and directly with advanced pathologic stage, high tumor grade, clear cell histology, and sarcomatoid features (all P < 0.01). PVR≥25% associated with shortened recurrence-free, cancer-specific, and overall survival (all P < 0.01). Male sex, ≥pT3a, tumor grade 4, positive surgical margins, and PVR≥25% independently associated with reduced RFS (all P < 0.02).

CONCLUSIONS

Obliteration of normal parenchyma by RCC substantially impacts preoperative renal function and patient selection. Our data suggests that increased PVR is primarily driven by aggressive tumor characteristics and independently associates with reduced RFS, although further studies will be needed to substantiate our findings.

Parenchymal volume preservation during partial nephrectomy: improved methodology to assess impact and predictive factors

OBJECTIVE

To rigorously evaluate the impact of the percentage of parenchymal volume preserved (PPVP) and how well the preserved parenchyma recovers from ischaemia (Recischaemia) on functional outcomes after partial nephrectomy (PN) using an accurate and objective software-based methodology for estimating parenchymal volumes and split renal function (SRF). A secondary objective was to assess potential predictors of the PPVP.

PATIENTS AND METHODS

A total of 894 PN patients with available studies (2011-2014) were evaluated. The PPVP was measured from cross-sectional imaging at ≤3 months before and 3-12 months after PN using semi-automated software. Pearson correlation evaluated relationships between continuous variables. Multivariable linear regression evaluated predictors of ipsilateral glomerular filtration rate (GFR) preserved and the PPVP. Relative-importance analysis was used to evaluate the impact of the PPVP on ipsilateral GFR preserved. Recischaemia was defined as the percentage of ipsilateral GFR preserved normalised by the PPVP.

RESULTS

The median tumour size and R.E.N.A.L. nephrometry score were 3.4 cm and 7, respectively. In all, 49 patients (5.5%) had a solitary kidney. In all, 538 (60%)/251 (28%)/104 (12%) patients were managed with warm/cold/zero ischaemia, respectively. The median pre/post ipsilateral GFRs were 40/31 mL/min/1.73 m2, and the median (interquartile range [IQR]) percentage of ipsilateral GFR preserved was 80% (71-88%). The median pre/post ipsilateral parenchymal volumes were 181/149 mL, and the median (IQR) PPVP was 84% (76-92%). In all, 330 patients (37%) had a PPVP of <80%, while only 34 (4%) had a Recischaemia of <80%. The percentage of ipsilateral GFR preserved correlated strongly with the PPVP (r = 0.83, P < 0.01) and loss of parenchymal volume accounted for 80% of the loss of ipsilateral GFR. Multivariable analysis confirmed that the PPVP was the strongest predictor of ipsilateral GFR preserved. Greater tumour size and endophytic and nearness properties of the R.E.N.A.L. nephrometry score were associated with a reduced PPVP (all P ≤ 0.01). Solitary kidney and cold ischaemia were associated with an increased PPVP (all P < 0.05).

CONCLUSIONS

A reduced PPVP predominates regarding functional decline after PN, although a low Recischaemia can also contribute. Tumour-related factors strongly influence the PPVP, while surgical efforts can improve the PPVP as observed for patients with solitary kidneys.

Practical Prediction of New Baseline Renal Function After Partial Nephrectomy

BACKGROUND

Partial nephrectomy (PN) is generally preferred for localized renal masses due to strong functional outcomes. Accurate prediction of new baseline glomerular filtration rate (NBGFR) after PN may facilitate preoperative counseling because NBGFR may affect long-term survival, particularly for patients with preoperative chronic kidney disease. Methods for predicting parenchymal volume preservation, and by extension NBGFR, have been proposed, including those based on contact surface area (CSA) or direct measurement of tissue likely to be excised/devascularized during PN. We previously reported that presuming 89% of global GFR preservation (the median value saved from previous, independent analyses) is as accurate as the more subjective/labor-intensive CSA and direct measurement approaches. More recently, several promising complex/multivariable predictive algorithms have been published, which typically include tumor, patient, and surgical factors. In this study, we compare our conceptually simple approach (NBGFRPost-PN = 0.90 × GFRPre-PN) with these sophisticated algorithms, presuming that an even 90% of the global GFR is saved with each PN.

PATIENTS AND METHODS

A total of 631 patients with bilateral kidneys who underwent PN at Cleveland Clinic (2012-2014) for localized renal masses with available preoperative/postoperative GFR were analyzed. NBGFR was defined as the final GFR 3-12 months post-PN. Predictive accuracies were assessed from correlation coefficients (r) and mean squared errors (MSE).

RESULTS

Our conceptually simple approach based on uniform 90% functional preservation had equivalent r values when compared with complex, multivariable models, and had the lowest degree of error when predicting NBGFR post-PN.

CONCLUSIONS

Our simple formula performs equally well as complex algorithms when predicting NBGFR after PN. Strong anchoring by preoperative GFR and minimal functional loss (≈ 10%) with the typical PN likely account for these observations. This formula is practical and can facilitate counseling about expected postoperative functional outcomes after PN.

Functional recovery after partial nephrectomy in a solitary kidney

OBJECTIVES

Partial nephrectomy (PN) is the reference standard for renal mass in a solitary kidney (RMSK), although factors determining functional recovery in this setting remain poorly defined.

PATIENTS/METHODS

Single center, retrospective analysis of 841 RMSK patients (1975-2022) managed with PN with functional data, including 361/435/45 with cold/warm/zero ischemia, respectively. A total of 155 of these patients also had necessary studies for detailed analysis of parenchymal volume preserved. Acute kidney injury (AKI) was classified by RIFLE (Risk/Injury/Failure/Loss/Endstage). Recovery-from-ischemia (Rec-Ischemia) was defined as glomerular filtration rate (GFR) saved normalized by parenchymal volume saved. Logistic regression identified predictive factors for AKI and predictors of Rec-Ischemia were analyzed by multivariable linear regression.

RESULTS

Overall, median preoperative GFR was 56.7 ml/min/1.73m2 and new-baseline and 5-year GFRs were 43.1 and 44.5 ml/min/1.73m2, respectively. Median follow-up was 55 months; 5-year dialysis-free survival was 97%. In the detailed analysis cohort, a primary focus of this study, median warm (n = 70)/cold (n = 85) ischemia times were 25/34 minutes, respectively; and median preoperative, new-baseline and 5-year GFRs were 57.8, 45.0, and 41.7 ml/min/1.73m2, respectively. Functional recovery correlated strongly with parenchymal volume preserved (r = 0.84, p < 0.001). Parenchymal volume loss accounted for 69% of the total median GFR decline associated with PN, leaving only 3 to 4 ml/min/1.73m2 attributed to ischemia and other factors. AKI occurred in 52% of patients and the only independent predictor of AKI was ischemia time. Independent predictors of reduced Rec-Ischemia were increased age, warm ischemia, and AKI.

CONCLUSION

The main determinant of functional recovery after PN in RMSK is parenchymal volume preservation. Type/duration of ischemia, AKI, and age also correlated, although altogether their contributions were less impactful. Our findings suggest multiple opportunities for optimizing functional outcomes although preservation of parenchymal volume remains predominant. Long-term function generally remains stable with dialysis only occasionally required.

Can the Abdominal Aortic Atherosclerotic Plaque Index Predict Functional Outcomes after Robot-Assisted Partial Nephrectomy?

This study aims to evaluate the abdominal aortic atherosclerotic plaque index (API)'s predictive role in patients with pre-operatively or post-operatively developed chronic kidney disease (CKD) treated with robot-assisted partial nephrectomy (RAPN) for renal cell carcinoma (RCC). One hundred and eighty-three patients (134 with no pre- and post-operative CKD (no CKD) and 49 with persistent or post-operative CKD development (post-op CKD)) who underwent RAPN between January 2019 and January 2022 were deemed eligible for the analysis. The API was calculated using dedicated software by assessing the ratio between the CT scan atherosclerotic plaque volume and the abdominal aortic volume. The ROC regression model demonstrated the influence of API on CKD development, with an increasing effect according to its value (coefficient 0.13; 95% CI 0.04-0.23; p = 0.006). The Model 1 multivariable analysis of the predictors of post-op CKD found that the following are independently associated with post-op CKD: Charlson Comorbidity Index (OR 1.31; p = 0.01), last follow-up (FU) Δ%eGFR (OR 0.95; p < 0.01), and API ≥ 10 (OR 25.4; p = 0.01). Model 2 showed API ≥ 10 as the only factor associated with CKD development (OR 25.2; p = 0.04). The median follow-up was 22 months. Our results demonstrate API to be a strong predictor of post-operative CKD, allowing the surgeon to tailor the best treatment for each patient, especially in those who might be at higher risk of CKD.

Parenchymal volume analysis to assess longitudinal functional decline following partial nephrectomy

OBJECTIVE

To identify factors associated with longitudinal ipsilateral functional decline after partial nephrectomy (PN).

PATIENTS AND METHODS

Of 1140 patients managed with PN (2012-2014), 349 (31%) had imaging/serum creatinine levels pre-PN, 1-12 months post-PN (new baseline), and >3 years later necessary for inclusion. Parenchymal-volume analysis was used to determine split renal function. Patients were grouped as having significant renal comorbidity (CohortSRC : diabetes mellitus with insulin-dependence or end-organ damage, refractory hypertension, or severe pre-existing chronic kidney disease) vs not having significant renal comorbidity (CohortNoSRC ) preoperatively. Multivariable regression was used to identify predictors of annual ipsilateral parenchymal atrophy and functional decline relative to new baseline values post-PN, after the kidney had healed.

RESULTS

The median follow-up was 6.3 years with 87/226/36 patients having cold/warm/zero ischaemia. The median cold/warm ischaemia times were 32/22 min. Overall, the median tumour size was 3.0 cm. The preoperative glomerular filtration rate (GFR) and new baseline GFR (NBGFR) were 81 and 71 mL/min/1.73 m2 , respectively. After establishment of the NBGFR, the median loss of global and ipsilateral function was 0.7 and 0.4 mL/min/1.73 m2 /year, respectively, consistent with the natural ageing process. Overall, the median ipsilateral parenchymal atrophy was 1.2 cm3 /year and accounted for a median of 53% of the annual functional decline. Significant renal comorbidity, age, and warm ischaemia were independently associated with ipsilateral parenchymal atrophy (all P < 0.01). Significant renal comorbidity and ipsilateral parenchymal atrophy were independently associated with annual ipsilateral functional decline (both P < 0.01). Annual median ipsilateral parenchymal atrophy and functional decline were both significantly increased for CohortSRC compared to CohortNoSRC (2.8 vs 0.9 cm3 , P < 0.01 and 0.90 vs 0.30 mL/min/1.73 m2 /year, P < 0.01, respectively).

CONCLUSIONS

Longitudinal renal function following PN generally follows the normal ageing process. Significant renal comorbidities, age, warm ischaemia, and ipsilateral parenchymal atrophy were the most important predictors of ipsilateral functional decline following establishment of NBGFR.