Split renal function in patients with renal masses: utility of parenchymal volume analysis vs nuclear renal scans

Can parenchymal volume analysis replace nuclear renal scans for split renal function before and after partial nephrectomy with warm ischemia?

BACKGROUND

The assessment of split renal function (SRF) before and after partial nephrectomy (PN) is crucial. While nuclear renal scan (NRS) is a traditional method for evaluating SRF, its extensive use is hindered by concerns regarding radioactivity. Parenchymal volume analysis (PVA) has been employed to assess SRF for kidney donors. Nonetheless, the efficacy of PVA in evaluating SRF in kidneys with renal masses before and after PN with warm ischemia remains uncertain.

AIM

The current study probed into the potential of PVA as a substitute for NRS in assessing SRF before and after PN with warm ischemia.

METHODS

This study included 318 patients who underwent unilateral PN with warm ischemia at Sun Yat-Sen University Cancer Center (SYSUCC) and had a functional contralateral kidney. All patients underwent PVA and NRS assessments both pre-PN and at 1-12 months post-PN. PVA was analyzed using Mimics software in the venous phase. The estimated glomerular filtration rate (eGFR) was calculated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) 2021 equation. The correlation between ipsilateral eGFR values derived from SRF assessed via PVA and NRS was examined using Pearson correlation. Concordance between different methods of SRF estimation was analyzed using the Friedman test, Bland-Altman plots, and Kendall's consistency coefficient. Similar study was conducted on a comparable cohort from Sun Yat-Sen Memorial Hospital.

RESULTS

The median tumor size was 3.5cm, and the median warm ischemia time was 25min. Preoperatively, ipsilateral SRF values based on PVA were notably consistent with those derived from NRS (49.4% vs 50.0%, P = .501). A strong correlation was observed between preoperative ipsilateral eGFR based on SRF from PVA and NRS (r = 0.89, P < .0001). Bland-Altman plots indicated minimal bias (-0.36%) between PVA and NRS in assessing SRF. However, post-PN, the median ipsilateral SRF based on PVA was slightly higher than that based on NRS (45.6% vs. 43.6%, P < .0001). Although there was still a strong correlation between post-PN ipsilateral eGFR based on SRF from PVA and NRS (r = 0.87, P < .0001), Bland-Altman plots revealed a non-negligible bias between the 2 methods (2.19 %). External study supported our findings.

CONCLUSIONS

PVA shows promise as a substitute for NRS in assessing SRF before PN with warm ischemia. However, this substitution may result in an overestimation of ipsilateral renal function in the post-PN phase.

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.

Quantifying preserved renal volume and function in patients undergoing standard partial nephrectomy vs. tumor enucleation for localized renal tumors

INTRODUCTION

Renal parenchymal volume loss from standard partial nephrectomy (SPN) is a significant prognosticator for postoperative renal function. Tumor enucleation (TE) minimizes parenchymal loss compared to SPN. Little is known regarding discrete changes in renal function associated with volume loss. We sought to quantify the differences between SPN and TE in preserving parenchymal volume and estimated glomerular filtration rate (eGFR).

METHODS

We identified 420 patients who underwent robotic partial nephrectomy (SPN or TE) at our tertiary care center from 2009 to 2022. Parenchymal volumes were calculated using TeraRecon 3D reconstruction software from axial imaging performed preoperatively and within 6 months postoperatively. Renal volume preserved and renal function were evaluated with multivariable linear and logistic regression models.

RESULTS

At 1 year, eGFR was 7% lower in patients undergoing SPN compared to TE (P < 0.01). Across both SPN and TE, only volume of preserved parenchyma was predictive of eGFR and chronic kidney disease (CKD) progression (both P < 0.01). TE preserved more healthy parenchymal volume compared to SPN (median percentage 97.6% vs 89.2%; P < 0.001). Each 1% of volumetric loss corresponded to a 0.35% decrease in eGFR at 1 year postoperatively (P < 0.01).

CONCLUSIONS

Volume of preserved renal parenchyma was the strongest factor associated with preserved eGFR and reduced odds of CKD progression. TE preserved more parenchyma than SPN, which translated to higher eGFR preservation at 1 year postoperatively.

Utilizing computed tomography-based renal parenchymal volumes to calculate split renal function in patients with ureteral stricture disease

PURPOSE

Evaluation of split renal function (SRF) is critical for guiding surgical treatment decisions for patients with ureteral stricture disease (USD). We aimed to determine whether computed tomography (CT)-based renal parenchymal volumes may be used to predict SRF in patients with USD.

METHODS

We retrospectively reviewed all patients undergoing surgical management for USD at a single institution from October 2021 to January 2024. Patients who had preoperative nuclear medicine scan (NMS) and CT scan with intravenous contrast that were obtained within six weeks of each other were included. Interval between NMS and CT could be longer if the affected renal unit was drained with ureteral stent and/or percutaneous nephrostomy. Volume measurements were obtained using the 3D Region of Interest (ROI) Tool on Visage®7 Enterprise Imaging Platform (Visage Inc., San Diego, USA) by two investigators that were blinded to NMS derived SRF. Intraclass correlation coefficient (ICC) was used to assess consistency between investigators. Predictive accuracy was assessed using Pearson correlation coefficient (r) and linear regression.

RESULTS

40 of 160 patients met inclusion criteria. There was excellent reliability in calculating renal parenchymal volume between raters (ICC = 0.990). There was a strong linear correlation between estimated CT SRF and NMS SRF (r = 0.912, p < 0.00001). A linear regression model found RObservedSRF = -0.013 + 1.015(REstimatedSRF), with r2 = 0.832.

CONCLUSION

CT-derived parenchymal volume analysis may be used to estimate SRF in patients with USD. This may obviate the need to obtain preoperative renal scans for SRF measurement in selected patients when assessing surgical management options.

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.

Evaluation of split renal dysfunction using radiomics based on magnetic resonance diffusion-weighted imaging

BACKGROUND

Accurate and noninvasive assessment of split renal dysfunction is crucial, while there is lack of corresponding method clinically.

PURPOSE

To investigate the feasibility of using diffusion-weighted imaging (DWI)-based radiomics models to evaluate split renal dysfunction.

METHODS

We enrolled patients with impaired and normal renal function undergoing renal DWI examination. Glomerular filtration rate (GFR, mL/min) was measured using 99mTc-DTPA scintigraphy, which is reference standard of GFR measurement. The kidneys were classified into normal (GFR ≥40), mildly impaired (20≤ GFR < 40), moderately impaired (10≤ GFR < 20), and severely impaired (GFR < 10) renal function groups. Optimized subsets of radiomics features were selected from renal DWI images and radiomics scores (Rad-score) calculated to discriminate groups with different renal function. The radiomics model (Rad-score based) was developed in a training cohort and validated in a test cohort. Evaluations were conducted on the discrimination, calibration, and clinical application of the method.

RESULTS

The final analysis included 330 kidneys. Logistic regression was used to develop three radiomics models, model A, B, and C, which were used to distinguish normal from impaired, mild from moderate, and moderate from severe renal function, respectively. The area under the curve of the three models were 0.822, 0.704, and 0.887 in the training cohort and 0.843, 0.717, and 0.897 in the test cohort, respectively, indicating efficient discrimination performance.

CONCLUSIONS

DWI-based radiomics models have potential for evaluating split renal dysfunction and discriminating between normal and impaired renal function groups and their subgroups.

Real-time estimation of nephron activity with a linear measurement system (RENAL-MS) predicts postoperative estimated glomerular filtration rate

OBJECTIVE

To determine whether a simple point-of-care measurement system estimating renal parenchymal volume using tools ubiquitously available could be used to replace nuclear medicine renal scintigraphy (NMRS) in current clinical practice to predict estimated glomerular filtration rate (eGFR) after nephrectomy by estimating preoperative split renal function.

PATIENTS AND METHODS

We performed a retrospective review of patients who underwent abdominal cross-sectional imaging (computed tomography/magnetic resonance imaging) and mercaptoacetyltriglycine (MAG3) NMRS prior to total nephrectomy at a single institution. We developed the real-time estimation of nephron activity with a linear measurement system (RENAL-MS) method of estimating postoperative renal function via the following technique: renal parenchymal volume of the removed kidney relative to the remaining kidney was estimated as the product of renal length and the average of six renal parenchymal thickness measurements. The utility of this value was compared to the utility of the split renal function measured by MAG3 for prediction of eGFR and new onset Stage 3 chronic kidney disease (CKD) at ≥90 days after nephrectomy using uni- and multivariate linear and logistic regression.

RESULTS

A total of 57 patients met the study criteria. The median (interquartile range [IQR]) age was 69 (61-80) years. The median (IQR) pre- and postoperative eGFR was 74 (IQR 58-90) and 46 (35-62) mL/min/1.73 m2 , respectively. [Correction added on 29 December 2023, after first online publication: The data numbers in the preceding sentence have been corrected.] Correlations between actual and predicted postoperative eGFR were similar whether the RENAL-MS or NMRS methods were used, with correlation using RENAL-MS being slightly numerically but not statistically superior (R = 0.82 and 0.76; P = 0.138). Receiver operating characteristic curve analysis using logistic regression estimates incorporating age, sex, and preoperative creatinine to predict postoperative Stage 3 CKD were similar between RENAL-MS and NMRS (area under the curve 0.93 vs. 0.97). [Correction added on 29 December 2023, after first online publication: The data numbers in the preceding sentence have been corrected.] CONCLUSION: A point-of-care tool to estimate renal parenchymal volume (RENAL-MS) performed equally as well as NMRS to predict postoperative eGFR and de novo Stage 3 CKD after nephrectomy in our population, suggesting NMRS may not be necessary in this setting.

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.

Predicting new-baseline glomerular filtration rate (NBGFR) after donor nephrectomy: validation of a split renal function (SRF)-based formula

BACKGROUND

Accurate prediction of post-donor nephrectomy (DN) glomerular filtration rate is potentially useful for evaluating and counselling living kidney donors. Currently, there are limited tools to evaluate post-operative new-baseline glomerular filtration rate (NBGFR) in kidney donors. We aim to validate a conceptually simple formula based on split renal function (SRF) previously developed for radical nephrectomy patients.

METHODS

Eighty-three consecutive patients who underwent DN from 2010 to 2016 were included. Pre-operative CT imaging and functional data including pre-DN baseline Global GFR (108.2 ± 13.2 mL/min/1.73m2) were included. Observed NBGFR was defined as the latest eGFR 3-12 months post-DN. SRF, defined as volume of the contralateral non-resected kidney normalised by total volume of kidneys, was determined from pre-operative cross-sectional imaging (49.2 ± 2.36%). The equation derived from Rathi et al. is as detailed: Predicted NBGFR = 1.24 × (Global GFR Pre-DN) x (SRF).

RESULTS

The relationship between predicted NBGFR (66.0 ± 8.29 mL/min/1.73m2) and observed NBGFR (74.9 ± 16.4 mL/min/1.73m2) was assessed by evaluating correlation coefficients, bias, precision, accuracy, and concordance. The new SRF-based formula for NBGFR prediction correlated strongly with observed post-operative NBGFR (Pearson's r = 0.729) demonstrating minimal bias (median difference = 7.190 mL/min/1.73m2) with good accuracy (96.4% within ± 30%, 62.7% within ± 15%) and precision (IQR of bias =  - 0.094 to 16.227).

CONCLUSION

The SRF-based formula was also able to accurately discriminate all but one patient to an NBGFR of > 45 mL/min/1.73m2. We utilised the newly developed SRF-based formula for predicting NBGFR in a living kidney donor population. Counselling of donor post-operative renal outcomes may then be optimised pre-operatively.

Predicting estimated glomerular filtration rate after partial and radical nephrectomy based on split renal function measured by radionuclide: a large-scale retrospective study

PURPOSE

The purpose of this study was to develop predictive models for postoperative estimated glomerular filtration rate (eGFR) based on the split glomerular filtration rate measured by radionuclide (rGFR), as choosing radical nephrectomy (RN) or partial nephrectomy (PN) for complex renal masses requires accurate prediction of postoperative eGFR.

METHODS

Patients who underwent RN or PN for a single renal mass at Xijing Hospital between 2008 and 2022 were retrospectively included. Preoperative split rGFR was evaluated using technetium-99 m-diethylenetriaminepentaacetic acid (Tc-99 m DTPA) renal dynamic imaging, and the postoperative short-term (< 7 days) and long-term (3 months to 5 years) eGFRs were assessed. Linear mixed-effect models were used to predict eGFRs, with marginal R2 reflecting predictive ability.

RESULTS

After excluding patients with missing follow-up eGFRs, the data of 2251 (RN: 1286, PN: 965) and 2447 (RN: 1417, PN: 1030) patients were respectively included in the long-term and short-term models. Two models were established to predict long-term eGFRs after RN (marginal R2 = 0.554) and PN (marginal R2 = 0.630), respectively. Two other models were established to predict short-term eGFRs after RN (marginal R2 = 0.692) and PN (marginal R2 = 0.656), respectively. In terms of long-term eGFRs, laparoscopic and robotic surgery were superior to open surgery in both PN and RN.

CONCLUSIONS

We developed novel tools for predicting short-term and long-term eGFRs after RN and PN based on split rGFR that can help in preoperative decision-making.

Preoperative Renal Parenchyma Volume as a Predictor of Kidney Function Following Nephrectomy of Complex Renal Masses

Background

The von Hippel-Lindau disease (VHL) is a hereditary cancer syndrome with multifocal, bilateral cysts and solid tumors of the kidney. Surgical management may include multiple extirpative surgeries, which ultimately results in parenchymal volume loss and subsequent renal function decline. Recent studies have utilized parenchyma volume as an estimate of renal function prior to surgery for renal cell carcinoma; however, it is not yet validated for surgically altered kidneys with multifocal masses and complex cysts such as are present in VHL.

Objective

We sought to validate a magnetic resonance imaging (MRI)-based volumetric analysis with mercaptoacetyltriglycine (MAG-3) renogram and postoperative renal function.

Design setting and participants

We identified patients undergoing renal surgery at the National Cancer Institute from 2015 to 2020 with preoperative MRI. Renal tumors, cysts, and parenchyma of the operated kidney were segmented manually using ITK-SNAP software.

Outcome measurements and statistical analysis

Serum creatinine and urinalysis were assessed preoperatively, and at 3- and 12-mo follow-up time points. Estimated glomerular filtration rate (eGFR) was calculated using serum creatinine-based CKD-EPI 2021 equation. A statistical analysis was conducted on R Studio version 4.1.1.

Results and limitations

Preoperative MRI scans of 113 VHL patients (56% male, median age 48 yr) were evaluated between 2015 and 2021. Twelve (10.6%) patients had a solitary kidney at the time of surgery; 59 (52%) patients had at least one previous partial nephrectomy on the renal unit. Patients had a median of three (interquartile range [IQR]: 2-5) tumors and five (IQR: 0-13) cysts per kidney on imaging. The median preoperative GFR was 70 ml/min/1.73 m2 (IQR: 58-89). Preoperative split renal function derived from MAG-3 studies and MRI split renal volume were significantly correlated (r = 0.848, p < 0.001). On the multivariable analysis, total preoperative parenchymal volume, solitary kidney, and preoperative eGFR were significant independent predictors of 12-mo eGFR. When only considering patients with two kidneys undergoing partial nephrectomy, preoperative parenchymal volume and eGFR remained significant predictors of 12-mo eGFR.

Conclusions

A parenchyma volume analysis on preoperative MRI correlates well with renogram split function and can predict long-term renal function with added benefit of anatomic detail and ease of application.

Patient summary

Prior to kidney surgery, it is important to understand the contribution of each kidney to overall kidney function. Nuclear medicine scans are currently used to measure split kidney function. We demonstrated that kidney volumes on preoperative magnetic resonance imaging can also be used to estimate split kidney function before surgery, while also providing essential details of tumor and kidney anatomy.

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.

Long-term effect of acute ischemic injury on the kidney underwent clamped partial nephrectomy

GFR reaches a new baseline, primarily correlating with nephron-mass preservation, 1-12 months after partial nephrectomy (PN). However, does the ipsilateral GFR experience subsequent decline, and does acute ischemic injury has long-term effect on the operated kidney? 319 patients with two kidneys and unilateral clamped PN were analyzed. All had preoperative, new-baseline, and latest follow-up imaging/serum creatinine levels. Annual ipsilateral GFR decline rate (AIGDR) was defined as new-baseline GFR minus latest follow-up GFR normalized by new-baseline GFR, per year. Spectrum score was used to reflect the degree of acute ischemic injury in the operated kidney. 100 subjects searching for health screening served as controls. Predictive factors for AIGDR were assessed. The median AIGDR was 2.25%, significantly higher than controls (0.88%, p = 0.036). With some contralateral hypertrophy, the global annual GFR decline was similar to that of controls (0.81% vs. 0.88%, p = 0.7). Spectrum score correlated significantly with AIGDR (p = 0.037). These results support that acute ischemic injury has long-term effect on the operated kidney.

Volumetric and functional outcomes at 1-year between percutaneous-ablation and partial-nephrectomy for T1b renal tumors

INTRODUCTION

Indication for percutaneous-ablation (PA) is gradually expanding to renal tumors T1b (4-7cm). Few data exist on the alteration of renal functional volume (RFV) post-PA. Yet, it is a surrogate marker of post partial-nephrectomy (PN) glomerular filtration rate (GFR) impairment. The objective was to compare RFV and GFR at 1-year post-PN or PA, in this T1b population.

METHODS

Patients with unifocal renal tumor≥4cm treated between 2014 and 2019 were included. Tumor, homolateral (RFVh), contralateral RFV, and total volumes were assessed by manual segmentation (3D Slicer) before and at 1 year of treatment, as was GFR. The loss of RFV, contralateral hypertrophy, and preservation of GFR were compared between both groups (PN vs. PA).

RESULTS

144 patients were included (87PN, 57PA). Preoperatively, PA group was older (74 vs. 59 years; P<0.0001), had more impaired GFR (73 vs. 85mL/min; P=0.0026) and smaller tumor volume(31.1 vs. 55.9cm3; P=0.0007) compared to PN group. At 1 year, the PN group had significantly more homolateral RFV loss (-19 vs. -14%; P=0.002), and contralateral compensatory hypertrophy (+4% vs. +1,8%; P=0.02, respectively). Total-RFV loss was similar between both (-21.7 vs. -19cm3; P=0.07). GFR preservation was better in the PN group (95.9 vs. 90.7%; P=0.03). In multivariate analysis, age and tumor size were associated with loss of RFVh.

CONCLUSION

For renal tumors T1b, PN is associated with superior compensatory hypertrophy compared with PA, compensating for the higher RFVh loss, resulting in similar ΔRFV-total between both groups. The superior post-PN GFR preservation suggests that the preserved quantitative RFV factor is insufficient. Therefore, the underlying quality of the parenchyma would play a major role in postoperative GFR.

Functional recovery after partial nephrectomy: next generation analysis

OBJECTIVES

To provide a more rigorous assessment of factors affecting functional recovery after partial nephrectomy (PN) using novel tools that allow for analysis of more patients and improved accuracy for assessment of parenchymal volume loss, thereby revealing the potential impact of secondary factors such as ischaemia.

PATIENTS AND METHODS

Of 1140 patients managed with PN (2012-2014), 670 (59%) had imaging and serum creatinine levels measured before and after PN necessary for inclusion. Recovery from ischaemia was defined as the ipsilateral glomerular filtration rate (GFR) saved normalised by parenchymal volume saved. Acute kidney injury was assessed through Spectrum Score, which quantifies the degree of acute ipsilateral renal dysfunction due to exposure to ischaemia that would otherwise be masked by the contralateral kidney. Multivariable regression was used to identify predictors of Spectrum Score and Recovery from Ischaemia.

RESULTS

In all, 409/189/72 patients had warm/cold/zero ischaemia, respectively, with median (interquartile range [IQR]) ischaemia times for cold and warm ischaemia of 30 (25-42) and 22 (18-28) min, respectively. The median (IQR) global preoperative GFR and new baseline GFR (NBGFR) were 78 (63-92) and 69 (54-81) mL/min/1.73 m2 , respectively. The median (IQR) ipsilateral preoperative GFR and NBGFR were 40 (33-47) and 31 (24-38) mL/min/1.73 m2 , respectively. Functional recovery correlated strongly with parenchymal volume preserved (r = 0.83, P < 0.01). The median (IQR) decline in ipsilateral GFR associated with PN was 7.8 (4.5-12) mL/min/1.73 m2 with loss of parenchyma accounting for 81% of this loss. The median (IQR) recovery from ischaemia was similar across the cold/warm/zero ischaemia groups at 96% (90%-102%), 95% (89%-101%), and 97% (91%-102%), respectively. Independent predictors of Spectrum Score were ischaemia time, tumour complexity, and preoperative global GFR. Independent predictors of recovery from ischaemia were insulin-dependent diabetes mellitus, refractory hypertension, warm ischaemia, and Spectrum Score.

CONCLUSIONS

The main determinant of functional recovery after PN is parenchymal volume preservation. A more robust and rigorous evaluation allowed us to identify secondary factors including comorbidities, increased tumour complexity, and ischaemia-related factors that are also independently associated with impaired recovery, although altogether these were much less impactful.

Long-Term Renal Function Following Renal Cancer Surgery: Historical Perspectives, Current Status, and Future Considerations

Knowledge of functional recovery after partial (PN) and radical nephrectomy for renal cancer has advanced considerably, with PN now established as the reference standard for most localized renal masses. However, it is still unclear whether PN provides an overall survival benefit in patients with a normal contralateral kidney. While early studies seemingly demonstrated the importance of minimizing warm-ischemia time during PN, multiple new investigations over the last 10 years have proven that parenchymal mass lost is the most important predictor of new baseline renal function. Minimizing loss of parenchymal mass during resection and reconstruction is the most important controllable aspect of long-term post-operative renal function preservation.

Point of care parenchymal volume analyses to estimate split renal function and predict functional outcomes after radical nephrectomy

Accurate prediction of new baseline GFR (NBGFR) after radical nephrectomy (RN) can inform clinical management and patient counseling whenever RN is a strong consideration. Preoperative global GFR, split renal function (SRF), and renal functional compensation (RFC) are fundamentally important for the accurate prediction of NBGFR post-RN. While SRF has traditionally been obtained from nuclear renal scans (NRS), differential parenchymal volume analysis (PVA) via software analysis may be more accurate. A simplified approach to estimate parenchymal volumes and SRF based on length/width/height measurements (LWH) has also been proposed. We compare the accuracies of these three methods for determining SRF, and, by extension, predicting NBGFR after RN. All 235 renal cancer patients managed with RN (2006-2021) with available preoperative CT/MRI and NRS, and relevant functional data were analyzed. PVA was performed on CT/MRI using semi-automated software, and LWH measurements were obtained from CT/MRI images. RFC was presumed to be 25%, and thus: Predicted NBGFR = 1.25 × Global GFRPre-RN × SRFContralateral. Predictive accuracies were assessed by mean squared error (MSE) and correlation coefficients (r). The r values for the LWH/NRS/software-derived PVA approaches were 0.72/0.71/0.86, respectively (p < 0.05). The PVA-based approach also had the most favorable MSE, which were 120/126/65, respectively (p < 0.05). Our data show that software-derived PVA provides more accurate and precise SRF estimations and predictions of NBGFR post-RN than NRS/LWH methods. Furthermore, the LWH approach is equivalent to NRS, precluding the need for NRS in most patients.

Every decade counts: a narrative review of functional recovery after partial nephrectomy

OBJECTIVE

To provide a narrative review of the major advances regarding ischaemia and functional recovery after partial nephrectomy (PN), along with the ongoing controversies.

METHODS

Key articles reflecting major advances regarding ischaemia and functional recovery after PN were identified. Special emphasis was placed on contributions that changed perspectives about surgical management. Priority was also placed on randomized trials of off-clamp vs on-clamp cohorts.

RESULTS

A decade ago, 'Every minute counts' was published, showing strong correlations between duration of ischaemia and development of acute kidney injury (AKI) and chronic kidney disease after clamped PN. This reinforced perspectives that ischaemia was the main modifiable factor that could be addressed to improve functional outcomes and helped spur efforts towards reduced or zero ischaemia PN. These approaches were associated with strong functional recovery and some peri-operative risk, although they were generally safe in experienced hands. Further research demonstrated that, when parenchymal volume changes were incorporated into the analyses, ischaemia lost statistical significance, and percent parenchymal volume saved proved to be the main determinant. Cold ischaemia was confirmed to be highly protective, and limited warm ischaemia also proved to be safe. The reconstructive phase of PN, with avoidance of parenchymal devascularization, appears to be most important for functional outcomes. Randomized trials of on-clamp vs off-clamp PN have shown minimal impact of ischaemia on functional recovery.

CONCLUSIONS

The past decade has witnessed great progress regarding functional recovery after PN, with many lessons learned. However, there are still unanswered questions, including: What is the threshold of warm ischaemia at which irreversible ischaemic injury begins to develop? Are some cohorts at increased risk for AKI or irreversible ischaemic injury? and Which patients should be prioritized for zero-ischaemia PN?

Evaluation of N-(6-[18F]Fluoropyridin-3-yl)glycine PET renography to detect renal function progression in a rat model of diabetic nephropathy

OBJECTIVE

Given the limitation of biomarkers to predict the renal function progression in diabetic nephropathy, N-(6-[¹⁸F]Fluoropyridin-3-yl)glycine (6-[¹⁸F]FPyGly) was used to evaluate renal function progression in a rat model of diabetic nephropathy.

METHODS

Twenty male Sprague-Dawley rats were randomly divided into four groups, including the healthy control group (HC group), diabetic nephropathy group (DNM group), routine diet treated diabetic nephropathy group (RDNM group), and high fat/high sucrose -diet-fed diabetic nephropathy group (HDNM group). All renal function parameters were determined from animal PET renograms. P and T_max represent the curve peak counts and the time to the curve peak counts of 6-[¹⁸F]FPyGly in kidneys after injection, C_1/2 and the 15 min/Peak ratio represent the time from peak to 1/2 peak in the clearance phase, and the ratio of the curve counts at 15 min to the curve peak counts.

RESULTS

P, T_max, C_1/2, and 15 min/peak ratio of each rat were significantly correlated with S-Cr, BUN. There were significant differences in T_max, P, serum creatinine (SCr), and blood urea nitrogen (BUN) levels between HC and DNM groups. P and the 15 min/Peak ratio were significantly different among DNM, RDNM, and HDNM groups, while T_max and C_1/2 were only significantly different between DNM and RDNM or HDNM groups. There only was a significant difference in BUN between the DNM and HDNM groups.

CONCLUSION

The renal function parameters P, T_max, C_1/2 and 15 min/peak value obtained by dynamic renal imaging based on 6-[¹⁸F]FPyGly could reflect changes of renal function in rats, which had a good correlation with SCr and BUN, and showed more efficient in the diagnosis of diabetic nephropathy and renal function classification than SCr and BUN.

Predicting GFR after radical nephrectomy: the importance of split renal function

PURPOSE

To evaluate a conceptually simple model to predict new-baseline-glomerular-filtration-rate (NBGFR) after radical nephrectomy (RN) based on split-renal-function (SRF) and renal-functional-compensation (RFC), and to compare its predictive accuracy against a validated non-SRF-based model. RN should only be considered when the tumor has increased oncologic potential and/or when there is concern about perioperative morbidity with PN due to increased tumor complexity. In these circumstances, accurate prediction of NBGFR after RN can be important, with a threshold NBGFR > 45 ml/min/1.73m² correlating with improved overall survival.

METHODS

236 RCC patients who underwent RN (2010-2012) with preoperative imaging (CT/MRI) and relevant functional data were included. NBGFR was defined as GFR 3-12 months post-RN. SRF was determined using semi-automated software that provides differential parenchymal-volume-analysis (PVA) from preoperative imaging. Our SRF-based model was: Predicted NBGFR = 1.24 (× Global GFR_Pre-RN) (× SRF_{Contralateral}), with 1.24 representing the mean RFC estimate from independent analyses. A non-SRF-based model was also assessed: Predicted NBGFR = 17 + preoperative GFR (× 0.65)-age (× 0.25) + 3 (if tumor > 7 cm)-2 (if diabetes). Alignment between predicted/observed NBGFR was assessed by comparing correlation coefficients and area-under-the-curve (AUC) analyses.

RESULTS

The correlation-coefficients (r) were 0.87/0.72 for SRF-based/non-SRF-based models, respectively (p = 0.005). For prediction of NBGFR > 45 ml/min/1.73m², the SRF-based/non-SRF-based models provided AUC of 0.94/0.87, respectively (p = 0.044).

CONCLUSION

Previous non-SRF-based models to predict NBGFR post-RN are complex and omit two important parameters: SRF and RFC. Our proposed model prioritizes these parameters and provides a conceptually simple, accurate, and clinically implementable approach to predict NBGFR post-RN. SRF can be easily obtained using PVA software that is affordable, readily available (FUJIFILM-Medical-Systems), and more accurate than nuclear-renal-scans. The SRF-based model demonstrates greater predictive-accuracy than a non-SRF-based model, including the clinically-important predictive-threshold of NBGFR > 45 ml/min/1.73m².

Ability of volume measures of hydronephrosis to predict need for surgery and evaluate renal function in children with ureteropelvic junction obstruction

OBJECTIVE

To explore the efficacy of quantitative renal volume measures on magnetic resonance urography images in predicting need for surgery among children with ureteropelvic junction obstruction and their ability to evaluate renal function.

METHODS

A total of 88 cases of hydronephrosis in 50 patients were collected between 1 April 2018 and 31 March 2020, including 30 operated kidney and 58 unoperated kidney cases. Clinical data were collected, and quantitative analysis of magnetic resonance urography was performed. Renal volume, hydronephrosis volume and the volume ratio of hydronephrosis (hydronephrosis volume/renal volume) were measured and calculated. We analyzed the relationships between the above indices in the two groups and compared these with renal function.

RESULTS

Compared with the unoperated kidney group, hydronephrosis volume, renal volume and hydronephrosis volume/renal volume of the operated kidney group increased significantly. Hydronephrosis volume (area under the curve 0.972, 95% confidence interval 0.943-1.000; P < 0.001) and hydronephrosis volume/renal volume (area under the curve 0.968, 95% confidence interval 0.939-0.998; P < 0.001) were superior to ultrasonography and renal function examination in predicting the probability of surgery, and their sensitivity values (hydronephrosis volume/renal volume: 96.67%; hydronephrosis volume: 93.33%) were higher than those of the renal function test (50%). There was a significant difference among different renal function groups in the pairwise comparison of hydronephrosis volume and hydronephrosis volume/renal volume (P < 0.05).

CONCLUSION

Quantitative volume measures of hydronephrosis by magnetic resonance urography had a greater ability to predict need for surgery than ultrasonography and dynamic renal imaging, and it can be used as method by which to evaluate surgery. Hydronephrosis volume and hydronephrosis volume/renal volume have greater predictive ability, and play an important role in the deterioration of renal function.

Parenchymal Volume Replacement by Renal Cell Carcinoma Prior to Intervention: Predictive Factors and Functional Implications

OBJECTIVE

To analyze predictors, extent and functional implications associated with renal parenchymal volume replacement (PVR) by renal cell carcinoma (RCC) prior to intervention. This phenomenon is well-recognized yet not adequately studied, and, if severe, can influence management.

MATERIALS AND METHODS

A retrospective review was performed of partial nephrectomy (PN) and radical nephrectomy (RN) patients with available preoperative nuclear-renal-scan and imaging demonstrating solitary RCC with normal contralateral kidney. Normal renal parenchymal volume of each kidney was measured by free-hand scripting from preoperative axial images. Primary endpoint was percent PVR which was estimated assuming that the contralateral-kidney serves as a control: PVR = (volume contralateral kidney - volume ipsilateral kidney) normalized by volume contralateral kidney. Multivariable linear-regression analysis assessed factors associated with preoperative PVR. Further analysis evaluated the functional effect of PVR prior to surgery.

RESULTS

146 PN and 136 RN patients with necessary studies were analyzed. For RN, the median PVR was 15% and a quarter of patients had PVR ≥27%. In contrast, PVR was negligible in PN patients for whom median preoperative parenchymal volumes were nearly identical in the ipsilateral/contralateral kidneys (179/180cc, respectively). PVR inversely correlated with preoperative renal function in the ipsilateral kidney (P <.01). Tumor-size (P <.01), stage (P = .03), and endophytic properties (P = .03) associated with PVR on multivariable-analysis.

CONCLUSION

Our data suggest that substantial replacement of normal parenchyma by RCC occurs in many patients selected for RN and can contribute to preexisting renal-insufficiency. PVR prior to intervention is mainly driven by tumor characteristics in RN patients, but is negligible in most PN patients.

Quantitative evaluation of chronically obstructed kidneys from noncontrast computed tomography based on deep learning

OBJECTIVE

To quantitatively report renal parenchymal volume (RPV), renal sinus volume (RSV), and renal parenchymal density (RPD) for chronically obstructed kidneys from noncontrast computed tomography (NCCT).

METHODS

This retrospective study was approved by the institutional review board of our hospital with a waiver of informed consent. We retrospectively collected 304 consecutive NCCT scans of urinary obstruction and constructed two datasets: one with 167 patient scans for parenchyma and sinus segmentation (segmentation dataset) and the other containing 137 scans from different patients diagnosed with chronic urinary obstruction (CUO dataset) and paired with split glomerular filtration rate (sGFR). A cascaded three-dimensional (3D) U-Net model was developed and validated for parenchyma and sinus segmentation. The RPV, RSV, and RPD of the CUO dataset were calculated by the model with manual editing. A multivariate analysis was performed to show the association between all parameters and the sGFR.

RESULTS

In the test dataset, the Dice values for parenchyma and sinus segmentation were 0.95 ± 0.04 and 0.90 ± 0.05, respectively. Compared with those of nonobstructed kidneys, the RSV and RPD of obstructed kidneys increased, but RPV and sGFR decreased (P < .001). For chronically obstructed kidneys, age (r = -0.292, P < .001), RPV (r = 0.849, P < .001), RSV (r = -0.331, P < .001), and RPD (r = -0.296, P < .001) were significantly correlated with sGFR. The fitted regression model was sGFR = 10.873-0.111 Age + 0.211 RPV - 0.022 RSV (r² = 0.712).

CONCLUSIONS

NCCT combined with deep learning has the potential to be a single radiological procedure for morphological and functional evaluation of chronically obstructed kidneys.