Modified R.E.N.A.L nephrometry score for predicting the outcome following partial nephrectomy

This was a prospective study for adult patients (≥ 18 years old) who presented consecutively between September 2014 and December 2016 with cT_1-2N₀M₀ renal masses amenable for PN. Indications for PN were patients with solitary kidney, bilateral renal masses, chronic kidney disease or risk of future renal impairment as in cases of hypertension or diabetes, to preserve renal function. Additionally, patients with small renal masses < 4 cm were included even with normal contralateral kidney. We excluded patients with previous renal or abdominal surgeries. The study was approved by institutional review board, and written informed consent was obtained from all patients.

Routine preoperative investigations were performed including CBC, coagulation profile and serum creatinine. Estimated glomerular filtration rate (eGFR) was calculated using the Modification of Diet in Renal Disease (MDRM) equation [19]. Contrast-enhanced cross-sectional imaging of chest, abdomen and pelvis (CT or MRI) for each patient was assessed by two uro-oncologists familiar with the Renal Pelvic Score (RPS) [20] and the R.E.N.A.L [12]. If the two members disagreed in the scoring, a third opinion was obtained.

After positioning of the patient in the lateral decubitus position, all patients underwent open PN with a flank incision performed with excision of the 11th rib to gain access to the targeted kidney. Trans-gerotal approach was adopted in all cases, where dissection of the peri-renal fat was done except the area surrounding the mass. Site of the mass was identified intraoperatively by either direct visualization of the mass or ultrasound guidance, especially if the mass was totally endophytic. After intraoperative mass assessment, we decided to proceed with either warm ischemia or no ischemia. The incision line for the mass, outside its capsule and surrounding a rim of normal parenchyma, was outlined then deepened using a combination of blunt and sharp dissection, then the mass was removed with its surrounding fat. A sample from the deepest point of the bed was obtained for histopathological examination. Bleeding vessels and injuries to pelvi-calyceal system were repaired. Reconstruction of the renal bed was done by placement of hemostatic materials in the form of an oxidized cellulose polymer and/or oxidized regenerated cellulose. Parenchymal closure with the covering capsule was done using interrupted absorbable 2/0 sutures with the aid of oxidized cellulose polymer to support the sutures. We didn’t routinely insert a ureteric stent. Urethral catheter was removed on (day 1) while the drain was left for an average of 3 days then removed with discharge of the patient.

Follow-up visits were at 1, 4 and 12 week then at 6 and 12 months postoperatively. In each visit, evaluation was done by serum creatinine, eGFR, urine analysis and US. Additionally, CT or MRI was performed at 6 and 12 months.

Different outcome parameters were reported including warm ischemia time (WIT), operative time, estimated blood loss, blood transfusion, renal vascular injury, ureteric or renal pelvis injury, pelvi-calyceal system (PCS) entry, conversion to RN, urinary leakage, length of hospital stay, postoperative renal function and pathology findings.

We compared different outcome parameters according to R.E.N.A.L. and RPS. We modified R.E.N.A.L. with incorporation of new items in the score including hilar position of the mass as a numerical score not only a descriptive character (scored 0 or 5) and RPS (scored 1 or 3 according to the percentage of renal pelvis area contained inside the volume of the renal parenchyma whether less or more than 50%; respectively). Furthermore, we changed the score points given to some items of the original R.E.N.A.L. according to our point of view regarding their importance in describing the complexity of the mass. We kept the score of the radius “R” and relation to polar lines “L” as 1, 2 or 3, but we changed the score of the nearness to PCS and sinus “N” to 1, 2 or 4 and the score of the endophytic nature of the mass “E” to 1, 2 or 5. Accordingly, the new score is ranging from 5 to 23. It is classified into mild complexity (5–9), moderate complexity (10–14) or high complexity (15–23). A renal mass can be described using the MNS as (R + E + N + apx + L + H + RPS). The newly modified nephrometry score was used to compare the different outcome parameters to evaluate its predictability and whether it was better or not than R.E.N.A.L.

The Statistical Package of Social Science (SPSS) Software program, version 20, was used for statistical analysis. Nominal values were compared using Chi-square (χ²) test or Fisher-exact test as appropriate. For comparing numerical values of the three complexity groups, the one way ANOVA (with Post Hoc analysis) or Kruskal–Wallis test were used. p values < 0.05 were considered statistically significant.

Fifty-one consecutive patients with renal masses were included. The baseline characteristics are shown in Table 1. Perioperative data are presented in Table 2. Perioperative complications were detected in 17 (33.3%) patients. Injury to the renal artery was reported in 2 patients. Exploration of the renal artery revealed an intimal crack in the first patient; which was repaired, and a blood clot in the second patient; which was dislodged by Fogarty catheter. Postoperative hematuria that failed to respond to intravenous fluid and anti-bleeding measures were detected in 2 patients on day 5 and day 7, respectively. Diagnostic angiography was done and showed AV fistula formation which was controlled by injection of histoacryl. There were 6 cases of postoperative urine leakage. This was associated with perinephric collection in 2 patients. Four cases required double-J stent insertion, while the other 2 cases were successfully managed conservatively by urethral catheter insertion or extending the duration of the already inserted catheter. No pre- or intraoperative stenting was done except for 1 patient who had ureteric injury during dissection of a lower polar mass. Conversion to RN was mandated in 4 (7.8%) patients due to inadequate residual renal tissue after PN (1), severe injury to PCS after excision of the mass with impossible repair (1), failure to localize the site of a completely endophytic renal mass close to renal hilum even after the use of ultrasound (1) and involvement of the hilar vessels by the renal mass in the 4th patient.

Six patients developed postoperative renal function deterioration. Only one of these six patients had normal preoperative renal functions. The preoperative eGFR was (91 ml/min). The creatinine raised from 1 to 3.5 mg/dl immediately postoperatively. On follow-up after 3 months, eGFR improved to 88 ml/min; which was very close to preoperative reading. No patient developed recurrence after a 1 year follow-up.

The clear cell type was the most dominant pathological finding (26 cases) (Table 2). The cases of positive surgical margins (5.9%) were followed up every 3 months with cross-sectional imaging.

Different perioperative factors were compared according to complexity level in R.E.N.A.L. (Table 3) and MNS (Table 4). There was no statistically significant difference between the complexity groups in the preoperative characteristics in both scores. In R.E.N.A.L., the only detected variable that was affected significantly (p = 0.039) by the complexity level was the need for secondary intervention. The hilar position (H) and RPS showed statistically significant difference only according to MNS as they were not included in the original R.E.N.A.L. In MNS, the complication rate was significantly higher with increase in the complexity level (p = 0.037). Furthermore, the rate of complications was nearly doubled while moving from a low complexity level to a higher level (13.3% vs 30% vs 56.3%) which was completely different from the original R.E.N.A.L. The rate of positive surgical margin showed statistically significant difference according to MNS (p = 0.049) and was found only in the highest complexity level while it showed no significant difference according to the original R.E.N.A.L in which it was found in both moderate and high complexity levels. Although secondary intervention showed statistically significant difference in the original score (p = 0.039), it was higher in the low complexity level (18.2%) than in the high complexity level (5%). The relation of the rate of secondary intervention became better associated with the complexity level in the MNS although the significant difference was abolished (p = 0.757). Although the rate of PCS entry did not show statistically significant difference according to complexity level in both scores, it was more associated with the complexity level in MNS with nearly doubling when comparing the low and high levels (33.3% vs 62.5%, respectively) while in R.E.N.A.L, the rate of PCS entry was higher in the low than the moderate complexity. This more association with the level of complexity, in the absence of significant difference, was also observed in MNS when compared with the original score in many other perioperative outcome variables including operative time, WIT, blood loss, hemoglobin loss, blood transfusion, ureteric injury and conversion to RN.

This was confirmed by analysis of predicting factors for postoperative complications (Table 5). The detected significant predicting factors were the complexity level according to MNS (p = 0.037), MNS (p = 0.014) and hilar position (p = 0.001).