Purpose or Case Report: Nephron sparing surgery for renal masses is indicated for pediatric patients with bilateral renal masses and masses associated with syndromic conditions predisposed to recurrence. However, there is a paucity of literature on MRI-based biomarkers in patients undergoing partial nephrectomy. Relating these imaging biomarkers to patient outcomes might inform surgical decision making and patient counseling.
Methods & Materials: An IRB approved urologic surgical database was searched for all patients who underwent partial nephrectomy. Relevant preoperative MR was retrieved with axial DWI and T2-weighted fat-saturated (T2W-FS) sequences.

ADC calculation using the log model was performed in the pMRI software package for the following segmented tissue types: (1) Whole tumor (2) Solid Tumor (excluding cystic areas) (3) kidney ipsilateral and (4) contralateral to the tumor. 3 b-values were used for ADC calculation (0 or 50, 500, 1000). Visual reference was made to T2W-FS images for anatomic deliniation. For each segmented region, the volume and mean ADC values were tabulated.
Results: 28 patients underwent 33 partial nephrectomy surgeries and, among these, 22 had adequate preoperative MRI with DWI. Median age at diagnosis was 24.5 months (IQR 13.1-35.2). Mean tumor volume = 49 cc (SD = 62).

No significant differences were seen between whole tumor mean ADC values for Wilms Tumor (n=18) and RCC (n=2) and Angiomyolipoma (n=2), 1454 vs 1468 vs 913 mm²/sec (ANOVA, p=0.38). ADC_mean [SD] for the following tissue types was Whole Tumor = 1429 mm²/sec [450], Solid Tumor (excluding cystic area) =1180 mm²/sec [673] , Ipsilateral Kidney = 1561 mm²/sec [450], Contralateral Kidney = 1220 mm²/sec[665].

Positive correlations were seen between patient length of stay and both whole tumor and solid tumor volumes (β=19.4, adjusted R²=0.38, p=0.001 and β=5.7, adjusted R²=0.37, p=0.002). Weak negative correlation was seen between estimated blood loss and the mean ADC value of the ipsilateral kidney (β=-0.41, adjusted R²=0.12, p=0.06) and mean ADC value of the solid-portion tumor ADC (β=-0.72, adjusted R²=0.12, p=0.07). Patients who experienced any postoperative complications had higher solid-tumor ADC values (1712 vs 1188 mm²/sec, p=0.01).
Conclusions: For pediatric patients undergoing partial nephrectomy, MRI is a vital tool for surgical staging. Our work suggests that tumor volumetrics and DWI may provide information regarding surgical outcomes including intraoperative blood loss, length of stay and post-operative complications.