Biparametric magnetic resonance imaging as a diagnostic tool for differentiating RCC and renal pseudotumor in CKD patients

Introduction: Pseudotumors are benign lesions which may mimic like a malignant tumor on conventional imaging. They are formed in kidneys which are scarred and deformed by chronic pyelonephritis, glomerulonephritis, trauma or infarction. There is a diagnostic dilemma in most of the cases as to differentiate RCC and pseudotumors. Our study shows bp-MRI (T2w, DW MRI) can distinguish pseudotumors from RCCs and offers a non-contrast non-invasive alternative in CKD patients.

Materials and methods: Prospective evaluation of 80 CKD patients (CKD IV/V), having suspicious renal mass <4 cm on Ultrasound, were subjected to bp-MRI. Two groups were defined on the basis of restriction pattern on DWI. ADC values were calculated. Group I (suspected RCC or malignant tumor) underwent surgical management according to the institutional protocol. Group II (suspected pseudotumor) were subjected to biopsy. ROC curves were drawn to find out area under curve for differentiation of groups and cut-off ADC values calculated so as to achieve highest average sensitivity and specificity. A p-value of <0.05 was considered as statistically significant.

Results: Sixty patients (Group I) had restricted pattern on DWI imaging whilst 20 had no restriction (Group II), hence ruling out malignancy. It showed a sensitivity of 81.82%, specificity 96.55% in the correct diagnosis. Mean ADC-value for CKD pseudotumors (Group II) was significantly higher than RCCs and surrounding diseased parenchyma (2.20 vs 1.52 (×10^-3 mm²/s; p < 0.0001) and 1.99 (×10^-3 mm²/s; p = 0.0001) respectively). ROC analysis for differentiating CKD pseudotumors and RCC yielded high sensitivity (85%) and specificity (99%) for cut-off ADC-value of 1.71 (×10^-3 mm²/s).

Conclusion: bp-MRI is a highly reliable imaging modality for the evaluation of renal lesions. Its ability to accurately differentiate pseudotumors from renal cell carcinomas, even in the absence of contrast administration can be a boon in the diagnostic armamentarium.