Percutaneous Kidney Biopsy for a Small Renal Mass: A Critical Appraisal of Results.

ABSTRACT

PURPOSE: We report the diagnostic accuracy of renal mass biopsy for a small renal mass (4 cm or less) and identify predictors of successful renal mass biopsy in a contemporary cohort of patients from 2 large tertiary referral centers. MATERIALS AND METHODS: A total of 442 biopsies of renal tumors 4 cm or less at 2 tertiary centers between 2008 and 2015 were included in study. Biopsy outcomes (malignant, benign or nondiagnostic) and concordance rates between renal mass biopsy and final surgical pathology were determined. Univariate and multivariate logistic regression analyses were performed to identify factors indicative of nondiagnostic biopsy. RESULTS: The initial biopsy was diagnostic in 393 cases (88.9%) and nondiagnostic in 49 (11.1%). Of diagnostic biopsies 76% revealed renal cell carcinoma and 24% were benign. Renal cell carcinoma histological subtyping and grading was possible in 90.2% and 31.3% of cases, respectively. A second biopsy was performed in 11 of the 49 nondiagnostic cases and a diagnosis was possible in 100%, including renal cell carcinoma in 10 and oncocytoma in 1. Small tumor size, cystic nature of tumors and biopsy during the initial years of the study were independent predictors of nondiagnostic biopsy. The rates of accuracy in identifying malignancies, histiotyping and 2-tier grading between renal mass biopsy and surgical pathology were 97.1%, 95.1% and 68.8%, respectively. CONCLUSIONS: Renal mass biopsy for a small renal mass can be performed accurately. Nondiagnostic renal mass biopsy was common for smaller masses and cystic masses, and during the initial years of the study. A second biopsy should be considered in nondiagnostic biopsy cases.