Renal Oncocytic Neoplasms: Review of Classification Updates, Imaging, and Management

Renal oncocytic neoplasms present diagnostic challenges, both at imaging and pathologic evaluation. The World Health Organization classification of renal neoplasms defines a spectrum of oncocytic neoplasms, including emerging entities that help define previously uncharacterized or mischaracterized tumors. Low-grade oncocytic tumors and eosinophilic vacuolated tumors are distinguishable from other oncocytic neoplasms at pathologic evaluation and typically demonstrate indolent behavior. No-menclature regarding hybrid neoplasms has been clarified in reference to hereditary cases associated with Birt-Hogg-Dubé syndrome. Preoperative diagnostic difficulties at imaging contribute to high rates of resected benign renal tumors, the majority being renal oncocytomas. The imaging appearances of oncocytic neoplasms are similar, and the inability to confidently diagnose them at imaging has led to increased resection rates. Preoperative renal mass biopsy may be preventative, but its utilization remains low, diagnoses can be equivocal, and establishing tumor aggressiveness may not always be reliable. Malignant renal oncocytic tumors, including chromophobe renal cell carcinoma, are generally considered the less aggressive subtypes of renal cell carcinoma. However, distinguishing them from the more aggressive clear cell subtype remains challenging, despite imaging frameworks designed to aid categorization. Active surveillance is a safe management option among biopsy-confirmed renal oncocytic neoplasms, but it remains uncertain which patients are suitable for this approach. Diagnostic imaging may assist in risk-stratifying oncocytic neoplasms, with mass enhancement, heterogeneity, and calcification potentially differentiating benign from malignant oncocytic neoplasms. Mass attenuation and heterogeneity may differentiate low-grade and high-grade cancers. Molecular imaging and other emerging techniques, such as MR fingerprinting, may play a role in the future.