Renal oncocytoma: sonographic analysis of 14 cases.

The sonographic features of 15 histologically confirmed renal oncocytomas in 14 patients are presented. Lesions were evaluated for homogeneity, echogenicity, margination, venous invasion, and nodal enlargement. Nine were less than 5.5 cm in diameter, homogeneous, and well circumscribed. Three lesions were greater than 8 cm in diameter, contained areas of central necrosis or calcification, and were nonspecific for renal oncocytoma. One of these lesions (12 cm) contained a central scar. Two masses were slightly inhomogeneous and, at best, moderately circumscribed. In no case were metastatic nodes or venous invasion present. Since about 6% of renal cell carcinomas may have this appearance, the homogeneous, well marginated renal mass that is isoechoic with cortex and less than 5.5 cm in diameter is as likely to represent renal cell carcinoma as it is an oncocytoma. Although only present in one of the cases, the central fibrotic scar in a larger mass has been described in oncocytoma and may be the most specific feature. Preoperative investigation with fine-needle aspiration biopsy for cytology may be indicated in an attempt to avoid radical nephrectomy in selected patients.