Drawbacks of the Simplified Imaging Approach for Evaluation of the Solid Renal Mass in Adults.

In the May 2008 issue of Radiology, Dr Dyer and colleagues (1) proposed a strategy for analyzing the imaging characteristics of renal masses in adults on the basis of the lesion's growth pattern (“ball” versus “bean” type) and reported that percutaneous biopsy for the diagnosis of oncocytoma remains controversial. In this letter, we discuss some drawbacks of the simplified imaging approach for evaluation of the solid renal mass in adults to avoid incorrect diagnosis of the transitional cell carcinoma (TCC) and of the oncocytoma. The authors described TCC as the “prototypic bean-type lesion.” Renal TCC starts most frequently in the extrarenal pelvis and migrates next to the infundibulocaliceal region. Eighty-five percent of upper-tract TCCs are superficial and papillary low-stage neoplasms (2). These tumors are seen as sessile filling defects in the excretory phase, which expand centrifugally with compression of the renal sinus fat. Early tumors confined to the muscularis are separated from the renal parenchyma by sinus fat or excreted contrast material and have normal appearing peripelvic fat. These superficial papillary tumors do not infiltrate the renal parenchyma and can not be assigned to the bean-type category. These lesions present as central masses within the renal pelvis (“intrapelvic ball”) (3). Less than 15% of TCCs can be categorized as ball-type lesions. For the diagnosis of oncocytoma, Dr Dyer and colleagues wrote that percutaneous biopsy is controversial because “it is hard to tell a truly benign oncocytoma...from an RCC [renal cell carcinoma] that contains some oncocytic cells.” In the differential diagnosis between oncocytoma and other solid renal neoplasms, the major problem is chromophobe RCC. In our experience, the percutaneous biopsy of RCC may contain oncocytic cells, but malignant clear cells are prevalent, and a necrotic background is found. Diffuse necrosis is absent in oncocytoma. Immunohistochemical staining with antimitochondrial antibody demonstrates the oncocytic nature of tumor cells in cytologic or histologic specimens and excludes the tumors simulating oncocytoma. For the diagnosis of oncocytoma, radiologic procedures and immunohistochemistry applied to cytohistologic specimens are the reference standard.