Renal adenoma and oncocytoma.

Renal adenoma and oncocytoma are relatively common, benign solid renal tumors. These lesions rarely present with specific genitourinary symptoms and are most often incidentally detected as small renal masses. While some radiologic findings are suggestive of either lesion, there are no pathognomonic radiologic features that can dependably differentiate them from renal cell carcinoma. Renal adenoma is often histologically indistinguishable from renal cell carcinoma, and renal oncocytoma shares many cellular features with granular renal cell carcinoma, thereby limiting the utility of needle biopsy or aspiration cytology for diagnosis. These tumors are also often found associated with renal cell carcinoma in the same or contralateral kidney, so that surgical excision is the only reliable means to achieve both definitive diagnosis and treatment.