Small renal neoplasms: clinical, pathologic, and imaging features.

Small renal neoplasms are being found more often because of the widespread use of abdominal CT and sonography. Little is known about their natural history. We therefore retrospectively reviewed clinical, pathologic, and imaging findings in 22 patients with surgically confirmed solitary renal neoplasms that were 3 cm or less in diameter. Eighteen lesions were first found by CT, three by sonography, and one by IV urography. Three lesions were discovered because the patients had hematuria. Nineteen were incidental radiologic diagnoses in patients without renal symptoms. Of 22 neoplasms, 15 (68%) were renal cell carcinomas, six (27%) were oncocytomas, and one (5%) was a lymphoma. Fourteen (93%) of the 15 carcinomas were confined to the kidney, and one showed microscopic capsular invasion. Metastases did not develop in any patient with carcinoma, indicating that small carcinomas usually have good prognoses. Patients with carcinomas had a mean follow-up of 42 months. All neoplasms were visible on CT. However, characterization of these lesions sometimes required a combination of CT and sonography and occasionally angiography. The carcinomas, oncocytomas, and solitary renal lymphoma could not be distinguished radiologically. Small renal neoplasms are most often found incidentally by CT performed in patients without renal complaints. Most are low-stage carcinomas, and some are oncocytomas.