The fate of small renal masses, less then 1 cm size: outcome study.

Purpose: We evaluated the outcome and etiologies of small renal masses (less than 1 cm in size) discovered incidentally on 2 consecutive CTs that investigated nonurologic abdominal complaints.

Materials And Methods: A retrospective search for incidentally discovered small renal masses, less then 1 cm in size, was carried out in the files of 6 major US medical centers. 4822 such lesions had been reported over a 12 year period. A search of these patients' records revealed 1082 subsequent new CTs for non urologic complaints, allowing the assessment of the fate of the masses. Lesions enlarging, of ambivalent contour or enhancement were examined by a third multiphasic MDCT. The findings were interpreted by 2 blinded radiologists.

Results: Six hundred and four masses could no longer be identified, 231 were significantly smaller, 113 unchanged in size and 134 larger. Of the disappearing lesions 448 were located in the medulla, 94 both in medulla and cortex and 62 in cortex. Multiphasic MDCTs obtained in 308 masses enlarging, unchanged in size or of ambivalent appearance, revealed 7 neoplasms, 45 inflammatory lesions, 8 abscesses and 62 renal medullary necrosis. Concurrent antibiotic therapy of GI conditions may have caused some of the 496 lesions to disappear.

Conclusion: It is questionable whether the small number of malignant neoplasms (0.4%), inflammatory lesions (5%) and renal medullary necrosis (6%) justify routine follow-up CTs and exposure to radiation. The delay in intervention in neoplastic lesions probably didn't influence tumor-free survival potential and clinical symptoms would soon have revealed inflammatory conditions. With exception of ambivalent lesions, clinical surveillance appears adequate.