Sonographically identified echogenic renal masses up to 1 cm in size are so rarely malignant they can be safely ignored

Objectives-The purpose of this study was to determine whether small echogenic renal masses up to 1 cm in size incidentally detected by sonography are rarely malignant and thus do not need further workup. Methods-We reviewed approximately 13,600 reports of all abdominal sonographic examinations performed between November 2001 and October 2007 that identified a small echogenic mass in a kidney. Patients with known malignancy of any kind, tuberous sclerosis, lesions larger than 1.0 cm, lesions with heterogeneous echogenicity, and lesions with posterior ring-down artifacts or posterior acoustic shadowing were excluded. All patients without magnetic resonance imaging or computed tomographic scans that completely characterized the lesions were excluded unless a follow-up study (sonography, magnetic resonance imaging, or contrast-enhanced computed tomography) at least 5 years later was available for comparison to prove that the lesion was benign. Results-A total of 120 lesions in 111 patients satisfied the inclusion criteria. Lesion sizes were 0 to 5 mm (n = 16) and 6 to 10 mm (n = 104). Of these, 54 lesions were characterized as definitely benign (47 angiomyolipomas and 7 other benign entities: calcifications in stones or within a cyst or calyx and cysts that were either simple on follow-up studies or complicated with hemorrhagic or proteinaceous content). For the remaining 66 lesions, follow-up results after at least 5 years were normal in 24 cases (which meant that the lesion was no longer visible), and the remaining 42 lesions were stable in size. The mean duration of follow-up for these 66 lesions was 7.4 years. Conclusions-Small echogenic renal masses up to 1 cm in size that fulfill our study criteria are so likely to be benign that they can be safely ignored.