Cystic adrenal lesions: CT features

PURPOSE: To define computed tomographic (CT) features of cystic ad renal lesions that differentiate them from similar-appearing adenoma. MATERIALS AND METHODS: CT scans of 13 cystic adrenal lesions (four endothelial cysts, three benign pseudocysts, one nonspecific benign cyst, one carcinoma, one pheochromocytoma, and three stable lesions with no histologic diagnosis) were analyzed retrospectively. Reports in the literature of 26 benign adrenal cysts were also reviewed. RESULTS: Mean lesion diameter was 6.2 cm, and six lesions were less than 5.0 cm. Mean attenuation value was 21 HU, and in eight cases it was less than 15 HU. Partial adrenal involvement was noted in six cases. Ten lesions contained wall or septal calcification. Wall thickness was 3 mm or less in nine and exceeded 6 mm in three lesions; one of the latter was cystic carcinoma. Wall enhancement (but no intralesional enhancement) was found in two of six lesions. Of 37 reviewed benign cysts, 19 had mural and seven had central calcification, 28 were unilocular, and seven had high attenuation value. Wall thickness was 3 mm or less in 31 lesions. CONCLUSION: CT findings of a nonenhancing mass with or without wall calcification allow differentiation of adrenal cyst from adenoma. A small adrenal cyst with near- water attenuation and a thin (≤3-mm) wall is likely to be benign.