True adrenal mesothelial cyst in a patient with flank pain and hematuria

True mesothelial (epithelial) cysts in the adrenal gland are rare lesions. They represent 9% of adrenal cysts and are much less common than vascular adrenal cysts. We report a case of a true adrenal mesothelial cyst in a patient with flank pain and hematuria that was diagnosed on imaging as a renal cyst. Immunohistochemical studies were performed to investigate the nature of the cyst lining. The positive immunostains for calretinin and WT-1 lend support to the postulate of Medeiros et al nearly 20 years ago of a mesothelial origin for these cysts. The clinical presentation and salient radiologic and pathologic features are described.