RESUMO
OBJECTIVE: To present two cases of infrequent renal masses, trying to achieve the diagnosis before surgery. METHODS: We describe a case referred from the Department of Hematology in which bilateral perirrenal masses were described in the CT scan; after biopsy they where classified as extramedullary hematopoietic tissue. The other case was a patient presenting to the emergency room with dyspnea. CT Scan showed lungs with multiple cysts, chylothorax and a cystic-solid mass in the left perirenal space. In the lung biopsy they reported lung lymphangiomatosis, so we didn't perform renal biopsy. RESULTS: Most renal masses are renal carcinomas (856%). The less common diagnosis are sarcomas, lymphomas, upper urinary tract transitional cell carcinomas, metastases of other primary tumors, the Erdheim-Chester disease, the Castleman disease and benign tumors. All these diseases might show similar images in the CT scan and MRI, being the biopsy and histological study necessary for the diagnosis CONCLUSIONS: Perirenal extramedullary hematopoiesis and perirenal lymphangioma are rare diseases that need a pathologic study for their diagnosis.