CT of thrombosed renal vein presenting as a hyperdense mass.

We report a patient with focal renal vein thrombosis that presented as a hyperdense mass mimicking a hyperdense cyst or a pelvic or parenchymal tumor. The lesion was described as a well-defined round hyperdense mass in the right renal sinus on noncontrast CT and was surgically proven to be acute thrombosis of the renal vein. Renal vein thrombosis should be considered in the differential diagnosis of a hyperdense mass in the renal sinus even if the patient has no underlying renal abnormality.