Pyelocaliceal diverticulum presenting as a disappearing renal mass.

We report a rare case of a disappearing cystic mass of the kidney. Pyelocaliceal diverticulum has to be considered in the differential diagnosis of patients with pyelonephritis and a space-occupying lesion of the kidney. Initial conservative therapy with antibiotics helps to determine the definitive diagnosis. Surgical management is recommended to prevent sequelae of pain and infection.