[A case of renal pseudotumor caused by pyelonephritis]

A case of renal pseudotumor due to pyelonephritis is reported. A 70-year-old female was admitted to our hospital for the evaluation of right renal mass in pyelogram. She had had episodes of pyelonephritis many times. Computed tomography (CT) revealed poorly marginated low density mass that exhibits inhomogenous enhancement with contrast medium. Angiography showed an avascular mass. On magnetic resonance imaging (MRI), the mass was isointensity or slightly low intensity on T1 weighted scan, while it showed low intensity on T2 weighted scan. The patient died from small cell carcinoma in the lung two years later. Autopsy was performed and no malignancy was found in the kidney. MRI was useful to differentiate such inflammatory change from renal tumor, which is mostly high intensity on T2 weighted scan.