[A case of retroperitoneal pseudotumor (xanthogranuloma)].

A 57-year-old male patient was admitted to our hospital for left flank pain and a slight increase in serum creatinine. He had left hydronephrosis and extrinsic stenosis of left lower ureter shown by intravenous and retrograde pyelography. Computed tomography (CT) and magnetic resonance imaging (MRI) demonstrated a mass along the bilateral lower ureters, the left side of which was larger (5 x 3 x 4 cm). After surgical exploration and biopsy of the tumor the patient was diagnosed as having xanthogranulomatous inflammatory pseudotumor. No malignant findings were observed. Tumor size spontaneously decreased to 20% of the original size at 2 weeks after laparotomy. The patient underwent ureterolysis because of prolonged left hydronephrosis. Approximately 3 years after development of disease, hydronephrosis has improved and the pelvic tumor has almost diminished.