Giant kidney worm (Dioctophyma renale) infection mimicking retroperitoneal neoplasm

A 50-year-old Chinese man was found by ultrasound and computed tomography to have a retroperitoneal mass in the right upper quadrant of the abdomen. At operation, a hemorrhagic cyst was detected at the upper pole of the right kidney adjacent to the adrenal gland. Microscopic examination revealed that the cyst wall was composed of granulomatous tissue loaded with eggs and cross-sections of parasites, identified as Dioctophyma renale. The eggs were characterized by a birefringent striated double wall. The presence of cross sections of adult worms of D. renale in human tissue has not been previously described. Another unique feature of this case was that the right kidney was intact, as examined grossly at laparotomy and by intravenous pyelography. Eggs were not detected in the urine.