[A case of mesothelioma of perinephric space origin].

Cystic mesothelioma of perinephric retroperitoneum origin are very uncommon tumors and considered potentially malignant. We report one such case and discuss the clinical and pathological findings. A 70-year-old man was seen with complaint of discomfort in the right flank and hospitalized in May 1989. Computerized tomography revealed multiple cystic masses in the right retroperitoneal space which appeared to be infiltrating the kidney and the iliopsoas muscles. Magnetic resonance imaging showed deformation of the right kidney with many impressions in the parenchyma. The cystic lesions and the right kidney were extirpated on June 2, 1989. Grossly the specimen was 16 x 10 x 8 cm in size and 630 g in weight. The multiple cysts surrounding the kidney were each approximately 10 mm in diameter and had thin outer walls. The cyst fluid was clear and serous. The kidney had not been infiltrated but had only external impressions caused by the cystic lesions. Microscopically, the cysts were lined by a single layer of cuboidal cells accompanied by some hobnail-shaped cells, and no evidence of malignancy was found. The epithelium was focally positive for periodate acid Schiff and slightly positive for Alcian blue. It was strongly positive for cytokeratin and vimentin, and slightly positive for EMA but negative for lectins. The diagnosis was diffused benign multicystic mesothelioma. However, CT taken four months after the operation revealed local recurrence and radiotherapy (40 Gy) was instituted. Since the cystic mass tended to grow in size thereafter, the lesion appeared to be malignant clinically. We consider this is the first case of cystic mesothelioma of perinephric retroperitoneum origin reported in Japan.