Mesenteric pseudocyst of the sigmoid colon.

A 31-year-old woman with right lower abdominal pain was hospitalized. Palpation revealed both tenderness and rebound tenderness in the right lower quadrant of her abdomen. Abdominal ultrasonography (US) indicated a multilocular cystic mass on the right side of the pelvic area, and a computed tomography (CT) scan showed a low-density mass measuring 7 cm in diameter. Torsion of the pedicle of a right ovarian cyst was suspected, and emergency laparotomy was performed. At operation, however, the uterus and both ovaries appeared normal, and exploration revealed a yellow-reddish cystic mass, approximately 10 cm in size, in the subserosa of the sigmoid colon. The mass was excised together with a 10-cm segment of the sigmoid colon. Macroscopically, it was a multilocular cyst, measuring 10 x 10 cm in size, and it contained white gelatinous fluid. Histological examination showed the cyst wall to be composed of neutrophils, lymphocytes, fibrin, and fibroblasts, but neither a specific endothelial lining nor proliferating lining was detected. The final pathological diagnosis was a mesenteric pseudocyst. Mesenteric pseudocysts are rare, and only 14 cases have been reported previously in the Japanese literature. Emergency operation was performed in 3 patients, including our own. The etiology of these three pseudocysts (manifested by acute abdomen) was unknown. We suspect that inflammation spread and injured lymph vessels, causing lymph to leak out and pool under the subserosal layer.