A case of a mesenteric cyst in the sigmoid colon of a 3-year-old girl.

Mesenteric cysts are rare. In this paper we present a case of a mesenteric cyst in the sigmoid colon of a 3-year-old girl. On the first visit to our department, a smooth-surfaced soft mass approximately 15 cm in diameter was noticed in the right lower abdomen. Although the patient complained of lower abdominal pain, there was no tenderness or guarding. Laboratory tests indicated no abnormality except a slightly increased level of C-reactive protein (2.3 mg/dL). A plain abdominal X-ray film revealed displacement of colonic gas from the right lower abdomen, and abdominal ultrasonography and computed tomography revealed a smooth cystic mass measuring 9.5 x 8.7 x 4.7 cm that contained many internal septa. Because the patient had several symptoms, we performed a surgical operation under general anesthesia. We found a light-red cystic mass, 8.5 x 8.0 x 3.0 cm in size, in the mesentery of the sigmoid colon and surrounding the sigmoid colon, without adhesion to any other organ. We approached the cystic mass from the sigmoid colon and the mesentery of sigmoid colon and completely resected it without complications. The content of the cystic mass was a pale-yellow serous fluid. A cytological examination revealed mainly lymphocytes with reactive mesothelial cells. The resulting pathological diagnosis was a multi-lobular mesenteric cyst. Immunohistochemical staining with D2-40 antibody was positive value along the wall of the cyst, indicating that the cyst was derived from a lymphatic vessel.