Cystic mesothelioma of the peritoneum: a rare cause of 'ascites' in children.

A 2-year-old girl presented with a 3-month history of progressive painless abdominal distension. Results of the clinical examination suggested massive ascites, but no other symptoms or signs could be elicited. There was no history of any other illness preceding the onset of distension. Ultrasonography and a computed tomography scan confirmed gross ascites, with multiple thin-walled loculi throughout the abdomen, from the diaphragm to the pelvis. The preoperative diagnosis was intraabdominal lymphangioma. During laparotomy, multiple transparent cysts were found throughout the peritoneum. There was no evidence of malignancy in any organ, and the cysts appeared almost completely avascular. Histological and ultrastructural appearances were those of benign cystic mesothelioma of the peritoneum, a condition that hitherto has been recognized only in adults. It is thought to represent a borderline variant between a truly benign adenomatoid lesion and the better-known malignant mesothelioma. The experience with adult cases suggests a high potential for recurrence but no progression to malignancy. It is possible that some cases of intraabdominal lymphangioma may have been misdiagnosed in the past; future cases should be fully evaluated, both immunohistochemically and ultrastructurally, to establish the true incidence of mesothelial proliferative disease in children.