Benign mesothelial proliferation with effusion. Clinicopathologic entity that may mimic malignancy.

The clinical and pathologic features of five cases of a previously poorly defined syndrome, benign mesothelial proliferation with effusion, are described. Although this is a benign process, both the gross and the microscopic findings may mimic metastatic papillary adenocarcinoma. Three of five patients had dysynchronous involvement in more than one body cavity developing over intervals of one, two, and six years. The clinical course is unpredictable and is usually associated with a good prognosis, but two of three patients with pericardial involvement required pericardectomy for pericardial tamponade. The entity of benign mesothelial proliferation with effusion and its distinction from true malignant conditions are discussed.