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6 May 2011 Case of the Week #205

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Thanks to Eddie Fridman, The Chaim Sheba Medical Center (Israel), for contributing this case. This case was reviewed in May 2020 by Dr. Jennifer Bennett, University of Chicago and Dr. Carlos Parra-Herran, University of Toronto.

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Case of the Week #205

Clinical History

A previously healthy 36 year old woman was operated on due to multiple small cystic lesions of the pelvic peritoneum and small bowel mesentery. Both ovaries were unremarkable. Sections are of the cystic areas.

Micro images:



Left: CD31, Right: MNF-116

What is your diagnosis?


Benign cystic mesothelioma


Benign cystic mesothelioma, also called multicystic mesothelioma, is a rare tumor that occurs most frequently in women of reproductive age, and is difficult to diagnose preoperatively (J Med Case Reports 2010;4:385). It is often associated with prior pelvic surgery, endometriosis or pelvic inflammatory disease (J Obstet Gynaecol Res 2011;37:1126), but is not associated with asbestos. Some cases may be neoplastic, and others may be caused by inflammation and adhesions (Int J Gynecol Pathol 2011;30:163).

Grossly, the tumors are usually large, and may be multifocal or unilocular. Free floating cysts may also occur. Morphologically, the mesothelial cells lining the cysts vary from flattened to endothelial-like to cuboidal. The cysts are thin-walled, and may contain eosinophilic fluid. Inflammatory cells are often present within the stroma between the cysts. Foci of mesothelial hyperplasia may also be present, as in this case. The lining cells are immunoreactive for keratin and calretinin (Hum Pathol 2003;34:369).

The differential diagnosis includes:

- lymphangioma: younger patients, may contain chylous fluid grossly, often lymphoid aggregates and smooth muscle within walls, D2-40+
- other mesenteric / omental cysts / pseudocysts: usually unilocular, no distinct cyst wall or internal septa, keratin and calretinin negative
- cystic teratoma: usually contains adipose and calcifications
- loculated ascitis: usually has irregular borders, is surrounded by bowel loops or abdominal / pelvic organs

Complete surgical resection of benign cystic mesothelioma is recommended. Follow up is necessary, because 50% of tumors recur after excision.

Nat Pernick, M.D., President
and Liz Parker, B.A., Associate Medical Editor
PathologyOutlines.com, Inc.
30100 Telegraph Road, Suite 408
Bingham Farms, Michigan (USA) 48025
Telephone: 248/646-0325
Email: NatPernick@Hotmail.com
Alternate email: NatPernick@gmail.com