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Pelvis » Female Pelvis (Gynecology)
Recurrent multicystic pelvic mesothelioma
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Presentation A 61 yearold woman with history of bilateral salpingo-oopherectomy and appendectomy has a palpable pelvic mass. She states that she has had surgery for a pelvic tumor 8 years ago.
Caption: Transabdominal transverse scan of the pelvis
Description: A complex heterogeneous mass with cystic spaces within is noted filling the posterior cul de sac and displacing the uterus and broad ligaments anteriorly.
Caption: Transvaginal right sagittal scan
Description: A complex right sided cystic mass is noted with the mass showing very thin septations.
Caption: Transvaginal mid-sagittal scan
Description: Transvaginal scan demonstrating better the characteristics of the cystic mass in the pelvis.
Caption: Transvaginal left sagittal image
Description: Again seen is a cystic septated mass in the pelvis with no obvious mural nodularity or solid components within.
Caption: Transvaginal transverse scan
Description: The cystic mass demonstrated in another view. The bands of weak echoes seen crossing the larger cystic compartments are artifacts.
Differential Diagnosis Multiseptated cystic mass, the differential of which is ovarian mucinous cystadenoma/carcinoma, loculated pelvic fluid, peritoneal inclusion cyst, pseudomyxoma peritonei, abdominal lymphangioma, bilateral endometriosis, malignant mesothelioma, multicystic pelvic mesothelioma
Final Diagnosis Recurrent multicystic pelvic mesothelioma

Peritoneal cystic mesothelioma is a rare benign tumor that arises from mesothelial cells of the peritoneum and is seen more commonly in young and middle-aged women. It tends to have a local recurrence. Its common location is in the pelvis and may extend into the abdomen, although it can affect any part of the peritoneum or omentum.

The etiology of this tumor is not known. Unlike its malignant counterpart, the cystic variety of mesothelioma has no relation to asbestos exposure. Chronic peritoneal irritation and previous laparotomy are implicated risk factors. Confirmatory diagnosis is usually achieved by immuno-histochemical and electron microscopic methods.

Imaging findings:
Ultrasound: This is usually the first imaging modality that is used when a woman presents with either abdominal fullness or a palpable tumor. The presence of a thin-walled cyst attached to the peritoneum on ultrasound should arouse suspicion for this rare entity. The ultrasound findings are quite non-specific and include-
1. A complex cystic mass that may show either single or multiple thin-walled cysts with septations.
2. The septations are thin-walled (less than 5 mm in thickness) and show no nodularity.

CT and MRI also show a similar non-specific appearance of the cystic mass but allow for a more complete assessment of the extent of the disease.

Differential diagnosis: It is important to distinguish this tumor from the following other cystic masses-
1. Ovarian mucinous cystadenoma/carcinoma: A predominantly pelvic mixed solid-cystic mass with involvement of the ovary. Additional findings of ascites, omental thickening and serosal deposits may also be seen.
2. Loculated pelvic fluid or a seroma: seen as a large cystic collection with the patient giving a history of peritoneal surgery. 
3. Peritoneal inclusion cyst: Also known as peritoneal pseudocyst or inflammatory cysts of the pelvic peritoneum.  The development of this lesion requires the presence of pelvic adhesions [usually following surgery] and functioning ovaries. The normal ovary produces an exudates that forms a substantial component of the peritoneal fluid.  If the peritoneum is damaged or inflamed it fails to resorb the fluid which may accumulate in locules formed by pelvic adhesions, resulting in a complex multicystic mass. The normal ovaries may be trapped within the mass. This condition forms the closest differential for benign cystic mesothelioma and can be differentiated from the latter on histology by the absence of smooth muscle cells within the septa.
4. Pseudomyxoma peritonei: This condition occurs secondary to a mucin producing neoplasm and has a predominant solid component and may involve the viscera.
5. Abdominal lymphangioma: This occurs in children and young adults with a pelvic location being uncommon. Demonstration of fat may be helpful.
6. Malignant mesothelioma: Occurs after exposure to asbestos and has a solid component.

Case References 1. Demopoulos RI, et al. Epidemiology of cystic mesothelioma. Int J Gyne Path. 1986; 5(4):379.
2. O`Neil JD, et al. Cystic mesothelioma of the peritoneum. Radiology. 1989 Feb; 170(2):333.
3. Chen YC, et al. Benign cystic mesothelioma of the peritoneum. J Formos Med Assoc. 1990 Jun; 89(6):479.
4. Bhandarkar DS, et al. Benign cystic peritoneal mesothelioma. J Clin Pathol. 1993 Sep; 46(9):867.
5. Ozgen A, et al. Giant benign cystic peritoneal mesothelioma. Abdom Imag 1998 Sep-Oct; 23(5):502.
6. Villaschi S, et al. Cystic mesothelioma of the peritoneum. Am J Clin Pathol. 1990 Dec; 94(6):758.
7. G. Bastarrika, et al [2002, Jun 24]. Cystic peritoneal mesothelioma, {Online}.
8. Jones S, et al. Pelvic pain and history of previous pelvic surgery.
9. Jain KA. Imaging of peritoneal inclusion cysts. AJR 2000 Jun;174(6):1559.
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