165 Malignant Mesothelioma Presenting as Small Bowel Obstruction: A Rare Case Report

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Abstract Introduction/Objective Malignant mesothelioma is a rare, aggressive neoplasm of mesothelial origin, most commonly affecting the pleura. Primary involvement of the small bowel is exceedingly rare. Methods/Case Report We report a unique case of malignant mesothelioma presenting as acute small bowel obstruction (SBO) in a 67-year-old male. The patient presented with abdominal pain, nausea and vomiting. Imaging revealed multiple ileal and mesenteric masses. Exploratory laparotomy identified three firm ileal masses and a large omental mass adherent to the transverse colon, all of which were resected. Histologic evaluation revealed biphasic malignant neoplasm composed of ∼80% epithelioid and ∼20% sarcomatoid components, with a high mitotic rate and extensive necrosis. Immunohistochemically, the tumor cells were positive for AE1/3, Cam5.2, CK5/6, CK903NBF, CK7, WT-1 (patchy), D2-40 (patchy), Calretinin (diffuse), and GATA3 (patchy), and negative for MOC-31, BerEP4, CK20, CDX2, PAX8, TTF-1, NKX3.1, SOX10, Melan A, S100, ERG, DOG1, SMA, and Desmin. Nuclear expression of BAP1, INI-1, and BRG1 was retained. Ki-67 proliferative index ranged from 20–30%. In conjunction with absence of other masses in body, this tumor was eventually diagnosed as a biphasic malignant mesothelioma arising in the abdomen. Results NA Conclusion This case represents an extremely rare intra-abdominal presentation of malignant mesothelioma presenting as SBO. Accurate diagnosis relies on histopathologic examination and broad immunohistochemical evaluation. Awareness of this rare entity is crucial to include in the differential diagnosisfor patients presenting with SBO and unexplained mesenteric masses.

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