[933] Florid Reactive Mesothelial Hyperplasia of the Tunica Vaginalis Mimicking Malignant Mesothelioma: A Study of 10 Cases

Stephen Lee, Jonathan I Epstein, Peter B Illei. The Johns Hopkins Hospital, Baltimore

Background: Florid reactive mesothelial proliferation of serosal surfaces can morphologically mimic malignant mesothelioma. Homozygous deletion of 9p21 as detected with fluorescence in-situ hybridisation (FISH) assays has been reported to be a specific finding in the majority (67%) of epithelioid mesotheliomas.
Design: Ten cases were identified from the archival material of our institution and the consult files of one of the authors were reviewed. FISH for 9p21 was performed in five cases, where blocks were available.
Results: All 10 cases were incidental findings on routine examination of hydrocele sacs (n=7), epidydimal or paraepidydimal cysts (n=2), or pyocele (n=1). Microscopically, all cases were characterized by linear arrays of simple tubular formations and cords of mesothelial cells orientated parallel to the surface, and embedded within fibrous and inflamed tunica. Irregular solid nests and cribriform glands were noted in two cases. The mesothelial proliferation typically showed a sharply demarcated linear deep border at the junction between more reactive fibrous tissue and subjacent fibroadipose soft tissue or dense fibrous tissue. In only one case was there was a significant associated surface papillary component. No confluent growth, spindle cell morphology, necrosis or atypical mitotic figures were identified. No homozygous deletion of 9p21 was detected by FISH in the five cases tested.
Conclusions: Reactive mesothelial proliferation of the tunica vaginalis is often an incidental finding on routine excision specimens of hydroceles. Microscopically there is a characteristic linear proliferation of mesothelial cells with a well defined deep border at the interface of more reactive fibrous tissue and either dense fibrous tissue or subjacent fibroadipose tissue. In contrast to malignant mesothelioma, the tubular proliferation is not present in more acellular dense fibrous tissue or adipose tissue and only involves more reactive appearing fibrous tissue. Negative FISH assays for 9p21 deletion may be a useful ancillary tool to aid distinction from mesothelioma.
Category: Genitourinary (including renal tumors)

Monday, March 19, 2012 1:00 PM

Poster Session II # 140, Monday Afternoon


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