MESOTHELIAL/MONOCYTIC INCIDENTAL CARDIAC EXCRESCENCE (MICE)
Sections show a mesothelial/monocytic incidental cardiac excrescence (MICE) with stromal fibrosis and a nodular outline. Most of the lesion consists of small clusters of epithelioid cells located between thick bundles of collagen. Immunostains show that the epithelioid cells proliferating on the surface of the nodule stains with mesothelial markeras like Calretinin. Most of the cells stains for Vimentin. CD34 is only positive in endothelial cells. If you order CD68 or CD163 you can see clusters monocytic cells positive for these stains.
MICE is a very rare benign entity only diagnosed incidentally after cardiac surgical procedures. To date, only few cases have been reported. On microscopic evaluation, the findings may be consused with other neoplasm, for example Solitary Fibrous Tumor, but the lesion is virtually negative for CD34.