Mesothelial/monocytic incidental cardiac excrescences: cardiac MICE.

We have identified four new cases of the cardiac lesion resembling a histiocytoid (epithelioid) hemangioma from the consultation and surgical pathology files of the Mayo Clinic from 1979 to 1992. The lesions occurred in two men and two women, mean age 60 yr (range, 55 to 63), three of whom had undergone previous cardiac catheterization. All were found incidentally, two as separate tissue fragments obtained by right ventricular endomyocardial biopsy during investigations for dilated cardiomyopathy, and two during mitral valve replacement (one free floating in the left atrium and the other attached to the mitral valve). The latter two lesions measured 1.0 and 0.8 cm. All were composed of histiocytes (macrophages) focally admixed with cuboidal cells which formed strips and tubular arrays in three cases. Immunohistochemistry (two cases) confirmed their biphasic nature with cytokeratin positivity of the cuboidal cells and CD68 (KP-1) positivity (macrophage-myeloid lineage) of the histiocytes. Carcinoembryonic antigen and Leu-M1 were negative for both cell types. Transmission electron microscopy (two cases) showed macrophage-like cells and cuboidal cells with intracytoplasmic intermediate filaments, desmosome-like cellular junctions, and rough endoplasmic reticulum consistent with mesothelial cells. All four patients had a benign clinical course (range, 2 mo to 13 yr). This mesothelial and monocytic (histiocytic) process is postulated to relate to previous cardiac catheterization (applicable in three of our patients). The importance of these nodules, which are likely reactive, is their potential confusion with metastatic adenocarcinoma. We propose the name mesothelial/monocytic incidental cardiac excresences (cardiac MICE) for these lesions.