Mesothelial or monocytic incidental cardiac excrescence on anterior leaflet of mitral valve

From the archives of MD Anderson Cancer Center. Mesothelial/monocytic incidental cardiac excrescence with a review of the literature

Mesothelial/monocytic incidental cardiac excrescence (MICE) is a rare benign lesion composed of monocytes and mesothelial cells that is most often encountered during cardiothoracic surgery. We describe a case in a 71-year-old man with known aortic valve stenosis who presented with gradual onset dyspnea over a few weeks, made worse with minimal exertion. A transesophageal echocardiogram revealed severe aortic stenosis and mild pericardial effusion. The patient underwent aortic valve replacement, coronary artery bypass, and amputation of the left atrial appendage. Histological examination of a 0.8 cm blood clot received along with the atrial appendage showed an aggregation of bland cells with features of monocytes associated with small strands and nodules of mesothelial cells, fat cells, fibrin and a minute fragment of bone. Immunohistochemical analysis showed that the monocytic cells were positive for CD4 and CD68 (strong) and negative for calretinin and keratin. By contrast, the mesothelial cells were positive for calretinin and keratin and negative for all other markers. In sum, the morphologic and immunohistochemical findings support the diagnosis of MICE. Based on our review of the literature, about 60 cases of MICE have been reported previously which we have tabulated. We also discuss the differential diagnosis.