Mesothelial/monocytic incidental cardiac excrescence (MICE) is a rare benign lesion composed of histiocytes and mesothelial cells that is most often encountered during cardiothoracic surgery. One of the earliest cases reported by Rosai and colleagues was originally designated as histiocytoid hemangioma [1]. However, they later corrected this error and recognized mesothelial origin in a subsequent study of 14 cases by Luthringer and colleagues in 1990 [2]. The term mesothelial/monocytic incidental cardiac excrescence was first coined by Veinot et al. in 1994 [3]. As captured in this term, most cases of MICE are discovered incidentally during cardiothoracic surgery performed to treat various forms of cardiac disease. However, rare cases of MICE are sufficiently large to be detected by imaging studies, mimicking a mass or involving valves and mimicking endocarditis, and rare cases may cause valvular dysfunction or embolism [4].

As MICE is a benign lesion and has no impact on patient prognosis, its primary importance lies in recognizing this entity and avoiding confusion with other lesions, particularly neoplastic lesions such as cardiac myxoma, metastatic adenocarcinoma, histiocytic neoplasms and myeloid sarcoma. Here we report a case of MICE, tabulate the literature and discuss the differential diagnosis.