Two cases of mesothelial/monocytic incidental cardiac excrescences of the heart.

Two cases of mesothelial/monocytic incidental cardiac excrescences in a 66-year-old female and an 80-year-old male are presented. Lesions had solid and tubular pattern formations which were composed of two predominant cell types of histiocytoid cells and cuboidal cells arranged in strips. The histiocytoid cells were round and had well-defined nuclei with prominent nuclear grooves. They had a low nuclear to cytoplasmic ratio. There were no atypical mitoses. Immunohistochemically, these cells were positive for leukocyte common antigen (LCA) and CD68 (KP-1) but negative for keratin. The cuboidal cells were present in strips, had haphazardly arranged surface microvilli and had small round non-cleaved nuclei. These cells were positive for keratin but negative for LCA, CD68, p53, proliferative cell nuclear antigen, alpha-smooth muscle actin, Factor VIII, epithelial membranous antigen and vimentin. These lesions are probably reactive because of their heterogeneous components; an expected feature for an essentially artifactual lesion that is related to cardiac surgery and invasive catheterization. Immunohistochemical studies are useful for avoiding misdiagnosis of neoplasms.