Epithelial cyst of the cardiac papillary muscle: case report and review of the literature.

BACKGROUND: Reports of endodermal heterotopia (previously known as inclusion cysts) in cardiac atria are rare and there is only a single previous case report of endodermal heterotopia in a cardiac papillary muscle. AIM AND METHODS: A cyst in a cardiac papillary muscle was identified during the autopsy of an 87-year-old man who had died from an unrelated myocardial infarction. The cyst was examined histologically and mucin staining and immunostaining were carried out. RESULTS: We report a unilocular cyst in a cardiac papillary muscle, which is lined by low cuboidal, pseudostratified and occasionally ciliated respiratory-type epithelium, surrounded by a layer of smooth muscle. The immunohistochemical features (MNF116+, cytokeratin (CK)7+, CK8+, CK18+, CK19+, epithelial membrane antigen positive, scattered cells positive for neuroendocrine markers) suggest that this is an endodermal heterotopia. Immunostaining of positive thyroid transcription factor-1 provides evidence for bronchogenic differentiation. DISCUSSION: The differential diagnoses of cystic structures in cardiac papillary muscle and the origin and importance of endodermal heterotopias are discussed.