Adenomatoid Tumor of the Pericardium: A Case Report and Literature Review.

Adenomatoid tumors (ATs) are rare benign neoplasms of mesothelial origin, commonly found in the genital tracts but occasionally reported in extragenital locations, including the thoracic cavity. We describe the second case of a pericardial AT in a 65-year-old male with multiple comorbidities, including end-stage renal disease, diabetes mellitus, and heart failure. A small pericardial nodule was incidentally discovered during coronary artery bypass graft surgery without any clinical evidence of pericardial thickening. Histopathologic evaluation showed a well-circumscribed nodule with solid nests of epithelioid to spindled cells with bland cytology within a fibrous stroma. Immunohistochemical analysis demonstrated strong and diffuse positivity for calretinin, D2-40, WT-1, and pan-cytokeratin, confirming mesothelial differentiation. Markers of epithelial origin like MOC-31 and BerEp4 were negative, excluding the possibility of carcinomas of unknown origin. BAP1 nuclear expression was retained, and fluorescence in situ hybridization (FISH) for p16 (CDKN2A) was negative for homozygous deletion, distinguishing the lesion from mesothelioma. Besides contributing to the limited body of knowledge on extragenital and thoracic ATs, this case adds to the limited number of reports on pericardial ATs, providing an understanding of the rare occurrence of these tumors arising from the pericardium.