Mesothelial/monocytic incidental cardiac excrescence in autoimmune disease

Mesothelial/monocytic incidental cardiac excrescence (MICE) is a rare benign finding made of mesothelial cells, histiocytes, and fibrin, usually found during heart valve surgery. The clinical relevance resides in the potential misdiagnosis as metastatic carcinoma or arterial embolism. The pathogenesis remains uncertain, with artifactual and reactive hypotheses. Here we present a case of MICE with paradigmatic clinical, imaging, and histological features in a 28-year-old woman with undifferentiated connective tissue disease without previous cardiac catheterization with possible pathogenesis, highlighting the importance of awareness of the existence of this lesion in patients with autoimmune disease.