The Deceptive Myxoid Appearance of a Low-Grade Cardiac Sarcoma and Its Accompanying Diagnostic Challenges: A Case Report

We present a 40-year-old man with a recurrent left atrial mass, previously diagnosed as cardiac myxoma elsewhere. His new admission was due to a regrowth of the mass. Progressive exertional dyspnea was his major complaint. A large lobulated tumor was seen in echocardiography in the posterior wall of left atrium involving the posterior leaflet of mitral valve, and resulting in severe stenosis and diastolic protrusion of the mass into the left ventricle. Surgery showed a non-homogenous myxomatous mass which infiltrated the posterior wall of the left atrium and parts of the inter-atrial septum. As a result, the surgeon excised parts of the septum and the posterior wall and did a reconstruction with pericardial patches. The pathologic examination revealed soft creamy-brown tumoral fragments, m: 10 × 4 cm altogether. Contrary to his previous diagnosis, we observed a malignant neoplasm with cells that had plump, round to oval nuclei, set in a myxoid and vascular background, but mitotic figures and necrosis were not conspicuous. Therefore, we made a diagnosis of recurrent myxoid round cell sarcoma and recommended immunohistochemical (IHC) studies. Multiple IHC and histopathological studies elsewhere favored a diagnosis of myxoma which was not compatible with our diagnosis. A second recurrent mass was soon found in the left atrium making further surgical attempts impossible. At last, a diagnosis of myxoid leiomyosarcoma confirmed our diagnosis, but the patient was not fortunate enough to survive and passed away before heart transplantation could be done as a remedy.