1356664 - Wolf in sheep's clothing: not everything in the left atrium is a myxoma.

An echocardiogram (Figure 1) exhibited a large heterogeneous soft-tissue mass filling the left atrium (LA) adherent to the anterior mitral leaflet with an anterior mobile component, prolapsing into the LV in diastole without significant functional stenosis. Although the origin of the mass was not appropriately visualized in the study, there was concern for pulmonary vein (PV) involvement. Thus, the differential included malignancy, thrombus, or myxoma. 

Hence, a CMR was ordered to further characterize the lesion (Figure 2). The large complex soft tissue mass (5.8 x 4.8 cm) centered in the LA extended into the inferior right PV. The mass was isointense in T2, with a posterior component demonstrating first pass perfusion and heterogenous late gadolinium enhancement, including a central and anterior non-enhanced area suggestive of necrosis or superimposed thrombus. Findings were most suggestive of malignancy due to a primary cardiac sarcoma originating from PVs versus metastasis. 

Under the suspicion of malignancy, a cardiac CT with delayed acquisition and chest/abdomen imaging were obtained to evaluate extension (Figure 3). The posterior component demonstrated delayed contrast uptake with extension to the distal bronchus intermedius associated with multiple sub-centimeter bilateral mediastinal lymph nodes and a 16 mm left adrenal nodule, although nonspecific, concerning metastasis. Furthermore, the inferoposterior margin of the mass seemed to be in continuity with the retrocardiac esophagus. Additionally, isolated upper right PV draining into SVC was noticed, which explained right chambers enlargement seen on echo/CMR.   

A bronchoscopy with fine needle biopsy depicted a high-grade malignant sarcoma with spindle cell (SC) features. The patient was evaluated by CT surgery and deemed unresectable. Radiation therapy was provided intended to attain shrinkage of the mass as palliative treatment. 


Learning Points from this Case:

Cardiac SC sarcomas typically involve the LA and are often misdiagnosed as myxomas. Unlike myxomas, this tumor has a non-septal origin of mass, a broad attachment on the LA wall, semisolid consistency, high vascularization, and hyper-enhancement on contrast echocardiography, CT or CMR (1). These highly aggressive tumors infiltrate the heart and metastasize rapidly, often via tumor emboli (2). In this case, the morphologic appearance of the tumor was suggestive of myxoma, but the infiltration of the PVs was not typical, therefore, further investigation was pursued. The consideration of malignant lesions under uncommon scenarios is paramount to obtain the proper diagnosis.