Cardiac tumor - undifferentiated pleomorphic sarcoma

PA and lateral chest x-ray demonstrate enlargement of the cardiac silhouette. No effusions or masses. 

There is an ill-defined soft tissue mass almost entirely occupying the left atrium, crossing the interatrial septum into the left atrium and also appearing to protrude into the proximal inferior vena cava. It is of relatively homogenous hypoattenuation. No significant enhancement, no evidence of central necrosis or calcifications.

There is also a moderate pericardial effusion measuring up to 4 cm in depth and collected predominantly along the inferior cardiac borders; it is uncertain if there is non-enhancing solid tissue within the pericardial space.

The origin of the left inferior pulmonary vein is mildly narrowed. The right coronary artery posterolateral branch also appears encased by soft tissue.

A couple of small non-specific nodules and linear atelectasis in the left lower lobe. Lungs are otherwise clear. No pleural effusions. No bony suspicious abnormalities.

Abdomen and pelvis: Liver, spleen, adrenal glands, pancreas, and kidneys are unremarkable in appearances. No nodal enlargement. Bowels are unremarkable, with no evidence of dilation. No free fluid or free gas. No bony suspicious abnormalities.

Conclusion: Features are those of a cardiac mass centered in the left atrium, crossing the interatrial septum into the right atrium with pericardial effusion and IVC extension. Findings are not classic for atrial myxoma; sarcoma, metastasis, lymphoma +/- thrombus need to be considered. 

A homogeneous T1 isointense and mildly T2 hyperintense to muscle infiltrative mass is centered at the inferior aspect of the left atrium, crossing the inter-atrial septum into the right atrium as well as infiltrating beyond the mitral annulus to the basal inferior left ventricular wall. A lobulated small frond-like component in the right atrium is minimally mobile, and not prolapsing into the right ventricle. No T1 hyperintensity to suggest the presence of fat within the mass.

Perfusion imaging shows relatively hypovascularity, and mild enhancement is demonstrated on both early and late gadolinium imaging. Normal LV function with ejection fraction 62%. No solid component is seen within a moderate to large pericardial effusion. 

Conclusion: Mildly enhancing hypovascular soft tissue mass that is homogeneously T1 isointense and mildly T2 hyperintense to muscle centered at the left atrium infiltrates through the interatrial septum into the RA and through the mitral annulus into the basal inferior LV wall. Moderate pericardial effusion without MRI evidence of tamponade. 

The patient went on to have surgery.

Histology

MICROSCOPIC DESCRIPTION: The sections show a malignant pleomorphic tumor. The tumor forms nests and cords. No glandular structures are seen. No anastomosing vascular channels are noted. The tumor cells are mainly epithelioid in appearance with enlarged pleomorphic nuclei, prominent nucleoli and scanty ill-defined cytoplasm. Some cells have intranuclear pseudoinclusions. No brown cytoplasmic pigment is seen. Mitoses are inconspicuous. There is no evidence of lymphovascular invasion. Occasional eosinophils are noted in the background.

The tumor cells show positive staining for CD31 (histiocytic and vascular marker) and CD99 with some possible faint CD10 reactivity. There is patchy granular cytoplasmic staining for melan-A, of uncertain significance. All other melanocytic markers are negative (S-100, SOX-10, HMB-45, Tyrosinase). The Ki-67 index is about 20%. CAM5.2, AE1/3, CK7, CK20, CDX-2, TTF-1, p40, calretinin, CD34, c-kit, desmin, actin, myogenin, CD3, CD15, CD20, CD30, CD43, CD68 and ALK-1 are also negative. Carcinoma, melanoma and lymphoma have been excluded. The features are consistent with undifferentiated pleomorphic sarcoma, as a diagnosis of exclusion.

FINAL DIAGNOSIS: Undifferentiated pleomorphic sarcoma.