Tumors of the heart mimicking myxoma: what else should we consider when reporting MRI? A case of Primary Cardiac Synovial Sarcoma Myxoid Variant. (QF_TH_007)

A 23 years-old woman with no previous significant history presented with dyspnea on exertion for the past year and worsening of symptoms in the last two weeks associated with palpitations. Echocardiogram showed a hyperechogenic large round mass attached to the lateral wall of the left atrium, highly likely to be a myxoma. She underwent cardiac surgery for removal of the mass. Histo-pathological and immunohistochemistry tests demonstrated monophasic myxoid synovial sarcoma. The patient received neoadjuvant chemotherapy and radiation therapy. Six months postoperatively, she presented oligosymptomatic, although follow-up MRI showed more aggressive recurrence of the tumour. She continued with chemotherapy treatment and MRI 18 months after surgery showed a small residual tumor and thrombosis in the surgical site. 

Diagnostic Techniques and Their Most Important Findings: On MRI performed six months after surgery, it was found a large lobulated mass attached to the lateral wall of the left atrium, nearly touching the anterior leaflet of the mitral valve, which was thickend. Mass extended towards the left pulmonary veins (PV) and towards the left atrium appendage (LAA). The tumor was hypointense on cine steady-state free precession sequences, hyperintense on T1-weighted double inversion-recovery (DIR) with fat saturation and hyperintense on T2-weighted DIR without fat suppression sequences. On first-pass perfusion imagens, there was partial gadolinium enhancement and on late gadolinium enhancement (LGE) sequences there was highly heterogeneous enhancement. A follow-up cardiac MRI 18 months post-surgery and chemotherapy, showed residual mass in the left atrium and resolution of the thickening of the mitral valve leaflet.  There was also residual mass in the left PV and in the LAA. On a phase-sensitive inversion recovery sequence with a 600 ms TI, the mass appeared with no LGE, consistent with thrombotic component.

Learning Points from this Case: Synovial sarcomas are extremely rare therefore its features on cardiac MRI have never been comprehensively studied. Nonetheless there are characteristics found on MRI which must raise suspicion for a malignant mass. The reported patient had a confounding factor which was the myxoid variant of the synovial sarcoma. Myxoid variants of sarcomas may fairly mimic a myxoma on cardiac imaging and, specially for this case, it was not until the aggressive recurrence of the neoplasm that the characteristics of a malignant tumor was brought to surface. This case shows that a careful follow up with cardiac MRI may help identify new findings, which can be precisely assessed, and is the modality of choice for differential diagnosis and follow-up.