The Thymoma Threat: Getting to the Heart of an Intracardiac Mass (QF_TH_001)

A 76-year-old male is admitted with significant upper extremity and facial swelling. He had presented 2 months prior to an outside ED with palpitations, irregular heartbeat, dizziness, and left arm swelling. At that time a chest X ray did not demonstrate any active cardiopulmonary disease. Subsequently, he saw an outside cardiologist who ordered an event monitor that demonstrated numerous runs of SVT and one run of NSVT.  

During the present admission, chest CT revealed a heterogenous lobulated anterior mediastinal mass communicating with large filling defect in the left brachiocephalic vein extending into the SVC and right atrium consistent with tumor thrombus. An echocardiogram showed a large mass in the right atrium. A FDG PET/CT showed FDG avidity of the mass extending into the SVC and right atrium.  The thoracic surgery team recommended a CMR to assess the right atrial mass in anticipation of future surgery.




Diagnostic Techniques and Their Most Important Findings: Cine steady state free precession imaging and Half Fourier Single-shot Turbo spin-Echo (HASTE) imaging showed an anterior mediastinal mass with extension into the left brachiocephalic vein, SVC, and right atrium with partial prolapse across the tricuspid valve during diastole. The SVC was significantly dilated with near total occlusion by the mass (Fig 1). The mass was heterogenous, mostly isointense to the myocardium on T1 weighted imaging and relatively hyperintense on T2 weighted imaging. T1 mapping and T2 mapping showed increased T1 and T2 values relative to the myocardium (Fig 2). Dixon fat-water separation imaging showed that the mass did not contain fat. Dynamic contrast uptake was seen on perfusion images. There was heterogeneous enhancement on late gadolinium enhancement images. Additionally, focal areas of filling defect were seen on post contrast images suggesting thrombus on the periphery of the mass (Fig 3). Overall CMR findings were concerning for thymoma, which was confirmed from a CT-guided biopsy (Fig 3). Surgical resection is being planned.

Learning Points from this Case: The classic differential diagnosis for anterior mediastinal mass is given by the 4Ts mnemonic: Thymus, Thyroid, Teratoma, and “Terrible” lymphoma. Thymoma is a rare neoplasm, with an overall incidence of 0.13 per 100,000 person-years in the US. However it is the most common anterior mediastinal tumor, accounting for 50% of all anterior mediastinal masses. Approximately 30% of thymomas are invasive, but extension into the right atrium is rare. This case illustrates thymoma as an unusual cause of palpitations and SVC syndrome. CMR enabled the precise delineation of the relationship of the tumor with valves and vessels, characterization of tissue, and assessment of internal morphology. In this case, the mass had low to intermediate T1 intensity, high T2 intensity, no significant fat content as evidenced by fat-water separated imaging, and enhancement on post contrast images. There was also evidence of “bland” thrombus adherent to the mass and patient was started on anticoagulation. These imaging characteristics were suggestive of thymoma, as was confirmed on pathology.