Recurrent Thymoma with Direct Myocardial Involvement: A Rare Case of Cardiac Infiltration Identified by CMR

Description of Clinical Presentation: A 66-year male with a history of stage III thymoma resected 8 years prior (without pericardial involvement) presented with an enlarging left pericardial mass found on CT during admission for pneumonia. Cardiac MRI (CMR) was obtained to assess myocardial involvement. PET-CT revealed two new pericardial lesions (up to 4.1 cm, SUV 3.2) and new pulmonary nodules concerning for metastatic disease. Pathology of the resected pericardial mass confirmed recurrent thymoma with degenerative changes, and histologic similarity to previously resected anterior mediastinal mass.

Diagnostic Techniques and Their Most Important Findings: CMR was performed on a Siemens Aera 1.5T scanner using cine imaging, T1- and T2-weighted sequences, native T1/T2 parametric mapping, first-pass perfusion, and late gadolinium enhancement (LGE) following administration of 12 mL of gadolinium contrast. Two mediastinal masses were identified: one involving the apical interventricular septum and right ventricular (RV) apex anteriorly, and another involving the basal-mid lateral free wall. These lesions were hyperintense on T2-weighted imaging, with elevated native T1 (1225 ms) and T2 (75 ms), consistent with soft tissue malignancy. Perfusion imaging showed no abnormal early enhancement, and LGE was minimal and patchy with peripheral enhancement.





The surrounding (non-mass) myocardium had preserved parametric values, with native T1 of 1045 ms, T2 of 48 ms, and normal extracellular volume. Additionally, the biventricular size was normal with low-normal systolic function (LVEF 52%, RVEF 44%). There was no myocardial or pericardial LGE, further excluding prior infarction, scarring, inflammation or infiltrative disease.





Overall, findings were consistent with recurrent thymoma with myocardial involvement, without evidence of associated edema or ischemia.

Learning Points from this Case: This case demonstrates the value of CMR in evaluating cardiac and pericardial masses, aiding in guiding prognosis and management. In a patient with previous history of thymoma, presence of the mass with peculiar characteristics raised suspicion of recurrent thymoma. The combination of cine function, perfusion, parametric mapping, and LGE sequences allowed differentiation of benign versus malignant mass.

Figure 1. Cine Long-Axis and Axial Imaging with Pericardial Mass
Figure 2. Cine Short-Axis Imaging of Lateral Wall and Septal Involvement
Figure 3. T1 Mapping, T2-Weighted, LGE Images and Histology of Recurrent Thymoma