Benign Intramyocardial Mesothelial Cyst in the Right Ventricular Outflow Tract

A 51-year-old man presented to the emergency department with chest pain. The patient had undergone a cavotricuspid-isthmus ablation 2 weeks prior, after which he was placed on anticoagulant therapy. He was investigated with a contrast-enhanced thoracic computed tomography (CT) scan that revealed a well-defined, ovoid, low-density, nonenhancing right ventricular outflow tract lesion abutting the septum (Figure 1). The lesion was not visualized on transthoracic echocardiography. On cardiac MRI, the lesion was homogenously bright on steady-state free precession images (Figure 2, Movies I and II in the online-only Data Supplement) and of intermediate to low signal intensity on T1-weighted images (Figure 3). The lesion did not enhance on first-pass perfusion imaging (Figure 4, Movie III online-only Data Supplement) and was hypointense to myocardium on delayed postgadolinium phase-sensitive inversion recovery images (Figure 5). The differential diagnosis included gelatinous myxoma and blood cyst. The patient was already anticoagulated, making thrombus unlikely. The lesion was surgically excised. Intraoperatively, a thin layer of myocardium (Figure 6) was …