1355040 - Rare presentation of a giant cardiac rhabdomyoma needing cardiac transplantation

We present a term newborn with prenatally diagnosed cardiac mass with frequent premature beats. Initial postnatal echocardiogram confirmed large 4 cm x 4 cm mass in the anterior interventricular groove, extending anteriorly to the mediastinum and posteriolaterally over the left ventricle (LV). There was no inflow or outflow obstruction with preserved systolic function. Right coronary artery (RCA) originated normally from the right aortic sinus, left main coronary artery (LMCA) was not well visualized. Cardiac MRI was performed for tumor characterization. Given suspicion for rhabdomyoma, genetic testing for tuberous sclerosis was sent which was negative. Following several days of worsening ventricular ectopy and clinical evidence of low cardiac output on DOL 7, patient developed severe global LV dysfunction with ejection fraction 35% and electrocardiogram with diffuse ST depression. He was urgently initiated on extracorporeal membrane oxygenation (ECMO). Cardiac catheterization revealed atresia of the left coronary arterial system with tiny collateral arteries from the dilated RCA system. Surgical resection was not feasible given absence of the LMCA. Medical therapy with everolimus was considered, however given critical condition and inability to tolerate weaning ECMO, patient was listed for transplant and received orthotopic heart transplant at 3 months. Explanted heart pathology confirmed rhabdomyoma.

Diagnostic Techniques and Their Most Important Findings: Cardiac MRI was performed under general anesthesia. A large homogenous mass arising from the interventricular septum and attached to the left ventricular myocardium laterally, extended anteriorly towards mediastinum and the aortic valve and posteriorly towards the left atrium with mechanical displacement of the left ventricle. The mass appeared isointense on SSFP sequences and T1-weighted TSE sequences. T2-weighted STIR sequence demonstrated mild hyperintensity particularly in the central part. First pass perfusion imaging was consistent with absent vascularity and LGE sequences did not reveal intense scar. This was consistent with large cardiac rhabdomyoma.

Learning Points from this Case: Rhabdomyomas are the most common pediatric cardiac tumor and usually present as multiple intramural masses associated with tuberous sclerosis in 50% of patients. Although uncommon, solitary rhabdomyoma has been well described and difficult to differentiate from fibromas on echocardiography and MRI is critical for tumor characterization. This is a unique case of cardiac rhabdomyoma with absence of the LMCA system causing significant left ventricular dysfunction. Although there was high suspicion of cardiac fibroma based on ventricular ectopy and coronary artery compromise, findings which have been well described in literature with cardiac fibromas, cardiac MRI findings were suggestive of a rhabdomyoma which was confirmed by pathology on explanted heart.