Purpose or Case Report: Congenital anomalies of the coronary sinus can present with a variety of morphological features. An unroofed coronary sinus is a rare type of atrial septal defect (ASD), also known as a coronary sinus ASD. This partial or complete absence of the roof of the coronary sinus results in a communication between the coronary sinus and left atrium. We present the first reported case of this rare intra-atrial communication in the setting of a right-sided aortic arch and a Kommerell diverticulum (KD) in an asymptomatic pediatric patient. A 16-year-old male presented for cardiology consultation for an asymptomatic heart murmur. Cardiac auscultation revealed a soft, low-pitched continuous hum audible in the right clavicular region, consistent with a venous hum and a soft grade I/VI systolic murmur heard along the left sternal border. Electrocardiography (ECG) showed a normal sinus rhythm with early repolarization. Given his age and new onset murmur, an echocardiogram was obtained, demonstrating flow acceleration in the coronary sinus as it opened into the right atrium, a right-sided aortic arch, and a dilated coronary sinus. Further evaluation with an ECG gated cardiac computed tomography (CT) angiography illustrated unroofing of the coronary venous sinus with a jet of contrast from the coronary sinus into the right atrium. The cardiac CT also confirmed a right-sided aortic arch with mirror image branching pattern and an isolated diverticulum of Kommerell without the presence of an aberrant left subclavian artery. Given an oxygen saturation of 100% and lack of any symptoms, no surgical intervention was recommended and regular follow-up was scheduled. The presence of an unroofed coronary sinus is most often found as part of a complex congenital heart defect. While an isolated coronary sinus ASD is often difficult to diagnose, patients are considered to have excellent prognosis. However, both the unroofed coronary sinus and KD predispose a patient to long-term complications if not diagnosed and monitored in a timely manner. This case highlights the importance of clinical judgement in the setting of new heart murmurs, the use of sensitive imaging modalities for diagnosis of rare cardiac anomalies, and the need for long-term follow-up.
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