Anomalous Origin of the Left Main Coronary Artery From the Proximal Right Coronary Artery With a Benign Prepulmonic Course: A Rare Single Coronary Artery Variant.

Coronary artery anomalies (CAAs) are rare congenital variations with a broad spectrum of clinical implications. While certain configurations are associated with myocardial ischemia and sudden cardiac death (SCD), many remain clinically silent and are discovered incidentally. An anomalous origin of the left main coronary artery (LMCA) from the right coronary artery (RCA) represents an exceptionally uncommon variant, particularly when it arises from the proximal RCA and follows a prepulmonic course. We report the case of a 56-year-old female with a history of immune thrombocytopenic purpura who presented with atypical chest discomfort. She underwent coronary computed tomography angiography (CCTA), which revealed an LMCA originating from the proximal RCA with a prepulmonic (anterior) course, consistent with a Lipton right sinus of valsalva, type II, anterior (RIIA) single coronary artery (SCA) pattern. The coronary artery calcium score was zero, and no evidence of obstructive coronary artery disease was identified. Given the absence of ischemia and the benign anatomical course, the patient was managed conservatively. She underwent periodic outpatient surveillance with symptom reassessment and cardiovascular risk factor monitoring, remaining asymptomatic over three years without adverse cardiac events. Single coronary artery anomalies are rare, with reported prevalence estimates of approximately 0.06% in angiographic series, although these data may be influenced by referral bias. Among these, LMCA arising from the RCA accounts for only 0.0024%-0.02% of reported cases. Clinical significance depends on vessel course as well as associated morphological features. Interarterial variants carry higher risk, whereas prepulmonic and retroaortic courses are generally considered lower risk. CCTA is valuable for defining anatomy and guiding individualized risk stratification, while functional testing may be considered selectively when symptoms or uncertain hemodynamic significance are present. This case highlights a rare but benign coronary anomaly and underscores the importance of integrating anatomical findings, clinical presentation, and selective adjunctive testing to guide management while avoiding unnecessary invasive intervention.