Unique Prenatal Diagnosis of a Coronary Sinus Aneurysm

BACKGROUND: Congenital cardiac aneurysms are very rare in pediatric and fetal populations and can compose a range of anomalies, including ventricular, atrial, and coronary sinus aneurysm. Accurate recognition is essential because embryologic origins, imaging features, and clinical implications significantly differ. CASE SUMMARY: A 16-year-old primigravida young woman was evaluated at 23 5/7 weeks' gestation in the fetal cardiology clinic for evaluation of a suspected thoracic cyst. Fetal echocardiography and magnetic resonance imaging demonstrated a large aneurysm arising from dilated coronary sinus with impressive posterior and inferior extension without persistent left superior vena cava. No hydrops, arrhythmia, or pericardial effusion were present. Postnatal echocardiography and computed tomography angiography confirmed a rare presentation of a coronary sinus aneurysm. DISCUSSION: Coronary sinus aneurysms arise from abnormal venous wall development or hemodynamic stress and must be distinguished from ventricular or atrial outpouchings, which carry variable risks of rupture, arrhythmia, or hydrops. Early fetal diagnosis permits accurate classification, anticipatory counseling, and tailored postnatal management. TAKE-HOME MESSAGES: This case illustrates the importance of distinguishing coronary sinus aneurysm from ventricular or atrial aneurysms. Prenatal recognition facilitates accurate diagnosis, risk assessment, counseling, and delivery planning.