Partial anomalous pulmonary venous return (PAPVR) has a prevalence of 0.5% in the general population¹. Anomalous pulmonary vein drains into the pulmonary circulation via the superior vena cava (SVC), azygos, innominate veins, inferior vena cava (IVC), coronary sinus or right atrium) creating a pulmonary-to-systemic shunt ^1,2. 

Patients may be asymptomatic if the shunt is small. However, when the shunt is large or when there is associated cardiopulmonary anomalies, the patient may be symptomatic ^1,2. The most common configuration is when the right upper lobe pulmonary vein drains into SVC or - as in this case - a left upper lobe pulmonary vein draining into left innominate vein ¹. Surgical correction is suggested if the pulmonary-to-systemic flow ratio is greater than 1.5 to avoid late sequelae of pulmonary hypertension and right ventricular failure ^1,2.