Partial anomalous pulmonary venous drainage (PAPVD) is a congenital anomaly in which a pulmonary vein drains into the right atrium or one of its tributaries,
instead of the left atrium. This therefore creates a left to right shunt. Patients are usually acyanotic. In the paediatric population the incidence of PAPVD is approximately 0.4-0.7%, is twice as
common in males and the anomalous vein is right sided in 90% of cases. 80-90% of patients have an associated atrial septal defect (ASD). The size of the shunt is usually larger in children, when
compared to adults and surgical correction is indicated if the ratio of pulmonary-to-systemic blood flow exceeds 1.5:1.
A recent series described PAPVD diagnosed with CT in adults and reported an incidence of 0.2%. The anomalous vein was left sided in approximately 80% and
the majority of patients were female (66%). In adults PAPVD is infrequently associated with an ASD. The difference in the distribution of PAPVD in this study may be attributable to the fact that
left sided anomalies are easier to detect with CT than right sided ones.
The anomalous vein in adults most commonly arises form the left upper lobe and connects to the left brachiocephalic vein via a persistent left vertical
vein. Less frequently a right upper lobe vein can drain into the SVC or a right lower lobe vein can drain into the supra-hepatic portion of the IVC.
Differentiation of a left upper lobe PAPVD and a left sided SVC can be difficult. With a left upper lobe PAPVD the pulmonary veins drain into a left
sided anomalous mediastinal vein called a vertical vein. This vein drains into the left brachiocephalic vein which subsequently drains into the SVC. A left sided SVC arises at the junction of the
left internal jugular vein and subclavian vein. It descends down the left mediastinum in the left para-aortic space and then drains into the coronary sinus, which is usually enlarged. It can
therefore appear similar to a vertical vein of PAPVD. A right sided SVC may or may not be also present.