Partial Anomalous Pulmonary Venous Return

Partial anomalous pulmonary venous return (PAPVR) has an overall incidence of less than 1% and occurs more frequently on the right. On the right, drainage can be into the superior or inferior vena cava, azygos vein, right atrium, or coronary sinus. The most common pattern on the right is a clinically insignificant anomalous drainage of the right upper lobe into the superior vena cava. If you see this type of drainage, however, it is important to look for a sinus venosus type of atrial septal defect, which is commonly associated with partial anomalous pulmonary venous return.

The scimitar syndrome is a special case of PAPVR, where there is right-sided drainage into veins below the diaphragm (e.g., inferior vena cava or portal or hepatic veins) associated with right lung hypoplasia. Other associated anomalies include an atrial septal defect, systemic blood supply to the lung, extralobar sequestration, horseshoe lung, pulmonary arteriovenous malformation, and various forms of congenital heart disease. The appearance has been described ad nauseum in multiple sources and will not be repeated here.

The pseudoscimitar syndrome has a similar radiographic appearance, but has anomalous drainage into the left atrium rather than the inferior vena cava.

On the left, anomalous drainage is also most frequent in the upper lobe, where drainage is into a vertical vein lateral to the aortic arch that joins the left brachiocephalic vein. The main differential consideration on CT for this pattern is a left-sided superior vena cava, which can mimic the vertical vein on slices above the aortic arch. The two can be differentiated below the left main bronchus, where a single vessel (left superior pulmonary vein) is normally found anterior to the left main bronchus. In patients with the anomalous left upper lobe drainage, the left superior pulmonary vein is absent, so no vessel is seen anterior to the left main bronchus. In patients with a left-sided superior vena cava, both the left superior pulmonary vein and the left superior vena cava are found anterior to the left main bronchus.

The case shown here reveals anomalous venous drainage (red) of the medial basal segment of the right lower lobe into the azygos vein (blue). As shown here, all PAPVRs are left-to-right shunts, but most are not hemodynamically significant.

References

Demos TC, Posniak HV, Pierce KL, Olson MC, Muscato M. Venous anomalies of the thorax. AJR Am J Roentgenol. 2004 May;182(5):1139-50.