Scimitar sign | Radiology Signs

The Scimitar sign is caused by partial anomalous pulmonary venous return (PAPVR) of the right lung, where the pulmonary veins abnormally drain into the inferior vena cava or other systemic veins instead of the left atrium. This anomaly is part of Scimitar syndrome, a rare congenital cardiopulmonary defect often accompanied by right lung hypoplasia, right pulmonary artery hypoplasia, and dextroposition of the heart.

Clinically, it may present with recurrent respiratory infections, pulmonary hypertension, or may be incidentally found in asymptomatic patients.

Why is it called so?

The sign is named for the characteristic curvilinear radiographic shadow seen along the right cardiac border on chest X-ray, which resembles a scimitar, a Middle Eastern curved sword with a distinct hooked shape.

Pathophysiology

The anomalous right pulmonary vein courses in a curvilinear path along the right lower lung field, draining aberrantly into the inferior vena cava. This creates a tubular, vertically oriented opacity on imaging. The associated right lung hypoplasia reduces right lung volume causing the heart to shift into the right hemithorax (dextroposition). The abnormal venous drainage results in a left-to-right shunt, which can lead to volume overload and potential pulmonary hypertension. Additional vascular and parenchymal abnormalities, such as systemic arterial supply to the right lower lobe and pulmonary artery hypoplasia, contribute to the overall clinical picture.

Alternative names: Congenital pulmonary venolobar syndrome, hypogenetic lung syndrome, Halasz syndrome, vena cava bronchovascular syndrome

Other associated imaging features: Dextroposition of the heart and right lung hypoplasia visible on chest X-ray or CT.