During the first eight weeks of fetal development, the lungs drain to the systemic veins, and the common primitive pulmonary vein originates from the dorsal wall of the left atrium (LA). When the pulmonary splanchnic plexus fuses with the primitive pulmonary vein, its communication with the systemic veins is obliterated. Then, the common pulmonary vein is incorporated into the LA, giving rise to four separate pulmonary veins (PV) (1,2). Abnormality of the embryological PV development can lead to abnormalities in the diameter, number, drainage or connections of the PV (2–6). 

In a normal PV connection, the PV finally connect with the LA and there is no haemodynamic abnormality. On the other hand, an abnormal drainage results in the return of oxygenated pulmonary venous blood to the right side of the heart (left-to-right shunt) (6-8).

The scimitar syndrome, the scimitar variant and the meandering right pulmonary vein can be considered as a spectrum of pulmonary venous anomalies with a common embryological and pathogenic mechanism, although with differences in the venous drainage. The stage of embryogenesis at which the anomaly occurs determines which condition develops (6). 

The scimitar syndrome is a rare pulmonary anomaly which consists in an anomalous pulmonary venous drainage of the right lung to the inferior vena cava (IVC) (giving rise to the scimitar sign and a left-to-right shunt), associated with anomalous systemic arterial supply of the right lower lobe from either the thoracic or abdominal aorta and hypoplasia of the right pulmonary artery and lung, resulting in cardiac dextroposition (3). 

A meandering right pulmonary vein, as described by Goodman et al., is a PV draining part of the right lung into the LA through an anomalous course (9), reserving the scimitar variant, as described by Pearl et al., for those with a dual connection to the IVC and the LA (3, 6, 10). The term anomalous unilateral single pulmonary vein has also been used to refer to this condition (2). Patients with meandering veins are asymptomatic, and the diagnosis is frequently incidental. 

A wide spectrum of anomalies and anatomical variations of the PV has been described in patients with congenital heart disease (CHD) (2, 11). The existing literature basically describes the congenital anomalies of the PV. However, the treatment of these patients often requires surgical repair which, in some cases, may also cause secondary PV stenosis or occlusion, especially if the procedure involves the LA. The global incidence of pulmonary venous obstruction following intra-atrial repair of transposition of the great arteries was reported to range from 0 to 27% in 1982 (11).

The purpose of this study was to identify unexpected anomalies of the PV (excluding anomalous pulmonary venous return) in patients who underwent routine cardiac CTA for their CHD and to describe alternative drainage routes to the LA.