Anomalous unilateral single pulmonary vein versus scimitar syndrome: Comparison of two paediatric cases and a review of the literature.

The 'scimitar sign' on plain chest radiograph is most commonly attributed to the presence of a scimitar vein, which is a variant of partial anomalous pulmonary venous drainage (PAPVD). An anomalous unilateral single pulmonary vein (AUSPV) is a very rare anomaly, albeit benign, which can also present with the scimitar sign. Despite a similar radiographic appearance, these two anomalies have very different prognostic implications. Moreover, differentiation between the two is important in the paediatric population to prevent unnecessary investigations. We present two paediatric patients who presented with the scimitar sign on plain chest radiograph, with one having PAPVD and the other having AUSPV, and provide a review of the literature on AUSPV, an anomaly which most likely shares a similar pathogenesis to the scimitar vein of PAPVD.