Left-sided scimitar vein causing cyanosis after Fontan operation: successful transcatheter device occlusion using magnetic resonance imaging X-ray fusion.

We present the case of a 3-year-old boy with asplenia-type heterotaxy syndrome and functionally single ventricle congenital heart disease who developed cyanosis early after the Fontan operation. Combined cardiac magnetic resonance imaging (MRI) and catheterization identified a large hepatic vein to pulmonary vein connection as the source of right to left shunt. The anatomy was quite unusual, suggesting an underlying diagnosis of mixed total anomalous pulmonary venous connection with left-sided scimitar vein. This pattern of pulmonary venous return has not been previously reported in a patient with asplenia. MRI x-ray fusion was used to guide transcatheter device occlusion of the scimitar vein, resulting in marked clinical improvement.