ON THE COVER This is a maximum-intensity projection image, derived from a contrast-enhanced 3-dimensional magnetic resonance angiogram, from a 57-year-old man who recently presented with right heart failure and paroxysmal atrial fibrillation. The image clearly depicts a rare combination of cardiac lesions: complete unroofing of the coronary sinus and partial anomalous pulmonary venous drainage of the left upper pulmonary vein. These lesions caused a cumulative, significant left-to-right shunt. Phase contrast flow velocity mapping demonstrated a pulmonary to systemic flow ratio of 3.5:1. The embryological origin of defects in the roof of the coronary sinus is believed to be through a process of abnormal dissolution that occurs after the initial formation of the walls of the coronary sinus within the left atrioventricular groove.

Controversy continues regarding the embryologic origin of the pulmonary veins. Recent evidence indicates that the pulmonary and systemic venous tributaries have different primordial origins. The factors in our patient, which lead to this rare pattern of disruption of the venous modeling and dissolution of both the left cardinal venous system and the primordial left pulmonary vein, are uncertain. However, despite presenting late in his life, magnetic resonance imaging simplified and clarified the diagnostic process. Images provided by Marina L. Hughes, DPhil, MRCP, FRACP, Robert M. Anderson, MD, FRCPATH, Andrew M. Taylor, MD, MRCP, FRCR, from the Cardiothoracic Unit, Institute of Child Health & Great Ormond Street Hospital for Children, London, United Kingdom

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