The patient is an 8 year old boy born with double outlet right ventricle, mitral atresia, hypoplastic left ventricle, and pulmonary stenosis who underwent an atrial septectomy as a neonate. He suffered a stroke at the age of 2 years, which manifested as left hemiparesis. Computed tomographic scan of the head revealed infarction in the region of the basal ganglia. He was placed on aspirin and an intensive regimen of physical therapy, which resulted in progressive improvement in his neurological deficit, though compliance with medication was questionable. A year later he had a Fontan operation during which the main pulmonary artery was ligated distal to the pulmonary valve. Five years after surgery a routine surveillance echocardiogram revealed an echogenic mass in his pulmonary artery stump. This was confirmed on angiography shown below (anteroposterior (left panel) and lateral (right panel) angiograms showing the ovoid lucency of the clot in the pulmonary artery stump which lies to the left and posterior to the aorta). Despite the absence of symptoms, his past history and the known risk of embolic strokes in the Fontan population prompted urgent surgical removal of the thrombus. The pulmonary valve leaflets were oversewn and the cul-de-sac of the pulmonary artery stump was obliterated.

It is now recognised that this procedure, rather than pulmonary artery ligation, should be performed at the time of the Fontan operation. These images illustrate an uncommon but potentially serious and easily preventable complication in Fontan patients. They also reinforce the fact that even in asymptomatic patients with a single ventricle and a patent pulmonary valve, the pulmonary artery stump must be carefully imaged at frequent intervals to exclude thrombus formation.