False Positive Perfusion/Ventilation SPECT Study for Pulmonary Embolism in a Patient with Fontan Circulation.

Fontan circulation is the consequence of an operation that results in the flow of systemic venous blood to the lungs without passing through a ventricle. An 18-year old man with a history of congenital heart disease surgically treated with Fontan circulation, presented with pleuritic chest pain and a raised D-dimer level. Perfusion/ventilation SPECT was performed to exclude the possibility of pulmonary embolism (PE) that showed unilateral reduced perfusion of the left lung with a mismatched right upper lobe defect, suspicious of PE. However, subsequent computed tomography pulmonary angiogram and clinical follow-up excluded the possibility of PE, emphasizing the need for knowledge of potential pitfalls to avoid false interpretations. Given the fact that adult congenital heart disease population is growing, with the majority having single ventricle/Fontan circulation and being at risk for thromboembolic disease, knowledge of the perfusion pattern pitfalls is important to avoid false interpretation and preventing the misdiagnosis of PE in patients with Fontan physiology.