Key teaching points:

• Fontan circulation may mimick a pulmonary embolism on a perfusion scan.
• Due to passive venous return to the pulmonary circulation, pedal injection during perfusion scan may reveal normal perfusion to both lungs.

Patient with a history of tricuspid atresia type IA status post right-sided cavopulmonary anastomosis, extracardiac Fontan, and left pulmonary artery stent placement during childhood. 

The initial VQ scan performed with a right upper extremity IV line demonstrates a complete lack of perfusion to the left lung and normal ventilation imaging. Unilateral flow to the right pulmonary artery may be seen, as in this case, mimicking a pulmonary embolism on perfusion scan.

Repeat perfusion images the same day following pedal injection shows homogeneous perfusion to both lungs.

Case prepared with the help of Dr Suzanne Parets and Dr Samuel Valle.