**6.2 Development of obstruction in Fontan pathways**

Obstructions in Fontan circulation may occur. Obstructive lesions in the SVC or IVC may arise but are less frequently seen. However, branch pulmonary artery stenoses may be seen more often. Obstructions within the lateral tunnel or extracardiac conduit are also uncommon, but may occur due to thrombus formation and will be addressed in the section on "Thrombus formation." In the presence of signs and symptoms indicative of obstruction in the Fontan pathway, prompt investigation to confirm such obstruction should be made. While echo studies are useful in young children, poor echo windows in adolescents and adults may require MRI and CT, and/or angiographic studies to confirm or exclude such obstructive lesions. If the obstructive lesions are detected, they should be promptly relieved by balloon angioplasty or stent implantation (**Figure 11**) [88]. Surgery may be needed in rare occasions.
