[CT imaging and fourth branchial pouch fistula in adults]

We report two cases of fourth branchial pouch in adult. This rare and little-known pathology is indeed responsible for suppurative thyroiditis and left lower cervical abscess recurring in spite of antibiotic treatment and incision-drainage. CT scan using, iv contrast, air as a agent contrast with Valsalva test, shows air in the thyroid and perithyroid soft tissue infection, proving communication between the pyriform fossa and the thyroid. Bubble of air behind the left thyroid alar in the sinus track is the best argument for diagnosis. Hypopharyngoscopy shows the mucous opening of the bottom at the pyriform sinus.