Clinical presentation
Four of five PSF cases with 3rd pouch origin passed outside the inferior horn of the thyroid cartilage (Fig. 1b), and two cases did not cause deep neck abscess, which was localized within acute suppurative thyroiditis. Meanwhile, half of PSF cases originated from the 4th pouch run inside the horn (Fig, 1a), and almost all cases had deep neck abscess. Three of five PSF cases from the 3rd pouch showed extrathyroidal thyroid tissue around the fistula (Fig. 3 for Case 8) although only one of seven cases from the 4th pouch had thyroid tissue.