Recurrent Suppurative Thyroiditis Due to Piriform Sinus Fistula

Introduction

Anomalies arising from the third and fourth branchial cleft remnants are quite rare. In particular, branchial abnormalities related to the pharynx are only a small subset of the already rare collection of branchial cleft lesions. Branchial abnormalities with a sinus tract connecting to the pharynx usually present with acute suppurative thyroiditis and a thyroid abscess. The sinus tract connecting to the pharynx serves as a conduit for transmission of hypopharyngeal flora. Most cases of piriform sinus fistulas appear to have an inferiorly coursing branchial sinus with an aperture at the piriform sinus apex. They almost always present with a neck infection, frequently involving the left thyroid lobe. Therefore, anomalies thought to arise from the third and fourth branchial remnants do not seem to conform to the theoretic pathways of third or fourth arch fistulas. The discrepancy between the classical course of either third or fourth branchial anomalies and the observed course of infection related to the piriform sinus apex have led to alternative explanations related to the thymopharyngeal duct. The thymopharyngeal duct forms as the thymus descends during fetal development along a tract that more accurately accounts for the observed infection with thyroid involvement. Therefore, piriform sinus duct abnormalities are most likely secondary to an incompletely obliterated embryologic remnant of the thymopharyngeal duct (of the third branchial pouch). As such, the term “third branchial sinus” is likely most appropriate for branchial lesions with an aperture at the piriform apex and infection involving the thyroid gland ( Figs. 38.1 and 38.2 ).