Fourth pharyngeal pouch sinus.

This is the first description and documentation of an extremely rare developmental anomaly of the pharyngeal apparatus in a 15-year-old female. The clinical, radiological, histological, and anatomical findings indicated that the anomaly originated in the pharyngeal fourth pouch. It presented as a recurrent lateral neck abscess which was due to a paratracheal sinus. This sinus penetrated the larynx and after a translaryngeal course ended in the pyriform sinus. It was caudad to the superior laryngeal nerve and external to the recurrent laryngeal nerve. Its penetration into the larynx at the cricothyroid joint region could serve as a useful surgical landmark.