Fourth branchial pouch anomaly.

We present an extremely rare case of fourth branchial fistula in a 23-year-old male. The characteristic clinical feature was a recurrent left lower neck abscess which did not respond to appropriate medical and surgical therapy. Radiography and a computed tomographic scan with contrast material revealed a fistula running from the apex of the left pyriform sinus (internal opening) to the left lower neck abscess. The fistula tract was excised surgically. Histological examination of the excised fistula revealed a squamous epithelial lining and subepithelial lymphoid tissue. This pyriform sinus fistula is thought to be of fourth pharyngeal pouch origin, because of its surgical aspects and the histological findings of the excised fistula.