First branchial cleft cysts: clinical update.

First branchial cleft cysts develop as a result of incomplete fusion of the cleft between the first and second branchial arches and give rise to two distinct anomalies, termed type I and type II anomalies. Type I anomalies are purely ectodermal while type II anomalies exhibit ectodermal and mesodermal elements. The type II anomaly incorporates some portion of the first and second arch as well as the cleft. Type I lesions are extremely rare. They appear histologically as cysts lined by squamous epithelium. Clinically, they present as a cystic mass or fistula posterior to the pinna and concha. The cyst is usually superior to the main trunk of the facial nerve and ends in a cul-de-sac on or near a bony plate at the level of the mesotympanum. Type II lesions are more numerous and represent a duplication of both membranous and cartilaginous portions of the external auditory canal. They contain skin as well as adnexal structures and cartilage and may be associated with the parotid gland. Most frequently they are associated with fistulae in the concha or external auditory canal as well as fistulous openings in the neck.