R. NICKBRYANMDS. JAMESZINREICHMD
A foregut derivative, the fetal branchial apparatus, develops during the second fetal week and consists of 5 paired pharyngeal arches, separated internally by 4 endodermal pouches and externally by 4 ectodermal clefts. First branchial cleft anomalies may occur anywhere from the external auditory canal to the angle of the mandible, including the parotid gland. Although several attempts have been made to classify first branchial cleft anomalies by location and histologic characteristics, they are currently considered to represent a spectrum of malformations. Cysts associated with the external auditory canal may present with aural fistulae, auricular swelling, otitis, and otorrhea. Those involving the parotid gland may be found lying either deep within or superficial to it. The differential diagnosis of other cystic lesions of the parotid gland includes neoplasms, lymphadenopathy, and lymphoepithelial cysts. A sialocele, representing ductal obstruction caused by trauma or a calculus, could also mimic a first branchial cleft cyst. During the development of both osseous and cartilaginous parts of the ear canal, at about the third month of intrauterine life, the anteroinferior surface of the tympanic plate is deficient, a condition that is known as the foramen of Huschke.1 Later, this nonosseous portion is closed with fibrous tissue, giving it a ring shape.2 However, this bony defect may persist throughout life, resulting in cystic lesions and fistulae. In a review of 377 temporal bones, Wang et al3 reported that the incidence of persistence of the foramen of Huschke is about 7%. The formation of a fistula between the auditory canal and the ductal system of the parotid gland may lead to infection of the skin of the external canal and/or chronic infection of the salivary gland.
Radiology Quiz Case 1—Diagnosis. Arch Otolaryngol Head Neck Surg. 2003;129(5):596. doi:10.1001/archotol.129.5.594