Excision of branchial cysts

The abnormal persistence of branchial apparatus remnants gives rise to branchial anomalies (ie, cysts, fistulae, and sinuses). A cyst is lined by epithelium but has no external opening. A sinus is a blind pocket that opens internally (persistence of a pouch) or externally (persistence of a cleft). A fistula is a tract that has both internal and external openings.

The origin of fistulae and sinuses seems directly related to the branchial apparatus as a result of the anatomic similarities. However, the origin of lateral cervical cysts remains controversial. A likely explanation is that cysts form from entrapped remnants of either pouches, clefts, or persistent ectoderm of the cervical sinus. Histologically, squamous epithelium lines most cysts, although some are lined by respiratory (pseudostratified ciliated columnar) epithelium and some by both types of epithelium. The cysts are often lined by subepithelial lymphoid tissue, replete with follicles and germinal centers. However, sinuses and fistulae are more likely to be lined by respiratory epithelium. Associated lymphoid tissue tends to lack well-formed follicles.

The thymopharyngeal duct theory suggests that the cysts are remnants of the original connection between the thymus and third pouch. However, a persistent thymopharyngeal duct has not been found, and the cysts only rarely have parathyroid or thymic tissue in them. Another theory suggests that cysts result from deposition of salivary gland (parotid) inclusions within cervical lymph nodes, but salivary tissue is only rarely seen in the cysts.

Another theory suggests that epithelial metaplasia occurs in cervical lymph nodes. Up to 96% of specimens contain well-differentiated lymphoid tissue that cannot easily be explained by a branchial origin. Also, many of these cysts first become apparent during a respiratory tract infection.

Several classification schemes for these anomalies have been proposed, the most widely accepted being that of Work in 1972.^,  Type I lesions are duplication anomalies of the membranous EAC, ectodermal in origin and without cartilage (Figure 6). Type II lesions are duplication anomalies of both the membranous and cartilaginous EAC, containing both skin and cartilage from both ectodermal and mesodermal origins. Anatomically, type I lesions run parallel to the EAC, involving parotid tissue and usually passing superior to the facial nerve. They usually are parallel to the EAC and open in the preauricular region. Type II lesions are more commonly located within the substance of the parotid gland and more closely related to the facial nerve, running either lateral, medial, or even through the main trunk of the nerve (Figure 7). With time, exceptions to the WorkApproximately 8% to 10% of all branchial anomalies are first cleft origin. The lesions have been found in all age groups, more often on the left side. There is probably no gender predominance. Cysts occur twice as often as sinuses or fistulae, with cystic lesions more common in adults, and fistulae and sinuses more common in children. The location of cysts and external sinus openings varies, usually occurring around the ear (anterior, inferior, and posterior to the pinna) or in the upper neck, anterior to the sternocleidomastoid muscle (SCM). The internal tracts for both sinuses and fistulae are most often found along any portion of the EAC, with the anteroinferior bony-cartilaginous junction being most common.

These defects represent 67% to 93% of all branchial anomalies; approximately 10% are bilateral. Such lesions would be expected to pass deep to second arch structures and over third arch structures. Thus, a fistula extends from an external opening along the anterior border of the SCM, pierces the platysma muscle, and then follows the carotid sheath upward to the level of the hyoid bone. It then turns medially to pass over the hypoglossal nerve, beneath the posterior belly of the digastric muscle, between the internal and external carotid arteries, over the glossopharyngeal nerve, deep to the stylohyoid ligament to an internal opening at the upper pole of the tonsillar fossa. Although cysts can occur anywhere along this tract, they are most common just lateral to the internal jugular vein, at the level of the carotid bifurcation (Figure 8).

Anomalies are relatively uncommon, with third arch anomalies at 2% to 8% and fourth at 1% to 2% of all branchial anomalies.^,  Distinguishing between the 2 can be difficult because both enter the pyriform sinus and have similar presentations. Tracts originating in the pyriform sinus have been associated with recurrent acute thyroiditis.

Theoretically, a third arch pouch and cleft anomaly should pass between third and fourth arch structures. Therefore, a complete fistula would then start in the pyriform sinus, pierce the thyroid-hyoid membrane, pass above the superior laryngeal and hypoglossal nerves, go beneath the glossopharyngeal nerve and carotid artery, pierce the platysma and surface in the skin anterior to the SCM (Figure 17).

Theoretically, a fourth pouch anomaly would pass between the fourth and sixth arch structures (the fifth arch is rudimentary). A complete fistula would start in the pyriform sinus, exit the larynx near the cricothyroid joint, pass between the superior and recurrent laryngeal nerves, then track down the tracheoesophageal groove. On the left side, it would curve around the aorta from posterior to anterior. On the right side, it would curve around the subclavian artery. The tract would then lie posterior to the carotid, pass over the hypoglossal nerve, and exit near the anterior border of the SCM. A fourth arch fistula has never been described; a possible fourth pouch sinus tract has been described but was not completely dissected inferior to the clavicle.

Clinically, both types begin at the pyriform sinus and end blindly in the paratracheal or thyroid regions. The fourth pouch sinuses only rarely extend beneath the clavicles. Histologically, both third and fourth pouch tracts may be associated with ectopic thymus and aberrant parathyroid tissue (both third pouch).

Most fourth pouch anomalies are diagnosed in childhood, and 97% occur on the left side. There are 2 types of clinical presentation. In the first, lateral neck cysts or abscesses occur in neonates and may be a cause of neonatal stridor. In the second, recurrent lateral neck abscesses or recurrent episodes of acute suppurative thyroiditis present in children, adolescents, and occasionally adults.