Branchial cysts and fistulas are caused by abnormal development of the branchial grooves or pouches during embryogenesis. In human embryos, there are four visible pairs of branchial grooves and pharyngeal pouches, with the elevations between them referred to as branchial arches, of which there are five pairs. The indentation between the first and second branchial arches is the first branchial groove, the indentation between the second and third arches is the second branchial groove, and so on. During normal embryonic development, the first branchial groove forms the external auditory canal, while the second, third, and fourth branchial grooves gradually fuse and disappear. Failure of fusion or incomplete closure of any of the first to fourth branchial grooves can result in the formation of corresponding branchial cysts and fistulas.
Based on embryonic origin, branchial cysts and fistulas are classified into four types:
First Branchial Cysts and Fistulas
These are rare and result from the failure of normal fusion between the first and second branchial arches. The external opening of the fistula is often located at the anterior margin of the sternocleidomastoid muscle, below and behind the angle of the mandible, extending to the level of the hyoid bone. The internal opening is located within structures like the external auditory canal, tragus, or mastoid region, which is why first branchial fistulas or cysts are also referred to as auriculocervical fistulas or cysts. The fistulous tract is closely related to the facial nerve and exhibits significant variability. The cyst may be located along any portion of the fistulous tract.
Second Branchial Cysts and Fistulas
These account for the majority of cases, resulting from incomplete closure of the second branchial groove. Most external openings are located at the junction of the middle and lower thirds of the anterior margin of the sternocleidomastoid muscle or nearby regions. The fistulous tract traverses the platysma muscle and ascends along the carotid sheath, crossing the carotid bifurcation, and reaches the tonsillar fossa, where the internal opening is located. The cyst is commonly found at the middle third of the anterior margin of the sternocleidomastoid muscle.
Third Branchial Cysts and Fistulas
These are rare and result from incomplete closure of the third branchial groove. The external opening is located at the lower end of the anterior margin of the sternocleidomastoid muscle, and the fistulous tract passes anterior to the carotid artery, entering the pyriform sinus where the internal opening is located.
Fourth Branchial Cysts and Fistulas
These are extremely rare and result from incomplete closure of the fourth branchial groove. The external opening is located in the skin above the clavicle, while the internal opening typically opens into the pyriform sinus or the esophageal inlet.
Clinical Manifestations
For branchial fistulas, persistent or intermittent discharge from the external opening is the primary symptom. Some patients report a foul odor in their mouth, and in complete fistulas, larger in size, leakage of water or milk from the fistula may occur during eating. Secondary infections may cause redness, swelling, and pain around the fistulous opening, accompanied by purulent discharge, which can recur.
For branchial cysts, symptoms are generally absent, and an asymptomatic, painless mass on the neck may be discovered incidentally. The size of the cyst varies and is usually round or oval, mobile, non-adherent to the skin, and exhibits a cystic consistency. Secondary infections may cause rapid enlargement of the mass and localized tenderness. Larger cysts protruding toward the lateral wall of the pharynx may lead to discomfort during swallowing.
Diagnosis
Preliminary diagnoses are based on the patient’s medical history and the location of the fistula or cyst. Diagnostic imaging techniques, including ultrasound, CT, MRI, and lipiodol fistulography, are useful in confirming the diagnosis and determining the extent of the lesion. However, fistulas should be differentiated from tuberculous fistulas in cervical lymph nodes. When the first branchial fistula is accompanied by purulent discharge from the ear, differentiation from suppurative otitis media is necessary. Cysts should be distinguished from lymphatic malformations, which are typically located in the posterior triangle of the neck and present as multilocular, translucent cysts.
Treatment
The treatment involves complete excision of the cyst and fistula. For finer or branched fistulas, careful attention is necessary to avoid remnants and postoperative recurrence. For cases with secondary infection, controlling the infection is prioritized before elective surgery is performed. Pyriform sinus fistulas can be treated with transoral endoscopic ablation of the internal opening, which offers advantages such as minimal trauma, no scarring, fewer complications, and effective outcomes.