Third branchial cleft fistulae arise from abnormal development of the third pharyngeal cleft, when the cyst forms a tract to the skin. As third branchial cleft fistulae are rare, there is no standardized diagnosis or treatment of the condition.
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Epidemiology
The third branchial cleft fistula is the rarest type of branchial anomaly, accounting for 2% to 8% of all branchial cleft anomalies 1. It occurs more frequently in males than females, and has a strong left laterality preference (89% vs 11% on the right) 2. Approximately 10% of all branchial arch anomalies occur bilaterally.
Clinical Presentation
Third branchial cleft fistula are usually diagnosed in the first decade of life 2. Their clinical presentation varies. Patients usually present with a recurrent cervical abscess or suppurative thyroiditis. These abscesses are usually located in the lower neck or at the thyroid isthmus and are often accompanied by fever, pain, and tenderness. Some patients may also experience dysphagia or dyspnea due to compression of the esophagus or trachea, respectively, by the abscess. The fistulous tract may present as a small opening at the lower third of the anterior border of the sternocleidomastoid muscle, with transudative discharge 2,3.
Pathology
The embryology of the branchial apparatus is complex and is associated with various malformations further described in the branchial cleft anomalies article. Third branchial cleft fistulae arise from incomplete obliteration of the third and fourth branchial pouches during embryonic development. This leads to the persistence of the cleft between these pouches, resulting in the formation of a fistulous tract that originates from the pyriform sinus and courses through the thyroid gland to end at the skin of the neck 3.
Radiographic features
Imaging modalities, such as CT, MRI, ultrasound, and fistulography, can be used to confirm the diagnosis of a third branchial cleft fistula. Fistulography involves injecting contrast into the fistula to outline the tract's course, allowing for surgical planning. Ultrasound can be used to identify the fistulous tract and to guide percutaneous aspiration of abscesses. CT and MRI can provide detailed information about the extent and location of the fistulous tract and the surrounding structures.
Fistulography
contrast material filling the tract and draining into the neck
may visualize a fistulous tract extending from the pyriform sinus to the cervical region 4
Ultrasound
fluid-filled tract or cystic lesion with well-defined walls and anechoic contents from the pyriform sinus to the cervical region
debris can be seen along the echogenic wall of the tract
color Doppler ultrasound can be useful in differentiating third branchial cleft fistulae from other neck lesions by demonstrating absence of intralesional vascularity 4
CT
low attenuation (hypodense) cystic mass with thin wall, extending from the pyriform sinus to the cervical region, with no calcification
CT can also help identify the course of the fistulous tract and its relationship to surrounding structures 4
MRI
MRI can provide better soft tissue detail than CT and is particularly useful for evaluating the relationship of the fistulous tract to adjacent structures, such as the common or internal carotid artery and internal jugular vein
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cystic lesion with with tract to the cervical region 4
T1: low signal intensity
T2: high signal intensity
Treatment and prognosis
The definitive treatment for third branchial cleft fistulae is surgical excision of the entire fistulous tract. The surgical approach may be challenging due to the proximity of the tract to vital structures (common or internal carotid artery, hypoglossal nerve, glossopharyngeal nerve). Therefore, a preoperative evaluation of the tract's extent and the surrounding anatomy is necessary for successful surgical management. In cases of acute infection, the use of antibiotics along with incision and drainage of the abscess may be required before definitive surgery 2,3,5.
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