Branchial cleft anomalies comprise of a spectrum of congenital defects that occur in the head and neck.
Pathology
The anomalies result from branchial apparatus (six arches; five clefts), which are the embryologic precursors of the ear and the muscles, blood vessels, bones, cartilage, and mucosal lining of the face, neck, and pharynx 1.
During the 3rd to 5th week of embryonic development, the second arch grows caudally and covers the third, fourth and sixth arches. When it fuses to the skin caudal to these arches, the cervical sinus is formed. Eventually, the edges of cervical sinus fuse and the ectoderm within the tube disappears 9. Persistence of branchial cleft or pouch results in a cervical anomaly located along the anterior border of the sternocleidomastoid muscle from the tragus of the ear to the clavicle 10.
The range of anomalies can include:
cyst: no internal or external communication
fistula: communicates both internally and externally
sinus: incomplete tract
Cysts are the most common, outnumbering fistulas and sinuses ~2:1 6. Among fistulae and sinuses, the order prevalence is thought to be: external draining sinus > complete fistula > internal draining sinus 6; although some anomalies can occur in combination.
The full list of branchial anomalies includes:
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first branchial cleft anomalies (5-8%) 1-8: seen above the level of the mandible near the external auditory canal within or close to the parotid gland.
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second branchial cleft anomalies (commonest by far: 90-95%) 8: between the level of the mandible angle and the carotid bifurcation, deeper than the platysma and superficial layer of deep cervical fascia
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third branchial cleft anomalies (rare): infrahyoid neck
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fourth branchial cleft anomalies (rare): infrahyoid neck, usually adjacent to the thyroid gland
the fifth cleft does not give rise to the cervical sinus of His which is part of the reason that there are no fifth branchial cleft anomalies
The 3rd and 4th branchial arches tend to be very close and therefore the distinction between these two cleft anomalies can be difficult on imaging 7,8.
Differential diagnosis
paramedian thyroglossal duct cysts (usually branchial cleft cysts are well away from the midline)
thyroid nodules and cysts
necrotic lymph node metastases (e.g. from squamous cell and papillary thyroid carcinomas)
infectious adenitis (e.g. tuberculosis)
vascular lesion on non-enhanced CT images (e.g. mycotic aneurysm)
lymphatic malformations
neurogenic tumors with cystic degeneration (e.g. schwannomas)
cervical dermoid cysts
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