Branchial arches are akin to ancient gill apparatus (FIG 1).
Humans have five branchial/pharyngeal arches, 1 to 4 and 6 (there is no 5th branchial arch), which form craniocaudally from week 4.
Membrane ectoderm externally and endoderm internally covers the arches.
Cleft externally separates each arch.
Pouch internally separates each arch.
Each arch forms an artery, cartilaginous structure, nerve and muscle.
Arches 1 and 3 mainly form the face, and arches 3, 4, and 6 form the neck, with 4 and 6 fusing.
Ectodermal clefts obliterate except for the 1st branchial cleft, which forms the external auditory canal with outer side of the tympanic membrane forming the medial limit.
Failure of branchial pouch or cleft to obliterate during embryonic development can lead to fistula, sinus, or cyst formation:
A cyst is an epithelial-lined fluid-filled sac.
A sinus is a blind-ended epithelial lined tract opening on to skin or mucosa.
A fistula is an epithelial-lined tract connecting two surfaces (skin/mucosa).
The resultant anomaly from failure of this process relates to the specific arch, pouch or cleft derivatives.
The main branchial anomalies associated with sinuses and fistulae are 1st and 2nd cleft anomalies and 3rd and 4th pouch anomalies.
Type 1 branchial anomalies are rare anomalies resulting in duplication of the external ear canal and are classified as Work’s type 1 or 2.
Branchial cleft cysts are regarded as 2nd branchial anomalies. Several theories exist as to their origin including3:
Lymph node inclusion theory—cystic transformation of lymph nodes
Branchial cleft remnant theory—remnant of branchial cleft/pouch
Thymopharyngeal duct theory—remnant of the connection between the thymus and 3rd pouch
Cervical sinus of His theory—cyst is formed by remains of the cervical sinus.
Branchial sinuses and fistulas may present as a discharging neck punctum +/- neck swelling.
Type 1 branchial anomaly is rare.
Often a late diagnosis
May present with a mass in parotid or submandibular region
Discharging neck punctum or discharging ear
Type 2 branchial anomalies are the most common branchial anomaly.
Often present at or just after birth
External opening in the skin (punctum) along anterior border sternocleidomastoid muscle +/- discharge
Type 3 and 4 brachial sinus
Neonates—lateral neck cyst/abscess +/- airway obstruction
Child/young adult—thyroiditis/recurrent neck abscess
Most commonly diagnosed in childhood (delayed diagnosis)
May present as a cystic neck swelling +/- infection/abscess
Table 1 Branchial Arch and Pouch Derivatives
Part of terminal branches maxillary artery
Meckel cartilage: malleus and incus, anterior malleolar ligament, mandible template, maxilla, zygomatic bone and squamous temporal bone, mandible
Muscles of mastication, mylohyoid, tensor tympani, anterior belly digastric
Tubo-tympanic recess, tympanic cavity, mastoid antrum, Eustachian tube
Reichert cartilage: stapes, styloid process, stylohyoid ligament, lesser cornu, and superior body of hyoid
Muscles of facial expression, stapedius, stylohyoid, posterior belly digastric
Common carotid arteries, internal carotid arteries
Greater cornu and inferior part of hyoid
Inferior parathyroid glands and thymus
Left forms part of aortic arch, right forms part right subclavian artery
X—vagus, superior laryngeal
Cricothyroid, pharynx constrictors
Superior parathyroid glands and possibly the calcitonin-producing cells of thyroid
Pulmonary arteries, ductus arteriosus
X—vagus, recurrent laryngeal
Intrinsic muscles of larynx
Peak age 3rd decade
Most are located anterior to the upper part of the sternocleidomastoid muscle
Branchio-oto-renal syndrome is an autosomal dominant syndrome with a prevalence of 1 in 40 000 people. It is caused by mutations in the EYA1, SIX1, and SIX5 genes.4
Children born with this typically have branchial anomalies, ear abnormalities (including pits, tags, atresia, hearing loss) and kidney abnormalities (including hypoplastic/absent kidneys). If suspected, these children require audiometry, an ultrasound of the renal tract, and genetic counseling.
Imaging varies depending on the branchial anomaly.
Cysts—ultrasound (USS) is obtained usually, but an MRI may be helpful when the diagnosis is not clear on USS.
Type 1—CT to image middle ear and MRI for soft tissues and course of sinus/fistula (FIG 2A).
Type 2—clinical diagnosis; usually no imaging required.
Types 3 and 4—barium swallow/and direct laryngoscopy to assess for sinus/fistula entrance at the pyriform fossa; USS +/- MRI to assess thyroid involvement and any cystic component (FIG 2B).