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Description

• The fetal branchial apparatus is a foregut derivative and develops in the 2nd fetal week.
• 5 paired pharyngeal arches are separated by 4 endodermal pouches internally and 4 ectodermal clefts externally.
• Overgrowth of the 2nd through 4th cleft creates the cervical sinus and occurs during weeks 4 and 5 of gestation.
• Persistence of the cervical sinus produces a spectrum of cysts, sinus tracts, and fistulas.
• Cyst: Epithelial lined structure without an external opening
• Sinus: Blind tract with an opening either externally through the skin (representing persistence of a branchial groove) or internally into the foregut (representing persistence of branchial pouch)
• Fistula tract: Communicates between the skin externally and the foregut internally (representing persistence of branchial groove with its corresponding pouch, with no branchial membrane between them).
• Classification:
  • 1st branchial cleft anomalies:
    • Site: Anywhere from external auditory canal to angle of mandible, usually superior to or within parotid
    • Fistula tract: External auditory canal
  • 2nd branchial cleft anomalies:
    • Site: Ventral to anterior border of sternocleidomastoid muscle, lateral to carotid sheath, and dorsal to submandibular gland
    • Fistula tract: Palatine tonsil
  • 3rd branchial cleft anomalies:
    • Site: Posterior triangle in middle to lower left side of the neck, near level of upper thyroid lobe
    • Fistula: Upper lateral piriform sinus wall to lower lateral neck posterior to sternocleidomastoid muscle
  • 4th branchial cleft anomalies:
    • Site: Close association to thyroid gland and associated with clinical thyroiditis if cyst infected
    • Fistula: Apex of piriform sinus to base of neck anterior to sternocleidomastoid muscle

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