First branchial cleft cyst

First branchial cleft cysts are a type of branchial cleft anomaly.

Pathology

They are uncommon and only represent ~7% of all branchial cleft cysts.

They develop as a result of incomplete fusion of the cleft between the first and second branchial arches. They may have a sinus with drainage to the external ear or skin.

That typically occur within or close to the parotid gland or external auditory canal region.

Usually manifest early in first decade of life.

Subtypes

They can be divided into 3 types based on location:

• type I: inferoposteromedial to pinna
• type II: angle of mandible to external auditory canal
• type III: periparotid

They are also by divided into 2 types based on histology

• type I -
  • purely ectodermal while.
  • extremely rare
  • appear histologically as cysts lined by squamous epithelium.
  • clinically presents as a cystic mass or fistula posterior to the pinna and concha.
  • usually located superior to the main trunk of the facial nerve and ends in a cul-de-sac on or near a bony plate at the level of the mesotympanum. 
• type II -
  • contain ectodermal and mesodermal elements
  • comparatively commoner
  • represent a duplication of both membranous and cartilaginous portions of the external auditory canal.
  • contain skin as well as adnexal structures and cartilage
  • may be associated with the parotid gland.
  • often associated with fistulae in the concha or external auditory canal +/- fistulous openings in the neck.
  • incorporates some portion of the first and second arch as well as the cleft.