A branchial cyst is a congenital abnormality that occurs when part of the second branchial cleft fails to disappear during fetal development, leaving a fluid-filled lump in the side of the neck. Branchial cysts arising from the first, third and fourth branchial clefts are possible but much more rare.
Sinuses and Fistulas
A sinus is a blind ending pouch. A fistula is an abnormal connection between two epithelial surfaces.
A branchial cleft sinus occurs when the branchial cyst is connected via a tract to the outer skin surface. There will be a small hole visible in the skin associated with the cyst. There may be a noticeable discharge from the sinus.
A branchial pouch sinus is an internal sinus opening to the oropharynx, which may connect to a branchial cyst.
A branchial fistula describes a tract connecting the oropharynx to the outer skin surface via the branchial cyst.
Sinuses and fistulae increase the risk of infection in branchial cysts, as they provide pathways for pathogens to enter.
Presentation
Branchial cysts present as a round, soft, cystic swelling between the angle of the jaw and the sternocleidomastoid muscle in the anterior triangle of the neck.
Branchial cysts tend to present after age 10, most commonly in young adulthood, when they become noticeable or infected.
TOM TIP: Branchial cysts may appear in exams as a differential of neck lumps in teenagers or as part of a neck examination in an OSCE. Remembering the key features will help you differentiate them in your exams. They are along the anterior border of the upper third of the sternocleidomastoid, round, soft and non-tender. If the lump transilluminates, it is more likely to be a cystic hygroma. They may ask you where it is most likely to have originated, and the answer would be the second branchial cleft.
Management
Ultrasound is usually the initial investigation to confirm the diagnosis.
Conservative management may be appropriate where the branchial cyst is not causing any functional or cosmetic issues.
Surgical excision is the definitive treatment, particularly when there are recurrent infections, diagnostic uncertainty, functional or cosmetic issues.
Last updated June 2026
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