A branchial cyst is a congenital abnormality arising when the second branchial cleft fails to properly form during fetal development. This leaves a space surrounded by epithelial tissue in the lateral aspect of the neck. This space can fill with fluid. This fluid filled lump is called a branchial cyst. Branchial cysts arising from the first, third and fourth branchial clefts are possible, although they are much more rare.
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. This swelling will transilluminate with light, as the fluid in the cyst transmits the light throughout the cyst. To transilluminate the cyst, hold a pen torch flat against the skin and watch as the whole lump lights up.
Branchial cysts tend to present after the age of 10 years, most commonly in young adulthood when the cyst becomes 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 it in your exams. It is just anterior to the sternocleidomastoid muscle, round and soft and transilluminates with light.
Sinuses and Fistulas
A sinus is a blind ending pouches. A fistula is an abnormal connection between two epithelial surfaces.
A branchial cleft sinus describes when the branchial cyst is connected via a tract to the outer skin surface. There will be a small hole visible in the skin beside the cyst. There may be a noticeable discharge from the sinus.
A branchial pouch sinus describes when the branchial cyst is connected via a tract to the oropharynx.
A branchial fistula describes when there is a tract connecting the oropharynx to the outer skin surface via the branchial cyst.
Sinuses and fistula pose an increased risk of infections in the branchial cyst, as they are a way for pathogens to get in.
Where the branchial cleft is not causing any functional or cosmetic issues, conservative management may be appropriate.
Where recurrent infections are occurring, there is diagnostic doubt about the cause of the neck lump or it is causing other functional or cosmetic issues, surgical excision may be appropriate.
Last updated January 2020