Branchial cyst as a lateral neck lump
A branchial cyst is a congenital fluid-filled sac in the lateral neck, left when the branchial apparatus (the embryo's ridges and grooves) fails to close completely.
Remember
In a young adult, a soft, fluctuant (fluid-filled) lump, usually painless, at the side of the neck in front of the upper sternocleidomastoid (the large muscle running from behind the ear to the collarbone) is typical of a branchial cyst, and infection can make it painful.
In the embryo, ridges called branchial arches form in the neck, separated by grooves called clefts. Normally the surfaces of the arches fuse and the gaps close. If a cleft is not completely obliterated (closed off), a gap is left and fluid collects, forming a branchial cyst. The second cleft is the commonest source.
The cyst sits at the side of the neck, on the front edge of the sternocleidomastoid, most often in its upper third. It is soft, slow growing and fluctuant, and it is normally painless. If the fluid becomes infected, the lump becomes painful and may enlarge, as after an upper respiratory tract infection. Because it is not attached to the thyroid tract (the path of the thyroid's descent) or to the tongue base, it does not move with swallowing or with tongue protrusion (sticking the tongue out). It also does not pulsate.
In a young adult, the way to tell it from other neck lumps is its location and behaviour. A thyroglossal cyst is a midline cyst, left along the path the thyroid took as it descended from the base of the tongue, and it rises when the tongue is protruded. A pulsating lump along the carotid artery points to a vascular cause instead. A cystic hygroma (a malformation of lymphatic vessels) is typically noticed before the age of two years.
In an adult, a persistent cystic lump in this position still needs assessment, because a cystic lymph node metastasis (a node filled with fluid and containing cancer that has spread) can look similar. Treatment is surgical excision, and the cyst tends to recur (come back) if it is not completely removed.
Key facts
- Site
- the lateral neck, on the front edge of the sternocleidomastoid, most often in its upper third.
- Cause
- incomplete obliteration of the branchial apparatus, most often the second cleft.
- Feel
- smooth, soft and fluctuant, and usually painless.
- Movement
- no movement on swallowing or tongue protrusion, and not pulsatile.
- Timing
- present from birth but often noticed in teenagers and young adults.
- Treatment
- surgical excision.
Exam traps
- A midline cyst that rises when the tongue is protruded is a thyroglossal duct cyst, not a branchial cyst, which lies in the lateral neck and does not rise with the tongue.
- Reactive lymph nodes (nodes that enlarge in response to infection) are tempting because the lump turns painful during an infection, but swelling from infection usually settles within 1 to 2 weeks, whereas a branchial cyst is soft, fluctuant and slow growing.
- A carotid body tumour lies along the carotid artery and is a firm, solid mass that may pulsate or have a bruit (a whooshing sound on listening with a stethoscope), whereas a branchial cyst is soft and fluctuant.
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