Second branchial cleft cysts are a cystic dilatation of the remnant of the 2nd branchial apparatus, and along with 2nd branchial fistulae and sinuses accounts for 95% of all branchial cleft anomalies.
Although a congenital abnormality, they tend to present in early adulthood (10-40 years of age) often after minor trauma or infection. Second branchial cleft sinus or fistulas, on the other hand, present earlier. Fistulas extend from the skin surface anterior to the middle of the sternocleidomastoid muscle, pass between the internal and external carotid arteries and eventually drain into the tonsillar fossa.
Typically, second branchial cleft cysts present as a rounded swelling just below the angle of mandible, anterior to sternocleidomastoid (although the position is variable - see classification below).
The cyst is typically filled with mucoid material, is well circumscribed and other than presenting as localised swelling, is asymptomatic. However, if infected, surrounding fat stranding and skin changes are evident.
Cysts can occur anywhere along the course of the second branchial apparatus, from the pharyngeal wall to the skin, as it passes laterally and inferiorly between the internal and external carotid arteries. The angle of the mandible is a common location.
- sharply demarcated
- posterior acoustic enhancement: 70% 3
- imperceptible walls: 82%
- echogenicity is variable 3
- anechoic: 41%
- homogeneously hypoechoic with internal debris: 24%
- pseudo solid: 12%
- heterogeneous: 23%
- rounded or spheric, sharply circumscribed
- fluid density centrally
- thin wall
- extension of the cyst wall between the ICA and ECA just above the carotid bifurcation (features sometimes referred to as the notch sign, tail sign or beak sign 6), long-established as pathognomonic, is still highly suggestive of the diagnosis; down-classification due to an example of Schwannoma mimicking a branchial cleft cyst in rarity section 7
T1: variable signal dependent on protein content
- high protein content: high signal
- low protein content: low signal
- T2: usually high signal
- T1 C+ (Gd): no enhancement in uncomplicated lesions
Treatment and prognosis
- superimposed infection
- paramedian thyroglossal duct cyst
- cystic lymph nodes
- vascular lesions
- neurogenic tumours
- cervical dermoid cyst
- cavernous lymphangioma
- thyroid nodule/cyst
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