Second branchial cleft cysts are a cystic dilatation of the remnant of the second branchial cleft (see branchial apparatus), and along with second branchial fistulae and sinuses accounts for 95% of all branchial cleft anomalies.
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Clinical presentation
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 the sternocleidomastoid (although the position is variable - see classification below).
Pathology
The cyst is typically filled with mucoid material, is well circumscribed and other than presenting as localized swelling, is asymptomatic. However, if infected, surrounding fat stranding and skin changes are evident.
Location
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.
Classification
Radiographic features
Ultrasound
sharply demarcated
posterior acoustic enhancement: 70% 3
imperceptible walls: 82%
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echogenicity is variable 3
anechoic: 41%
homogeneously hypoechoic with internal debris: 24%
pseudo solid: 12%
heterogeneous: 23%
CT
usually rounded or spheric, sharply circumscribed
fluid density centrally
thin wall
extension of the cyst wall between the internal and external carotid arteries just above the carotid bifurcation (features sometimes referred to as the notch sign, tail sign or beak sign 6), is highly suggestive of the diagnosis but not pathognomonic 7
MRI
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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
Complete surgical excision is the treatment of choice for these lesions if they do not resolve. Prognosis is excellent if the lesion is resected completely. Sclerotherapy is another excellent management option, particularly in the unilocular cysts 8.
Complications
superimposed infection
Differential diagnosis
Imaging differential considerations include
paramedian thyroglossal duct cyst
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necrotic nodal metastases, especially squamous cell carcinoma and papillary thyroid cancer
-
vascular lesions
mycotic aneurysm of the neck
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neurogenic tumors
cervical cavernous lymphangioma
thyroid nodule/cyst
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