Branchial Cleft Cyst (BCC)

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Diagnosis Definition

The tissues of the neck are embryologically derived from branchial arches and pouches; incomplete arch fusion can result in cysts, fistulas, and sinuses
Branchial apparatus anomalies (BAAs) are categorized into 1st, 2nd, 3rd, and 4th types based on location
95% of BAAs arise from the second cleft and ¾ of these are cysts, which typically present between 10 and 40 years of age
Second BCCs typically present as a painless, fluctuant mass adjacent to the anteromedial sternocleidomastoid muscle at the mandibular angle, lateral to the carotid space, and posterior to the submandibular gland
BCCs can enlarge slowly over time and become painful if secondarily infected

Imaging Findings

On MRI, BCCs are seen as circumscribed, round/oval/lobular masses with thin or imperceptible walls
The signal intensity varies depending on prior infection or hemorrhage, which can result in cysts having high signal on T1 relative to muscle and low signal on T2 due to proteinaceous debris; uninfected BCCs should not enhance
In the classic location, second BCCs can displace the sternocleidomastoid muscle laterally, the carotid artery medially, and the submandibular gland anteriorly

Pearls

Surgical excision is the recommended therapy for a branchial cleft anomaly because of the frequency of secondary infection
In a young patient, a history of recurrent inflammation in the region of the mandibular angle is highly suggestive of a second BCC
A curved rim of tissue (so-called “beak” sign) pointing medially between the internal and external carotid arteries is considered a pathognomonic imaging feature of one form of a second BCC

References

Koeller KK, Alamo L, Adair CF, et al. Congenital cystic masses of the neck: radiologic-pathologic correlation. RadioGraphics 1999; 19:121-146
Mukherji SK, Fatterpekar G, Castillo M, et al. Imaging of congenital anomalies of the branchial apparatus. Neuroimaging Clin N Am 2000; 10:75-93

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