Neuro 29

Salient findings:

• Cystic left neck mass located at the level of the angle of the mandible, with the posterior lobulated aspect of the mass lying between the ICA/carotid bifurcation and sternocleidomastoid muscle.
• Its margins are well-defined and thin-walled and measures up to 46 mm AP by 27 mm transverse by 55 mm CC.
• Internal Hounsfield units measure approximately 55 consistent with proteinaceous or haemorrhagic content.

Other important features/points:

• No surrounding inflammatory fat stranding or wall thickening
• No further neck mass and lesion appears solitary.
• No cervical lymphadenopathy.
• Unremarkable aerodigestive tract.

Principal Diagnosis: Second branchial cleft cyst.

Differential diagnoses: Necrotic lymph node from a head and neck malignancy (often a primary squamous cell oropharyngeal carcinoma).

Learning points:

What is the embryological basis for branchial cleft cysts?

• The branchial arches develop embryologically between week 4 and week 7 of gestation.
• These arches are the precursors to various structures in the face, neck and pharynx.
• Between 5th and 6th weeks of gestation, the arches thicken and combine together and form a sinus tract lined with ectoderm, known as the cervical sinus of His.
• By the end of the 7th gestational week, there is rapid involution of the cervical sinus of His, which in adults can be identified as the region between the sternocleidomastoid muscle and infrahyoid strap muscles anteriorly.
• If there is failure of the sinus of His to completely involute during embryogenesis, there remains cells within the remnant tract, enabling various types of branchial cleft anomalies to develop, such as cysts, sinuses and fistulae.
• The most common branchial cleft anomalies are the second branchial cleft lesions. The second most common being first branchial cleft lesions. The first branchial cleft lesions lie more superiorly at the level of the external auditory canal and parotid gland.

When do patients usually present and with what symptoms?

• Second branchial cleft cysts usually present in childhood or adolescence, although across the spectrum of all branchial anomalies, they can frequently present anytime within the first 4-5 decades.
• Clinically, patients can present with a painless lump, unless there is secondary infection when there may be pain and other sequelae on inflammation (swelling, skin changes).

How are Branchial Cleft Cysts Classified?

• There is a classification system called the Bailey classification, which divides the branchial cleft cysts up into 4 distinct categories based on anatomical location.
  • Type I: The most superficially location, lying superficial to the sternocleidomastoid muscle and deep to the platysma.
  • Type II (most common): Lies deep to the SCM but remains lateral to the carotid sheath.
  • Type III: Between the internal and external carotid arteries
  • Type IV: The deepest location lying medial/deep to the carotid sheath within the parapharyngeal / pharyngeal mucosal space

Associated findings you may see:

• Superimposed infection.
• Intralesional haemorrhage particularly if presented following minor facial trauma or after iatrogenic procedure such as FNA. This can make the lesion look more complex with internal fluid levels and hyperdensity of contents.

Key diagnostic and management issues:

• A cystic lesion within this characteristic location in the neck in an adult patient, despite it having all the hallmark features of a branchial cleft cyst, still is required to be treated with high index of suspicion for underlying primary head and neck malignancy, usually oropharyngeal squamous cell carcinoma.
• Other differentials for a lesion in this location could include infectious adenitis such as tuberculous cervical adenitis particularly in endemic geographical locations and in immunocompromised patients.