Nonneoplastic Conditions

Thyroglossal duct cyst: probably the commonest developmental neck cyst, due to failure of the embryonic thyroglossal duct (extending from the posterior tongue into the neck) to atrophy.

Midline in 90%, below hyoid in 70%; associated with a sinus in 40% of cases. Lined by squamous and/or respiratory epithelium; less than half contain thyroid follicles; may represent the patient's only functioning thyroid tissue.

Branchial cleft cyst: derived from remnants of the embryonic branchial apparatus following incomplete obliteration of the branchial pouches; the most common form is believed to derive from the second branchial pouch. Cyst lies in the lateral neck near the angle of the jaw at the anterior border of sternocleidomastoid; the sinus may open onto the skin at the junction of the middle one-third and lower one-third while the tract follows the carotid sheath and may fistu-late into tonsillar fossa. Lined by squamous epithelium with reactive lymphoid tissue in the wall; 10% contain respiratory epithelium.

Miscellaneous lesions: other developmental cysts in the neck include dermoid cyst (often extending into the neck from the sublingual region), cervical thymic cyst and cervical bronchial cyst. The "plunging ranula" is a mucous extravasation cyst from the sublingual gland that extends into the neck through mylohyoid. Cutaneous and subcutaneous haemangiomas are relatively common but do not differ from their counterparts elsewhere. Lymphangiomas are uncommon in the neck but usually arise low in the posterior triangle. Lesions composed of very dilated vessels can be termed cystic hygroma, although all forms are more usually described as "lymphatic malformations".

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