What is the differential diagnosis for a pediatric cystic neck mass?
This has a broad differential that may be narrowed by location. Type II branchial cleft cysts (the most common) are suprahyoid lesions that classically push the sternocleidomastoid muscle posteriorly and have a tongue of tissue arising between the external and internal carotid arteries. Thyroglossal duct cysts are remnants of the thyroglossal duct and are found in the midline, usually at or below the hyoid bone beneath the strap muscles. Teratomas or dermoids may occur anywhere but can be identified by the presence of fat, calcium, or both. A venolymphatic malformation has a typical appearance of a cystic mass, often with septations, which insinuates through fascial planes (sometimes inferiorly into the mediastinum). They may also contain blood-fluid levels, best appreciated on MRI.