MRI of a 50-year-old with a neck mass shows a well-defined cystic lesion posterior to the sternocleidomastoid muscle, posterior to the submandibular gland, anterior to the scalene muscles, and at the level of the mandibular angle. The most likely diagnosis is:

• A Second branchial cleft cyst ✓
• B Cystic hygroma (lymphatic malformation)
• C Cervical thymic cyst
• D Necrotic lymph node from HPV-related oropharyngeal cancer

Explanation

Second branchial cleft cysts (the most common type, ~95% of branchial anomalies) present as a smooth, unilocular, thin-walled cystic neck mass at the anterior border of the SCM, typically at or below the angle of the mandible, anterior to the SCM. Bailey's classification describes their tract passing between the internal and external carotid arteries. On MRI they are T2 hyperintense, T1 hypointense, non-enhancing (unless infected). Cystic hygroma is multilocular, trans-spatial. Necrotic HPV-related nodes are more irregular with rind enhancement and occur in the posterior triangle or level II. Thymic cysts are in the lower neck/anterior mediastinum.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.