On MRI of the parotid gland, a well-defined lesion with homogeneous low T1, very high T2 signal (brighter than parotid parenchyma), and absent enhancement is seen in a 45-year-old. The MOST likely diagnosis is:

• A Pleomorphic adenoma (mixed tumor)
• B Warthin tumor (papillary cystadenoma lymphomatosum)
• C Mucoepidermoid carcinoma
• D Parotid gland lymphoepithelial cyst ✓

Explanation

A parotid cyst with very bright T2, near-water signal, and absent enhancement represents a simple lymphoepithelial cyst of the parotid — common in HIV-positive patients where bilateral parotid cysts with lymphadenopathy are a recognized presentation (benign lymphoepithelial lesions/BLELs). Pleomorphic adenoma has heterogeneous high T2 signal due to myxoid areas but enhances. Warthin tumor is classically bilateral, shows restricted diffusion on DWI due to thick lymphocytic stroma, and occurs almost exclusively in males. Mucoepidermoid carcinoma has mixed signal and irregular enhancement. A purely cystic, non-enhancing parotid lesion in an adult warrants HIV serology.

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

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Written and medically reviewed by the StethoPrep medical team.