MRI of a 35-year-old shows a bilobed cystic mass with high T2 signal, low T1 signal, no enhancement, and a 'notch' or 'dumbbell' shape through the stylomandibular tunnel. The likely diagnosis is:

• A Second branchial cleft cyst
• B Ranula extending into the neck (plunging ranula)
• C Pleomorphic adenoma of the deep lobe of the parotid (parapharyngeal space extension) ✓
• D Warthin's tumour

Explanation

A dumbbell-shaped (bilobed) parotid mass extending through the stylomandibular tunnel into the parapharyngeal space is pathognomonic of deep lobe parotid pleomorphic adenoma with parapharyngeal extension. The narrow waist at the stylomandibular notch creates the dumbbell shape. On MRI it is T2 hyperintense (myxoid/chondroid matrix) and T1 hypointense with heterogeneous internal signal; benign pleomorphic adenoma does not enhance homogeneously. This anatomy explains why deep lobe parotid tumours require transparotid/transmandibular approach for resection. Warthin's tumour is T1 isointense with cystic areas and bilateral in 10%. Branchial cysts are in the posterior triangle.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.