On CT neck with contrast, a mass in the carotid space at the carotid bifurcation shows a 'lyre sign' (widening of the fork between ICA and ECA). This is pathognomonic of:

• A Schwannoma of the vagus nerve
• B Cervical lymph node metastasis from oropharyngeal cancer
• C Carotid body tumor (paraganglioma) ✓
• D Thrombosed carotid aneurysm

Explanation

The 'lyre sign' (also called 'splaying' sign) on CT angiography or conventional angiography refers to widening of the angle between the internal and external carotid arteries due to a highly vascular tumor interposed at the carotid bifurcation — pathognomonic of carotid body tumor (glomus caroticum, a paraganglioma). These tumors are markedly vascular with intense enhancement ('salt-and-pepper' pattern on MRI). Vagal schwannomas displace the carotid vessels anteriorly without splaying the bifurcation. Cervical lymph nodes compress but do not splay the bifurcation. Carotid aneurysm is typically fusiform or saccular in the vessel wall.

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

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Written and medically reviewed by the StethoPrep medical team.