A mass located between the internal and external carotid arteries is most consistent with which diagnosis?

• A. Carotid body tumor
• B. Aneurysm
• C. Atherosclerotic plaque
• D. Dissection

Answer: (A)

A mass that sits directly between the internal and external carotid arteries at the bifurcation is most consistent with a carotid body tumor. The carotid body is located right at that split, and a tumor arising from it (a paraganglioma) grows outward between the two vessels, classically seen as a mass splaying the internal and external carotid arteries on imaging (the lyre sign). This location distinguishes it from other possibilities: an aneurysm is a dilation within the vessel wall itself rather than a separate mass between the vessels; atherosclerotic plaque is intraluminal and within the vessel lining; dissection creates a tear leading to a false lumen rather than a discrete mass between the arteries.