Which cranial nerve is most commonly affected by an internal carotid artery dissection?

• A. Trigeminal Nerve
• B. Facial Nerve
• C. Hypoglossal Nerve
• D. Vagus Nerve

Answer: (C)

The hypoglossal nerve is most commonly affected by an internal carotid artery dissection due to its anatomical proximity and the implications of vascular compromise. An internal carotid artery dissection can lead to ischemic injury of surrounding structures, especially in regions where cranial nerves interact with blood vessels. The hypoglossal nerve (CN XII) is closely associated with the internal carotid artery as it traverses the anterior portion of the neck and travels in the vicinity of the vessel.

Ischemia can disrupt the neuronal pathways of the hypoglossal nerve, leading to dysfunction, which can manifest as weakness of the tongue and difficulty with speech or swallowing. This nerve is responsible for motor control of the muscles of the tongue, and damage due to vascular issues can lead to clinical symptoms associated with its dysfunction.

In contrast, the trigeminal, facial, and vagus nerves, while also important cranial nerves with various roles, are generally less directly affected by changes or complications associated with dissection of the internal carotid artery, especially in terms of the most common presentations and outcomes. The anatomical relationship and the potential for ischemic effects make the hypoglossal nerve the most likely candidate to be impacted in such scenarios.