What is the most commonly injured cranial nerve during carotid (carotid artery) endarterectomy (surgical procedure to remove plaque from the carotid artery)?

Hypoglossal Nerve (CN XII) is the Most Commonly Injured Cranial Nerve During Carotid Endarterectomy

The hypoglossal nerve (CN XII) is the most commonly injured cranial nerve during carotid endarterectomy. This corresponds to answer choice D. XII.

Cranial Nerve Injury Patterns in Carotid Endarterectomy

Cranial nerve injuries represent a significant complication of carotid endarterectomy (CEA). Based on the evidence, the frequency of injury to specific cranial nerves during CEA can be ranked as follows:

1. Hypoglossal nerve (CN XII): Most commonly injured, with reported incidence of 3.3% 1
2. Vagus nerve (CN X): Second most commonly injured, with reported incidence of 2.6% 1
3. Glossopharyngeal nerve (CN IX): Less commonly injured, with reported incidence of 0.7% 1
4. Accessory nerve (CN XI): Rarely reported in the literature as being injured during CEA

Anatomical Considerations

The hypoglossal nerve is particularly vulnerable during CEA due to its anatomical course:

• It crosses the external carotid artery and runs close to the carotid bifurcation
• It must be identified and carefully retracted during the procedure
• High carotid bifurcations increase the risk of hypoglossal nerve injury 2

According to the American College of Radiology guidelines, the hypoglossal nerve (CN XII) arises in the dorsal medulla, traverses the premedullary cistern, and enters the hypoglossal canal. After exiting the skull, it travels within the carotid space before coursing anteriorly to innervate the tongue musculature 2.

Clinical Manifestations of Hypoglossal Nerve Injury

Injury to the hypoglossal nerve during CEA presents with:

• Unilateral tongue weakness
• Deviation of the tongue toward the affected side upon protrusion
• Dysarthria (difficulty with speech)
• Potential difficulty with swallowing

Risk Factors for Cranial Nerve Injury During CEA

Several factors increase the risk of cranial nerve injury during carotid endarterectomy:

• High carotid bifurcation 2
• Atheromatous lesions extending into the internal carotid artery beyond the exposed surgical field
• Lesions at or above the level of the second cervical vertebra
• Prior radical neck surgery or radiation
• Reoperative CEA for recurrent stenosis
• Extensive dissection cephalad to the level of the hypoglossal nerve 3

Prognosis and Management

Fortunately, most cranial nerve injuries during CEA are transient:

• The majority of patients show improvement within weeks
• Complete resolution typically occurs within 2 weeks to 14 months 1
• Permanent deficits are rare

Patients with symptoms of cranial nerve dysfunction should undergo thorough otolaryngological evaluation and follow-up 1.

Prevention of Cranial Nerve Injury

To minimize the risk of cranial nerve injury during CEA:

• Thorough knowledge of regional anatomy is essential
• Careful surgical technique with gentle tissue handling
• Avoid excessive retraction
• Identify and protect cranial nerves during dissection
• Limit dissection to what is necessary for adequate exposure
• Be aware of anatomical variations, such as non-recurrent laryngeal nerves 4

The overall incidence of cranial nerve injuries during CEA has decreased over time with improved surgical techniques, with current rates reported between 5-10% 1, 5, 6.