What is the management of hypoglossal nerve injury?

Management of Hypoglossal Nerve Injury

MRI is the preferred imaging modality for evaluating hypoglossal nerve injury, with contrast-enhanced studies providing the best opportunity to identify and characterize lesions along the entire course of the nerve. 1

Etiology and Clinical Presentation

Hypoglossal nerve (CN XII) palsy typically presents with:

• Dysarthria
• Deviation of the tongue to the affected side upon protrusion
• Possible dysphagia
• Atrophy and fatty infiltration of the tongue may develop over time

Common causes include:

• Neoplasms (most common cause, especially involving the hypoglossal canal) 1
• Vascular lesions (including internal carotid artery dissection) 1
• Brainstem infarcts or hemorrhages
• Trauma (including iatrogenic injury during surgeries) 2, 3
• Inflammatory and infectious processes
• Demyelinating diseases

Diagnostic Approach

Imaging Studies

1. MRI Head and Neck (First-line):

   • Provides direct visualization of CN XII and surrounding structures 1
   • Evaluates the entire course: brainstem nucleus, cisternal segment, hypoglossal canal, and extracranial path
   • Protocol should include:
     • Thin-cut high-resolution techniques
     • Focus on posterior fossa, skull base, and neck
     • Pre- and post-contrast imaging (tumors are the most common cause) 1
     • MRI has 100% sensitivity for detecting hypoglossal canal invasion 1

2. CT Neck with Contrast (Complementary):

   • Characterizes osseous integrity of hypoglossal canal and skull base 1
   • Include thin-cut high-resolution bone windows
   • CT has 87.5% sensitivity and 66.7% specificity for hypoglossal canal invasion 1

3. CTA Head and Neck:

   • Indicated when internal carotid artery dissection is suspected 1
   • Particularly useful in emergent settings

Special Considerations

• Nuclear lesions (in brainstem) are usually accompanied by additional neurologic deficits
• Denervation changes in the tongue vary with acuity and are better visualized on MRI 1
• Ultrasound is not routinely used in the initial evaluation of hypoglossal nerve palsy 1

Management Approach

Immediate Management

1. Identify and treat underlying cause:

   • Surgical intervention for tumors
   • Medical management for inflammatory/infectious causes
   • Vascular intervention for dissection if appropriate

2. Supportive care for functional deficits:

   • Speech therapy for dysarthria
   • Swallowing evaluation and therapy for dysphagia

Long-term Management

1. Speech and swallowing rehabilitation:

   • Regular therapy sessions to improve functional outcomes
   • Compensatory techniques for tongue movement

2. Monitoring for recovery:

   • Most iatrogenic cases (e.g., post-anesthesia) resolve within 2-4 months 2
   • Complete nerve transection has poor prognosis for spontaneous recovery 4, 3

3. Prevention of complications:

   • Nutritional support if dysphagia is significant
   • Monitoring for aspiration risk

Special Clinical Scenarios

Iatrogenic Injury

• Anesthesia-related: Self-limited in most cases, with 50% resolving within 2 months and 80% within 4 months 2
• Surgical injury: Poor prognosis for spontaneous recovery if nerve is transected 3
• Aberrant reinnervation: Can cause paradoxical worsening of symptoms 4+ months after injury due to abnormal coactivation of tongue muscles 4

Anatomical Variants

• Rare variations in nerve course (e.g., superficial to internal jugular vein) may increase risk during neck surgery 5
• Surgeons should exercise extra caution during neck dissections 5

Pitfalls and Caveats

1. Delayed diagnosis: Symptoms may have delayed onset after procedures, leading to missed diagnosis in recovery room 2

2. Aberrant reinnervation: Unlike simple nerve injury, aberrant reinnervation can cause paradoxical worsening of symptoms months after initial injury 4

3. Multiple cranial nerve involvement: Hypoglossal nerve palsy may be part of syndromes involving other lower cranial nerves (IX-XI), requiring broader evaluation 1

4. Anatomical variations: Rare but significant variations in nerve course can increase surgical risk 5