What is the recommended examination and management approach for a patient with suspected twelfth cranial nerve dysfunction, particularly those with a history of stroke, trauma, or neurological disorders?

Twelfth Cranial Nerve (Hypoglossal) Examination

Direct Examination Technique

The hypoglossal nerve (CN XII) examination should focus on tongue inspection, protrusion, lateral movement, and strength testing, with the tongue deviating toward the side of the lesion when damaged. 1, 2

Motor Function Assessment

• Inspect the tongue at rest in the mouth for visible atrophy, fasciculations, or asymmetry, which indicate lower motor neuron pathology 3, 4
• Ask the patient to protrude the tongue and observe for deviation—the tongue deviates toward the affected side due to unopposed contraction of the intact genioglossus muscle 2, 3
• Test tongue strength by having the patient push the tongue against the inside of each cheek while you apply external resistance with your finger 3, 4
• Assess lateral tongue movements by asking the patient to move the tongue rapidly from side to side 3, 4
• Evaluate speech quality for dysarthria, particularly difficulty with lingual consonants (t, d, l, n) 2, 4

Anatomical Localization

Central vs. Peripheral Lesions

• Brainstem lesions affecting the hypoglossal nucleus cause ipsilateral tongue weakness with associated brainstem signs such as contralateral hemiparesis or sensory loss 2
• Peripheral lesions along the nerve's course from the medulla through the hypoglossal canal to the tongue produce isolated tongue weakness and atrophy without other neurological deficits 2, 5
• The hypoglossal nerve exits the skull through the hypoglossal canal and descends in the neck alongside the carotid sheath, making it vulnerable to trauma, tumors, and vascular lesions 2, 6

Diagnostic Imaging Approach

For any confirmed CN XII deficit, contrast-enhanced MRI of the brain, skull base, and neck is the gold standard imaging modality. 2

Imaging Protocol

• MRI of the head without and with IV contrast combined with MRI of the orbit, face, and neck is the preferred imaging approach (rated 8/9 by ACR guidelines) 7, 2
• Thin-section imaging with high spatial resolution is required to directly visualize the nerve from the brainstem nuclei through the hypoglossal canal to the tongue musculature 2
• CT neck with IV contrast is an appropriate alternative (rated 7/9) and can be complementary to MRI for better visualization of bony foramina 7
• Intravenous contrast is imperative for comprehensive evaluation of cranial neuropathy to detect enhancement patterns suggesting inflammation, infection, or tumor 2

Common Etiologies and Clinical Context

High-Risk Causes Requiring Urgent Evaluation

• Malignant tumors are the most common cause, accounting for nearly half of all hypoglossal nerve palsies (49%), making imaging essential in all cases 6
• Trauma (particularly gunshot wounds and penetrating neck injuries) is the second most common cause (12%) 6
• Stroke affecting the medulla can cause hypoglossal palsy, often with other brainstem signs 6
• Skull base tumors including paragangliomas, schwannomas, meningiomas, and metastases can compress the nerve at the hypoglossal canal 2

Additional Considerations

• Multiple sclerosis, Guillain-Barré syndrome, and infection together account for approximately 14% of cases 6
• Surgical injury during neck procedures can damage the nerve in its peripheral course 6
• Prognosis is generally poor, with only 15% of patients experiencing complete or nearly complete recovery, emphasizing the importance of early diagnosis 6

Management Approach Based on Clinical Context

Acute Presentation with Focal Neurological Deficit

• If stroke is suspected (sudden onset with other brainstem signs), imaging should be guided by cerebrovascular disease protocols with urgent MRI including diffusion-weighted imaging 8
• If trauma is present, imaging should follow head and neck trauma protocols to assess for skull base fractures and vascular injury 8

Subacute or Chronic Presentation

• For isolated hypoglossal palsy without trauma or acute stroke, proceed directly to contrast-enhanced MRI of the brain and neck to evaluate for tumor, infection, or inflammatory causes 2
• Multiple cranial nerve involvement suggests skull base pathology (jugular foramen syndrome) or systemic disease requiring comprehensive imaging and laboratory evaluation 5

Critical Pitfalls to Avoid

• Do not delay imaging in any patient with confirmed hypoglossal nerve palsy, as malignancy is the leading cause and early detection impacts prognosis 6
• Do not assume a benign cause in elderly patients—while vascular risk factors are common, tumor remains the most frequent etiology across all age groups 6
• Do not limit imaging to the brain alone—the nerve's course through the neck requires visualization of the entire pathway from brainstem to tongue 2
• Do not overlook associated cranial nerve deficits, as combined CN IX, X, XI, and XII palsies suggest jugular foramen pathology requiring specific imaging protocols 1, 2