What is the best imaging protocol for a patient presenting with symptoms of trigeminal neuralgia, possibly due to compression of the trigeminal nerve by a blood vessel or tumor, and with a potential history of multiple sclerosis or other conditions affecting the trigeminal nerve?

Imaging for Trigeminal Neuralgia

MRI with contrast covering the entire trigeminal nerve course is the gold-standard imaging modality for trigeminal neuralgia, utilizing 3-D heavily T2-weighted sequences combined with MR angiography to assess for both neurovascular compression and secondary causes. 1, 2

Essential MRI Protocol Components

The optimal imaging protocol must include specific technical elements:

• 3-D heavily T2-weighted sequences are mandatory for optimal nerve visualization and represent the cornerstone of the imaging protocol 1, 2
• MR angiography (MRA) should be performed concurrently with anatomic MRI, achieving 97-100% sensitivity and 100% specificity for detecting neurovascular compression 2
• Pre- and post-contrast imaging provides the best characterization, particularly when evaluating for secondary causes like tumors or inflammatory conditions 1, 2
• Thin-cut high-resolution techniques through the entire trigeminal nerve course from brainstem to peripheral branches are necessary 1, 3

Critical Coverage Requirements

Imaging must extend from the brainstem nuclei through all peripheral branches—standard brain MRI protocols are insufficient and will miss extracranial pathology. 1, 3

The trigeminal nerve can be affected at multiple anatomical levels:

• Brainstem nuclei and fascicular segments (particularly important in multiple sclerosis) 1, 4, 5
• Cisternal portion and root entry zone (most common site for neurovascular compression) 1, 6
• Meckel cave and cavernous sinus 1
• Skull base foramina 1
• Extracranial branches in the masticator space and pterygopalatine fossa 1

When to Prioritize Contrast Administration

IV gadolinium contrast is mandatory when evaluating for trigeminal neuropathy (sensory deficits, facial numbness) but may be optional in pure trigeminal neuralgia cases. 3

Contrast is essential for detecting:

• Nerve enhancement indicating inflammation or injury 3
• Tumors and perineural spread 1
• Inflammatory or infectious processes (meningitis, encephalitis, sarcoidosis) 1
• Demyelinating lesions in multiple sclerosis 1, 7, 5

Age-Specific Considerations and Red Flags

Younger patients (<40 years) and those with pain in multiple trigeminal branches have significantly higher rates of secondary causes (tumors, multiple sclerosis) requiring thorough imaging evaluation. 8

• Patients under 40 years: 45% have tumor or multiple sclerosis 8
• Patients under 29 years: 100% have secondary pathology 8
• Pain in more than one trigeminal branch: 33% have tumors 8
• Patients over 60 years: 18% have secondary causes 8

Interpreting Neurovascular Compression Findings

Both false-positives and false-negatives occur when assessing neurovascular contact—imaging must be interpreted in the context of symptom laterality and clinical presentation. 2

Critical interpretation principles:

• 30% of asymptomatic individuals show vascular contact at the root entry zone, but only 2% show actual nerve deformity 6
• Neurovascular compression must be ipsilateral to the patient's pain to be clinically significant 1, 2
• The presence of nerve deformity or displacement is more specific than simple contact 6
• Congruence rates between MRI and intraoperative findings range from 83-100% 2

Multiple Sclerosis Considerations

In patients with known or suspected multiple sclerosis, brainstem imaging is essential as demyelinating plaques affecting the intrapontine trigeminal primary afferents are the most common cause of MS-related trigeminal neuralgia. 1, 4, 5

• Pontine plaques damaging primary afferents at the root entry zone are the primary mechanism 4, 5
• However, neurovascular compression can still occur as a concurrent mechanism in MS patients 7
• All seven patients in one series with MS and trigeminal neuralgia had identifiable structural causes on MRI (vascular compression, tumors, or plaques) 7

Role of CT Imaging

CT is relegated to a complementary role, primarily for evaluating osseous skull base integrity and treatment planning—it should not be used as the primary imaging modality. 1

CT limitations:

• Standard CT head coverage is insufficient to evaluate the full trigeminal nerve course 1
• MRI offers superior detection of perineural tumor spread (88-89% sensitivity/specificity for CT versus near 100% for MRI) 1
• CT provides inferior soft tissue contrast compared to MRI 1
• Thin-section contrast-enhanced CT is useful only for noninvasive treatment planning in patients with established trigeminal neuralgia 1

Common Pitfalls to Avoid

• Never order standard brain MRI alone—it will miss extracranial nerve pathology 1, 3
• Never omit contrast in suspected neuropathy—noncontrast MRI is inadequate for comprehensive evaluation 3
• Never use standard brain sequences—thin-cut high-resolution protocols are mandatory 3
• Never interpret vascular contact without clinical correlation—asymptomatic contact is common 2, 6

Technical Superiority Considerations

3T MRI offers superior resolution compared to 1.5T, particularly for detecting smaller vessel compression, though both are acceptable. 2

One study reported lower sensitivity at 1.5T (33%) versus 3T (50%) for detecting compression by smaller vessels like the anterior inferior cerebellar artery, though both sensitivities are lower than for larger vessel compression 1