What causes trigeminal neuralgia?

What Causes Trigeminal Neuralgia

Trigeminal neuralgia is most commonly caused by neurovascular compression of the trigeminal nerve root, typically by the superior cerebellar artery, leading to focal demyelination of nerve fibers. 1

Primary Mechanism: Neurovascular Compression

The central pathophysiology involves direct compression of the centrally myelinated portion of the trigeminal nerve root, usually at the root entry zone near the brainstem. 2 This compression causes:

• Focal demyelination of trigeminal sensory fibers with close apposition of demyelinated axons and absence of intervening glial processes 1
• Ectopic impulse generation and ephaptic conduction between adjacent demyelinated fibers, producing the characteristic electric shock-like pain 1
• Increased spontaneous nerve activity from pulsatile vascular indentation and deformity of the nerve 1

The superior cerebellar artery is the most common offending vessel, though other vascular structures including veins, aneurysms, and vertebrobasilar dolichoectasia can cause compression. 2

Secondary Causes of Trigeminal Neuralgia

When evaluating patients, you must distinguish classical trigeminal neuralgia from secondary causes that require different management:

Demyelinating Disease

• Multiple sclerosis can produce trigeminal neuralgia through brainstem demyelinating plaques affecting the trigeminal nerve nuclei or pathways 2, 1
• This necessitates brainstem imaging to identify demyelinating lesions 2

Structural Lesions Along the Nerve Course

The trigeminal nerve can be affected anywhere from brainstem to peripheral branches: 2

• Tumors: gliomas, lymphomas, metastases, epidermoid tumors (particularly at the pontocerebellar angle) 2, 3
• Vascular lesions: compressing aneurysms, arteriovenous malformations, exposed petrous internal carotid artery 2, 4
• Inflammatory/infectious processes: meningitis, encephalitis, sarcoidosis 2
• Brainstem lesions: infarction, hemorrhage 2

Anatomical Variants

• Meckel cave encephaloceles with associated vascular compression 4
• Lesions affecting the cisternal, cavernous, foraminal, or extracranial nerve segments as they traverse the Meckel cave, pterygopalatine fossa, orbit, skull base, and masticator space 2

Critical Diagnostic Distinction

You must distinguish trigeminal neuropathy from classical trigeminal neuralgia, as they have different etiologies and management approaches. 2

• Classical trigeminal neuralgia: neurovascular compression without sensory or motor deficits between attacks 2
• Trigeminal neuropathy: includes additional sensory deficits (facial numbness) or motor deficits (weakness with mastication), suggesting a structural lesion along the nerve course 2

Imaging to Identify Cause

MRI with high-resolution sequences covering the entire trigeminal nerve course is mandatory to identify the specific cause and guide treatment. 5

• Pre- and post-contrast MRI provides optimal lesion detection 5
• 3D heavily T2-weighted sequences and MRA characterize neurovascular compression 5
• Imaging must extend from brainstem nuclei through all peripheral branches 2, 5

Common Pitfall

Neurovascular contact on MRI occurs in asymptomatic individuals, so imaging findings must correlate with the patient's clinical symptoms and pain distribution. 5 Congruence between imaging and intraoperative findings ranges from 83-100%. 5