Trigeminal Neuralgia

Definition

Classification (ICHD-3)

Epidemiology

• Incidence: ~4 per 100,000 individuals
• Onset after age 40 in ~90% of cases; peak incidence 50-70 years
• Slightly more common in women (F:M ratio ~1.5:1)
• Rare familial cases suggest a genetic component in some families
• In younger patients, think multiple sclerosis as an underlying cause
• Goldman-Cecil Medicine; Bradley and Daroff's Neurology

Pathophysiology

• Superior cerebellar artery (most common)
• Anterior and posterior inferior cerebellar arteries
• Superior petrosal vein

• Bradley and Daroff's Neurology in Clinical Practice, p. 2498

Clinical Features

Pain Characteristics

• Quality: Electric shock-like, shooting, lancinating, stabbing
• Duration: Seconds (up to 2 minutes per episode)
• Location: V2 (cheek) and V3 (chin/lower teeth) most common; V1 (periorbital) alone is extremely rare; V2+V3 combination is the most frequent pattern
• Laterality: Unilateral; bilateral cases are rare and should raise concern for MS
• Trigger zones: Typically near the nasolabial fold; may be remote from the pain site
• Triggers: Light touch, chewing, talking, teeth brushing, cold breeze on the face
• Refractory period: After a volley, there is a period where pain cannot be re-triggered
• Attacks during sleep: Uncommon but possible

Interplay of Pain

• Most patients have only episodic pain between attacks (staccato-like volleys)
• Some develop a continuous dull interictal background pain (especially secondary TN)
• Frequent attacks may cause weight loss, dehydration, and depression

Physical Examination

• Classical TN: Neurological exam is normal - no sensory loss, intact motor function
• Red flag: Any sensory impairment or masticatory muscle weakness should prompt search for a secondary cause (this is better termed trigeminal neuropathy)
• Goldman-Cecil Medicine; Bradley and Daroff's Neurology

Diagnosis

1. Paroxysmal attacks lasting 1 second to 2 minutes
2. Pain in the distribution of one or more trigeminal nerve branches
3. Intensely sharp, stabbing, or electric shock-like quality
4. Precipitated by innocuous stimuli (touch trigger)
5. Stereotypical attacks
6. No other neurological deficits (in classical/idiopathic TN)

Investigations

• MRI of brain/posterior fossa: Recommended in all patients to rule out secondary causes (demyelinating plaques, tumors, vascular loops). High-resolution MRI and MRA can sometimes identify the offending vessel
• Blink reflex / EMG: Normal in classical/idiopathic TN
• Lab tests: Not diagnostic; check when starting carbamazepine (CBC, LFTs, sodium)

Differential Diagnosis

• Trigeminal autonomic cephalalgias (SUNCT, cluster headache) - have autonomic features
• Atypical facial pain
• Dental pathology (must be excluded first)
• Tolosa-Hunt syndrome
• Idiopathic stabbing headache
• Goldman-Cecil Medicine, p. 1086

Treatment

Medical Management

• Gabapentin (900-1800 mg/day) - favorable side-effect profile, often tried early
• Pregabalin
• Baclofen (50-60 mg/day)
• Lamotrigine (100-400 mg/day)
• Phenytoin (200-300 mg/day)
• Valproate, clonazepam, topiramate, levetiracetam

• Bradley and Daroff's Neurology, p. 2499; Goldman-Cecil Medicine

Surgical Management

1. Microvascular Decompression (MVD) - Jannetta Procedure

• Gold standard for classical TN with confirmed vascular compression
• Open posterior fossa surgery; a Teflon pad is placed between the offending vessel and the nerve
• Best long-term results: ~70-80% pain-free at 1 year, ~60-70% at 5 years
• Preserves sensory function
• A 2025 meta-analysis (PMID 40889405) examined second-line strategies for recurrent TN after MVD

2. Percutaneous Rhizotomy (Ablative procedures)

• Radiofrequency thermocoagulation (heat lesioning)
• Glycerol rhizotomy (chemical destruction)
• Balloon compression

3. Stereotactic Radiosurgery (Gamma Knife)

• Non-invasive; delivers focused radiation to the trigeminal root
• Delayed onset of pain relief (weeks to months)
• Lower morbidity; option for patients unsuitable for open surgery

4. Peripheral Nerve Blocks

• Alcohol block of peripheral trigeminal branches (infraorbital, mental/mandibular, supraorbital)
• Provides temporary relief; high relapse rate; useful for short-term control
• Bradley and Daroff's Neurology, p. 2499

Course and Prognosis

• TN has an exacerbating and remitting course over years
• Spontaneous remissions can last months to years
• With microvascular decompression, patients with vascular compression have excellent outcomes and can achieve durable remissions
• Patients on carbamazepine can often be tapered off during remission phases; re-introduction is effective when attacks recur

Key Points Summary

1. Most severe pain syndrome - described as "suicide disease" historically
2. V2+V3 distribution is the most common; V1 alone is rare
3. Trigger - light touch (allodynia in a specific zone)
4. Normal neuro exam in classical TN; sensory loss = red flag for secondary cause
5. MRI mandatory to exclude MS, tumors, vascular loops
6. Carbamazepine is first-line (~90% initial response)
7. MVD is best surgical option when vascular compression confirmed; ablative procedures for elderly/unfit patients
8. MS is the most important secondary cause in younger patients

• Bradley and Daroff's Neurology in Clinical Practice (primary reference)
• Goldman-Cecil Medicine, International Edition
• Dermatology 2-Volume Set, 5e
• EAN Guidelines on TN (2019, updated recommendations)
• Recent evidence: Botulinum toxin meta-analysis [PMID 38385501]; MVD recurrence meta-analysis [PMID 40889405] (2025)

Microvascular Decompression (MVD) - Jannetta Procedure

Overview

Indications

• Classical TN with MRI or clinical evidence of neurovascular compression
• Failure or intolerance of medical therapy (carbamazepine, oxcarbazepine)
• Patient is medically fit for posterior fossa craniotomy (generally younger patients, no major comorbidities)
• Preferred over ablative procedures when the patient is healthy enough for open surgery

Pre-operative Evaluation

• High-resolution MRI and MRA: Identifies the offending vessel, nerve morphology (atrophy/displacement), and rules out secondary causes (tumors, MS plaques)
• Arterial compression has better MVD outcomes than venous compression (meta-analysis evidence: OR = 2.72 for worse outcome with venous compression)
• BAEP (Brainstem Auditory Evoked Potential) baseline established for intraoperative monitoring

Surgical Anatomy - Key Structures

Surgical Technique

1. Patient Positioning

• Lateral decubitus (park bench) position, with the affected side up
• Alternatively, semi-sitting (Concorde) position - higher CSF drainage but risk of air embolism
• Head fixed in a Mayfield pin clamp

2. Approach - Retromastoid / Retrosigmoid Craniectomy

• A small craniotomy/craniectomy posterior to the mastoid and behind the sigmoid sinus
• Entry into the posterior fossa, just lateral to the sigmoid sinus

3. Dural Opening and Cerebellar Retraction

• The dura is opened and the cerebellum is gently retracted medially to expose the CPA cistern
• Caution: retraction stretches CN VII and VIII
• Intraoperative BAEP monitoring is mandatory - prolongation of interpeak latency between peaks I and V warns of impending cochlear nerve damage from retraction; failure to relieve retraction causes permanent hearing loss

4. Arachnoid Dissection and Nerve Identification

• The arachnoid of the CPA cistern is opened
• The trigeminal nerve is traced from the pons to Meckel's cave
• The root entry zone (REZ) - the area where the nerve enters the pons - is the focus

5. Vessel Identification and Decompression

• The offending vessel is identified (most commonly the SCA looping over or under the nerve)
• The vessel is carefully dissected away from the nerve
• A Teflon (polytetrafluoroethylene) felt pad is interposed between the vessel and the nerve to prevent re-contact
• Two techniques:
  • Interposition: Teflon pad placed between vessel and nerve (most common)
  • Transposition: Vessel is moved away and secured with suture/clip - a 2025 meta-analysis (PMID 40338347) compared these techniques for both TN and hemifacial spasm

6. When No Vessel Is Found

• If no vascular loop is identified, options include:
  • Partial sensory root section (rhizotomy)
  • Proceeding later to a radiofrequency percutaneous procedure
  • Nerve combing - for atypical TN with arachnoid adhesions

7. Closure

• Meticulous dural closure to minimize CSF leak risk
• Cranioplasty with bone flap replacement or craniectomy with abdominal fat graft

Intraoperative Monitoring

• Miller's Anesthesia, 10e, p. 5265

Outcomes

• 70% had excellent pain relief continuing at 10 years post-operatively
• General published series: ~70-80% pain-free at 1 year, ~60-70% at 5 years

• Arterial (not venous) compression
• Classical TN (not idiopathic/atypical)
• Shorter duration of TN before surgery
• V2/V3 distribution (not V1)

Advantages Over Ablative Procedures

• Bradley and Daroff's Neurology, p. 2499

Complications

Minor (Transient - resolve within 12 months)

• Dizziness, tinnitus
• Mild facial hypoesthesia / numbness
• Transient ataxia
• Diplopia
• Headache, wound pain
• Trigeminal motor weakness

Major (Permanent or life-threatening)

• NCBI Bookshelf - MVD Complications

Endoscopic vs. Microscopic MVD

• Endoscopic assistance allows visualization of hidden corners behind the nerve
• A minimally invasive refinement using endoscopic assistance (2025 series, n=154, 10-year follow-up from Neurosurg Focus) showed good pain relief with reduced complication rates
• Current trend: microscope-guided MVD with endoscopic assistance for difficult angles

Key Summary Points

1. Approach: Retromastoid/retrosigmoid posterior fossa craniotomy
2. Target: Trigeminal nerve REZ at the pons
3. Mechanism: Teflon pad between offending vessel (usually SCA) and nerve
4. Monitoring: BAEP mandatory; EMG for CN VII
5. Best outcomes: Young, fit patients; arterial compression; short TN duration
6. Outcomes: ~70% excellent pain relief at 10 years (Jannetta series)
7. Critical complication: Hearing loss from CN VIII retraction injury; prevented by BAEP monitoring
8. Advantage: Preserves sensation; no nerve destruction; treats the cause

• Bradley and Daroff's Neurology in Clinical Practice, p. 2499
• Miller's Anesthesia, 10e, p. 5265
• Schwartz's Principles of Surgery, 11e
• Endoscopic vs. microscopic MVD meta-analysis [PMID 37776679] (2023)
• Recurrent TN after MVD meta-analysis [PMID 40889405] (2025)
• Transposition vs. interposition meta-analysis [PMID 40338347] (2025)