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Differential Diagnosis

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1. INTRACRANIAL SPACE-OCCUPYING LESIONS (SOL)

Meningioma ⭐ (Top Diagnosis)

• Headache (from raised ICP or direct mass effect)
• Visual field defects or blurring (especially sphenoid wing or olfactory groove meningiomas pressing on optic structures)
• Frontal lobe involvement causing personality change and disinhibited/antisocial behavior
• Harrison's Principles of Internal Medicine, 22E confirms meningioma as a major cause of headache, visual changes, and behavioral symptoms

Pituitary Macroadenoma

• Classic triad: headache + bitemporal hemianopia (blurring/visual loss) + hormonal effects
• Post-menopausal status means subtle hormonal effects can be masked
• Large adenomas compress optic chiasm causing visual field defects
• Frameworks for Internal Medicine notes "headache, visual field defect - pituitary adenoma" as a classic presentation

Glioma / Brain Metastases

• Frontal lobe glioma or metastasis (breast, lung are common in elderly women) can produce all three features
• Subacute onset over weeks-months is consistent
• Breast cancer is a leading source of brain metastases in women

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2. VASCULAR CAUSES

Giant Cell Arteritis (Temporal Arteritis) ⭐

• Almost exclusively affects individuals >50 years - post-menopausal women are prime candidates
• Cardinal features: severe unilateral headache (temporal), visual disturbances (amaurosis fugax progressing to permanent loss), jaw claudication, constitutional symptoms
• Personality changes can occur from cerebral ischemia
• Goldman-Cecil Medicine and Tintinalli's Emergency Medicine both describe this pattern
• This is a medical emergency - risk of irreversible blindness

Cerebral Venous Sinus Thrombosis (CVST)

• Subacute onset headache, visual blurring (from raised ICP/papilledema), and encephalopathic/behavioral changes
• Post-menopausal women may have thrombophilic risk factors

Hypertensive Encephalopathy / PRES

• Severe uncontrolled hypertension causing headache, visual disturbances (cortical blindness), and confusion/behavioral changes

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3. NEURODEGENERATIVE / PSYCHIATRIC

Behavioral Variant Frontotemporal Dementia (bvFTD) ⭐

• Antisocial behavior and personality change are the hallmark of bvFTD, distinguishing it from Alzheimer's disease
• Bradley and Daroff's Neurology in Clinical Practice specifically describes "disinhibition and antisocial behavior" as characteristic features
• Headache is less typical here, but can coexist
• Visual symptoms less prominent unless posterior cortical involvement

Alzheimer's Disease with Behavioral Symptoms

• Behavioral and personality changes (aggression, disinhibition) can occur, especially in moderate stages
• Visual agnosia can cause apparent "blurring"

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4. METABOLIC / SYSTEMIC

Wilson's Disease (Hepatolenticular Degeneration) - if younger; less likely in elderly

• Yamada's Gastroenterology specifically notes the neuropsychiatric manifestations can include antisocial behavior, personality change, dementia - must rule out in the right setting

Hypothyroidism (Myxedema)

• Common in post-menopausal women
• Can cause: headache, slowed mentation/personality change, visual blurring (from periorbital edema or cerebellar dysfunction)

Hypercalcemia

• Causes "bones, stones, groans, and psychic moans"
• Behavioral changes (depression, psychosis, antisocial acts), headache, visual symptoms from raised calcium

Normal Pressure Hydrocephalus (NPH)

• Classic triad: cognitive decline (behavioral change), gait disturbance, urinary incontinence
• Headache less prominent but can occur

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5. CHRONIC SUBDURAL HEMATOMA

• Very common in elderly patients (cerebral atrophy allows blood to accumulate without obvious trauma)
• Presents with headache, cognitive/behavioral change, and focal neurological signs including visual disturbances
• Neuroanatomy through Clinical Cases specifically states: "chronic subdural hematoma often seen in elderly patients, presenting weeks after minor trauma" and is "a common cause of cognitive impairment in the elderly"

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Summary Table

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Key Investigations to Order

• MRI Brain with contrast - will identify SOL (meningioma, pituitary, glioma, metastases, subdural hematoma)
• ESR + CRP - markedly elevated in giant cell arteritis (ESR often >80 mm/hr)
• Temporal artery biopsy - definitive for GCA if suspected
• Thyroid function tests (TSH, T4) - hypothyroidism screen
• Serum calcium, PTH - hypercalcemia screen
• Neuropsychological testing - to characterize behavioral symptoms
• Visual field testing / fundoscopy - papilledema (raised ICP), optic disc pallor (GCA), bitemporal hemianopia (pituitary)
• Pituitary hormone panel - if pituitary adenoma suspected

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Differential Diagnosis with Points in Favour & Against

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1. MENINGIOMA ⭐ (Most Likely)

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2. GIANT CELL ARTERITIS (Temporal Arteritis) ⭐ (Must Not Miss)

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3. PITUITARY MACROADENOMA

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4. CHRONIC SUBDURAL HEMATOMA

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5. BEHAVIORAL VARIANT FRONTOTEMPORAL DEMENTIA (bvFTD)

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6. BRAIN METASTASES

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7. NORMAL PRESSURE HYDROCEPHALUS (NPH)

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8. HYPOTHYROIDISM / MYXEDEMA

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Priority Summary for This Patient

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Minimum Investigations to Narrow the Differential

1. MRI Brain with contrast - single best test; identifies meningioma, SDH, pituitary tumor, metastases
2. ESR + CRP - if giant cell arteritis suspected (ESR >80 mm/hr is highly suggestive)
3. Temporal artery biopsy - gold standard for GCA
4. Visual fields (perimetry) + fundoscopy - bitemporal hemianopia = pituitary; papilledema = raised ICP; disc pallor = GCA
5. Pituitary hormone panel (prolactin, GH, cortisol, TSH) - pituitary adenoma screen
6. TSH, Free T4 - hypothyroidism screen
7. Serum calcium - hypercalcemia causing behavioral change
8. CT chest/abdomen/pelvis - if metastases suspected, search for primary

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Differential Diagnosis: Blurring of Vision After Epidermoid Cyst Excision

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IMMEDIATE POST-OPERATIVE (Hours to Days)

1. Chemical (Aseptic) Meningitis ⭐ - Most Characteristic Complication

• During surgery, cholesterol crystals and keratin debris from the cyst contents spill into the subarachnoid space
• This triggers intense chemical/sterile inflammation of the meninges
• Schwartz's Principles of Surgery explicitly states: "Intraoperative spillage of cyst contents may lead to severe chemical meningitis... aseptic meningitis may occur due to release of irritative cyst contents into the subarachnoid space (Mollaret's meningitis)"
• Robbins Pathology confirms: "An aseptic meningitis-like picture develops following rupture of an epidermoid cyst into the subarachnoid space - CSF is sterile with neutrophilic pleocytosis"
• Blurring of vision results from raised ICP due to meningeal inflammation, or from cranial nerve VI palsy (false localizing sign), or direct optic nerve irritation

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2. Postoperative Hematoma (Surgical Site Bleed)

• Epidural, subdural, or intracerebral hematoma in the operative bed
• Mass effect compresses visual pathways depending on location:
  • Posterior fossa hematoma - obstructive hydrocephalus → papilledema → blurred vision
  • Parasellar hematoma - optic chiasm compression → bitemporal field defect
• Presents with sudden neurological deterioration in the early post-op period

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3. Cerebral Edema / Perioperative Ischemia

• Surgical manipulation of surrounding brain parenchyma causes edema
• Retraction injury to optic nerve, chiasm, or occipital/parietal cortex → visual field defects or blurring
• Vascular injury to posterior cerebral artery (PCA) or its branches → cortical blindness (occipital ischemia)
• Anterior choroidal artery injury → visual field defect

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4. Ischemic Optic Neuropathy (ION) - Perioperative

• Sabiston Textbook of Surgery: "Causes of postoperative visual loss include central retinal artery occlusion, cortical blindness, and ischemic optic neuropathy"
• Risk factors: prolonged surgery, significant blood loss, hypotension, prone positioning (though less typical for cranial surgery)
• Both anterior (AION) and posterior (PION) variants can occur
• Presents as painless visual loss, sometimes irreversible

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5. Cranial Nerve Injury (Direct Surgical Trauma)

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SUBACUTE (Days to Weeks)

6. Communicating Hydrocephalus

• Post-operative adhesions and inflammatory debris from chemical meningitis block CSF reabsorption at the arachnoid granulations
• Leads to gradually rising ICP
• Papilledema causes progressive blurring, visual obscurations (transient grayouts on Valsalva), then permanent visual field loss if untreated
• A well-recognized delayed complication after epidermoid excision

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7. Bacterial Meningitis / Post-operative Infection

• Surgical site infection ascending to meninges
• Severe meningitis with raised ICP causes papilledema and visual blurring
• Cranial nerve palsies (CN VI most vulnerable) further impair vision
• Distinguished from chemical meningitis by: fever, positive CSF culture, elevated CSF glucose consumption

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8. Cerebral Venous Sinus Thrombosis (CVST)

• Post-surgical thrombosis of dural sinuses (transverse, sigmoid, superior sagittal)
• Raises venous pressure → raised ICP → papilledema → visual blurring
• Blurring is often positional and worse in the morning
• Risk increased by dehydration, surgery, blood loss, and hypercoagulable states

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9. Subdural Hygroma / Effusion

• Post-operative CSF accumulation in the subdural space
• Causes mass effect and raised ICP
• More gradual onset of visual symptoms

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LATE / RECURRENT (Weeks to Months)

10. Tumor Recurrence / Residual Epidermoid Regrowth

• Epidermoids are notorious for incomplete excision because their capsule (squamous epithelium) is densely adherent to cranial nerves and vessels
• Residual capsule continues to produce keratin debris and slowly regrows
• Recurrent compression of optic structures as the cyst re-expands
• This is the most common reason for reoperation in epidermoid surgery
• On MRI: diffusion restriction (DWI bright) is the hallmark of epidermoid

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11. Radiation-Induced Optic Neuropathy

• Relevant if adjuvant radiotherapy was used post-excision for atypical or malignant transformation
• Delayed onset (months to years), painless progressive visual loss

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Organized Summary

By Timing

By Mechanism

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Key Investigations

1. MRI Brain (with DWI) - DWI bright = epidermoid recurrence; gadolinium enhancement = infection/meningitis; T2/FLAIR = edema/ischemia
2. CT Brain - rapid assessment for hematoma, hydrocephalus
3. Fundoscopy - papilledema (raised ICP), disc pallor (ION)
4. CSF analysis (if meningitis suspected) - chemical meningitis shows sterile neutrophilic pleocytosis; bacterial shows organisms and low glucose
5. Visual field perimetry - characterize the field defect anatomically
6. MR Venography - if CVST suspected
7. Ophthalmology review - formal assessment of ocular motility, pupil reflexes, visual acuity

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Key teaching point: The most characteristic cause of blurring of vision specifically after epidermoid excision (vs. any craniotomy) is chemical/aseptic meningitis from spillage of cyst contents - this is unique to this tumor type and is what makes epidermoid surgery technically demanding. All other causes (hematoma, hydrocephalus, CN injury) are shared with craniotomy in general.

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Trigeminal Neuralgia - Grading Systems

1. Etiological/Diagnostic Classification - what type of TN is it?
2. Pain Intensity/Outcome Grading - how severe is the pain and how well is it controlled?

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A. ETIOLOGICAL CLASSIFICATION (ICHD-3 / Maarbjerg et al. 2016)

3 Etiological Categories

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3-Level Diagnostic Certainty Grading (Neuropathic Pain Framework)

This grading acknowledges that typical classical TN (the most common form) is a clinical diagnosis - idiopathic TN without morphological nerve changes cannot reach "definite" grade without objective evidence. Triggered paroxysms allow "probable neuropathic pain" designation.

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B. ICHD-3 SUBTYPES (Clinical Phenotype)

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C. BURCHIEL CLASSIFICATION (Surgical / Neurosurgical Context)

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D. BNI PAIN INTENSITY SCORE (Outcome Grading)

• Grades I-IIIa = Success (pain free or medication free)
• Grades IIIb-V = Failure (inadequate pain control)

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E. VISUAL ANALOGUE SCALE (VAS) / NRS in TN

• 0 = no pain
• 1-3 = mild
• 4-6 = moderate
• 7-10 = severe/worst imaginable

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Summary of When Each Grading System Is Used

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Key clinical pearl: The ICHD-3 distinction between classical TN (neurovascular compression with morphological nerve changes on MRI) and idiopathic TN (no structural cause found) is not merely academic - it determines candidacy for microvascular decompression, which has the best long-term outcomes specifically in classical TN where the offending vessel can be identified and decompressed. (Bradley and Daroff's Neurology in Clinical Practice)

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BNI Pain Intensity Score for Trigeminal Neuralgia

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Interpretation

Surgical Success vs. Failure

• Grades I, II, IIIa, IIIb are collectively considered "satisfactory" outcomes in most published series
• Grades I + II + IIIa represent the "pain-free" group (the gold standard outcome)
• Grades IV + V represent treatment failure

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Why This Scale Matters

• A patient may be pain-free but still dependent on carbamazepine (Grade IIIa) - this is technically a success but not an ideal outcome
• A patient who is off all medication but has occasional tolerable pain (Grade II) is clinically better than one who is on maximum medication with some pain (Grade IIIb)
• Pure VAS/NRS scales miss the medication dimension entirely

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Application Across Procedures

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Important Notes

1. Pre-operative baseline is recorded as Grade IV or V in most operative candidates
2. The scale is applied at each follow-up visit (1 month, 6 months, 1 year, etc.) to track durability of pain relief
3. Recurrence is defined as return to Grade IV or V after achieving Grade I-IIIb post-procedure
4. Some series also record facial numbness (using a separate BNI facial numbness scale - Grades 1-3) as a complication parameter alongside the pain score

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BNI Facial Numbness Scale (Companion Scale)

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Bottom line: BNI Grade I (pain free, off all medication) is the target outcome. Grades I-IIIb are collectively "successful" outcomes in most published series. MVD achieves the highest rates of durable Grade I outcomes at 10-year follow-up compared to all other TN procedures.

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TRIGEMINAL NEURALGIA - Complete Neurosurgical Reference

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1. DEFINITION & EPIDEMIOLOGY

• Also called tic douloureux (painful twitch) - referring to the facial grimacing during attacks
• Incidence: 4-13 per 100,000/year
• Prevalence: approximately 0.1-0.2% of the population
• 90% present after age 40; incidence rises steeply with age
• Slightly more common in women (female:male ~1.5:1)
• Right side affected more commonly than left (ratio ~1.5:1)
• Rare familial cases exist - genetics may play a role in some families
• (Bradley and Daroff's Neurology in Clinical Practice)

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2. ANATOMY OF THE TRIGEMINAL NERVE

Divisions

Key Surgical Anatomy

• Gasserian (trigeminal) ganglion - located in Meckel's cave (a dural recess in the petrous apex of the temporal bone)
• All three divisions arise from the ganglion; only V3 carries motor fibers (mastication)
• Trigeminal root entry zone (REZ) - the transition zone between PNS-type myelin (Schwann cell) and CNS-type myelin (oligodendrocyte); located 2-4 mm from the pons entry point. This is the critical zone for neurovascular compression
• Foramina: V1 - superior orbital fissure; V2 - foramen rotundum; V3 - foramen ovale
• Foramen ovale is the key surgical landmark for percutaneous approaches to the gasserian ganglion

Offending Vessels (in order of frequency)

1. Superior cerebellar artery (SCA) - most common (~75% of cases)
2. Anterior inferior cerebellar artery (AICA)
3. Posterior inferior cerebellar artery (PICA)
4. Superior petrosal vein / venous compression (~10-15%)
5. Vertebral artery (in older patients with dolichoectasia)
6. Multiple vessels may be responsible

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3. PATHOPHYSIOLOGY

Neurovascular Compression Theory (Jannetta, 1967)

• An arterial or venous loop compresses the trigeminal nerve at the root entry zone (REZ)
• The pulsatile mechanical compression causes focal demyelination of primary trigeminal afferents
• Demyelination leads to ephaptic transmission (cross-talk between pain fibers and light-touch fibers) and ectopic discharge
• Even a gentle touch (light-touch fibers) triggers a barrage from pain fibers → the clinical feature of trigger zones
• Over time, this demyelination leads to axonal degeneration and sensory loss (seen in older/refractory patients)

Histopathology

• Vacuolated neurons, segmental demyelination, vascular changes in the gasserian ganglion
• Scanty or absent myelin sheaths at REZ
• Reactive gliosis at the entry zone

Why SCA most commonly?

• The SCA loops through the prepontine cistern in direct proximity to the trigeminal REZ
• Arterial elongation with age (atherosclerosis, hypertension) pushes the SCA loop into closer contact

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4. ETIOLOGICAL CLASSIFICATION (ICHD-3 / Maarbjerg 2016)

Three Categories

Note: Mere neurovascular contact (NVC) without morphological nerve change is seen in 30-40% of asymptomatic individuals - it is NOT sufficient to diagnose classical TN. The nerve must show atrophy, indentation, or dislocation.

Secondary TN - Causes

• Multiple sclerosis - most common secondary cause; demyelinating plaque at the trigeminal REZ in the pons
• CPA tumors - vestibular schwannoma, meningioma, epidermoid cyst
• Arteriovenous malformation (AVM) in the posterior fossa
• Skull base tumors - meningioma, chordoma
• Brainstem infarction - pontine lacunar infarct
• Herpes zoster - rarely causes typical paroxysmal TN
• Lyme disease, sarcoidosis - rare

Clinical Red Flags Suggesting Secondary TN (MUST investigate with MRI)

• Age <40 years
• Bilateral TN (think MS)
• Sensory loss in the trigeminal distribution
• Motor weakness (V3 - masticatory muscle weakness or wasting)
• Corneal reflex abnormality
• Other cranial nerve palsies
• History of MS or known intracranial neoplasm

Burchiel Surgical Classification

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5. CLINICAL FEATURES

Cardinal Features (ICHD-3 Diagnostic Criteria)

1. Recurrent paroxysms of unilateral facial pain
2. Distribution strictly in one or more divisions of CN V
3. Duration: fraction of a second to 2 minutes
4. Electric shock-like, shooting, stabbing, or sharp quality
5. Severe intensity
6. Precipitated by innocuous stimuli (trigger zones)
7. No radiation beyond the trigeminal distribution

Trigger Zones & Stimuli

• Nasolabial fold (most common trigger zone)
• Cheek, lip, gum, teeth, tongue
• Trigger stimuli: chewing, talking, brushing teeth, washing face, cool breeze, smiling
• Triggers are innocuous (non-painful) - this is diagnostically important
• There is typically a refractory period after each attack during which the pain cannot be triggered

Division Involvement (frequency)

• V2 + V3 - most common combination (~40%)
• V3 alone (~20%)
• V2 alone (~17%)
• V1 alone - extremely rare (<5%); if present, consider secondary cause
• All three divisions (~14%)

Pain-Free Interval

• Classical TN has remissions lasting weeks to months, especially early in the disease
• With time, remissions become shorter and eventually disappear
• "Status trigeminicus" - prolonged attacks without remission, may cause dehydration and weight loss

Physical Examination

• Neurologically NORMAL in classical TN
• No sensory loss, intact corneal reflex, intact motor function
• Any abnormality on exam = secondary TN until proven otherwise

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6. DIAGNOSTIC WORKUP

MRI (Mandatory for All New Diagnoses)

• Sequence of choice: 3D CISS (Constructive Interference in Steady State) or FIESTA at 3T
• These sequences give high resolution of the cisterns with excellent CSF-nerve contrast
• What to look for:
  • Neurovascular contact at the REZ
  • Morphological changes: root atrophy, indentation, dislocation (needed for classical TN diagnosis)
  • MS plaques (T2 FLAIR)
  • CPA tumors (gadolinium-enhanced T1)
  • Brainstem abnormalities
• MRI should be done with gadolinium contrast to assess enhancement

Neurophysiological Studies

• Blink reflex - tests trigeminal afferent and facial efferent pathways; abnormal in secondary TN
• Trigeminal SEPs (somatosensory evoked potentials) - may show prolonged latencies in MS-related TN
• MR-angiography (MRA) - can delineate offending vessel but less sensitive than surgical exploration
• DTI (Diffusion Tensor Imaging) - research tool; shows microstructural changes in trigeminal root

Diagnostic Certainty Grading (Neurology 2016)

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7. MEDICAL MANAGEMENT

First-Line Drugs

• Response to carbamazepine is so characteristic that it supports the diagnosis - failure to respond should prompt reassessment
• Initial response rate >70%; however, up to 50% develop tolerance or intolerable side effects over time

Second-Line Drugs

Acute Attack Management

• IV fosphenytoin 15-20 mg PE/kg IV - most rapid pharmacological option
• Local anesthetic block of peripheral branch (e.g., infraorbital, mental nerve)
• Topical ophthalmic anesthetic (proparacaine) applied to conjunctival sac - provides hours to days of relief

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8. SURGICAL MANAGEMENT

Decision Framework

TN refractory to ≥2 adequately trialed medications
          ↓
Is patient medically fit for craniotomy?
     YES                    NO / elderly / comorbidities
      ↓                              ↓
Is MRI positive for                Percutaneous procedure
neurovascular compression?         or Gamma Knife
   YES        NO
    ↓          ↓
   MVD    Consider MVD with intraop  
          RTz if no vessel found, or 
          percutaneous/GKS

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A. MICROVASCULAR DECOMPRESSION (MVD) - Jannetta Procedure

Patient Selection

• Young (ideally <70 years), medically fit patient
• Classical TN (MRI evidence of neurovascular compression with morphological change)
• Burchiel TN Type 1 (episodic > 50%)
• Failed medical therapy
• No prior ablative procedures (relative - prior procedures increase dysesthesia risk)

Surgical Approach

• Retrosigmoid (retromastoid) craniotomy - typically 3 cm craniectomy/craniotomy behind the mastoid
• Position: lateral (park bench) or semi-sitting
• Burr hole placed 1 cm posterior to the sigmoid sinus, 1 cm below the transverse sinus
• Opening of the cisterna magna - CSF drainage for brain relaxation; avoids retraction
• Cerebellum is gently retracted medially to expose the posterior fossa

Intraoperative Steps

1. Enter the prepontine cistern and expose the trigeminal nerve along its course from the pons to Meckel's cave
2. Identify the neurovascular conflict - note the offending vessel (SCA, AICA, vein), the site (usually REZ), and severity (atrophy, indentation)
3. Dissect the vessel away from the nerve using a dissector - minimize traction on CN VII/VIII
4. Place Teflon felt (PTFE) pledgets between the nerve and the vessel - the Teflon acts as a permanent spacer
5. Alternatively, the vessel can be mobilized and secured to the dura with a sling suture
6. If no vascular compression found: consider partial sensory rhizotomy (cut 50% of nerve fibers - pain fibers in superior portion)
7. Layered watertight closure; cranioplasty

Intraoperative Monitoring

• BAER (brainstem auditory evoked responses) - mandatory; monitors CN VIII and detects cochlear ischemia
• Facial nerve EMG - monitors CN VII
• Trigeminal evoked potentials - research use

Outcomes (Jannetta's Series - 1155 patients, NEJM 1996 - landmark study)

• 70% pain-free at 10 years
• Initial pain relief: >90%
• Recurrence rate: ~20-30% at 10 years
• BNI Grade I-II at 10 years: ~70%
• Best outcomes: Classical TN + arterial compression + no prior procedures + younger age

Complications of MVD

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B. PERCUTANEOUS PROCEDURES ON THE GASSERIAN GANGLION

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B1. Radiofrequency Thermocoagulation (RF Rhizotomy)

• Electrode inserted through cannula, temperature-controlled RF current heats the ganglion/root to 60-80°C for 60-90 seconds
• Higher temperatures produce more sensory loss and longer pain relief
• Pain relief: 93% initially; recurrence ~20% at 5 years
• Can be repeated on recurrence
• Complications: facial numbness (intentional - marker of success), corneal anesthesia (V1 lesion → risk of neuroparalytic keratitis), anesthesia dolorosa, masticatory weakness (if motor root involved), carotid injury, meningitis

B2. Percutaneous Balloon Compression (Mullan's Procedure)

• Fogarty catheter inserted through foramen ovale; balloon inflated in Meckel's cave at 1 atmosphere for 1 minute
• Pressure compression produces selective injury to large myelinated Aβ fibers (light touch, trigger fibers) while sparing unmyelinated C fibers and corneal afferents
• Particularly preferred when V1 is involved (lowest risk of corneal anesthesia of all percutaneous procedures)
• Also preferred for elderly patients and those who cannot cooperate (requires brief general anesthesia)
• Pain relief: ~90% initially; recurrence 20-30% at 2-3 years (higher than RF)
• Characteristic pear-shaped balloon in Meckel's cave on fluoroscopy confirms correct position
• Complications: transient masticatory weakness (very common), facial numbness, bradycardia/hypotension (trigeminocardiac reflex during inflation)

B3. Percutaneous Glycerol Rhizotomy (Hakanson's Procedure)

• Anhydrous glycerol (0.2-0.4 mL) injected into the trigeminal cistern (Meckel's cave)
• Neurotoxic glycerol causes selective demyelination
• Patient must remain sitting for 2 hours post-injection to prevent glycerol from spreading
• Least reliable of the three percutaneous procedures; lower pain relief rates (~80-85%)
• Lowest rate of facial numbness and dysesthesia
• Complications: facial numbness, meningitis (rare), corneal anesthesia, recurrence (highest rate)

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Comparison of Percutaneous Procedures

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C. STEREOTACTIC RADIOSURGERY (Gamma Knife / CyberKnife / Linear Accelerator)

Gamma Knife Radiosurgery (GKRS)

• Single high-dose radiation (70-90 Gy at 50% isodose) delivered to the trigeminal nerve at the REZ (4-5 mm target)
• Mechanism: axonal demyelination from radiation damage
• No anesthesia required - completely non-invasive
• Onset of pain relief delayed: 4-8 weeks to months (radiation effect)
• Initial pain relief: 80-90% (BNI I-IIIb)
• BNI Grade I (pain free, off medication): 50-70% at 1 year; drops with time
• Recurrence rate: 30-40% at 3 years (highest of all surgical modalities)
• Facial numbness: 10-30% (delayed, progressive)
• Dysesthesia risk increases in patients who previously had other surgical procedures

Indications for Radiosurgery

• Elderly or medically unfit for surgery
• No MRI evidence of neurovascular compression (idiopathic TN)
• Patient preference for non-invasive option
• Prior failed procedures
• MS-associated TN (MVD less effective in MS)
• Anticoagulation cannot be stopped

Limitations

• Delayed onset - not suitable for acute severe pain
• Highest recurrence rate of all surgical interventions
• Repeat radiosurgery possible but higher risk of dysesthesia
• Less effective than MVD for long-term pain control

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D. PERIPHERAL PROCEDURES

Peripheral Nerve Alcohol Block

• 0.5-0.75 mL absolute alcohol injected into the peripheral branch:
  • Infraorbital nerve - for V2
  • Mental/mandibular nerve - for V3
  • Supraorbital nerve - for V1
• Pain relief: 70-80% initially
• Duration: 6-18 months - temporary
• Can be repeated 1-2 times; subsequent injections less effective
• Advantages: simple, low morbidity, temporary sensory loss
• Used as a temporizing measure or when patient refuses more definitive procedures

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E. OTHER EMERGING SURGICAL OPTIONS

Neuromodulation

• Motor cortex stimulation (MCS) - reserved for refractory cases, particularly post-ablation dysesthesia
• Deep brain stimulation - experimental
• Spinal cord stimulation - not effective for TN

Trigeminal Nerve Stimulation (Peripheral)

• Transcutaneous supraorbital/infraorbital nerve stimulation - emerging evidence; non-invasive

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9. SURGICAL DECISION MAKING - ALGORITHM

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10. OUTCOMES COMPARISON ACROSS ALL MODALITIES

Bottom line: MVD provides the longest duration of pain relief and preserves facial sensation - it is the preferred operation for eligible patients. The major advantage of MVD is that it addresses the underlying mechanism rather than destroying nerve function. All ablative procedures trade pain relief for some degree of facial numbness.

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11. SPECIAL SITUATIONS

Bilateral TN

• Occurs in ~3% of cases; bilateral TN is a strong pointer toward MS
• Manage the more symptomatic side first
• MVD can be performed bilaterally at staged procedures

TN in Multiple Sclerosis

• Occurs in ~2-4% of MS patients
• Due to demyelinating plaque at trigeminal REZ rather than vascular compression
• MVD has lower success rates (vascular compression may coexist, but the plaque persists)
• GKRS or percutaneous procedures preferred

Failed MVD

• Most common reason for failure: missed or inadequate decompression, venous compression overlooked, wrong diagnosis
• Re-exploration: 60-70% success if initial partial response; lower if no response
• Alternative: percutaneous procedure or GKS

Anesthesia Dolorosa (Post-ablative Deafferentation Pain)

• Agonizing burning pain in a numb area - the worst complication of ablative procedures
• More common after repeated ablative procedures or excessive RF coagulation
• Virtually impossible to treat - MCS (motor cortex stimulation) may help
• Prevention is key - avoid excessive nerve destruction, especially in young patients

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12. PROGNOSTIC FACTORS

Favorable for MVD

• Classical TN (Type 1)
• Arterial compression (better than venous)
• Younger age
• No prior procedures
• Shorter duration of disease
• Right-sided TN
• SCA as offending vessel

Unfavorable for any procedure

• TN Type 2 (constant background pain)
• Bilateral TN
• MS-related TN
• Prior multiple ablations (anesthesia dolorosa risk)
• Absence of neurovascular compression on MRI

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13. BNI PAIN INTENSITY SCORE (Outcome Measurement)

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