Radiation Oncology/CNS/Trigeminal neuralgia/Overview

Trigeminal Neuralgia

Epidemiology

• 15,000 new cases in US per year; incidence 4/100,000 - 5/100,000
• Majority of idiopathic TN after age 50

Definition

• International Headache Society
  • Classical TN (also called Idiopathic, or tic douloureux)
    • A) Paroxysmal attack lasting from fraction of a second to 2 minutes, affecting one or more of the trigeminal nerve divisions
    • B) One of the two following: 1) intense, sharp, superficial, stabbing or 2) precipitated from trigger areas or by a trigger factor
    • C) Stereotyped in the individual patient
    • D) No other neurological deficits
    • E) Not attributed to another disorder
  • Symptomatic TN (also called Secondary)
    • Symptoms indistinguishable from Classical TN but caused by a demonstrable structural lesion (e.g. neuroma, vascular compression)

Signs and symptoms

• Idiopathic has five classical features:
  • Paroxysmal
  • Provokable
  • Unilateral
  • Confined to the trigeminal nerve distribution
  • Unassociated with gross trigeminal motor or sensory loss.
• Atypical TN is any pain that lacks the 5 classical features.
• Multiple sclerosis-associated TN similar pain as idiopathic, but in the setting of MS

• Typically does not wake patient up at night
• Unilateral in most cases, if bilateral then not simultaneously
• Trigger zones in distribution of CN V, include light touch, chewing, talking, brushing teeth, cold air, smiling/grimacing

Pain Scales

Barrow Neurological Institute (BNI)

Grade I	no pain, no medication
Grade II	occasional pain, no medication
Grade IIIa	no pain, medication
Grade IIIb	pain, medication controlled
Grade IV	pain, not well controlled
Grade V	no pain relief

Marseille scale

Class I	no pain, no medication
Class II	no pain, medication
Grade III	>90% pain frequency reduction
Grade IV	>50% pain frequency reduction
Grade V	no significant pain relief
Grade VI	pain worsening

Etiology

• Idiopathic TN
  • Compression of trigeminal nerve by aberrant artery or vein suspected in 80-90% of cases
  • Resulting demyelination somehow triggers TN (possibly via ephaptic cross-talk between fibers mediating light touch and pain)
  • Also evidence for central pain mechanisms (refractory period after episode, trans of pain after single stimulus, latency from stimulus to onset)
• Secondary TN
  • Caused by other structural compressions (e.g. vestibular schwannoma, meningioma, epidermoid cyst, aneurysm, AVM)

• Oregon, 2004 PMID 15540931 -- "Pathophysiology of trigeminal neuralgia: new evidence from a trigeminal ganglion intraoperative microneurographic recording. Case report. (Burchiel KJ, J Neurosurg. 2004 Nov;101(5):872-3.)
  • Intraop recordings suggest TN pain generated by an abnormal discharge within peripheral NS, both in trigeminal ganglion neurons and/or the nerve itself

Anatomy

• Trigeminal nerve (CN V) supplies sensory to the face, and sensory and motor to muscles of mastication
  • V1 - Ophthalmic
  • V2 - Maxillary
  • V3 - Mandibular

• Nerve exits at midlateral surface of the pons
• Meckel's cave - gasserian ganglion (sensory ganglion), located 2 cm anterior to trigeminal root entry zone.

Imaging

• Thin slice (1mm) MRI/MRA to rule out structural lesions. Sensitivity and specificity for identifying vascular compression 89% and 50%

• Tufts
  • 2006 PMID 16436823 -- "Nerve atrophy in severe trigeminal neuralgia: noninvasive confirmation at MR imaging--initial experience." (Erbay SH, Radiology. 2006 Feb;238(2):689-92.)
    • 31 patient MRIs reviewed. Mean diameter on symptomatic side 2.11 mm vs. 2.62 mm (SS). Mean cross-sectional area 4.50 mm2 vs. 6.28 mm2 (SS)
  • 2005 PMID 15662790 -- "Targeting the cranial nerve: microradiosurgery for trigeminal neuralgia with CISS and 3D-flash MR imaging sequences." (Zerris VA, J Neurosurg. 2005 Jan;102 Suppl:107-10.)
    • Multiple imaging sequences evaluated. CISS/3D-Flash preferred method

• MC Wisconsin PMID 16029818 -- "Effect of image uncertainty on the dosimetry of trigeminal neuralgia irradiation." (Jursinic PA, Int J Radiat Oncol Biol Phys. 2005 Aug 1;62(5):1559-67.)
  • Conclusion: uncertainty of target by MRI >2x than by CT. 4&8 mm collimator higher isodose line than 4mm collimator

• UCLA PMID 15730595 -- "Three-dimensional fast imaging employing steady-state acquisition magnetic resonance imaging for stereotactic radiosurgery of trigeminal neuralgia." (Chavez GD, Neurosurgery. 2005 Mar;56(3):E628; discussion E628.)
  • Evaluation of 3-D-FIESTA sequence in 15 patients. 3-D-FIESTA sequence successfully demonstrated the trigeminal complex (root entry zone, trigeminal ganglion, rootlets, and vasculature) in 14 patients (93.33%). The 3-D-FIESTA sequence also allowed visualization of the branches of the trigeminal nerve inside Meckel's cavity.
  • Conclusion: SRS targeting of specific trigeminal branches may be feasible

• Rosewell Park PMID 11733329 -- "Focal enhancement of cranial nerve V after radiosurgery with the Leksell gamma knife: experience in 15 patients with medically refractory trigeminal neuralgia." (Alberico RA, AJNR Am J Neuroradiol. 2001 Nov-Dec;22(10):1944-8.)
  • Retrospective. 15 patient MRIs. RT dose 35-45 Gy at 50% isodose line. Mean time to follow-up imaging 61 days
  • Target enhancement in 10/15; remaining 5 had RT dose 35 Gy

Treatment

• Please see the treatment and retreatment pages

Cost-Effectiveness

• Mayo
  • 1999-2001 PMID 15951649 -- "A prospective cost-effectiveness study of trigeminal neuralgia surgery." (Pollock BE, Clin J Pain. 2005 Jul-Aug;21(4):317-22.)
    • Prospective, nonrandomized. 126 patients (MVD 33, GR 51, SRS 69)
    • Outcomes (6 months, 24 months): MVD (85%, 78%) vs. GR (61%, 55%) vs. SRS (60%, 52%). MVD > GR = SRS
    • Cost per quality adjusted pain-free year: MVD $8174 vs. GR $6342 vs. SRS $8269
  • PMID 14677455 -- "CSNS Resident Award: the economics of trigeminal neuralgia surgery." (Ecker RD, Clin Neurosurg. 2003;50:387-95.)
    • No abstract