Radiation Oncology/CNS/Trigeminal neuralgia/Overview

Trigeminal Neuralgia

Epidemiology edit

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

Definition edit

  • 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 edit

  • 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 edit

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 edit

  • 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 edit

  • 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 edit

  • 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 edit

Cost-Effectiveness edit

  • 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