title: Radiosurgery target location and individual anatomical variation in trigeminal nerves.
abstract: OBJECTIVE
  The authors evaluated individual anatomical variations in the trigeminal nerves of patients with medically intractable trigeminal neuralgia and clarified the relationships among the variations, radiosurgical target locations, and the clinical outcomes after high-dose Gamma Knife surgery (GKS).
  
  
  METHODS
  From 2006 through 2011, the authors conducted a retrospective review of 106 cases of primary or secondary trigeminal neuralgia consecutively treated with GKS targeting the dorsal root entry zone (DREZ) for which a maximal dose of 90 Gy and a 20% isodose line to the brainstem were used. A questionnaire was used to evaluate patients' pre- and post-GKS clinical conditions. To evaluate individual anatomical variations among trigeminal nerves, the authors used 3 parameters: the length of the trigeminal nerve in the cistern (nerve length), the length of the target between the radiation shot and the brainstem (targeting length), and the ratio between nerve length and targeting length (targeting ratio).
  
  
  RESULTS
  The median length of the trigeminal nerves in the 106 patients was 9.6 mm (range 6.04-20.74 mm), the median targeting length was 3.8 mm (range 1.81-10.84 mm), and the median targeting ratio was 38% (range 13%- 80%). No statistically significant differences in pain relief and pain recurrence were detected among patients with these various nerve characteristics. However, radiation-induced facial hypesthesia correlated with nerve length and targeting ratio (p < 0.05) but not with absolute distance from the brainstem (targeting length).
  
  
  CONCLUSIONS
  In trigeminal neuralgia patients who received DREZ-targeted GKS, the rate of pain relief did not differ according to anatomical nerve variations. However, the frequency of facial hypesthesia was higher among patients in whom the nerve was longer (> 11 mm) or the targeting ratio was lower (< 36%). Adjusting the target according to the targeting ratio, especially for patients with longer nerves, can reduce facial hypesthesia and enable maintenance of effective pain control.
authors.affiliation: Division of Neurosurgery, Department of Surgery, Chi-Mei Foundation Hospital, Tainan;
authors.forename: Yi-Chieh
authors.initials: YC
authors.lastname: Hung
authors.forename: Cheng-Chia
authors.initials: CC
authors.lastname: Lee
authors.forename: Kang-Du
authors.initials: KD
authors.lastname: Liu
authors.forename: Wen-Yuh
authors.initials: WY
authors.lastname: Chung
authors.forename: David Hung-Chi
authors.initials: DH
authors.lastname: Pan
authors.forename: Huai-Che
authors.initials: HC
authors.lastname: Yang
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005157:Facial Pain / Q000209:etiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006987:Hypesthesia / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D012189:Retrospective Studies; D013126:Spinal Nerve Roots / Q000002:abnormalities / Q000601:surgery; D011795:Surveys and Questionnaires; D016896:Treatment Outcome; D014276:Trigeminal Nerve / Q000002:abnormalities* / Q000601:surgery*; D014277:Trigeminal Neuralgia / Q000473:pathology / Q000601:surgery*
keywords: BNI = Barrow Neurological Institute; DREZ = dorsal root entry zone; GKS = Gamma Knife surgery; Gamma Knife; RGZ = retrogasserian zone; radiation-induced facial numbness; radiosurgery; stereotactic radiosurgery; trigeminal neuralgia