title: Cyberknife stereotactic radiosurgical rhizotomy for trigeminal neuralgia: anatomic and morphological considerations.
abstract: OBJECTIVE
  To search for correlations between specific anatomic, geometric, and morphological properties of the trigeminal nerve and the success of radiosurgical treatment and elimination of facial hypesthesia as a complication.
  
  
  METHODS
  Forty-six patients with at least 6 months of follow-up after CyberKnife (Accuray, Inc., Sunnyvale, CA) rhizotomy were retrospectively reviewed. Patients treated after 2004 were entered into the study after congruity in treatment parameters was established. Anatomic variations regarding the length of each nerve segment and angle of trigeminal nerve takeoff from brainstem to Meckel's cave in the axial and sagittal planes were studied. Dose distribution to surrounding critical structures (brainstem and trigeminal ganglion) was measured. After spatial relationships of involved structures and dose distributions were recorded, their relationship to treatment success, failure, or complication (primarily facial numbness) was tabulated.
  
  
  RESULTS
  Forty-five patients (97.2%) experienced pain relief immediately or within weeks. Thirty-four patients maintained excellent outcome. Some degree of facial numbness developed in 18 patients (39.1%) and was mild in 11 of them (Grade II on the Barrow Neurological Institute scale). Patients with a sagittal-angle trigeminal nerve takeoff from the brainstem in the range of 150 to 170 degrees measured from the horizontal plane had a more favorable outcome (P = 0.03) than patients with less obtuse relationships to the proximal nerve origin. Patients who received higher doses of radiation to the brainstem/dorsal root entry zone of the trigeminal nerve experienced a higher rate of posttreatment facial anesthesia.
  
  
  CONCLUSIONS
  There may be important anatomic and geometric relationships between the treated trigeminal nerve and surrounding critical structures that warrant pretreatment target volume placement and dose distribution considerations.
authors.affiliation: Department of Neurosurgery, Stanford University Medical Center, Stanford, California 94305, USA.
authors.forename: John D
authors.initials: JD
authors.lastname: Borchers
authors.forename: Hee-Jin
authors.initials: HJ
authors.lastname: Yang
authors.forename: Gordon T
authors.initials: GT
authors.lastname: Sakamoto
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Howes
authors.forename: Gaurav
authors.initials: G
authors.lastname: Gupta
authors.forename: Steven D
authors.initials: SD
authors.lastname: Chang
authors.forename: John R
authors.initials: JR
authors.lastname: Adler
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D006987:Hypesthesia / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000009:adverse effects; D012189:Retrospective Studies; D019051:Rhizotomy / Q000379:methods*; D016896:Treatment Outcome; D014276:Trigeminal Nerve / Q000033:anatomy & histology*; D014277:Trigeminal Neuralgia / Q000601:surgery*