39 Technique Pt on horizontal recumbent position Head fixed on a radiolucent head rest by adhesive bandageUnder MAC (using TCI / TIVA technique)Fluoroscopic guidanceEssential to obtain an optimal picture of foramen ovaleC-arm 45 deg caudal / cranial & deg sideways
40 Technique (cont’d)22G 10cm RF needle with a 2mm free tip inserted along the direction of radiation beam (tunnel-vision technique)N.B. beware piercing of oral mucosaNeedle advanced towards foramen ovaleOnce needle enters the foramen, a clear “give” perceivedCheck with lateral view on the depth of penetration – intersection of clivus & os petrosum
41 Technique (cont’d) Sensory Stimulation Freq : 100 HzVoltage : VThe aim : to elicit paresthesia or pain in the division of trigeminal nerve, which you wish to lesionMotor StimulationFreq : 2 HzVoltage : less than 1VIf you see contractions of masseter muscle, advance the needle deeper into the foramen ovale.
42 Technique (cont’d)Lesion mode (additional bolus of IV propofol first) :Lesion at 60 deg C for 60 secAllow to wake up after 1st lesion retest with pin prick or sensory stimulationAdjust position of needle or advance further accordinglyRe-institute GARepeat lesioning in 5 deg C increments for 60 sec eachAt each stage, allow pt to wake up & retest with pin prick or sensory stimulationCheck corneal reflex
43 ResultsLong term (years) success rates vary from 80 – 90%
44 Complications Corneal anesthesia / hyperesthesia – 13.7% Dysesthesia in the treated area 5-7%Masseter weakness 1-2%
45 Morbidity & Mortality Low morbidity Can be performed on an out-patient basisMortality has not been reported
46 What if the pain recurs ? For repeated RF To review with CT or MRI brain at intervals to exclude SOLRefer to Neurosurgery for consideration of Gamma Knife or Radiosurgery
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