Quantitative analysis of lesion parameters in radiofrequency trigeminal rhizotomy.

A series of 144 lesions made during 32 radiofrequency rhizotomies was reviewed. The parameters of each lesion were compared with the sensory change resulting from the lesion. One-half of the lesions resulted in no sensory change, but 16.7% produced numbness in a division not predicted by stimulation. This was a barely detectable sensory change in 6% of lesions and more dense in 10%. The first lesion in a series was particularly likely to result in sensory deficit, and accounted for half of the more dense lesions not predicted by stimulation. When the threshold at which stimulation was perceived was 0.2 volts or less, a lesion was likely to produce numbness, and when it was 0.5 volts or greater, marked sensory loss did not occur. There was no apparent relationship between the likelihood of sensory change and lesion temperature or duration. Analysis of lesion temperature was made more difficult by the use of low temperatures when numbness should be easy to obtain. With careful technique, radiofrequency rhizotomy can be performed with acceptable risk of unpredicted sensory loss. Particular care should be taken during the first lesion in each procedure and when stimulation thresholds are 0.2 volts or less.