Reducing unnecessary morbidity from percutaneous thermocoagulation in the treatment of trigeminal neuralgia--part C: a starting point for a somatotopic map of the human Gasserian ganglion.

Objectives: An original method and technique has been designed to reduce the significant morbidity associated with techniques currently used for percutaneous thermocoagulation in the treatment of trigeminal neuralgia. The current report deals with the mathematical and biostatistical analysis of verbal responses gathered using such a method in an attempt, as a starting point, to establish the somatotopic organization of the human gasserian ganglion.

Method: A correspondence analysis was used to validate verbal responses. These were ordered in three 34 x 34 matrices, according the initial sequence of 34 subsegments of the face, which was based on the operative experience of one of the authors. After using a filter for the consistency of responses, and a maximum threshold below 0.5 V, 967 responses from 99 patients were selected for analysis. The frequencies obtained from each subsegment were compared, using all the possible pairwise combinations of the subsegments of the face, and the sequences were ordered using the least contradictory criterion.

Results: The incidence of each verbal response within each trigeminal division was analysed, resulting in a proposal of a sequence of 20 subsegments of the gasserian ganglion, listed from the depth to the surface.

Discussion: From the strict clinical point of view, the somatotopic map of each individual is invariant and easily analysed over long time periods. Its precise knowledge is critical for inducing smaller, properly placed lesions, in order to avoid unnecessary morbidity from percutaneous thermocoagulation in the treatment of trigeminal neuralgia. The proposed sequence of the gasserian somatotopic organization will be hopefully a useful guide for those interested in trigeminal physiological organization as well as for the therapeutic exploration of gasserian trigeminal fibers.