Trigeminal root recording in normal trigeminal function

Intraoperative Mapping of the Sensory Root of the Trigeminal Nerve in Patients with Pontocerebellar Angle Pathology

OBJECTIVE

The aim of the present study was to determine the position of the 3 sensory branches of the trigeminal nerve in the preganglionic tract using intraoperative neurophysiological mapping.

METHODS

We included consecutive adult patients who underwent neurosurgical treatment of cerebellopontine angle lesions. The trigeminal nerve was antidromically stimulated at 3 sites along its circumference with different stimulus intensities at a distance of ≤1 cm from the brainstem. The sensory nerve action potentials (SNAPs) were recorded from each main trigeminal branch (V1 [ophthalmic branch], V2 [maxillary branch], and V3 [mandibular branch]).

RESULTS

We analyzed 13 patients. The stimulation points at which we obtained the greatest number of congruous and exclusive SNAPs (SNAPs only on the stimulated branch) was the stimulation point for V3 (20.7%). The stimulation intensity at which we obtained the highest number of congruent and exclusive SNAPs with the stimulated branch was 0.5 mA.

CONCLUSIONS

Using our recording conditions, trigeminal stimulation is a reliable technique for mapping the V3 and V1 branches using an intensity not exceeding 0.5. However, reliable identification of the fibers of V2 is more difficult. Stimulation of the trigeminal nerve can be a reliable technique to identify the V3 and V1 branches if rhizotomy of these branches is necessary.

Identifying the trigeminal nerve branches for transovale radiofrequency thermolesion: "no pain, no stress"

BACKGROUND

Radiofrequency thermorhizotomy of the trigeminal nerve is a known treatment of trigeminal neuralgia. Analysis of verbal responses to electric stimulation of the trigeminal rootlets has been the only method available to localize the affected branch, but patient discomfort may lead to unreliable verbal responses, resulting in increased morbidity or even therapeutic failure. Orthodromically elicited evoked potentials of the trigeminal nerve have also been used, but their application is tedious and results may vary.

OBJECTIVE

To develop an electrophysiological method for intraoperative localization of the trigeminal nerve branches.

METHODS

A series of 55 patients under general anesthesia during radiofrequency thermorhizotomy were studied. The trigeminal nerve root was stimulated through the foramen ovale with the RF electrode. Antidromic responses were recorded from the 3 divisions of the trigeminal nerve in the face. Effectiveness rate, pain relief, recurrence, complications, and patient comfort after the procedure were analyzed.

RESULTS

Reproducible and easily obtained antidromic responses were clearly recorded in every subdivision of the trigeminal nerve in all patients. Ninety-four percent of patients experienced immediate pain relief after the procedure. The recurrence rate was 12.72%, and the surgical morbidity was 20%.

CONCLUSION

This method proved to be useful to determine the exact localization of individual subdivisions of the trigeminal nerve in anesthetized patients, making this procedure safer and more comfortable for them.

Intraoperative cranial nerve monitoring

The purpose of intraoperative monitoring is to preserve function and prevent injury to the nervous system at a time when clinical examination is not possible. Cranial nerves are delicate structures and are susceptible to damage by mechanical trauma or ischemia during intracranial and extracranial surgery. A number of reliable electrodiagnostic techniques, including nerve conduction studies, electromyography, and the recording of evoked potentials have been adapted to the study of cranial nerve function during surgery. A growing body of evidence supports the utility of intraoperative monitoring of cranial nerve nerves during selected surgical procedures.