Ninth cranial nerve stimulation for epilepsy control. Part 2: surgical feasibility in humans

To determine the anatomical and surgical feasibility of placement of a stimulator around the nerve of Hering (HN; a branch of cranial nerve nine). We previously determined the success of HN stimulation in controlling epileptiform activity in a canine model study. The present study assessed the ability to extrapolate the ease of surgical dissection and surrounding anatomy to humans.

Fifteen human cadavers (8 male, 7 female) were studied. The HN on each side was specifically evaluated in each specimen with respect to its presence, size, surgically accessible length below the mandibular angle, relationship to the internal carotid artery (ICA) and carotid bifurcation and relation to the common facial vein (CFV), thyroid cartilage (superior edge) and superior cervical ganglion (SCG).

All 15 cadavers exhibited specimens of HN bilaterally, with the nerve diameter ranging from 0.5 to 1.5 mm (mean 1.0 mm); in relation to the ICA, the HN coursed anteromedially in 60%, anteriorly in 33% and anterolaterally in 7% of cases, and appeared to distinctly emerge at the level of the carotid bifurcation in all specimens. The surgically accessible length below the mandibular angle ranged from 6 to 30 mm (mean 15 mm). Relative to the carotid bifurcation, the superior edge of the thyroid cartilage was -35 to 33 mm (mean -5.4 mm) above; the CFV, which was clearly identifiable in only two thirds of the specimens, was -10 to 15 mm (mean 3.0 mm) above; and the inferiormost portion of the SCG was 6-30 mm (mean 16.6 mm) above.

This study indicates that the HN was clearly present and surgically accessible in all human specimens. Based on the present study and our previous canine study, HN stimulation could be an important therapy for medically intractable epilepsy.