Subpially recorded cervical spinal cord evoked potentials in syringomyelia.

Intraoperative spinal cord evoked potentials (SCEPs) to median nerve stimulation were detected subpially from the dorsal surface of the cervical spinal cord in 5 patients with cervical syringomyelia and were compared to normal SCEPs obtained from the unaffected side in 6 patients during intraoperative monitoring of dorsal root entry zone lesion. Normal SCEP began with a positive deflection P9 and a complex N11/N13 with several low amplitude short potentials superimposed on the N11/N13. The complex was followed by a second negative potential N2 and a late prolonged positivity, P. In the 4 patients in whom median nerve somatosensory evoked potentials (SEPs) were present preoperatively, SCEP consisted of the N11 potential and the following low amplitude short (LAS) potentials, while the N13 wave was missing. In the fifth patient, in whom the preoperative median nerve SEP was missing, SCEPs were of much lower amplitude and shorter duration than normal. The potentials N2 and P were not recorded in any of our 5 patients. Changes in N13 wave, N2 and P potentials noted in syringomyelia were presumed to be the result of destruction of the spinal cord dorsal horn neurons caused by spinal cord central cavitation.     

En bloc resection of an intracavernous oculomotor nerve schwannoma and grafting of the oculomotor nerve with sural nerve. Case report and review of the literature

A case in which a left oculomotor nerve schwannoma treated by en bloc resection of the lesion and grafting of the oculomotor nerve with sural nerve is presented. Recovery of nerve function was partial, but useful and cosmetically good. The last follow-up examination performed 2 years after surgery revealed recovery of function in the elevator muscle of the upper eyelid, together with slight vertical movement of the eye.     

Electrical thresholds for biomechanical response in the ankle to direct stimulation of spinal roots L4, L5, and S1. Implications for intraoperative pedicle screw testing

STUDY DESIGN: A comparison of electrical thresholds for biomechanical response in the ankle and for evoked electromyographic signals from specific leg muscles during intraoperative extradural direct stimulation of roots L4, L5, and S1. OBJECTIVE: To determine whether a biomechanical response in the ankle to direct root stimulation occurs before evoked electromyographic signals and to determine differences in electrical excitability of the roots circumferentially. SUMMARY OF BACKGROUND DATA: Stimulus intensities of 1.2-5.7 mA are reported to evoke electromyographic response in corresponding muscles to direct stimulation of normal roots. Stimulus intensities of 6-8 mA were suggested to detect bony pedicular compromise by stimulation of a hole or a screw during pedicle instrumentation. Electrical thresholds of three-dimensional torque response in the ankle to direct root stimulation have not yet been evaluated and compared with thresholds of evoked electromyogram. METHODS: Direct monopolar stimulation of the surgically exposed roots L4, L5, and S1 was performed from different sites around the root by a cuff multielectrode. Biomechanical response was measured as an isometric torque in the ankle at each of three orthogonal axes. Compound muscle action potentials (CMAPs) from root-specific muscles were detected by a pair of surface or wire electrodes. RESULTS: Mean threshold for biomechanical response in the ankle to stimulation of roots L4, L5, and S1 was 0.72 +/- 0.39 mA and for CMAP response was 1.09 mA +/- 0.36 (N = 13). Thresholds for biomechanical responses were significantly lower than for CMAP responses (P = 0.0004; paired t test). Nerve roots were electrically most excitable on their ventral aspects. CONCLUSION: The biomechanical response in the joint to root stimulation can be used to test all root-related muscles crossing that joint at their individual innervation pattern and their residual innervation and to detect electrical excitation of the root at electric thresholds lower than those for detecting CMAP from single standard root-specific muscle. However, this method does not provide sufficient root specificity. It will be valuable in conjunction with multimodality neurophysiologic monitoring of the roots for earlier and more reliable detection of pedicle bone breakthrough or integrity. Further clinical investigations are suggested.     

Cellular dumbbell schwannoma of the hypoglossal nerve presenting without hypoglossal nerve palsy

A rare case of cellular schwannoma of the hypoglossal nerve, with intraspinal extension, presenting without any recognisable impairment of the function of the hypoglossal nerve is presented.