Intra-Operative electromyographic monitoring of extra-ocular motor nerves (Nn. III, VI) in skull base surgery.
BACKGROUND
Extraocular motor nerves (Nn. III, IV, VI) are at risk of damage during skull base surgery. A new recording technique was employed in 18 patients suffering from various skull base tumours in order to extend intra-operative EMG monitoring to the extra-ocular muscles.


METHODS
Selective intra-operative EMG recordings were obtained from extra-ocular muscles by placement of single-shafted bipolar needle electrodes under the guidance of B-mode ultrasound to visualise the needle tip within the target muscle in the orbital cavity.


RESULTS
Following bipolar electrical stimulation, the oculomotor nerve (N.III) was intra-operatively identified in 5 out of 7 cases, and the abducens nerve (N.VI) in 12 out of 18 cases. Postoperative (3-6 months) oculomotor nerve function remained unchanged in 5 and improved in 2 patients. No permanent deterioration was observed. Abducens nerve function deteriorated in two patients and improved in one case, but remained unchanged in 15 cases. No side effects occurred. There was neither any distinct relation of ocular motor nerve function to the kind and extent of SMA ("spontaneous muscle activity") patterns, nor could such relationship be detected with concern to neurophysiological parameters (latencies, amplitudes) of electrically evoked CMAP ("compound muscle action potentials").


CONCLUSIONS
The EMG technique proposed proved to be mainly effective as a mapping tool for intra-operative localisation and identification of ocular motor nerves in skull base surgery. However, the predictive value of conventional neurophysiological parameters for clinical outcome, seems to be rather poor. Further studies on a larger number of patients are therefore required to develop new quantification techniques which enable an intra-operative prediction of ocular motor nerve deficits. Further efforts are also necessary to extend this technique to the trochlear nerve.
Schlake
H P
HP
Department of Neurosurgery, Head Clinic, University of Würzburg, Germany.
Goldbrunner
R
R
Siebert
M
M
Behr
R
R
Roosen
K
K
D020222:Abducens Nerve Injury / Q000175:diagnosis* / Q000503:physiopathology; D000328:Adult; D004172:Diplopia / Q000175:diagnosis / Q000503:physiopathology; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004576:Electromyography / Q000295:instrumentation*; D019054:Evoked Potentials, Motor / Q000502:physiology; D005260:Female; D006801:Humans; D007431:Intraoperative Complications / Q000175:diagnosis* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000295:instrumentation*; D009046:Motor Neurons / Q000502:physiology*; D009801:Oculomotor Muscles / Q000294:innervation*; D009802:Oculomotor Nerve / Q000503:physiopathology; D061220:Oculomotor Nerve Injuries; D011183:Postoperative Complications / Q000175:diagnosis / Q000503:physiopathology; D011930:Reaction Time / Q000502:physiology; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation; D019292:Skull Base Neoplasms / Q000601:surgery*; D014321:Trochlear Nerve / Q000503:physiopathology; D061247:Trochlear Nerve Injuries