Intra-operative electrooculographic monitoring to prevent post-operative extraocular motor nerve dysfunction during skull base surgeries.
OBJECTIVE
Intra-operative identification and preservation of extraocular motor nerves is one of the main goals of surgeries for skull base tumours and this is done by monitoring the extraocular movement (EOM). Intra-operative electromyographic monitoring has been reported, but it is a complex and skilful process. Electrooculography (EOG) is a simple and reliable technique for monitoring EOMs. We aimed to assess the utility of EOG monitoring in preventing extraocular motor nerve dysfunction during skull base surgeries.


METHODS
In this retrospective cohort study, intra-operative EOG recordings were obtained using disposable needle electrodes placed on the periorbital skin and the polarity of the waves noted for interpretation. Triggered as well as continuous EOG responses were recorded after monopolar electrode stimulation of cranial nerve (CN) during tumour removal which helped the surgeon with careful dissection and avoiding potential nerve injuries.


RESULTS
Of the 11 cases monitored, oculomotor and abducent nerves were identified in all cases, but the trochlear nerve could not be definitively identified. Six patients had no pre- or post-operative extraocular motor nerve dysfunction. The other five patients had pre-existing deficits before surgery, which recovered completely in two, significantly in one, and did not improve in two patients at 3-6 months follow-up.


CONCLUSIONS
EOG was found to be a simple and reliable method of monitoring extraocular motor nerves (CNs III and VI) intraoperatively.
Department of Anaesthesia, Toronto Western Hospital, Toronto, Canada.
Veena
V
Sheshadri
Department of Anaesthesia and Perioperative Medicine, Schulich School of Medicine and Dentistry, London, Ontario, Canada.
Suparna
S
Bharadwaj
Department of Neurosurgery, Vikram Hospitals, Bengaluru, Karnataka, India.
B A
BA
Chandramouli
Extraocular motor nerves; extraocular movements; intra-operative electrooculographic monitoring; skull base surgery