Minimally invasive extraocular cranial nerve electromyography.

Area of Science:

• Neurosurgery
• Ophthalmology
• Neurology

Background:

• Monitoring extraocular cranial nerve (EOCN) function is crucial for skull base surgery but often limited.
• Electromyography (EMG) can detect nerve injury, but reliable compound muscle action potential (CMAP) collection is essential.
• Standard intraorbital electrodes carry a risk of ocular morbidity.

Purpose of the Study:

• To evaluate if minimally invasive 7-mm superficial needle electrodes can reliably record CMAPs compared to standard 13-mm intraorbital electrodes.
• To assess the efficacy and safety of a less-invasive approach for EOCN monitoring.

Main Methods:

• A prospective case-control study compared 7-mm superficial electrodes with 13-mm intraorbital electrodes placed in extraocular muscles.
• CMAPs were recorded and analyzed for presence, absence, and compared between the two electrode types.
• Sensitivity, specificity, and predictive values were calculated for each technique.

Main Results:

• Analysis of 429 CMAPs from 71 EOCNs revealed 106 false-positive (25%) and 17 false-negative (4%) responses with the 7-mm electrodes.
• The minimally invasive technique had a sensitivity of 91% but a specificity of only 57%.
• Transient ocular complications like edema and bruising occurred in 26 eyes; three eyes had minor complications.

Conclusions:

• The minimally invasive 7-mm EMG technique is not as reliable as the intraorbital method due to artifact contamination and false responses.
• Less-invasive techniques risk inaccurate EOCN assessment and potential postoperative morbidity.
• Intraorbital EMG monitoring remains the gold standard for reliable intraoperative EOCN assessment, prioritizing nerve function preservation.