A novel needle electrode for intraoperative fourth cranial nerve neurophysiological mapping

Area of Science:

• Neurosurgery
• Neurophysiology
• Ophthalmology

Background:

• Intraoperative mapping of the trochlear nerve (CN-IV) remains challenging due to low sensitivity and the anatomical characteristics of the superior oblique muscle (SOM).
• Conventional needle electrodes (CNEs) have limitations in recording compound muscle action potentials (CMAPs) for CN-IV.

Purpose of the Study:

• To evaluate the effectiveness of a novel needle electrode (NNE) for intraoperative mapping of the trochlear nerve (CN-IV).
• To assess the NNE's ability to record CN-IV CMAPs and differentiate them from other extraocular cranial nerves (ECNs).

Main Methods:

• NNEs were inserted into target extraocular muscles in 19 patients undergoing neurophysiological monitoring.
• CMAP amplitudes from NNEs were compared to those from CNEs.
• The study investigated the distinctiveness of CN-IV CMAPs from other ECNs and correlated mapping results with postoperative function.

Main Results:

• CN-IV CMAPs were successfully measured in 47.4% of patients using the NNE.
• The NNE recorded CMAP amplitudes approximately three times higher than CNEs.
• CN-IV CMAPs were distinguishable from other ECNs, though 4 cases experienced postoperative CN-IV dysfunction.

Conclusions:

• The study confirms the feasibility of intraoperative CN-IV mapping using an NNE inserted into the SOM.
• The NNE demonstrates potential for enhanced neurophysiological monitoring of the trochlear nerve.
• This novel electrode may also benefit other neurophysiological monitoring applications.