ABSTRACT
Surgical manipulation during skull base surgeries places various cranial nerves (CN) at risk, including the nerves innervating the extraocular muscles. It could be very challenging for the surgeon to identify these cranial nerves due to the distortion of the normal anatomy by the tumors. Despite the recent advancement in technology, surgeries involving the third, fourth, fifth, and sixth cranial nerves still carry a risk of temporary or permanent paralysis of the muscles supplied by these cranial nerves. Intraoperative Neurophysiological Monitoring (IONM) with spontaneous and triggered electromyography (EMG) can help in guiding the surgeon in locating the nerves and avoiding any injury to them during the resection. IONM for extraocular cranial nerves requires highly skilled personnel with knowledge of anatomy and expertise in the placement of the electrodes. Benign tumors of the nerve sheath that arise from the perineural Schwann cells are known as schwannomas. Various cranial nerves might be involved in schwannomas of the head and neck. Trigeminal schwannomas are rare tumors. In this report, we describe the setup and stimulation technique and parameters as well as the benefits of utilizing IONM during the aggressive resection of a trigeminal schwannoma. The main purpose of utilizing IONM during these high-risk surgical procedures is to minimize any intraoperative damage to the neural structures involved.
ABSTRACT
INTRODUCTION: Bowel and bladder function are at risk during tumor resection and other surgeries of the conus, cauda equina, and nerve roots. This study demonstrates the ability to acquire triggered electromyography (t-EMG) from the external urethral sphincter (EUS) muscles by utilizing a urethral catheter with an electrode attached. METHODS: A retrospective analysis of neurophysiological monitoring data from two medical centers was performed. Seven intradural tumors and three tethered cord release surgeries that used urethral sphincter electrodes to record t-EMG were included in the analysis. The patients consisted of five females and five males with ages ranging from eight months to 67 years (median: 49 years). Our neuromonitoring paradigm included upper and lower extremity somatosensory evoked potentials (SSEPs) and transcranial electrical motor evoked potentials (TCeMEPs), as well as spontaneous and triggered electromyography (EMG) from the external anal sphincter (EAS), EUS muscles and lower extremity muscles bilaterally. A catheter with urethral electrodes attached was used for recording spontaneous electromyography (s-EMG), t-EMG, and TCeMEPs from the skeletal muscle of the EUS. Train of four (TOF) was also recorded from the abductor hallucis muscle as well for monitoring the level of muscle relaxant. RESULTS: We were able to successfully record t-EMG responses from the EUS muscles in all patients (100%). It is worthy to note that only one patient presented preoperatively with bladder incontinence, urgency, and frequency. Almost immediately in the postoperative phase, the patient's frequency and urgency improved, and the bladder function normalized within two weeks of having the tumor removed. CONCLUSIONS: In this small series, we were able to acquire t-EMG in 100% of patients when recorded from the EUS using a urethral catheter with electrodes built into it. T-EMGs can be attempted in surgeries that put the function of the pelvic floor at risk. More study is needed to establish better statistical methods, better modality efficacy, and a better understanding of intraoperative countermeasures that may be employed when an alert is encountered to prevent impending neurological sequelae.
