CPA/Cerebellopontine Angle Tumor
5th, 6th, 7th, 8th, 11th, and right cranial nerves bilaterally for a left cerebellopontine angle tumor removal
Monitoring the left 5th, 6th, 7th, 8th, 11th and right 8th cranial nerves bilaterally was carried out as part of a left cerebellopontine angle tumor removal. The 57-year-old male presents with a left-sided cerebellopontine angle tumor. Discovery of CPA tumor was incidental and presented with no related neurological deficits. For electromyographic (EMG) recordings, intramuscular needle electrodes were inserted in left masseter, lateral rectus, orbicularis oculi, orbicularis oris and trapezius muscles for trigeminal, abducens, facial and accessory nerve monitoring, respectively. The 5th, 6th, 7th and 11th cranial nerves were monitored for possible mechanical displacement, stretching and/or heating due to electrocautery during tumor removal procedures. Evoked EMG activity could also be employed to identify the location of these nerves and used to determine their function throughout the case. Specifically, a 200-microsecond square wave pulse (0.01-2.0 mAmps, 5.1 stim/sec) was used to evoke EMG activity from muscles innervated by motor cranial nerves. The stimulus was delivered to the nerve or tissue in question using a hand-held stimulating probe with the return inserted into tissue near the wound retractor. Response threshold was used primarily to predict possible neuropraxia. Auditory brain stem responses (ABRs) were also recorded to monitor the status of both 8th cranial nerves. Each ear was tested separately using an electrode montage in which subdermal needle electrodes (inverting leads) were placed, respectively, within the ear canal ipsilateral to the ear that received stimulation (A1/A2). The non-inverting lead was also a subdermal electrode placed at vertex (Cz). One-hundred microsecond (100 us) square wave pulses produced alternating rarefaction and condensation clicks of 100 dB nHL and were presented at a rate 11.3 stim/sec. Stimuli were presented alternately to each ear every 45 milliseconds. Averages were collected to at least 3000 individual trials A subdermal needle electrode place on the right shoulder served as ground. EMGs were amplified (gain=105) using differential amplifiers (Cadwell-Cascade), monitored and averages collected on a computer (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures
Monitoring the left 5th, 6th, 7th, 8th, 11th and right 8th cranial nerves bilaterally was carried out as part of a left cerebellopontine angle tumor removal. The 57-year-old male presents with a left-sided cerebellopontine angle tumor. Discovery of CPA tumor was incidental and presented with no related neurological deficits. For electromyographic (EMG) recordings, intramuscular needle electrodes were inserted in left masseter, lateral rectus, orbicularis oculi, orbicularis oris and trapezius muscles for trigeminal, abducens, facial and accessory nerve monitoring, respectively. The 5th, 6th, 7th and 11th cranial nerves were monitored for possible mechanical displacement, stretching and/or heating due to electrocautery during tumor removal procedures. Evoked EMG activity could also be employed to identify the location of these nerves and used to determine their function throughout the case. Specifically, a 200-microsecond square wave pulse (0.01-2.0 mAmps, 5.1 stim/sec) was used to evoke EMG activity from muscles innervated by motor cranial nerves. The stimulus was delivered to the nerve or tissue in question using a hand-held stimulating probe with the return inserted into tissue near the wound retractor. Response threshold was used primarily to predict possible neuropraxia. Auditory brain stem responses (ABRs) were also recorded to monitor the status of both 8th cranial nerves. Each ear was tested separately using an electrode montage in which subdermal needle electrodes (inverting leads) were placed, respectively, within the ear canal ipsilateral to the ear that received stimulation (A1/A2). The non-inverting lead was also a subdermal electrode placed at vertex (Cz). One-hundred microsecond (100 us) square wave pulses produced alternating rarefaction and condensation clicks of 100 dB nHL and were presented at a rate 11.3 stim/sec. Stimuli were presented alternately to each ear every 45 milliseconds. Averages were collected to at least 3000 individual trials A subdermal needle electrode place on the right shoulder served as ground. EMGs were amplified (gain=105) using differential amplifiers (Cadwell-Cascade), monitored and averages collected on a computer (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures