Left Middle Fossa Craniotomy
Bilateral monitoring of 7th and 8th; orbicularis oculi and oris. left side for mechanical displacement, stretching and/or heating due to electrocautery of the facial nerve during skull defect repair. the right facial nerve monitored for anesthesia control.
Monitoring of the X electromyographical (EMG) 5th, 7th and 11th cranial nerves was carried out as part of a left posterior fossa craniotomy for a right acoustic schwannoma removal. The 48-year-old male presents with a 7-year history of progressive right-sided hearing loss and presently has no speech discrimination on the right. MRIs reveal a lesion characteristic of an acoustic schwannoma filling the right internal auditory canal and expanding on axial view 12x18 mm into the cerebellopontine angle, but on coronal view the maximum diameter is 32 mm. For electromyographic (EMG) recordings, intramuscular needle electrodes were inserted in the left masseter, orbicularis oculi, orbicularis oris and trapezius muscles for trigeminal, facial and accessory nerve monitoring, respectively. The above nerves were monitored for possible mechanical displacement, stretching and/or heating due to electrocautery of the 5th, 7th, and/or 11th cranial nerves during tumor removal procedures. Evoked EMG activity could also be employed to identify the location of the above 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. EMGs were amplified (gain=105) using differential amplifiers (Cadwell), monitored and collected on a computer (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures.
Localized 11th CN with stimulation, response recorded at 0.50 mAmps.
Monitoring of the X electromyographical (EMG) 5th, 7th and 11th cranial nerves was carried out as part of a left posterior fossa craniotomy for a right acoustic schwannoma removal. The 48-year-old male presents with a 7-year history of progressive right-sided hearing loss and presently has no speech discrimination on the right. MRIs reveal a lesion characteristic of an acoustic schwannoma filling the right internal auditory canal and expanding on axial view 12x18 mm into the cerebellopontine angle, but on coronal view the maximum diameter is 32 mm. For electromyographic (EMG) recordings, intramuscular needle electrodes were inserted in the left masseter, orbicularis oculi, orbicularis oris and trapezius muscles for trigeminal, facial and accessory nerve monitoring, respectively. The above nerves were monitored for possible mechanical displacement, stretching and/or heating due to electrocautery of the 5th, 7th, and/or 11th cranial nerves during tumor removal procedures. Evoked EMG activity could also be employed to identify the location of the above 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. EMGs were amplified (gain=105) using differential amplifiers (Cadwell), monitored and collected on a computer (Toshiba). Listed below is a summary of intraoperative activities pertinent to monitoring procedures.
Localized 11th CN with stimulation, response recorded at 0.50 mAmps.