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Colette Boëx, Shahan Momjian and Karl Schaller

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Eveline M. Gutzwiller, Ivan Cabrilo, Ivan Radovanovic, Karl Schaller and Colette Boëx

OBJECTIVE

The goal of this study was to determine the performance of intraoperative visual evoked potentials (VEPs) in detecting visual field changes.

METHODS

Assessments of VEPs were performed with simultaneous retinal responses by using white light-emitting diodes protected from scialytic microscope lights. The alarm criterion was a reproducible decrease in amplitude of the VEP P100 wave of 20% or more. Visual fields were assessed preoperatively and 1 month postsurgery (Goldmann perimetry).

RESULTS

The VEPs were analyzed for 29 patients undergoing resection of a brain lesion. In 89.7% of patients, steady VEP and retinal responses were obtained for monitoring. The absence of alarm was associated in 94.4% of cases with the absence of postoperative visual changes (specificity). The alarms correctly identified 66.7% of cases with any postoperative changes and 100% of cases with changes more severe than just a discrete quadrantanopia or deterioration of an existing quadrantanopia (sensitivity, new diffuse deterioration < 2 dB). In 11.5% of patients, a transitory VEP decrease with subsequent recovery was observed without postoperative defects.

CONCLUSIONS

Intraoperative VEPs were performed with simultaneous recording of electroretinograms, with protection from lights of the operating room and with white light-emitting diodes. Intraoperative VEPs were shown to be reliable in predicting postoperative visual field changes. In this series of intraaxial brain procedures, reliable intraoperative VEP monitoring was achieved, allowing at minimum the detection of new quadrantanopia. The standardization of this technique appears to be a valuable effort in regard to the functional risks of homonymous hemianopia.

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Arthur R. Kurzbuch, Benedict Rilliet, Maria-Isabel Vargas, Colette Boex and Enrico Tessitore

The authors report the case of a 58-year-old man presenting with a 3-year history of clinical signs of progressive cervical spondylotic myelopathy (CSM). Magnetic resonance imaging showed a severe stenosis of the cervical spinal canal at C3–4 and C5–6 levels due to multiple discopathies. High signal intensities on T2-weighted MR images of the spinal cord and low signal intensities on T1-weighted images at the C2–6 levels were noted, as was contrast enhancement at the C3–4 level. The patient underwent a bilateral decompressive laminectomy at C3–6. The patient did not show any clinical improvement. Thus, further cervical MR imaging was performed and the differential diagnosis of an intramedullary tumor was considered in view of the persisting intramedullary enhancement. This diagnosis prompted a second operation involving a posterior midline myelotomy and excision of an intramedullary ependymoma at the C3–4 level. Intramedullary tumors should be considered in the differential diagnosis of CSM with an atypical pattern of MR imaging features.

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Shahan Momjian, Rémi Tyrand, Basile N. Landis and Colette Boëx

OBJECTIVE

Intraoperative neuromonitoring of the chemical senses (smell and taste) has never been performed. The objective of this study was to determine if olfactory-evoked potentials could be obtained intraoperatively under general anesthesia.

METHODS

A standard olfactometer was used in the surgical theater with hydrogen sulfide (4 ppm, 200 msec). Olfactory-evoked potentials were recorded in 8 patients who underwent neurosurgery for resection of cerebral lesions. These patients underwent routine target-controlled propofol and sufentanil general anesthesia. Frontal, temporal, and parietal scalp subdermal electrodes were recorded ipsilaterally and contralaterally at the site of the surgery. Evoked potentials were computed if at least 70 epochs (0.5–100 Hz) satisfying the artifact rejection criterion (threshold 45 μV) could be extracted from signals of electrodes.

RESULTS

Contributive recordings were obtained for 5 of 8 patients (3 patients had fewer than 70 epochs with an amplitude < 45 μV). Olfactory-evoked potentials showed N1 responses (mean 442.8 ± 40.0 msec), most readily observed in the patient who underwent midline anterior fossa neurosurgery. No component of later latencies could be recorded consistently.

CONCLUSIONS

The study confirms that olfactory-evoked potentials can be measured in response to olfactory stimuli under general anesthesia. This demonstrates the feasibility of recording olfactory function intraoperatively and opens the potential for neuromonitoring of olfactory function during neurosurgery.

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Eveline M. Gutzwiller, Ivan Cabrilo, Ivan Radovanovic, Karl Schaller and Colette Boëx

OBJECTIVE

The goal of this study was to determine the performance of intraoperative visual evoked potentials (VEPs) in detecting visual field changes.

METHODS

Assessments of VEPs were performed with simultaneous retinal responses by using white light-emitting diodes protected from scialytic microscope lights. The alarm criterion was a reproducible decrease in amplitude of the VEP P100 wave of 20% or more. Visual fields were assessed preoperatively and 1 month postsurgery (Goldmann perimetry).

RESULTS

The VEPs were analyzed for 29 patients undergoing resection of a brain lesion. In 89.7% of patients, steady VEP and retinal responses were obtained for monitoring. The absence of alarm was associated in 94.4% of cases with the absence of postoperative visual changes (specificity). The alarms correctly identified 66.7% of cases with any postoperative changes and 100% of cases with changes more severe than just a discrete quadrantanopia or deterioration of an existing quadrantanopia (sensitivity, new diffuse deterioration < 2 dB). In 11.5% of patients, a transitory VEP decrease with subsequent recovery was observed without postoperative defects.

CONCLUSIONS

Intraoperative VEPs were performed with simultaneous recording of electroretinograms, with protection from lights of the operating room and with white light-emitting diodes. Intraoperative VEPs were shown to be reliable in predicting postoperative visual field changes. In this series of intraaxial brain procedures, reliable intraoperative VEP monitoring was achieved, allowing at minimum the detection of new quadrantanopia. The standardization of this technique appears to be a valuable effort in regard to the functional risks of homonymous hemianopia.