Intraoperative monitoring of facial nerve function in cerebellopontine angle surgery PAUL E. HAMMERSCHLAG, MD. and NOEL L. COHEN, MD. New York, New York
Facial nerve paralysis associated with cerebellopontlne angle surgery has been reported to range up to 26% In a recent series. Various methods of Intraoperatively monitoring the facial nerve have been developed to reduce the Incidence of facial paralysis. We report our experience with an Intraoperative monitoring technique using Intramuscular EMG electrodes to detect subclinical electrical responses that were amplified and made aUdible to the operating surgeon after gating stimulus artifacts. A 3.6% Incidence of facial paralysis In 111 consecutive cas.. with this Intraoperative monitoring method compared with 14.5"0 In 207 previously unmonltored case. Indicates significant reduction of this complication In cerebellopontlne angle surgery (p < 0.0(1). Along with this reduction In facial paralysis, an Increase In the percentage of partial facial paresis was observed In the monitored group (p < 0.05). Thepercentage of those with Intact facial function was similar In the monitored (82.0%) and unmonltored groups (78.3%). (OTOLARYNGOL HEAD NECK SURG 1990;103:681.)
Facial nerve paralysis associated with cerebellopontine angle (CPA) surgery has been reported to range up to 26.7% in a recent series. 1 Although the operating microscope, along with improved microsurgical instrumentation, skills, and increased appreciation of facial nerve anatomic landmarks in the temporal bone, has reduced the incidence of facial paralysis, it is still a vexing complication in the surgery of this region. Various methods of intraoperative monitoring of the facial nerve have been developed to increase the ability to preserve facial nerve function. The authors have preViously reported their experience with the noninvasive or orthodromic brainstem facial evoked response (BFER) evoked potential monitoring system. This is a far-field evoked response based on a cross-acoustic reflex elicited with auditory click stimulus that, along a poorly understood pathway, depolarizes the facial nerve. Although the BFER method provides real-time information, it requires sophisticated computer programming, optimal digital filtering, and personnel to obtain, interpret, and report the intraoperative data to the surgeon. 2
Fromthe Department of Otolaryngology, New York University Medical Center. Presented at the Annual Meetingof the American Neurotology Society, Palm Beach. Fla.• April 27-29, 1990. ReceiVed for publication April 27, 1990;accepted Aug. 14. 1990. Reprint requests: Paul E. Hammerschlag, MD. Department of Otolaryngology. New York University Medical Center.550 FirstAve.• New York, NY 10016. 23/1124558
Table 1. Postoperative facial nerve functional status along modified House-Brockmann classification by tumor size In the unmonltored historical group (N = 207) Facial status
:s1.5 cm
:s3cm
>3cm
Totals
Intact ItVl DUTR ItVl Paresis 1I11V1 Paralysis VIIVI
44 12 1
47 10 4
133 29 15
....Q
-4
42 7 10 26
2Q
57
65
85
207
TOTALS
DUTR respectively refer to delayed and transient paralysis that returned to normalllVl functional status.
An alternative technique, evoked electromyography, was introduced by Delgado et al.' and then modified by Sugita and Kobayoshi" with acoustic monitoring of facial nerve movements. In 1984, Moller and Janetta' reported their experience with 10 cases of intraoperative monitoring with intramuscular EMG electrodes, in which subclinical electrical responses were amplified and made audible through a speaker after gating stimulus artifacts. With the intramuscular EMG electrodes, discrete facial motor electrical activity could be followed instead of relying on gross muscle movement for signal detection. Monopolar constant voltage stimulation was utilized with this technique. Subsequent to our experience with BFER and EEMG (as described by Moller and Janette), we used the Xomed Nerve Integrity Monitor-2 (NIM-2) and the Prass Flush Tip Monopolar Stimulating Probe (monitor
681
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612
OtolaryngologyHead and Neck Surgery
HAMMERSCHLAG and COHEN
Table 2. Postoperative facial nerve functional status along House-Brockmann scale by tumor size in percentiles (N = 207) In unmonltored control group Facial statu.
l/VI Paresis IIIIVI Paralysis TOTALS
,,;1.5 cm (N 57)
=
,,;3 cm (N 65)
=
>3cm (N 85)
=
Totals (N 207)
98.2 1.8 0 100.0
87.6 6.2 6.2 100.0
57.6 11.8 30.6 100.0
78.2 7.3 14.5 100.0
=
For clarity, the previous DLlTR IIVI group was merged with the intact IIVI class because both were ultimately with normal (IIVI) function.
Table 3. Postoperative facial nerve functional status along House-Brockmann scale by tumor size In EEMG-monltored group (N = 111) Facial status
Intact IIVI DUTA IIVI Paresis Ill/Vi Paralysis VIIVI TOTALS
,,;1.5 cm
,,;3 cm
>3cm
Totals
42 4 5 1 52
23 10 6 0 39
6 6 5 3 20
71 20 16 4 111
and probe both available from Xomed-Treace, Jacksonville, Fla.). This system permitted constant current, variable threshold, and stimulus parameters, with intraoperative audible feedback of facial nerve activity, and automatic signal muting on electrocautery activation. Prass and Luders? facilitated this method with the flush-tip cathode probe to avoid cerebrospinal fluid shunting, permitting a constant current stimulus. To assess the efficacy of EEMG intraoperative monitoring, facial nerve function after surgery with this monitoring technique in III consecutive cases was compared with our previous experience with 207 unmonitored cases.
MATERIAU Before intraoperative monitoring, 207 cases without preoperative facial paralysis underwent CPA surgery and serve as historical control of this comparative series. There were 57 small tumors (:51.5 em), 65 medium (:s3 em), and 85 large (>3 em) tumors. The translabyrinthine and suboccipital approaches were used in 89 and 118 cases, respectively. In all these cases, the translabyrinthine surgery was performed by a neurotologist and the suboccipital approach by a combined team of neurotologist and neurosurgeon. 7 Acoustic monitoring with evoked electromyography (Xomed Nerve Integrity Monitor-2) was performed in III CPA procedures. These were consecutive cases, except when the monitor was not available (one case). This series of III cases was monitored from April 4, 1988, to March 26, 1990. The translabyrinthine and suboccipital approaches were used in 31 and 80 cases,
respectively. Tumor size ranged from intracanicular to 7 em, There were 52 small, 39 medium, and 20 large tumors in this monitored group. There were 314 acoustic neuromas, one meningioma, one hemangioma, one vascular loop, and 1 cholesterol cyst in this series of 318 cases. All of the above surgery was performed at New York University Medical Center.
METHODS For the intraoperative monitoring of patients, a pair of needle EEG-type electrodes were subdermally placed in the nasolabial groove and at the lateral orbicularis oculi, ipsilateral to the operative side. A separate needle electrode was inserted subdermally in the forehead (Fpz) as a ground for the two recording channels. Another needle electrode was subdermally inserted near the Fpz electrode to act as an anode electrode for the monopolar stimulator. The electrodes were secured with clear adhesive drapes. Electrode impedances and system integrity were assessed using the NIM-2 "status check" internal circuitry. The automatic muting unit, activated with monopolar and/ or bipolar cautery stimulus, was placed to prevent audible feedback from the speaker during electrocautery. For facial nerve identification and mapping, the constant current stimulus was lowered as much as possible, to eliminate volume conduction through tumor and permit differential depolarization of facial nerve upon direct application of the stimulus probe, as opposed to transmitted stimulation via adjacent tumor. This stimulus was initially set at 0.2 rnA at a ratio of 4 pulses
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Volume 103 Number 5 Part 1 November 1990
Intraoperative monitoring of facial nerve function
6.3
Table 4. Postoperative facial nerve functional status along house-Brockmann scale by tumor size in percentiles (N = 111) Facial slalus IIVI Paresis IIIIVI Paralysis VIIVI TOTALS
Facial nerve paralysis associated with cerebellopontlne angle surgery has been reported to range up to 26% In a recent series. Various methods of Intraoperatively monitoring the facial nerve have been developed to reduce the Incidence of facial paralysis. We report our experience with an Intraoperative monitoring technique using Intramuscular EMG electrodes to detect subclinical electrical responses that were amplified and made aUdible to the operating surgeon after gating stimulus artifacts. A 3.6% Incidence of facial paralysis In 111 consecutive cas.. with this Intraoperative monitoring method compared with 14.5"0 In 207 previously unmonltored case. Indicates significant reduction of this complication In cerebellopontlne angle surgery (p < 0.0(1). Along with this reduction In facial paralysis, an Increase In the percentage of partial facial paresis was observed In the monitored group (p < 0.05). Thepercentage of those with Intact facial function was similar In the monitored (82.0%) and unmonltored groups (78.3%). (OTOLARYNGOL HEAD NECK SURG 1990;103:681.)
Facial nerve paralysis associated with cerebellopontine angle (CPA) surgery has been reported to range up to 26.7% in a recent series. 1 Although the operating microscope, along with improved microsurgical instrumentation, skills, and increased appreciation of facial nerve anatomic landmarks in the temporal bone, has reduced the incidence of facial paralysis, it is still a vexing complication in the surgery of this region. Various methods of intraoperative monitoring of the facial nerve have been developed to increase the ability to preserve facial nerve function. The authors have preViously reported their experience with the noninvasive or orthodromic brainstem facial evoked response (BFER) evoked potential monitoring system. This is a far-field evoked response based on a cross-acoustic reflex elicited with auditory click stimulus that, along a poorly understood pathway, depolarizes the facial nerve. Although the BFER method provides real-time information, it requires sophisticated computer programming, optimal digital filtering, and personnel to obtain, interpret, and report the intraoperative data to the surgeon. 2
Fromthe Department of Otolaryngology, New York University Medical Center. Presented at the Annual Meetingof the American Neurotology Society, Palm Beach. Fla.• April 27-29, 1990. ReceiVed for publication April 27, 1990;accepted Aug. 14. 1990. Reprint requests: Paul E. Hammerschlag, MD. Department of Otolaryngology. New York University Medical Center.550 FirstAve.• New York, NY 10016. 23/1124558
Table 1. Postoperative facial nerve functional status along modified House-Brockmann classification by tumor size In the unmonltored historical group (N = 207) Facial status
:s1.5 cm
:s3cm
>3cm
Totals
Intact ItVl DUTR ItVl Paresis 1I11V1 Paralysis VIIVI
44 12 1
47 10 4
133 29 15
....Q
-4
42 7 10 26
2Q
57
65
85
207
TOTALS
DUTR respectively refer to delayed and transient paralysis that returned to normalllVl functional status.
An alternative technique, evoked electromyography, was introduced by Delgado et al.' and then modified by Sugita and Kobayoshi" with acoustic monitoring of facial nerve movements. In 1984, Moller and Janetta' reported their experience with 10 cases of intraoperative monitoring with intramuscular EMG electrodes, in which subclinical electrical responses were amplified and made audible through a speaker after gating stimulus artifacts. With the intramuscular EMG electrodes, discrete facial motor electrical activity could be followed instead of relying on gross muscle movement for signal detection. Monopolar constant voltage stimulation was utilized with this technique. Subsequent to our experience with BFER and EEMG (as described by Moller and Janette), we used the Xomed Nerve Integrity Monitor-2 (NIM-2) and the Prass Flush Tip Monopolar Stimulating Probe (monitor
681
Downloaded from oto.sagepub.com at The University of Iowa Libraries on June 5, 2016
612
OtolaryngologyHead and Neck Surgery
HAMMERSCHLAG and COHEN
Table 2. Postoperative facial nerve functional status along House-Brockmann scale by tumor size in percentiles (N = 207) In unmonltored control group Facial statu.
l/VI Paresis IIIIVI Paralysis TOTALS
,,;1.5 cm (N 57)
=
,,;3 cm (N 65)
=
>3cm (N 85)
=
Totals (N 207)
98.2 1.8 0 100.0
87.6 6.2 6.2 100.0
57.6 11.8 30.6 100.0
78.2 7.3 14.5 100.0
=
For clarity, the previous DLlTR IIVI group was merged with the intact IIVI class because both were ultimately with normal (IIVI) function.
Table 3. Postoperative facial nerve functional status along House-Brockmann scale by tumor size In EEMG-monltored group (N = 111) Facial status
Intact IIVI DUTA IIVI Paresis Ill/Vi Paralysis VIIVI TOTALS
,,;1.5 cm
,,;3 cm
>3cm
Totals
42 4 5 1 52
23 10 6 0 39
6 6 5 3 20
71 20 16 4 111
and probe both available from Xomed-Treace, Jacksonville, Fla.). This system permitted constant current, variable threshold, and stimulus parameters, with intraoperative audible feedback of facial nerve activity, and automatic signal muting on electrocautery activation. Prass and Luders? facilitated this method with the flush-tip cathode probe to avoid cerebrospinal fluid shunting, permitting a constant current stimulus. To assess the efficacy of EEMG intraoperative monitoring, facial nerve function after surgery with this monitoring technique in III consecutive cases was compared with our previous experience with 207 unmonitored cases.
MATERIAU Before intraoperative monitoring, 207 cases without preoperative facial paralysis underwent CPA surgery and serve as historical control of this comparative series. There were 57 small tumors (:51.5 em), 65 medium (:s3 em), and 85 large (>3 em) tumors. The translabyrinthine and suboccipital approaches were used in 89 and 118 cases, respectively. In all these cases, the translabyrinthine surgery was performed by a neurotologist and the suboccipital approach by a combined team of neurotologist and neurosurgeon. 7 Acoustic monitoring with evoked electromyography (Xomed Nerve Integrity Monitor-2) was performed in III CPA procedures. These were consecutive cases, except when the monitor was not available (one case). This series of III cases was monitored from April 4, 1988, to March 26, 1990. The translabyrinthine and suboccipital approaches were used in 31 and 80 cases,
respectively. Tumor size ranged from intracanicular to 7 em, There were 52 small, 39 medium, and 20 large tumors in this monitored group. There were 314 acoustic neuromas, one meningioma, one hemangioma, one vascular loop, and 1 cholesterol cyst in this series of 318 cases. All of the above surgery was performed at New York University Medical Center.
METHODS For the intraoperative monitoring of patients, a pair of needle EEG-type electrodes were subdermally placed in the nasolabial groove and at the lateral orbicularis oculi, ipsilateral to the operative side. A separate needle electrode was inserted subdermally in the forehead (Fpz) as a ground for the two recording channels. Another needle electrode was subdermally inserted near the Fpz electrode to act as an anode electrode for the monopolar stimulator. The electrodes were secured with clear adhesive drapes. Electrode impedances and system integrity were assessed using the NIM-2 "status check" internal circuitry. The automatic muting unit, activated with monopolar and/ or bipolar cautery stimulus, was placed to prevent audible feedback from the speaker during electrocautery. For facial nerve identification and mapping, the constant current stimulus was lowered as much as possible, to eliminate volume conduction through tumor and permit differential depolarization of facial nerve upon direct application of the stimulus probe, as opposed to transmitted stimulation via adjacent tumor. This stimulus was initially set at 0.2 rnA at a ratio of 4 pulses
Downloaded from oto.sagepub.com at The University of Iowa Libraries on June 5, 2016
Volume 103 Number 5 Part 1 November 1990
Intraoperative monitoring of facial nerve function
6.3
Table 4. Postoperative facial nerve functional status along house-Brockmann scale by tumor size in percentiles (N = 111) Facial slalus IIVI Paresis IIIIVI Paralysis VIIVI TOTALS
