lntraoperative facial nerve monitoring: Prognostic aspects during acoustic tumor removal DOUGLAS 1. BECK, MA, JAMES S. ATKINS, JR., MD,JAMES E. BENECKE, JR., MD, and DERALD E. BRACKMANN, MD, St. Louis, Missouri, San Antonio, Texas, and Los Angeles, California
lntraoperativefacial nerve monitoring with electrical stimulation (IFNMES) has become an integral part of acoustic tumor surgery. We reviewed the records of fifty-six patients who underwent translabyrinthine acoustic tumor removal with IFNMES. There was excellent correlation between intraoperative facial nerve activity and immediate postoperative facial nerve function (24 hours after surgery and at hospital discharge).Our data would suggest that patients who exhibit less than 500 microvolts of ongoing EMG activity during surgery, and who yield at least a 500-microvolt contraction when stimulated with 0.05 milliamps at the brainstem after tumor removal, can expect an excellent immediate facial nerve result (grade I or 11). (OTOLARYNGOLHEAD NECK SURG 1991;104:780.)
Facial nerve monitoring with electrical stimulation (IFNMES) has become a widely used modality during surgery of the cerebellopontine angle. It has proved itself to be especially useful during acoustic tumor removal. IFNMES provides the surgeon with real-time information about the status of the facial nerve and also allows for positive identification by electrically stimulating the nerve. Numerous surgical teams have reported decreased facial nerve morbidity by routinely using IFNMES. Convinced about the utility of IFNMES in improving facial function, we decided to turn our attention to its potential value in predicting facial nerve results in the immediate postoperative period (24 hours after surgery and at hospital discharge). The purpose of this study was to analyze intraoperative electrical events and compare them to immediate facial nerve results. METHODS
The IFNMES are accomplished using a XOMED Nerve Integrity Monitor (XOMED, Jacksonville, Fla.).
From the Department of Otolaryngology-Head and Neck Surgery (Drs. Beck and Benecke), St. Louis University Medical Center; Wilford Hall, Air Force Medical Center (Dr. Atkins); House Ear Clinic, Los Angeles (Dr. Brackmann). Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 9-13, 1990. Received for publication April 19, 1990; accepted Nov. 21, 1990. Reprint requests: Douglas L. Beck, MD, 3660 Vista Ave., Suite 3 12, St. Louis, MO 631 10. 23 I 1I26909
780
This device is a battery-powered unit and is therefore less susceptible to electromagnetic interference from the many sources within the operating room. Two bipolar hookwire electrodes constructed from Teflon-coated silver wire are placed in the superior and inferior orbicularis oris muscle. The reference electrode is a standard monopolar subdermal needle that is placed in the midline of the forehead. The stimulator is a monopolar flush-tipped cathode that delivers a constant current signal. The anode is a subdermal needle placed in the ipsilateral deltoid muscle. Both the anode and the cathode are hard wired to a headbox yielding a complete stimulation Electrical stimulation at the conclusion of tumor removal is achieved using a low-level (0.05 milliampere) constant current signal. This low-level signal, in combination with a flush-tipped monopolar cathode, eliminates electrical shunting to nearby structures through cerebrospinal The “stimulus artifact reject” incorporated in the nerve integrity monitor eliminates the possibility that the electrical stimulus may be interpreted as a motoric response. The stimulus is set at 100microseconds duration and is presented four times per second. The stimulus intensity is varied depending on the task undertaken. Unlike the auditory brainstem response, the IFNMES is highly dependent on evoked motor activity. Therefore, following the use of relaxants at intubation, the patient is allowed to recover from the paralysis and no further paralytic agents are used.5 The stimulus intensity may be varied during anatomic mapping (determining the course of the facial nerve in difficult anatomy). We typically use from 0.10 to 0.20 milliamps (mA). Direct stimulation of the nerve during
Downloaded from oto.sagepub.com at UNIV CALIFORNIA SANTA BARBARA on June 8, 2016
Volume 104 Number 6 June 1991
lntraoperative facial newe monitoring 781
Group A
Group B W Day 1
W Day1 rn Discharge
\
Number of Patients
Number N=4
of
Patients
-
1
8 . 1 116
216
316
516
416
216
616
Group C
316
416
516
616
516
616
Group D
7 Day I
6
Discharge
Number of Patients
5
Number of
4
Patients
3 2
2
1
1 0
116
216
316
416
516
616
0
0
116
216
316
416
Fig. 1. House-BrackmannFacial Grade.
and after tumor removal to assess the physiologic status of the nerve is initiated at 0.05 mA. The response of the facial musculature to the 0.05-mA stimulus is monitored acoustically through the loudspeaker of the nerve integrity monitor, and the magnitude of this contraction is visually assessed on the nerve integrity monitor screen. The records of 77 patients who underwent acoustic tumor removal with IFNMES were retrospectively reviewed. Twenty-one patients were eliminated from our study as a result of inadequate records. Fifty-six patients were available for analysis. Two parameters were studied. The first parameter was the magnitude of sustained ongoing EMG activity. The second parameter was the magnitude of the contraction of the orbicularis oris muscle on conclusion of acoustic neuroma removal, when stimulated at the brainstem using 0.05 mA. The ongoing EMG activity was defined by the maximum sustained (for more than 30 seconds) discharge recorded. This was divided into two categories: greater than 500 microvolts (pV), or less than 500 pV. This type of activity has been described previously as “train at tern."^ The recorded contraction to electrical stimulation at the brainstem was defined as either less than or greater than 500 pV.
These parameters were then correlated with facial nerve function as assessed by the six-point HouseBrackmann scale on the first postoperative day, and again at hospital discharge.x RESULTS
To aid in our analysis of the data, the patients were divided into four groups. Group A contained 29 patients (Fig. 1, A ) . These patients demonstrated less than 500 microvolts of ongoing EMG activity, and yielded a contraction greater than 500 FV to 0.05 mA when stimulated at the brainstem on conclusion of tumor removal. On the first postoperative day, all of these patients were found to have a 1/6 facial result. At discharge twenty-eight patients (97%) maintained a 1 / 6 result. One patient exhibited a 2/6 result upon discharge (Fig. 1, A). Group B contained 4 patients (Fig. 1, B ) . They all demonstrated greater than 500 FV of ongoing EMG activity for more than 30 seconds, but yielded a contraction of greater than 500 FV to electrical stimulation of 0.05 mA when stimulated at the brainstem upon conclusion of tumor removal. On the first postoperative day, three patients had a
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OtolaryngologyHead and Neck Surgery
782 BECKet a1
1 i 6 result and one patient had a 5 i 6 result. There was no change in facial status at discharge. Group C contained 15 patients (Fig. 1, C ) . These patients had less than 500 pV of ongoing EMG activity; however, a contraction of less than 500 p.V was elicited, with stimulation of 0.05 mA at the brainstem on conclusion of tumor removal. On the first postoperative day, five patients exhibited a 116 result, seven patients had a 216 result, two patients had a 3 I 6 result, and one patient had a 6 / 6 result. At discharge, four patients were 116, three patients were 216, four patients were 316, two patients were 516, and two patients were 616. Group D contained 8 patients (Fig. 1, D ) . These patients had greater than 500 pV of ongoing EMG activity, with contraction of less than 500 pV when stimulated at the brainstem (0.05 mA) on conclusion of tumor removal. The immediate postoperative facial function in this group was one patient with a 116 result, two patients with a 216 result, two patients with a 3 / 6 result, one patient with a 4J6 result, and two patients with a 6 i 6 . Before discharge there was a significant decrease in facial function in these patients. One patient had a 416, six had a 516, and one had a 616. DISCUSSION
Our results indicate that IFNMES is predictive of immediate postoperative facial nerve functions in patients who exhibit the identified characteristics of group A participants. We will endeavor to follow all patients for 1 year to evaluate long-term facial nerve function. Unfortunately, because of the small population studied, a statistical analysis of groups B, C, and D would reveal little information regarding statistically significant differences. However, it does seem apparent that increased EMG and reduced contractions to 0.05 mA stimulation are correlated with reduced postoperative facial function.
SUMMARY
The results of this study suggest that IFNMES may have an additional role as a prognostic indicator for immediate postoperative facial function. When patients undergoing acoustic tumor removal fit the group A criteria, we are very optimistic about the immediate (and the long-term) facial nerve result. This series is admittedly small. At the time of publication, we have monitored more than 350 cases and the trend reported here continues to hold true. We continue to endorse IFNMES as a safe and reliable tool in cerebellopontine angle surgery.
REFERENCES
1. Hamer SG, Daube JR, Ebersold MJ, Beatty CW. Improved preservation of facial nerve function with use of electrical monitoring during removal of acoustic neuromas. Mayo Clin Proc 1987; 62:92-102. 2. Kartush JM, Niparko JK, Bledsoe SC, Graham MD, Kemink JL. Intraoperative facial nerve monitoring: a comparison of stimulating electrodes. Laryngoscope 1985;95:1536-40. 3. Kartush JM, Prass RL. Facial nerve testing: electroneurography and intraoperative monitoring. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, Washington, D.C., Sept. 25-29, 1988. 4. Benecke JE, Calder HB, Chadwick G. Facial nerve monitoring during acoustic neuroma removal. Laryngoscope 1987;97:697700. 5. h a s s RL, Luders H. Acoustic (loudspeaker) facial electromyographic monitoring: Part 1 , Evoked electromyographic activity during acoustic neuroma resection. Neurosurgery 1986;19:392-
400. 6. Prass RL, Luders H. Constant-current versus constant-voltage stimulation. J Neurosurgery 1985;62:622-3. 7. Beck DL, Benecke JE. Intraoperative facial nerve monitoring: technical aspects. OTOLARYNGOL HEADNECKSURG 1990;102: 270-2. 8. House JW, Brackmann DE. Facial nerve grading system. OTOLARYNGOL HEADNECKSURG 1985;93:146-7.
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lntraoperativefacial nerve monitoring with electrical stimulation (IFNMES) has become an integral part of acoustic tumor surgery. We reviewed the records of fifty-six patients who underwent translabyrinthine acoustic tumor removal with IFNMES. There was excellent correlation between intraoperative facial nerve activity and immediate postoperative facial nerve function (24 hours after surgery and at hospital discharge).Our data would suggest that patients who exhibit less than 500 microvolts of ongoing EMG activity during surgery, and who yield at least a 500-microvolt contraction when stimulated with 0.05 milliamps at the brainstem after tumor removal, can expect an excellent immediate facial nerve result (grade I or 11). (OTOLARYNGOLHEAD NECK SURG 1991;104:780.)
Facial nerve monitoring with electrical stimulation (IFNMES) has become a widely used modality during surgery of the cerebellopontine angle. It has proved itself to be especially useful during acoustic tumor removal. IFNMES provides the surgeon with real-time information about the status of the facial nerve and also allows for positive identification by electrically stimulating the nerve. Numerous surgical teams have reported decreased facial nerve morbidity by routinely using IFNMES. Convinced about the utility of IFNMES in improving facial function, we decided to turn our attention to its potential value in predicting facial nerve results in the immediate postoperative period (24 hours after surgery and at hospital discharge). The purpose of this study was to analyze intraoperative electrical events and compare them to immediate facial nerve results. METHODS
The IFNMES are accomplished using a XOMED Nerve Integrity Monitor (XOMED, Jacksonville, Fla.).
From the Department of Otolaryngology-Head and Neck Surgery (Drs. Beck and Benecke), St. Louis University Medical Center; Wilford Hall, Air Force Medical Center (Dr. Atkins); House Ear Clinic, Los Angeles (Dr. Brackmann). Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, San Diego, Calif., Sept. 9-13, 1990. Received for publication April 19, 1990; accepted Nov. 21, 1990. Reprint requests: Douglas L. Beck, MD, 3660 Vista Ave., Suite 3 12, St. Louis, MO 631 10. 23 I 1I26909
780
This device is a battery-powered unit and is therefore less susceptible to electromagnetic interference from the many sources within the operating room. Two bipolar hookwire electrodes constructed from Teflon-coated silver wire are placed in the superior and inferior orbicularis oris muscle. The reference electrode is a standard monopolar subdermal needle that is placed in the midline of the forehead. The stimulator is a monopolar flush-tipped cathode that delivers a constant current signal. The anode is a subdermal needle placed in the ipsilateral deltoid muscle. Both the anode and the cathode are hard wired to a headbox yielding a complete stimulation Electrical stimulation at the conclusion of tumor removal is achieved using a low-level (0.05 milliampere) constant current signal. This low-level signal, in combination with a flush-tipped monopolar cathode, eliminates electrical shunting to nearby structures through cerebrospinal The “stimulus artifact reject” incorporated in the nerve integrity monitor eliminates the possibility that the electrical stimulus may be interpreted as a motoric response. The stimulus is set at 100microseconds duration and is presented four times per second. The stimulus intensity is varied depending on the task undertaken. Unlike the auditory brainstem response, the IFNMES is highly dependent on evoked motor activity. Therefore, following the use of relaxants at intubation, the patient is allowed to recover from the paralysis and no further paralytic agents are used.5 The stimulus intensity may be varied during anatomic mapping (determining the course of the facial nerve in difficult anatomy). We typically use from 0.10 to 0.20 milliamps (mA). Direct stimulation of the nerve during
Downloaded from oto.sagepub.com at UNIV CALIFORNIA SANTA BARBARA on June 8, 2016
Volume 104 Number 6 June 1991
lntraoperative facial newe monitoring 781
Group A
Group B W Day 1
W Day1 rn Discharge
\
Number of Patients
Number N=4
of
Patients
-
1
8 . 1 116
216
316
516
416
216
616
Group C
316
416
516
616
516
616
Group D
7 Day I
6
Discharge
Number of Patients
5
Number of
4
Patients
3 2
2
1
1 0
116
216
316
416
516
616
0
0
116
216
316
416
Fig. 1. House-BrackmannFacial Grade.
and after tumor removal to assess the physiologic status of the nerve is initiated at 0.05 mA. The response of the facial musculature to the 0.05-mA stimulus is monitored acoustically through the loudspeaker of the nerve integrity monitor, and the magnitude of this contraction is visually assessed on the nerve integrity monitor screen. The records of 77 patients who underwent acoustic tumor removal with IFNMES were retrospectively reviewed. Twenty-one patients were eliminated from our study as a result of inadequate records. Fifty-six patients were available for analysis. Two parameters were studied. The first parameter was the magnitude of sustained ongoing EMG activity. The second parameter was the magnitude of the contraction of the orbicularis oris muscle on conclusion of acoustic neuroma removal, when stimulated at the brainstem using 0.05 mA. The ongoing EMG activity was defined by the maximum sustained (for more than 30 seconds) discharge recorded. This was divided into two categories: greater than 500 microvolts (pV), or less than 500 pV. This type of activity has been described previously as “train at tern."^ The recorded contraction to electrical stimulation at the brainstem was defined as either less than or greater than 500 pV.
These parameters were then correlated with facial nerve function as assessed by the six-point HouseBrackmann scale on the first postoperative day, and again at hospital discharge.x RESULTS
To aid in our analysis of the data, the patients were divided into four groups. Group A contained 29 patients (Fig. 1, A ) . These patients demonstrated less than 500 microvolts of ongoing EMG activity, and yielded a contraction greater than 500 FV to 0.05 mA when stimulated at the brainstem on conclusion of tumor removal. On the first postoperative day, all of these patients were found to have a 1/6 facial result. At discharge twenty-eight patients (97%) maintained a 1 / 6 result. One patient exhibited a 2/6 result upon discharge (Fig. 1, A). Group B contained 4 patients (Fig. 1, B ) . They all demonstrated greater than 500 FV of ongoing EMG activity for more than 30 seconds, but yielded a contraction of greater than 500 FV to electrical stimulation of 0.05 mA when stimulated at the brainstem upon conclusion of tumor removal. On the first postoperative day, three patients had a
Downloaded from oto.sagepub.com at UNIV CALIFORNIA SANTA BARBARA on June 8, 2016
OtolaryngologyHead and Neck Surgery
782 BECKet a1
1 i 6 result and one patient had a 5 i 6 result. There was no change in facial status at discharge. Group C contained 15 patients (Fig. 1, C ) . These patients had less than 500 pV of ongoing EMG activity; however, a contraction of less than 500 p.V was elicited, with stimulation of 0.05 mA at the brainstem on conclusion of tumor removal. On the first postoperative day, five patients exhibited a 116 result, seven patients had a 216 result, two patients had a 3 I 6 result, and one patient had a 6 / 6 result. At discharge, four patients were 116, three patients were 216, four patients were 316, two patients were 516, and two patients were 616. Group D contained 8 patients (Fig. 1, D ) . These patients had greater than 500 pV of ongoing EMG activity, with contraction of less than 500 pV when stimulated at the brainstem (0.05 mA) on conclusion of tumor removal. The immediate postoperative facial function in this group was one patient with a 116 result, two patients with a 216 result, two patients with a 3 / 6 result, one patient with a 4J6 result, and two patients with a 6 i 6 . Before discharge there was a significant decrease in facial function in these patients. One patient had a 416, six had a 516, and one had a 616. DISCUSSION
Our results indicate that IFNMES is predictive of immediate postoperative facial nerve functions in patients who exhibit the identified characteristics of group A participants. We will endeavor to follow all patients for 1 year to evaluate long-term facial nerve function. Unfortunately, because of the small population studied, a statistical analysis of groups B, C, and D would reveal little information regarding statistically significant differences. However, it does seem apparent that increased EMG and reduced contractions to 0.05 mA stimulation are correlated with reduced postoperative facial function.
SUMMARY
The results of this study suggest that IFNMES may have an additional role as a prognostic indicator for immediate postoperative facial function. When patients undergoing acoustic tumor removal fit the group A criteria, we are very optimistic about the immediate (and the long-term) facial nerve result. This series is admittedly small. At the time of publication, we have monitored more than 350 cases and the trend reported here continues to hold true. We continue to endorse IFNMES as a safe and reliable tool in cerebellopontine angle surgery.
REFERENCES
1. Hamer SG, Daube JR, Ebersold MJ, Beatty CW. Improved preservation of facial nerve function with use of electrical monitoring during removal of acoustic neuromas. Mayo Clin Proc 1987; 62:92-102. 2. Kartush JM, Niparko JK, Bledsoe SC, Graham MD, Kemink JL. Intraoperative facial nerve monitoring: a comparison of stimulating electrodes. Laryngoscope 1985;95:1536-40. 3. Kartush JM, Prass RL. Facial nerve testing: electroneurography and intraoperative monitoring. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, Washington, D.C., Sept. 25-29, 1988. 4. Benecke JE, Calder HB, Chadwick G. Facial nerve monitoring during acoustic neuroma removal. Laryngoscope 1987;97:697700. 5. h a s s RL, Luders H. Acoustic (loudspeaker) facial electromyographic monitoring: Part 1 , Evoked electromyographic activity during acoustic neuroma resection. Neurosurgery 1986;19:392-
400. 6. Prass RL, Luders H. Constant-current versus constant-voltage stimulation. J Neurosurgery 1985;62:622-3. 7. Beck DL, Benecke JE. Intraoperative facial nerve monitoring: technical aspects. OTOLARYNGOL HEADNECKSURG 1990;102: 270-2. 8. House JW, Brackmann DE. Facial nerve grading system. OTOLARYNGOL HEADNECKSURG 1985;93:146-7.
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