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Standard sphenoidal and mini-sphenoidal electrodes: A direct comparison
1 Epilepsy 1991;4:29-31 0 1991 Demos Publications
Standard Sphenoidal and Mini-Sphenoidal A Direct Comparison J. R. Buchhalter,
Electrodes:
‘D. L. Schemer, and ‘S. C. Schachter
This study was designed to directly compare EEG recordings from standard sphenoidal (SS) electrodes to those obtained from subdermal “mini-sphenoidal” (MSP) electrodes. A montage was designed to include SS electrodes, MSP electrodes, and surface temporal leads. In a series of 100 consecutive patients, 9 cases demonstrated abnormalities in the SS and MSP electrodes only. An additional 6 patients had abnormalities present only in the SS electrodes. We conclude that MSP electrodes cannot be substituted for SS electrodes in the search for suspected abnormalities in temporal, inferior, or mesial brain regions. Key Words: Epilepsy-Sphenoidal electrodes-Mini-sphenoidai electrodes.
Sphenoidal electrodes are used to record electrographic abnormalities not evident with standard surface leads. However, patient discomfort and required insertion by a physician make this a procedure that is not utilized on a routine basis. In an effort to circumvent these difficulties, subdermal electrodes (“minisphendidals”-MSP) are placed in the same skin location as standard sphenoidals (SS), but to a depth of only 1 cm (1). In that study, EEGs were requested to “investigate possible seizures” with “standard, sleepinduced, or sleep-deprived” recordings. The yield of “epileptogenic abnormalities” was increased by approximately 33% by the MSPs in that series of 100 patients. However, a direct comparison of MSP and SS recording has not been reported. This study was deReceived February 23, 1990; accepted September 10, 1990. From the Department of Neurology, Children’s Hospital Medical Center, and the ‘Department of Neurology, Beth Israel Hospital, Boston, MA, U.S.A. Presented in part at the American Epilepsy Society Meeting, Baltimore, MD, December 7, 1987. Address correspondence and reprint requests to Dr. J. R. Buchhalter at Children’s Hospital of Philadelphia, 34th Street and Civic Center Boulevard, Philadelphia, PA 19104, U.S.A.
signed to compare simultaneous MSP and SS electrodes.
recordings
from
Methods One-hundred consecutive patients in whom technically satisfactory EEGs that included MSP and SS recordings were used for this study. The only inclusion criterion was referral to the EEG laboratory at the Beth Israel Hospital with a request for sphenoidal recording. The study population included patients with known epilepsy as well as those in whom the diagnosis was uncertain. It should be emphasized that the study was designed to provide an electrophysiologic comparison of potentials from MSP and SS leads and not to evaluate which technique would be most appropriate in a particular population. SS electrodes were inserted prior to placement of standard scalp leads. The skin overlying the zygomatic region was cleansed with an iodine solution, followed by alcohol and infiltration with 1 ml of 1% Xylocaine without epinephrine. The sterile SS electrode assembly (2) was a seven-stranded 20-gauge silver wire that was Teflon-coated and bared at the distal 3 mm. The bared end was end-hooked from the outside into the bevel of a 22-gauge needle. The elec] EPILEPSY,
VOL. 4, NO. 1,1991
29
1. R. BUCHHALTER
ET AL.
trode assembly was inserted below the zygomatic arch in a posterior and upward direction toward the foramen ovale to a depth of 3 cm (3,4). Once placed, the needle was removed. Prior studies in this laboratory have confirmed the location of the recording tip with a base view skull radiograph to be within 2 cm of the foramen ovale. The MSP electrode was a Grass 12-mm needle electrode inserted adjacent to the SS lead and taped in place. Scalp electrodes were attached with collodion or electrode paste in the standard lo-20 configuration. The following montage was used to record from surface, SS, and MSP leads simultaneously: CZ-C3, C3-T3, T9SP1, WI-SP2, SP2-T4, T4-C4, CCCZ, T3-MSPl, MSPl-MSP2, MSP2-T4, Fpl-F7, F7-T3, T3-T5, T5-01, Fp2-F8, FS-T4, T4-T6, and T6-02. Recordings commenced within 1 h of sphenoidal electrode placement. All records were reviewed by an ABCN-certified electroencephalographer (D.L.S.). Records were classified as “normal” or as containing “temporal-inferior-mesial” (TIM) abnormalities or “non-TIM” abnormalities. “TIM” abnormalities included spikes, sharp waves, or slow-wave abnormalities localized to the SS, MSP, and temporal surface leads in isolation or in any combination. All other abnormalities were considered “non-TIM.”
Results In the consecutive series of patients, only one record was considered unsatisfactory due to an MSP electrode artifact. No complications of the procedure were encountered other than mild, transient jaw discomfort. There were 37 males and 63 females. The mean age for the total group was 33.5 years (+ll years) with a range of 14-66 years. On the basis of the criteria described above, records were classified as “normal” (N = 36), “non-TIM” (N = 25), or “TIM” (N = 39). Results from the “TIM” group will form the basis of the discussion. In order to compare the recordings of individual leads, the TIM group was separated as to the leads in which the abnormalities appeared: SS electrode only (N = 6), SS and MSP electrodes (N = 9), SS and MSP electrodes and surface leads (N = 14), surface leads only (N = lo), and MSP electrode only (MSP = 0). Thus, in the group in which TIM abnormalities were found, 38% (15/39) would not have been detected without sphenoidal leads (MSP and/or SS electrodes). Furthermore, 6 of the 15 abnormalities would not have been found with MSP electrodes alone. The abnormalities found in the “SS electrodes only” group were spikes, sharp waves, and slowing in two records each. In three of the six patients in this 30
JEPILEPSY,
VOL.
4, NO. I,2991
group, an abnormal EEG had not been previously recorded, and the requested purpose of the study was to “rule out temporal lobe epilepsy.” Figure 1 illustrates several different findings recorded in a single patient. In the first 4 s of the record, rhythmic high-voltage spikes and sharp waves are recorded in the right SS lead, but not significantly recorded on the surface or MSP leads. A particularly high-voltage right SS spike during the 6th s is recorded as a suspicious low-voltage sharp wave reversal between MSP2 and T4. During the 7th s, sharp waves are found in the left SS and MSP leads with only a slight voltage predominance from the SS electrode.
Discussion Sphenoidal recordings have been used as an adjunct to standard surface recording when a temporal or inferior mesial epileptogenic focus has been suspected (3-8) and more sensitive than recordings from nasopharyngeal and ear electrodes in detection of mesial temporal spikes (9). However, the precise location of the signal generators has yet to be ascertained. In fact, it has been suggested that the wire electrode may migrate laterally without an apparent decrement in recording (10). Thus, the report of
SPHENOIDAL AND MINI-SPHENOIDAL ELECTRODES Laxer (1) provided hope that a less invasive subdermal electrode could provide the same information as that from an SS placement. The results of this study indicate that abnormalities revealed by SS electrodes (including spikes, sharp waves, and slowing) may not be represented in MSP leads. As illustrated in Fig. 1, epileptiform potentials recorded with SS electrodes can have quite variable representation in the homolateral MSP electrode. Furthermore, the lack of significant artifact in the SS electrodes indicates the feasibility of this technique for outpatient use if a physician is available for insertion. Since this study was designed to make an EEG comparison, no conclusions regarding the most appropriate patient population for SS versus MSP recording can be made. Although MSP recording cannot substitute for SS recording, the former provides information not available on routine EEG.
References 1. Laxer KD. Mini-sphenoidal electrodes in the investigation of seizures. Electroencephalogr C/in Neurophysiol 1984;58:127-9.
2. Ives JR, Gloor P. Update: chronic sphenoidal electrodes. Elechvencephalogr Clin Neurophysiol 1978;44: 789-90. 3. Rovit RR, Gloor P, Henderson LR. Temporal lobe epilepsy-a study using multiple basal electrodes. I. Description of method. Neurochirurgia (Stuttg) 1960;3:619. 4. Rovit RR, Gloor P. Temporal lobe epilepsy-a study using multiple basal electrodes. IL Clinical EEG findings.- Neuro’chirurgia (Stutt~ 1960;3:19-34. 5. Pampiglione G, Kerridge J. EEG abnormalities from the temporal lobe studied with sphenoidal electrodes. 1 Neural Neurosurg Psychiatry 1956;19:117-29. 6. Christodoulou G. Sphenoidal electrodes: their significance in diagnosing temporal lobe epileptogenic-foci. Acta Neural Stand 1967;43:587-93. 7. King DW, So EL, Marcus R, Gallagher BB. Techniques and applications of sphenoidal recording. J Clin Neurophysiol 1986;3:51-65. 8. Sperling MR, Engel J Jr. Sphenoidal electrodes. J Clin Neurophysiol 1986;3:67-73. 9. Sperling MR, Mendius JR, Engel J Jr. Mesial temporal spikes: a simultaneous comparison of sphenoidal, nasopharyngeal, and ear electrodes. Epilepsia 1986;27: 81-6. 110. Wilkus RJ,Thompson PM. Sphenoidal electrode positions and basal EEG during long-term monitoring. Epilepsia 1985;26:137-42.
J EPILEPSY,
VOL.
4, NO. 1, is91
31
Standard Sphenoidal and Mini-Sphenoidal A Direct Comparison J. R. Buchhalter,
Electrodes:
‘D. L. Schemer, and ‘S. C. Schachter
This study was designed to directly compare EEG recordings from standard sphenoidal (SS) electrodes to those obtained from subdermal “mini-sphenoidal” (MSP) electrodes. A montage was designed to include SS electrodes, MSP electrodes, and surface temporal leads. In a series of 100 consecutive patients, 9 cases demonstrated abnormalities in the SS and MSP electrodes only. An additional 6 patients had abnormalities present only in the SS electrodes. We conclude that MSP electrodes cannot be substituted for SS electrodes in the search for suspected abnormalities in temporal, inferior, or mesial brain regions. Key Words: Epilepsy-Sphenoidal electrodes-Mini-sphenoidai electrodes.
Sphenoidal electrodes are used to record electrographic abnormalities not evident with standard surface leads. However, patient discomfort and required insertion by a physician make this a procedure that is not utilized on a routine basis. In an effort to circumvent these difficulties, subdermal electrodes (“minisphendidals”-MSP) are placed in the same skin location as standard sphenoidals (SS), but to a depth of only 1 cm (1). In that study, EEGs were requested to “investigate possible seizures” with “standard, sleepinduced, or sleep-deprived” recordings. The yield of “epileptogenic abnormalities” was increased by approximately 33% by the MSPs in that series of 100 patients. However, a direct comparison of MSP and SS recording has not been reported. This study was deReceived February 23, 1990; accepted September 10, 1990. From the Department of Neurology, Children’s Hospital Medical Center, and the ‘Department of Neurology, Beth Israel Hospital, Boston, MA, U.S.A. Presented in part at the American Epilepsy Society Meeting, Baltimore, MD, December 7, 1987. Address correspondence and reprint requests to Dr. J. R. Buchhalter at Children’s Hospital of Philadelphia, 34th Street and Civic Center Boulevard, Philadelphia, PA 19104, U.S.A.
signed to compare simultaneous MSP and SS electrodes.
recordings
from
Methods One-hundred consecutive patients in whom technically satisfactory EEGs that included MSP and SS recordings were used for this study. The only inclusion criterion was referral to the EEG laboratory at the Beth Israel Hospital with a request for sphenoidal recording. The study population included patients with known epilepsy as well as those in whom the diagnosis was uncertain. It should be emphasized that the study was designed to provide an electrophysiologic comparison of potentials from MSP and SS leads and not to evaluate which technique would be most appropriate in a particular population. SS electrodes were inserted prior to placement of standard scalp leads. The skin overlying the zygomatic region was cleansed with an iodine solution, followed by alcohol and infiltration with 1 ml of 1% Xylocaine without epinephrine. The sterile SS electrode assembly (2) was a seven-stranded 20-gauge silver wire that was Teflon-coated and bared at the distal 3 mm. The bared end was end-hooked from the outside into the bevel of a 22-gauge needle. The elec] EPILEPSY,
VOL. 4, NO. 1,1991
29
1. R. BUCHHALTER
ET AL.
trode assembly was inserted below the zygomatic arch in a posterior and upward direction toward the foramen ovale to a depth of 3 cm (3,4). Once placed, the needle was removed. Prior studies in this laboratory have confirmed the location of the recording tip with a base view skull radiograph to be within 2 cm of the foramen ovale. The MSP electrode was a Grass 12-mm needle electrode inserted adjacent to the SS lead and taped in place. Scalp electrodes were attached with collodion or electrode paste in the standard lo-20 configuration. The following montage was used to record from surface, SS, and MSP leads simultaneously: CZ-C3, C3-T3, T9SP1, WI-SP2, SP2-T4, T4-C4, CCCZ, T3-MSPl, MSPl-MSP2, MSP2-T4, Fpl-F7, F7-T3, T3-T5, T5-01, Fp2-F8, FS-T4, T4-T6, and T6-02. Recordings commenced within 1 h of sphenoidal electrode placement. All records were reviewed by an ABCN-certified electroencephalographer (D.L.S.). Records were classified as “normal” or as containing “temporal-inferior-mesial” (TIM) abnormalities or “non-TIM” abnormalities. “TIM” abnormalities included spikes, sharp waves, or slow-wave abnormalities localized to the SS, MSP, and temporal surface leads in isolation or in any combination. All other abnormalities were considered “non-TIM.”
Results In the consecutive series of patients, only one record was considered unsatisfactory due to an MSP electrode artifact. No complications of the procedure were encountered other than mild, transient jaw discomfort. There were 37 males and 63 females. The mean age for the total group was 33.5 years (+ll years) with a range of 14-66 years. On the basis of the criteria described above, records were classified as “normal” (N = 36), “non-TIM” (N = 25), or “TIM” (N = 39). Results from the “TIM” group will form the basis of the discussion. In order to compare the recordings of individual leads, the TIM group was separated as to the leads in which the abnormalities appeared: SS electrode only (N = 6), SS and MSP electrodes (N = 9), SS and MSP electrodes and surface leads (N = 14), surface leads only (N = lo), and MSP electrode only (MSP = 0). Thus, in the group in which TIM abnormalities were found, 38% (15/39) would not have been detected without sphenoidal leads (MSP and/or SS electrodes). Furthermore, 6 of the 15 abnormalities would not have been found with MSP electrodes alone. The abnormalities found in the “SS electrodes only” group were spikes, sharp waves, and slowing in two records each. In three of the six patients in this 30
JEPILEPSY,
VOL.
4, NO. I,2991
group, an abnormal EEG had not been previously recorded, and the requested purpose of the study was to “rule out temporal lobe epilepsy.” Figure 1 illustrates several different findings recorded in a single patient. In the first 4 s of the record, rhythmic high-voltage spikes and sharp waves are recorded in the right SS lead, but not significantly recorded on the surface or MSP leads. A particularly high-voltage right SS spike during the 6th s is recorded as a suspicious low-voltage sharp wave reversal between MSP2 and T4. During the 7th s, sharp waves are found in the left SS and MSP leads with only a slight voltage predominance from the SS electrode.
Discussion Sphenoidal recordings have been used as an adjunct to standard surface recording when a temporal or inferior mesial epileptogenic focus has been suspected (3-8) and more sensitive than recordings from nasopharyngeal and ear electrodes in detection of mesial temporal spikes (9). However, the precise location of the signal generators has yet to be ascertained. In fact, it has been suggested that the wire electrode may migrate laterally without an apparent decrement in recording (10). Thus, the report of
SPHENOIDAL AND MINI-SPHENOIDAL ELECTRODES Laxer (1) provided hope that a less invasive subdermal electrode could provide the same information as that from an SS placement. The results of this study indicate that abnormalities revealed by SS electrodes (including spikes, sharp waves, and slowing) may not be represented in MSP leads. As illustrated in Fig. 1, epileptiform potentials recorded with SS electrodes can have quite variable representation in the homolateral MSP electrode. Furthermore, the lack of significant artifact in the SS electrodes indicates the feasibility of this technique for outpatient use if a physician is available for insertion. Since this study was designed to make an EEG comparison, no conclusions regarding the most appropriate patient population for SS versus MSP recording can be made. Although MSP recording cannot substitute for SS recording, the former provides information not available on routine EEG.
References 1. Laxer KD. Mini-sphenoidal electrodes in the investigation of seizures. Electroencephalogr C/in Neurophysiol 1984;58:127-9.
2. Ives JR, Gloor P. Update: chronic sphenoidal electrodes. Elechvencephalogr Clin Neurophysiol 1978;44: 789-90. 3. Rovit RR, Gloor P, Henderson LR. Temporal lobe epilepsy-a study using multiple basal electrodes. I. Description of method. Neurochirurgia (Stuttg) 1960;3:619. 4. Rovit RR, Gloor P. Temporal lobe epilepsy-a study using multiple basal electrodes. IL Clinical EEG findings.- Neuro’chirurgia (Stutt~ 1960;3:19-34. 5. Pampiglione G, Kerridge J. EEG abnormalities from the temporal lobe studied with sphenoidal electrodes. 1 Neural Neurosurg Psychiatry 1956;19:117-29. 6. Christodoulou G. Sphenoidal electrodes: their significance in diagnosing temporal lobe epileptogenic-foci. Acta Neural Stand 1967;43:587-93. 7. King DW, So EL, Marcus R, Gallagher BB. Techniques and applications of sphenoidal recording. J Clin Neurophysiol 1986;3:51-65. 8. Sperling MR, Engel J Jr. Sphenoidal electrodes. J Clin Neurophysiol 1986;3:67-73. 9. Sperling MR, Mendius JR, Engel J Jr. Mesial temporal spikes: a simultaneous comparison of sphenoidal, nasopharyngeal, and ear electrodes. Epilepsia 1986;27: 81-6. 110. Wilkus RJ,Thompson PM. Sphenoidal electrode positions and basal EEG during long-term monitoring. Epilepsia 1985;26:137-42.
J EPILEPSY,
VOL.
4, NO. 1, is91
31