278
Electroencephalography and Clinical Neurophysiology, 1978, 4 5 : 2 7 8 - - 2 8 0 © Elsevier/North-Holland Scientific Publishers, Ltd.
Clinical note
THE EFFECTS OF CHIASMAL COMPRESSION ON THE PATTERN VISUAL EVOKED POTENTIAL G.E. HOLDER
Regional Department of Clinical Neurophysiology, Brook General Hospital, Woolwich SE18 (England) (Accepted for publication: March 20, 1978)
This report presents the findings of an investigation into the effects of chiasmal compression on the visual evoked potentials (VEPs) to pattern reversal stimulation (PVEP). A report of PVEP changes has appeared (Halliday et al. 1976) which found abnormalities in 10/10 patients with pituitary tumours or craniopharyngiomas, but surprisingly the abnormalities were lateralised ipsilaterally to the stimulated eye and therefore to the field defect. This does not correspond with the findings that might have been predicted on a purely neuroanatomical basis. A preliminary account of the results of this investigation has been presented (Holder 1977).
Method and Materials Ten patients with chiasmal compression were studied. Eight had pituitary tumours, one a craniopharyngioma and one an aneurysm. These diagnoses were all confirmed at craniotomy except one of the pituitary tumours which was established by E M I scan. All patients had visual field defects (see Table I). Bipolar occipital-sylvian and occipital-parietal recordings were taken using silver-silverchloride stickon electrodes applied according to Pampiglione (1966) but with 2 occipital electrodes, situated 2 c m anterior and 2 c m lateral to the inion, replacing the original mid-line occipital electrode. This is c o m m o n l y k n o w n as the Modified Maudsley system of electrode placement. On-line averaging was performed with a Datalab Biomac 1000 receiving its input via an S L E E E G machine which was used to monitor eye movements, etc., in addition to the primary E E G trace. Pattern reversal stimulation was provided by a Digitimer stimulator situated 80 c m from the patient and subtending a total field of 11 ° with an individual check substance of 26'. In seven patients additional stimulation was also performed with a 13' individual check subtense pattern contained in an 8 ° total field. M o v e m e n t of the pattern and initiation of the Biomac sweep was controlled by a Digitimer 4030 pulse gen-
erator. T w o reversals/sec were used with an analysis time of 320 msec. Responses were generally the r~esult of 128 reversals but on occasions 256 or even '~512 reversals were needed to obtain a satisfactory trace. Each eye was examined at least twice in all pat!ents, the findings being assessed in relation to an extensive control group.
Results The results are documented in Table I. P2 has been used to describe the major positive component normally seen at approx. 100 msec, and N 3 the immediately following negative component. All latency measurements are taken from the peak of the component concerned. The findings were abnormal in all patients, the m a x i m u m abnormality being observed in the recordings taken over the hemisphere contralhteral to the stimulated eye and therefore contralateral to the field defect. Additional recordings with the 13' check stimulus were taken in patients 3, 4, 5, 6, 7, 8 and 9. In patient 9 the findings were unchanged. In all other patients the magnitude of the interhemispheric asymmetry seen with the 26' check stimulus was enhanced, and indeed, in patient 8 an 8 msec interhemispheric latency asymmetry (contralateral response delayed compared with ipsilateral)was observed in the major positive component which had not been present using the 26' check stimulus. A n example of the type of asymmetry found and an example of enhanced lateralisation with the 13' check pattern are shown in Figs. 1 and 2. The findings of Halliday et al. (1976) of the possibility of delayed V E P in compressive lesions are confirmed. In fact, the longest latency seen was some 35 m s e c above the upper limit of normal for age and therefore akin to those delays regularly seen in patients with demyelination. It is emphasised, however, that the interhemispheric asymmetry seen points towards a compressive lesion and the impor-
TABLE I VEP findings. B.T.H., b i t e m p o r a l h e m i a n o p i a ; N., normal; A., abnormal.
Females 1 M.F.
Age
Eye
V.A.
34
O.D. O.S.
6/36 6/9
Normal/ abnormal
Contralateral response (P2 unless specified)
Fields/pathology. All pituitary t u m o u r s unless specified
96 96
N N
Absent P2 lat 1' 6 msec; N3 lat t 20 msec A m p J~ 50% lat 1' 5--8 msec Absent As ipsilateral A m p ~ 70% lat f 4--6 msec A m p J~ 50--60% Lat 1" 4--8 msec; amp ~ 40--50% A m p ~ 70% Absent Variable, o f t e n lat 1" amp Absent
O.D. T e m p o r a l field loss
Ipsilateral P2 latency (msec)
2
L.C.
49
O.D.
6/9
104
N
3
P.G.
54
O.S. O.D. O.S.
6/9 6/18 6/24
108 104 100
A N N
4
M.P.
59
O.D. O.S.
6/5 6/6
96 106
N N *
5
J.D.
60
6
R.G.
63
O.D. O.S. O.D.
6/9 6/60 6/9
104 120--30 120
N A A
O.S.
6/18
140
A
O.D. O.S. O.D. O.S. O.D.
6/36 6/5 6/6 6/5 6/12
Absent 100 116 104 118
A N A N A
O.S. O.D. O.S.
6/60 6/24 6/24
140 145 Absent
A A A
Males 7 K.A.
30
8
B.S.
39
9
G.N.
63
10
H.F.
74
Absent As ipsilateral As ipsilateral As ipsilateral P2 lat t 4 msec; N3 lat 1 10--20 msec Absent Absent Absent
B . T . H . O . S . > O.D. Craniopharyngioma Paracentral s c o t o m a t a e x t e n d i n g to upper temporal fields B . T . H . O . S . > O.D.
B . T . H . O . S . > O.D. B . T . H . O . S . >> O.D. Aneurysm
O.D. T e m p o r a l field loss O.S. T e m p o r a l and nasal loss Slight loss b o t h u p p e r temporal fields B . T . H . O . S . >> O.D.
B . T . H . O . D . > O.S.
* In this patient, although the absolute latencies f r o m each eye are within normal limits, the m a g n i t u d e of the interocular a s y m m e t r y is a b n o r m a l l y large. LC
act 4 9
PG
VAR 6/9
VAL 6/9
act 54 VAL
5/24
P a t t e r n VER R eyg
Patt~zr n VER 26'
L ~y~
]3'
DCC - sylv R
)co -sylv
L~ j ' ~ / ~ "
5vVl
5~V lOOms
lOOms
128 reversals
128 reversals -
lOOms
Fig. 1. Findings typical o f chiasmal c o m p r e s s i o n seen in a lady with a c r a n i o p h a r y n g i o m a (patient 2, bitemporal h e m i a n o p i a affecting the left eye m o r e t h a n t h e right). S t i m u l a t i o n of the right eye results in a response which is delayed in the left h e m i s p h e r e traces; stimulation of t h e left eye evokes no response in the right h e m i s p h e r e traces (positivity down).
Fig. 2. T h e increased lateralisation p r o d u c e d with a small check size seen o n stimulation of the left eye of a lady with a pituitary a d e n o m a (patient 3, paracentral s c o t o m a e x t e n d i n g into the u p p e r t e m p o r a l field). Use of the 13' check results in a virtually absent right hemisphere response c o m p a r e d w i t h the reduced but clearly present response seen with the 26' check. N o t e the differing calibrations (positivity down).
G.E. H O L D E R
280 tance of m u l t i c h a n n e l recording using electrodes situated away from t h e midline is stressed.
Discussion The value of the P V E P in chiasmal compression is c o n f i r m e d , for, as in the previous report (Halliday et al. 1976), the findings were abnormal in all patients studied. However, in the present study the m a x i m u m a b n o r m a l i t y was, w i t h o u t e x c e p t i o n , localised contralaterally to the field defect. This contralateral localisation corresponds with the findings predictable f r o m a n e u r o a n a t o m i c a l view b u t is in disagreement with the findings of Halliday et al. (1976) w h o f o u n d the m a x i m u m a b n o r m a l i t y ipsilateral to the field defect. As there can be little d o u b t (Blumhardt et al. 1977) that the (relatively) intact response is actually generated in the hemisphere ipsilateral to the field defect it seems reasonable to assume t h a t the gross discrepancy in results b e t w e e n this study and that of Halliday's is due to differences in stimulus and recording parameters. Barrett et al. (1976) found, using half-field stimulation in normal subjects, that if stimulation is confined to the macular area t h e n their normally ipsilateral response m a y even have a contralateral predominance. This is postulated because the cortical representation of the macula is at the posterior pole of the occipital lobe and the generator neurones here would be facing posteriorly rather than medially. The 26' checks in an 11 ° field used in the present study give b e t t e r macular stimulation than the 50' checks in a 32 ° field used by Halliday et al. (1976) and it is also possible that electrodes 2 cm anterior and lateral to the inion are better placed to record f r o m the occipital poles than electrodes 5 cm anterior and lateral to the inion. The possible influence of stimulus parameters is s u p p o r t e d by the increased lateralisation seen with 13' checks in an 8 ° field which gives still better macular stimulation. These findings indicate that m o r e research is needed to elucidate these p r o b l e m s which are obviously o f critical i m p o r t a n c e in clinical interpretation, but as it seems likely (Halliday, personal c o m m u n i c a tion) that stimulus parameters and electrode placem e n t are indeed responsible for the apparent discrepancy b e t w e e n this report and previous findings, the i m p o r t a n c e of stringently controlling these variables c a n n o t be t o o strongly emphasised.
Summary T h e visual evoked potentials (VEPs) to pattern reversal stimulation (26' individual check subtense, 11 ° total field) have been e x a m i n e d in 10 patients with proven chiasmal compression. Bipolar occipitalsylvian and occipital-parietal recordings were taken with electrodes placed according to the Modified
Maudsley system. In all patients abnormalities, taking the form of latency delays or amplitude r e d u c t i o n s , were found in response to m o n o c u l a r stimulation which, w i t h o u t e x c e p t i o n , were m a x i m a l in the traces corresponding, to the hemisphere contralateral to the field defect. In seven patients responses to a 13' pattern were also e x a m i n e d . In six o f these the lateralisat i o n of abnormality was enhanced. The discrepancy b e t w e e n these and previous findings is discussed, the i m p o r t a n c e of stimulus and recording parameters being stressed.
R6sum6 Effets de la compression du chiasma optique sur les potentiels dvoquds par damier On a 6tudi6 les potentiels 6voqu6s visuels (PEV) en r6ponse ~ des stimulus alternants (carr6s de 26', c h a m p t o t a l de 11 ° ) sur 10 patients souffrant de c o m pression du chiasma. On a effectu6 des enregistrements bipolaires occipito-sylviens et occipito-pari6taux, au m o y e n d'61ectrodes plac6es selon le syst~me dit 'Modified Maudsley'. Chez t o u s l e s patients, on a relev6 des anomalies ( a u g m e n t a t i o n du t e m p s de latence ou r6ductions d ' a m p l i t u d e ) des potentiels des stimulus monoculaires; dans t o u s l e s cas, ces anomalies 6talent m a x i m a l e s sur les trac6s c o r r e s p o n d a n t l'h6misph~re contralat6ral au c h a m p d6ficitaire. On a 6galement examin6 chez sept p a t i e n t s j e s r6ponses un pattern de 13'. Pour six d ' e n t r e eux la lat6ralisat i o n de l ' a n o m a l i e s'est ainsi trouv6e accrue. Les contradictions entre ces observations et des r6sultats ant6rieurs sont discut6s; on met en particulier en cause des diff6rences dans les param6tres de stimulat i o n et d'enregistrement.
References Barrett, G., B l u m h a r d t , L.D., Halliday, A.M., Halliday, E. and Kriss, A. A p a r a d o x in the lateralisation of the visual evoked response. Nature (Lond.), 1976, 261: 253--255. Blumhardt, L.D., Barrett, G. and Halliday, A.M. The a s y m m e t r i c a l visual evoked potential to pattern reversal in one half field and its significance for the analysis of visual field defects. Brit. J. Ophthal., 1977, 61: 4 5 4 - - 4 6 1 . Halliday, A.M., Halliday, E., Kriss, A., M c D o n a l d , W.I. and Mushin, J. The pattern-evoked potential in compression of the anterior visual pathways. Brain, 1976, 99: 357--374. Holder, G.E. The pattern V E R in chiasmal compression. E l e c t r o e n c e p h . clin. Neurophysiol., 1977, 43: 772--773. Pampiglione, G. S o m e anatomical considerations upon electrode p l a c e m e n t in routine EEG. Proc. Electrophysiol. T e c h n o l . Ass., 1966, 13: 166--176.
Electroencephalography and Clinical Neurophysiology, 1978, 4 5 : 2 7 8 - - 2 8 0 © Elsevier/North-Holland Scientific Publishers, Ltd.
Clinical note
THE EFFECTS OF CHIASMAL COMPRESSION ON THE PATTERN VISUAL EVOKED POTENTIAL G.E. HOLDER
Regional Department of Clinical Neurophysiology, Brook General Hospital, Woolwich SE18 (England) (Accepted for publication: March 20, 1978)
This report presents the findings of an investigation into the effects of chiasmal compression on the visual evoked potentials (VEPs) to pattern reversal stimulation (PVEP). A report of PVEP changes has appeared (Halliday et al. 1976) which found abnormalities in 10/10 patients with pituitary tumours or craniopharyngiomas, but surprisingly the abnormalities were lateralised ipsilaterally to the stimulated eye and therefore to the field defect. This does not correspond with the findings that might have been predicted on a purely neuroanatomical basis. A preliminary account of the results of this investigation has been presented (Holder 1977).
Method and Materials Ten patients with chiasmal compression were studied. Eight had pituitary tumours, one a craniopharyngioma and one an aneurysm. These diagnoses were all confirmed at craniotomy except one of the pituitary tumours which was established by E M I scan. All patients had visual field defects (see Table I). Bipolar occipital-sylvian and occipital-parietal recordings were taken using silver-silverchloride stickon electrodes applied according to Pampiglione (1966) but with 2 occipital electrodes, situated 2 c m anterior and 2 c m lateral to the inion, replacing the original mid-line occipital electrode. This is c o m m o n l y k n o w n as the Modified Maudsley system of electrode placement. On-line averaging was performed with a Datalab Biomac 1000 receiving its input via an S L E E E G machine which was used to monitor eye movements, etc., in addition to the primary E E G trace. Pattern reversal stimulation was provided by a Digitimer stimulator situated 80 c m from the patient and subtending a total field of 11 ° with an individual check substance of 26'. In seven patients additional stimulation was also performed with a 13' individual check subtense pattern contained in an 8 ° total field. M o v e m e n t of the pattern and initiation of the Biomac sweep was controlled by a Digitimer 4030 pulse gen-
erator. T w o reversals/sec were used with an analysis time of 320 msec. Responses were generally the r~esult of 128 reversals but on occasions 256 or even '~512 reversals were needed to obtain a satisfactory trace. Each eye was examined at least twice in all pat!ents, the findings being assessed in relation to an extensive control group.
Results The results are documented in Table I. P2 has been used to describe the major positive component normally seen at approx. 100 msec, and N 3 the immediately following negative component. All latency measurements are taken from the peak of the component concerned. The findings were abnormal in all patients, the m a x i m u m abnormality being observed in the recordings taken over the hemisphere contralhteral to the stimulated eye and therefore contralateral to the field defect. Additional recordings with the 13' check stimulus were taken in patients 3, 4, 5, 6, 7, 8 and 9. In patient 9 the findings were unchanged. In all other patients the magnitude of the interhemispheric asymmetry seen with the 26' check stimulus was enhanced, and indeed, in patient 8 an 8 msec interhemispheric latency asymmetry (contralateral response delayed compared with ipsilateral)was observed in the major positive component which had not been present using the 26' check stimulus. A n example of the type of asymmetry found and an example of enhanced lateralisation with the 13' check pattern are shown in Figs. 1 and 2. The findings of Halliday et al. (1976) of the possibility of delayed V E P in compressive lesions are confirmed. In fact, the longest latency seen was some 35 m s e c above the upper limit of normal for age and therefore akin to those delays regularly seen in patients with demyelination. It is emphasised, however, that the interhemispheric asymmetry seen points towards a compressive lesion and the impor-
TABLE I VEP findings. B.T.H., b i t e m p o r a l h e m i a n o p i a ; N., normal; A., abnormal.
Females 1 M.F.
Age
Eye
V.A.
34
O.D. O.S.
6/36 6/9
Normal/ abnormal
Contralateral response (P2 unless specified)
Fields/pathology. All pituitary t u m o u r s unless specified
96 96
N N
Absent P2 lat 1' 6 msec; N3 lat t 20 msec A m p J~ 50% lat 1' 5--8 msec Absent As ipsilateral A m p ~ 70% lat f 4--6 msec A m p J~ 50--60% Lat 1" 4--8 msec; amp ~ 40--50% A m p ~ 70% Absent Variable, o f t e n lat 1" amp Absent
O.D. T e m p o r a l field loss
Ipsilateral P2 latency (msec)
2
L.C.
49
O.D.
6/9
104
N
3
P.G.
54
O.S. O.D. O.S.
6/9 6/18 6/24
108 104 100
A N N
4
M.P.
59
O.D. O.S.
6/5 6/6
96 106
N N *
5
J.D.
60
6
R.G.
63
O.D. O.S. O.D.
6/9 6/60 6/9
104 120--30 120
N A A
O.S.
6/18
140
A
O.D. O.S. O.D. O.S. O.D.
6/36 6/5 6/6 6/5 6/12
Absent 100 116 104 118
A N A N A
O.S. O.D. O.S.
6/60 6/24 6/24
140 145 Absent
A A A
Males 7 K.A.
30
8
B.S.
39
9
G.N.
63
10
H.F.
74
Absent As ipsilateral As ipsilateral As ipsilateral P2 lat t 4 msec; N3 lat 1 10--20 msec Absent Absent Absent
B . T . H . O . S . > O.D. Craniopharyngioma Paracentral s c o t o m a t a e x t e n d i n g to upper temporal fields B . T . H . O . S . > O.D.
B . T . H . O . S . > O.D. B . T . H . O . S . >> O.D. Aneurysm
O.D. T e m p o r a l field loss O.S. T e m p o r a l and nasal loss Slight loss b o t h u p p e r temporal fields B . T . H . O . S . >> O.D.
B . T . H . O . D . > O.S.
* In this patient, although the absolute latencies f r o m each eye are within normal limits, the m a g n i t u d e of the interocular a s y m m e t r y is a b n o r m a l l y large. LC
act 4 9
PG
VAR 6/9
VAL 6/9
act 54 VAL
5/24
P a t t e r n VER R eyg
Patt~zr n VER 26'
L ~y~
]3'
DCC - sylv R
)co -sylv
L~ j ' ~ / ~ "
5vVl
5~V lOOms
lOOms
128 reversals
128 reversals -
lOOms
Fig. 1. Findings typical o f chiasmal c o m p r e s s i o n seen in a lady with a c r a n i o p h a r y n g i o m a (patient 2, bitemporal h e m i a n o p i a affecting the left eye m o r e t h a n t h e right). S t i m u l a t i o n of the right eye results in a response which is delayed in the left h e m i s p h e r e traces; stimulation of t h e left eye evokes no response in the right h e m i s p h e r e traces (positivity down).
Fig. 2. T h e increased lateralisation p r o d u c e d with a small check size seen o n stimulation of the left eye of a lady with a pituitary a d e n o m a (patient 3, paracentral s c o t o m a e x t e n d i n g into the u p p e r t e m p o r a l field). Use of the 13' check results in a virtually absent right hemisphere response c o m p a r e d w i t h the reduced but clearly present response seen with the 26' check. N o t e the differing calibrations (positivity down).
G.E. H O L D E R
280 tance of m u l t i c h a n n e l recording using electrodes situated away from t h e midline is stressed.
Discussion The value of the P V E P in chiasmal compression is c o n f i r m e d , for, as in the previous report (Halliday et al. 1976), the findings were abnormal in all patients studied. However, in the present study the m a x i m u m a b n o r m a l i t y was, w i t h o u t e x c e p t i o n , localised contralaterally to the field defect. This contralateral localisation corresponds with the findings predictable f r o m a n e u r o a n a t o m i c a l view b u t is in disagreement with the findings of Halliday et al. (1976) w h o f o u n d the m a x i m u m a b n o r m a l i t y ipsilateral to the field defect. As there can be little d o u b t (Blumhardt et al. 1977) that the (relatively) intact response is actually generated in the hemisphere ipsilateral to the field defect it seems reasonable to assume t h a t the gross discrepancy in results b e t w e e n this study and that of Halliday's is due to differences in stimulus and recording parameters. Barrett et al. (1976) found, using half-field stimulation in normal subjects, that if stimulation is confined to the macular area t h e n their normally ipsilateral response m a y even have a contralateral predominance. This is postulated because the cortical representation of the macula is at the posterior pole of the occipital lobe and the generator neurones here would be facing posteriorly rather than medially. The 26' checks in an 11 ° field used in the present study give b e t t e r macular stimulation than the 50' checks in a 32 ° field used by Halliday et al. (1976) and it is also possible that electrodes 2 cm anterior and lateral to the inion are better placed to record f r o m the occipital poles than electrodes 5 cm anterior and lateral to the inion. The possible influence of stimulus parameters is s u p p o r t e d by the increased lateralisation seen with 13' checks in an 8 ° field which gives still better macular stimulation. These findings indicate that m o r e research is needed to elucidate these p r o b l e m s which are obviously o f critical i m p o r t a n c e in clinical interpretation, but as it seems likely (Halliday, personal c o m m u n i c a tion) that stimulus parameters and electrode placem e n t are indeed responsible for the apparent discrepancy b e t w e e n this report and previous findings, the i m p o r t a n c e of stringently controlling these variables c a n n o t be t o o strongly emphasised.
Summary T h e visual evoked potentials (VEPs) to pattern reversal stimulation (26' individual check subtense, 11 ° total field) have been e x a m i n e d in 10 patients with proven chiasmal compression. Bipolar occipitalsylvian and occipital-parietal recordings were taken with electrodes placed according to the Modified
Maudsley system. In all patients abnormalities, taking the form of latency delays or amplitude r e d u c t i o n s , were found in response to m o n o c u l a r stimulation which, w i t h o u t e x c e p t i o n , were m a x i m a l in the traces corresponding, to the hemisphere contralateral to the field defect. In seven patients responses to a 13' pattern were also e x a m i n e d . In six o f these the lateralisat i o n of abnormality was enhanced. The discrepancy b e t w e e n these and previous findings is discussed, the i m p o r t a n c e of stimulus and recording parameters being stressed.
R6sum6 Effets de la compression du chiasma optique sur les potentiels dvoquds par damier On a 6tudi6 les potentiels 6voqu6s visuels (PEV) en r6ponse ~ des stimulus alternants (carr6s de 26', c h a m p t o t a l de 11 ° ) sur 10 patients souffrant de c o m pression du chiasma. On a effectu6 des enregistrements bipolaires occipito-sylviens et occipito-pari6taux, au m o y e n d'61ectrodes plac6es selon le syst~me dit 'Modified Maudsley'. Chez t o u s l e s patients, on a relev6 des anomalies ( a u g m e n t a t i o n du t e m p s de latence ou r6ductions d ' a m p l i t u d e ) des potentiels des stimulus monoculaires; dans t o u s l e s cas, ces anomalies 6talent m a x i m a l e s sur les trac6s c o r r e s p o n d a n t l'h6misph~re contralat6ral au c h a m p d6ficitaire. On a 6galement examin6 chez sept p a t i e n t s j e s r6ponses un pattern de 13'. Pour six d ' e n t r e eux la lat6ralisat i o n de l ' a n o m a l i e s'est ainsi trouv6e accrue. Les contradictions entre ces observations et des r6sultats ant6rieurs sont discut6s; on met en particulier en cause des diff6rences dans les param6tres de stimulat i o n et d'enregistrement.
References Barrett, G., B l u m h a r d t , L.D., Halliday, A.M., Halliday, E. and Kriss, A. A p a r a d o x in the lateralisation of the visual evoked response. Nature (Lond.), 1976, 261: 253--255. Blumhardt, L.D., Barrett, G. and Halliday, A.M. The a s y m m e t r i c a l visual evoked potential to pattern reversal in one half field and its significance for the analysis of visual field defects. Brit. J. Ophthal., 1977, 61: 4 5 4 - - 4 6 1 . Halliday, A.M., Halliday, E., Kriss, A., M c D o n a l d , W.I. and Mushin, J. The pattern-evoked potential in compression of the anterior visual pathways. Brain, 1976, 99: 357--374. Holder, G.E. The pattern V E R in chiasmal compression. E l e c t r o e n c e p h . clin. Neurophysiol., 1977, 43: 772--773. Pampiglione, G. S o m e anatomical considerations upon electrode p l a c e m e n t in routine EEG. Proc. Electrophysiol. T e c h n o l . Ass., 1966, 13: 166--176.
