SHORT COMMUNICATION
hydranencephaly is rare. The present paper presents the multimodality evoked potentials and MRI findings on 2 cases of hydranencephaly.
Electrophysiological Study on Hydranencephaly Masanobu Tayama, MD, Toshiaki Hashimoto, MD, Kenji Mori, MD, Masahito Miyazaki, MD, Hiroshi Hamaguchi, MD, Yasuhiro Kuroda, MD, Kuniaki Fukuda, MD and Shoichi Endo, MD
An electrophysiological study was performed on 2 children with hydranencephaly diagnosed by CT and/or MRL Case 1 was a 4-month-old boy who had no rostral tissues above the midbrain. Case 2 was a 5-year-old boy in whom CT showed retention of the thalamus. Short latency somatosensory evoked potentials (SSEP) in both cases exhibited the absence of cortical activity (N1 and P4) with the preservation of waves of brain stem origin. However, in case 1, wave component No was not observed, while No was seen in case 2. It was postulated, thus, that the No component of SSEP on median nerve stimulation in children, which corresponds to N16 in adults, may originate in the thalamus. Key words: Hydranencephaly, short latency somatosensory evoked potentials (SSEP), ABR, YEP, MRJ.
METHOD Hydranencephaly was diagnosed by means of CT scanning and/or MRI. In two cases, EEG, SSEP, SEP, ABR, middlelatency ABR (MLR) and YEP were examined. The recordings of evoked potentials were performed during sleep induced by trichrofos sodium. Signal averaging was performed with a date processor (ATAC-450, Nihon Koden Co) for all tests. SSEP were obtained by stimulation of the median nerve at the wrist. The recording electrodes were placed on the scalp (C 3 or C4 ), Erb's points and cervical spine C7 . The reference electrodes were placed on the hand ipsilateral to the stimulation and Fpz. The frequency response of the amplifiers ranged between 50
Tayama M, Hashimoto T, Mori K, Miyazaki M, Hamaguchi H, Kuroda Y, Fukuda K, Endo S. Eiectrophysioiogicai study on hydranencephaiy. BrainDev 1992;14:185-7
Hydranencephaly is a congenital malformation of the CNS comprising a complete or near complete absence of the cerebral hemisphere, within a relatively normal cranium. The cerebral hemispheres are replaced by fluid·filled sacs. Hydranencephaly may be accompanied by abnormalities of the thalamus, cerebellum and spinal cord, usually unassociated with other congenital malformations [1-3]. Some case reports of hydranencephaly have been published, but the study of evoked potentials and MRI on
From the Department of Pediatrics, School of Medicine, University of Tokushima, Tokushima (MT, TH, KM, MM, HH, YK); Department of Pediatrics, Kagawa Children's Hospital, Kagawa (KF, SE). Received for publication: November 9, 1991. Accepted for publication: February 23, 1992. Correspondence address: Dr. Masanobu Tayama, Department of Pediatrics, School of Medicine, University of Tokushima, Kuramoto-cho, Tokushima 770, Japan.
Fig 1 MRI demon· strating the absence of cerebral hemispheres and the existence of brain stem withouta thala· mus in case 1.
',I i': lili
10 m, M. Hydranencephaly ,I: ,I I'
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!,
,i
i I '
! j" ~ •
~~:--~!-,--------~~----------~----,,-.,-- "
"j-'~~~~------~-----------
Fig 2 EEG showing a flat pattern in case 1.
Sy, M. Hydranencephaly
6m, M. Hydranencephaly
r
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l.J1Y
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1
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Fig 3 SSEP recording on median nerve stimulation showing that the components below No were absent in case 1.
Fig 4 CT scan showing a low density area occupying the whole cerebral hemispheres and a high density area in a portion of the right occipital region and basal ganglia. The thalamus remained and the brain stem below mid brain and the cerebellum were nor· mal in case 2.
and 3,000 Hz (-3dB).
RESULTS Case 1: a 4-month-old boy. CT and MRI demonstrated the absence of cerebral hemispheres and the existence of a brainstem without a thalamus (Fig 1). On electrophysiological examination, EEG revealed a flat pattern (Fig 2) and SSEP recording on median nerve stimulation demonstrated that the components of below P3 (P13) were absent (Fig 3). The cortical components of SEP were absent and spinal evoked potentials on peroneal nerve stimulation were normal. The latency of each component of ABR was shortened, but the interpeak latency of I-V was normal. The cortical component of MLR was absent. VEP recording demonstrated no response. Case 2: a 5-year-old boy. CT scanning showed a low density area occupying the whole cerebral hemispheres,
186 Brain & Development, Vol 14, No 3, 1992
H-Erb
Fig S SSEP recording on median nerve stimulation showing that No was present and the components below Nl were absent in case 2.
and a high density area in a portion of the right occipital region and basal ganglia. The thalamus remained, and the brain stem below the midbrain and the cerebellum were normal (Fig 4). EEG was flat: SSEP recording on median nerve stimulation showed that No (N16) was present and the components below Nl (N20) were absent (Fig 5). ABR were normal and VEP recording demonstrated no response.
DISCUSSION There are two types of hydranencephaly. One is not associated with hydrocephalus (simple hydranencephaly) and the other is associated with hydrocephalus due to aqueduct stenosis. As for our 2 cases, case 1 appears to have had the former and case 2 the latter. Recently, SSEP have been clinically used for evaluation of the function in the somatosensory pathway. For children, however, it is necessary to take age and other factors into consideration because of developmental changes to interpret the result properly. Moreover, the wave pattern in children is different from that in adults according to developmental process [4, 5]. Now the generators of the main components of SSEP are well established, but unknown generators remain [6,7]. The No component in children may correspond to N16 in adults, but there have been few studies on the N16 or N18 component [8,9], although it was suggested that the generator ofN16 might be the thalamus [10]. In studies on patients with brain stem lesions, N16 was found to be absent or to be of low amplitude, but the latency ofN16 was slightly prolonged in patients with thalamic lesions. In the present study, the No component was absent in case 1 without thalami, but present in case 2 with thalami. Our observation corroborates with the previous study cited above [10].
REFERENCES 1. Halsey JH, Allen N, Chamberlain HR The morphogenesis of hydranencephaly. J Neurol Sci 1971;12: 187-217. 2. Hoffman J, Liss L. Hydranencephaly. A case report with autopsy findings in a 7-year-old girl. Acta Pediatr Scand 1969;58:297-300. 3. Nau HE, Reinhardt V, Roosen K. Hydranencephaly - clinical and neuropathological aspects-. Acta Neurochir 1979;47: 219-33. 4. Hashimoto T, Tayama M, Hiura K, et al. Short latency somatosensory evoked potentials in children. Brain Dev (Tokyo) 1983;5: 390-6. 5. Taylor MJ, Fagan ER SEPs to median nerve stimulation: normative data for paediatrics. Electroencephalogr elin Neurophysiol 1988; 71: 323-30. 6. Nakanishi T, Tamaki M, Ozaki Y, Arasaki K. Origins of short latency somatosensory evoked potentials to median nerve
7. 8. 9.
10.
stimulation. Electroencephalogr Qin Neurophysiol 1983;56: 74-85 . Lueders H, Lesser R, Hahn J, et al. Subcortical somatosensory evoked potentials to median nerve stimulation. Brain 1983;106:341-72. Hashimoto I. Somatosensory evoked potentials from the human brain-stem: origins of short latency potentials. Electroencephalogr Qin Neurophysiol 1984;57:221-7. Mauguier F, Desmedt JE, Courjon J. Neural generators of N18 and P14 far-field somatosensory evoked potentials studied in patients with lesions of thalamus or thalamocortical radiations. Electroencephalogr Qin Neurophysiol 1983 ;56: 283-92. Tsuji S, Shibasaki H, Kato M, Kuroiwa Y, Shima F. Subcortical thalamic and cortical somatosensory evoked potentials to median nerve stimulation. Electroencephalogr Qin NeurophysioI1981;52:3.36-44.
Tayama et al: SSEP on hydranencephaly 187
hydranencephaly is rare. The present paper presents the multimodality evoked potentials and MRI findings on 2 cases of hydranencephaly.
Electrophysiological Study on Hydranencephaly Masanobu Tayama, MD, Toshiaki Hashimoto, MD, Kenji Mori, MD, Masahito Miyazaki, MD, Hiroshi Hamaguchi, MD, Yasuhiro Kuroda, MD, Kuniaki Fukuda, MD and Shoichi Endo, MD
An electrophysiological study was performed on 2 children with hydranencephaly diagnosed by CT and/or MRL Case 1 was a 4-month-old boy who had no rostral tissues above the midbrain. Case 2 was a 5-year-old boy in whom CT showed retention of the thalamus. Short latency somatosensory evoked potentials (SSEP) in both cases exhibited the absence of cortical activity (N1 and P4) with the preservation of waves of brain stem origin. However, in case 1, wave component No was not observed, while No was seen in case 2. It was postulated, thus, that the No component of SSEP on median nerve stimulation in children, which corresponds to N16 in adults, may originate in the thalamus. Key words: Hydranencephaly, short latency somatosensory evoked potentials (SSEP), ABR, YEP, MRJ.
METHOD Hydranencephaly was diagnosed by means of CT scanning and/or MRI. In two cases, EEG, SSEP, SEP, ABR, middlelatency ABR (MLR) and YEP were examined. The recordings of evoked potentials were performed during sleep induced by trichrofos sodium. Signal averaging was performed with a date processor (ATAC-450, Nihon Koden Co) for all tests. SSEP were obtained by stimulation of the median nerve at the wrist. The recording electrodes were placed on the scalp (C 3 or C4 ), Erb's points and cervical spine C7 . The reference electrodes were placed on the hand ipsilateral to the stimulation and Fpz. The frequency response of the amplifiers ranged between 50
Tayama M, Hashimoto T, Mori K, Miyazaki M, Hamaguchi H, Kuroda Y, Fukuda K, Endo S. Eiectrophysioiogicai study on hydranencephaiy. BrainDev 1992;14:185-7
Hydranencephaly is a congenital malformation of the CNS comprising a complete or near complete absence of the cerebral hemisphere, within a relatively normal cranium. The cerebral hemispheres are replaced by fluid·filled sacs. Hydranencephaly may be accompanied by abnormalities of the thalamus, cerebellum and spinal cord, usually unassociated with other congenital malformations [1-3]. Some case reports of hydranencephaly have been published, but the study of evoked potentials and MRI on
From the Department of Pediatrics, School of Medicine, University of Tokushima, Tokushima (MT, TH, KM, MM, HH, YK); Department of Pediatrics, Kagawa Children's Hospital, Kagawa (KF, SE). Received for publication: November 9, 1991. Accepted for publication: February 23, 1992. Correspondence address: Dr. Masanobu Tayama, Department of Pediatrics, School of Medicine, University of Tokushima, Kuramoto-cho, Tokushima 770, Japan.
Fig 1 MRI demon· strating the absence of cerebral hemispheres and the existence of brain stem withouta thala· mus in case 1.
',I i': lili
10 m, M. Hydranencephaly ,I: ,I I'
::
!,
,i
i I '
! j" ~ •
~~:--~!-,--------~~----------~----,,-.,-- "
"j-'~~~~------~-----------
Fig 2 EEG showing a flat pattern in case 1.
Sy, M. Hydranencephaly
6m, M. Hydranencephaly
r
H-CV7
l.J1Y
H-C4
I:
l~Y
C
1
I ~-
~Y
1 ~Y
TIME DI5ECl
Fig 3 SSEP recording on median nerve stimulation showing that the components below No were absent in case 1.
Fig 4 CT scan showing a low density area occupying the whole cerebral hemispheres and a high density area in a portion of the right occipital region and basal ganglia. The thalamus remained and the brain stem below mid brain and the cerebellum were nor· mal in case 2.
and 3,000 Hz (-3dB).
RESULTS Case 1: a 4-month-old boy. CT and MRI demonstrated the absence of cerebral hemispheres and the existence of a brainstem without a thalamus (Fig 1). On electrophysiological examination, EEG revealed a flat pattern (Fig 2) and SSEP recording on median nerve stimulation demonstrated that the components of below P3 (P13) were absent (Fig 3). The cortical components of SEP were absent and spinal evoked potentials on peroneal nerve stimulation were normal. The latency of each component of ABR was shortened, but the interpeak latency of I-V was normal. The cortical component of MLR was absent. VEP recording demonstrated no response. Case 2: a 5-year-old boy. CT scanning showed a low density area occupying the whole cerebral hemispheres,
186 Brain & Development, Vol 14, No 3, 1992
H-Erb
Fig S SSEP recording on median nerve stimulation showing that No was present and the components below Nl were absent in case 2.
and a high density area in a portion of the right occipital region and basal ganglia. The thalamus remained, and the brain stem below the midbrain and the cerebellum were normal (Fig 4). EEG was flat: SSEP recording on median nerve stimulation showed that No (N16) was present and the components below Nl (N20) were absent (Fig 5). ABR were normal and VEP recording demonstrated no response.
DISCUSSION There are two types of hydranencephaly. One is not associated with hydrocephalus (simple hydranencephaly) and the other is associated with hydrocephalus due to aqueduct stenosis. As for our 2 cases, case 1 appears to have had the former and case 2 the latter. Recently, SSEP have been clinically used for evaluation of the function in the somatosensory pathway. For children, however, it is necessary to take age and other factors into consideration because of developmental changes to interpret the result properly. Moreover, the wave pattern in children is different from that in adults according to developmental process [4, 5]. Now the generators of the main components of SSEP are well established, but unknown generators remain [6,7]. The No component in children may correspond to N16 in adults, but there have been few studies on the N16 or N18 component [8,9], although it was suggested that the generator ofN16 might be the thalamus [10]. In studies on patients with brain stem lesions, N16 was found to be absent or to be of low amplitude, but the latency ofN16 was slightly prolonged in patients with thalamic lesions. In the present study, the No component was absent in case 1 without thalami, but present in case 2 with thalami. Our observation corroborates with the previous study cited above [10].
REFERENCES 1. Halsey JH, Allen N, Chamberlain HR The morphogenesis of hydranencephaly. J Neurol Sci 1971;12: 187-217. 2. Hoffman J, Liss L. Hydranencephaly. A case report with autopsy findings in a 7-year-old girl. Acta Pediatr Scand 1969;58:297-300. 3. Nau HE, Reinhardt V, Roosen K. Hydranencephaly - clinical and neuropathological aspects-. Acta Neurochir 1979;47: 219-33. 4. Hashimoto T, Tayama M, Hiura K, et al. Short latency somatosensory evoked potentials in children. Brain Dev (Tokyo) 1983;5: 390-6. 5. Taylor MJ, Fagan ER SEPs to median nerve stimulation: normative data for paediatrics. Electroencephalogr elin Neurophysiol 1988; 71: 323-30. 6. Nakanishi T, Tamaki M, Ozaki Y, Arasaki K. Origins of short latency somatosensory evoked potentials to median nerve
7. 8. 9.
10.
stimulation. Electroencephalogr Qin Neurophysiol 1983;56: 74-85 . Lueders H, Lesser R, Hahn J, et al. Subcortical somatosensory evoked potentials to median nerve stimulation. Brain 1983;106:341-72. Hashimoto I. Somatosensory evoked potentials from the human brain-stem: origins of short latency potentials. Electroencephalogr Qin Neurophysiol 1984;57:221-7. Mauguier F, Desmedt JE, Courjon J. Neural generators of N18 and P14 far-field somatosensory evoked potentials studied in patients with lesions of thalamus or thalamocortical radiations. Electroencephalogr Qin Neurophysiol 1983 ;56: 283-92. Tsuji S, Shibasaki H, Kato M, Kuroiwa Y, Shima F. Subcortical thalamic and cortical somatosensory evoked potentials to median nerve stimulation. Electroencephalogr Qin NeurophysioI1981;52:3.36-44.
Tayama et al: SSEP on hydranencephaly 187
