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Aberrant neuronal development in hemimegalencephaly: Immunohistochemical and Golgi studies
Aberrant Neuronal Development in Hemimegalencephaly'. Immunohistochemical and Golgi Studies Sachio Takashima, M D * t , F a n n y Chan, P h D * , L a u r e n c e E. Becker, M D * , and H i r o m i Kuruta, MT*
Immunohistochemical and Goigi studies were performed on 6 patients with hemimegalencephaly. Immunohistochemical staining demonstrated glial, neuronal, and myelin heterotopia in the leptomeninges, cortex, and white matter with glial fibrillary acidic protein, myelin basic protein, and synaptophysin antisera. Golgi studies revealed small and deformed neurons in the superficial layers around abnormal sulci, and hypertrophic neurons with an increased number of dendrites and spines in the deeper cortex. The coexistence of a cell migration disorder, proliferation, and hypertrophy in each patient may imply a growth factor disturbance that controls cell proliferation. These unilateral cerebral malformations suggest that early surgical excision may be beneficial. Takashima S, Chart F, Becker LE, Kuruta H. Aberrant neuronal development in hemimegalencephaly: Immunohistochemical and Golgi studies. Pediatr Neurol 1991;7: 275-80.
Methods Clinical data are described in Table 1 [3]. Brain tissue was obtained from 6 patients at surgical resection or autopsy. The formalin-fixed and paraffin-embedded specimens were cut, deparaffinized, and stained with hematoxylin and eosin, luxol-fast blue, Holzer, and Bodian stains. Peroxidase and antiperoxidase immunohistochemistry using antisera against glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and synaptophysin was applied to brain sections. Fresh brain tissue from 3 patients was placed in Golgi fixative and stained by the rapid Golgi method [4]. The specimens were observed under light microscopy and camera lucida drawings prepared.
Results
Histology. In all 6 patients, histologic examination revealed abnormal gyration, poor gray-white matter differentiation, disturbed lamination, enlarged neurons (Fig 1), and increased neuronal heterotopia (subcortical and deep white matter).
Introduction Hemimegalencephaly or unilateral megalencephaly is a congenital malformation caused presumably by abnormal neuronal proliferation and migration during the second through fifth month of gestation, resulting in overgrowth and polymicrogyria of one cerebral hemisphere [1]. Patients with unilateral megalencephaly typically present with a triad of clinical findings: intractable seizures, developmental delay, and progressive hemiparesis. The etiology and pathogenesis are unknown. Because of the intractable seizure disorder, total or partial hemispherectomy has been advocated as a preferred treatment [2]. In this report, neuropathologic, immunohistochemical, and somatodendritic observations are described in the megalencephalic hemisphere of 6 patients.
Figure 1. Enlarged neurons with disturbed lamination in the cerebral cortex. Hematoxylin and eosin stain, original magnification x400.
From the *Department of Pathology, Division of Neuropathology; University of Toronto and The Hospital for Sick Children; Toronto, Canada; and tDivision of Mental Retardation and Birth Defect Research; National Institute of Neuroscience; National Center of Neurology and Psychiatry; Tokyo, Japan.
Communications should be addressed to: Dr. Takashima; Division of Mental Retardation and Birth Defect Research; National Institute of Neuroscience; NCNP; 4-1-1 Ogawahigashicho; Kodaira, Tokyo 187, Japan. Received January 14, 1991; accepted February 28, 1991.
Takashima et al: Hemimegalencephaly 275
Table 1.
Patients and neuropathology
1
2
3
Patients 4
5
6
7
M
M
F
F
M
M
1::
Seizure onset
18 mos PM G MC
4 days PM G MC
2 days PM G CPS
! day IS PM G
3 days PM G
14 days IS PM MC
Psychomotor
MR
DD
MR
DD
NA
DD
DD
Hemiparesis
+
+
+
+
-
+
+
8 yrs
10 mos
10 yrs
6 mos
3 days
5 mos
9 mos
Surgery/autopsy
S
S
S
S
A
SA
S
Laterality right/left
R
L
R
L
L
R
R
Focal/diffuse
D
D
D
D
D
D
F
Abnormal gyral pattern
+
+
+
+
+
+
+
Irregular neuron lamination
+
+
+
+
+
+
+
Submerged gyri
+
+
+
+
-
-
+
Subcortical heterotopia
+
+
+
+
+
+
+
Heterotopia in deep W
+
+
Rare
+
+
+
+
Neuronal radial pattern
-
+
-
Focal
-
Focal
+
Calcification CAV
-
-
-
C
C,W
Myelination into cortex
+
+
+
+
-
--
+
Poor myelination at C/W margin
+
+
+
+
+
+
+
Neurons increased in number
+
+
+
+
+
+
+
Neurons increased in size
+
+
+
+
+
+
+
Glial enlargement
-+
+
-
-
-+
Meningeal glioneurohal heterotopia
+
+
+
+
-
Sex Symptoms and signs
A g e at examination
+_
Abbreviations: C CPS DD G 1S MC MR
= = = = = = =
Cortex Complex partial seizure Developmental delay Gener',dized Infantile spasm Myoclonic Mental retardation
NA PM W + _+
= = = = = -
Not applicable Partial motor White matter Present Very slightly Absent
A spectrum of pathologic changes was observed; some brains exhibited only mild histologic distortion. In others
276
PEDIATRIC NEUROLOGY
Vol. 7 No. 4
(Patients (LGH)
1-4),
leptomeningeal
was found in association
glioneuronal
heterotopia
with submerged
gyri and
Table 2.
lmmunohistochemistry results Patients 1
2
3
4
5
6
7
Cerebral white matter
+
+
+
+
++
++
+
Cerebral cortex
+
+
+
+
++
++
+
Leptomeninges
+
+
+
+
--
--
--
Cerebral cortex
+
+
+
+
--
--
+
Molecular layer
+
-+
+
+
--
--
_
Leptomeninges
-
+
-I-
+
--
--
--
Cerebral white matter
+
+
+
+
+
+
+
Leptomeninges
+
+
+
+
--
--
+
Glial fibrillary acidic protein
Myelin basic protein
Synaptophysin
Abbreviations: = Negative + = Slight + = Moderate ++ = Marked
-
irregular myelination into the gray matter. In the cortical areas with LGH, there were many shallow sulci resembling polymicmgyria. The cortex was variable in thickness but consisted o f 6 cellular layers with numerous large pyramidal neurons identified predominately in the deeper layers. Patients 2 and 6 demonstrated marked neuronal enlargement and Patient 5 had neuronal multinucleation. A persistent, immature neuronal radial pattern, glial enlargement, and focal calcification were present in several patients (Table 1). lmmunohistochemistry. F i n d i n g s are s u m m a r i z e d in Table 2. G F A P was identified within astrocytes in the
cerebral cortex and white matter of all patients (Fig 2). In the 4 brains with LGH, positive astrocytes were present within these heterotopia. MBP-positive cells and processes were found in the cortical molecular layer and LGH. Synaptophysin staining was demonstrated in neurons of the cerebral cortex and in heterotopia of the white matter. In the areas of cerebral cortex with abnormally shallow sulci, there were protrusions of myelin-sheathed bundles which were synaptophysin-negative and MBP-positive, oriented perpendicular to the pial surface (Fig 3). Golgi Study. In Golgi-impregnated sections, most pyramidal neurons were arranged radially but some were orien-
Figure 2. Astrocytes are increased in the cerebral white matter and cortex. Enlarged neurons are also found in the deep cortex. GFAP immunohistochemical staining, original magnification xlO0.
Takashima et al: Hemimegalencephaly 277
/
II
ql,
o
) i
.i
r
J
Figure 3. Protrusion of myelin sheaths in the cerebral cortex with abnormal gyral formation. MBP immunohistoehemical staining, original magnification .v40.
tated obliquely and others horizontally (Fig 4). A small number of neurons were inverted with axons directed toward the pial surface. The somata were variable in size and basal dendrites were short in small neurons and their ramifications irregular in most of the pyramidal and stellate neurons. Particularly, adjacent to shallow sulci, there were deformed pyramidal and stellate neurons with irregularity of the somata and clustering of the basal dendrites. Spines were decreased on some neurons and abnormally thin on others. Occasionally, there were fusiform neurons with spines located on the soma similar to immature neurons. Identified in the deeper cortex were giant pyramidal and stellate neurons with large amounts of cytoplasm and thick dendrites. The large neuronal soma had a rounded contour or occasionally protrusions into many small processes. The dendrites disclosed complex ramifications and were covered with many spines (Fig 5). Pyramidal and stellate neurons with short dendrites and a small number of spines were observed in the heterotopia.
Discussion The gross pathology of hemimegalencephaly is characterized by cerebral hemihypertrophy with polymicrogyria and pachygyria. Irregular cortical laminations, cortical thickening, chaotically oriented neurons, and neuronal heterotopia in the white matter are evident histologically [1,5-8]. In this study, all brains had abnormal gyri, poor gray-white matter differentiation, loss of normal cortical lamination, enlarged neurons, increased number of neu-
278 PEDIATRIC NEUROLOGY Vol.7 No. 4
rons, and heterotopic neurons. In addition, LGH associated with abnormal shallow sulcal formation was lound in 4 of 7 patients, hnmunostaining with antiserum to MBP demonstrated abnormal cells and processes in the cortex and LGH in these patients. Synaptophysin-positive reactions were demonstrated in neuronal heterotopias of various sizes as well as in irregular cortical neuronal arrangements associated with the pial protrusions of MBP-positive myelin sheaths. Townsend et al. commented on the wide spectrum of pathologic changes encountered in hemimegalencephaly [9]. Bignami et al. reported polymicrogyria with prominent fusion of molecular cortical layers [11. Laurence described disorganization of the cytoarchitecture of gray matter with swollen, distorted neurons arranged in irregular layers with large vacuolated neurons [61. Numerous reports have documented various degrees of lissencephaly and pachygyria [110-12,14,15]. Similarly, we observed a spectrum of pathologic changes, ranging from mild disruption of cortical lamination with small increases in neuronal size and number to marked disorganization of the cortex with numerous, large, misaligned neurons dispersed throughout the cortex and white matter. Two patients demonstrated marked hemispheral enlargement with striking increases in neuronal size and number bordering on neoplastic proportions and one patient exhibited neuronal multinucleation. By using Golgi stains, Robain et al. found that the increased size of the giant neurons is associated with an increased size of the dendritic tree, an increased number of dendritic branches, and prominent perisomatic processes [81. The large size of the neurons may be due to an increased amount of DNA I1]. In our patients, small and deformed neurons were found in the superficial layers around abnormal sulci and giant neurons coexisted laminarly or diffusely in the deeper cortex of each patient. In the cortex, irregular orientation of small neurons associated with a few abnormally large neurons is well described in the polymicrogyria found in the Fukuyama type of congenital muscular dystrophy and in Walker-Warburg lissencephaly [13]; however, these dysplasias reveal marked disorganization of the cortical neuronal arrangement with extensive proliferation of glioneuronal tissue engulfing adjacent leptomeninges. The pathogenetic mechanism producing unilateral cerebral hypertrophy is unknown; however, Bignami et al. [1 I and Manz et al. [71 reported an increase in DNA, RNA, and protein content in the affected hemisphere, thus implicating heteroploidy of chromosomal DNA and increased transcription and translation in the hemimegalic hemisphere. In addition, cell morphometry 14] has demonstrated an increased number of neurons, suggesting an increase in proliferation or a decrease in neuronal cell death. Furthermore, Golgi studies reveal hypertrophic cortical neurons with an increased number of dendrites [8] and spines. It is unknown why the disturbance of cell proliferation is restricted to one hemisphere. Of great in-
A
B
C
Figure 4. Camera lucida drawing of neurons in the visual cortex stained by the Golgi method. Most neurons are large with an increased number of dendrites. (C) Control (6 months of age).
terest is the recent development of the first neuronal cell line established from cultures of human cerebral cortex
Number of s 3ines
©
10
[]
•
(A,B) Hemimegalencephaly (9 months of age).
[ 16]. The successful cell line was developed from a patient with HM suggesting that the hyperdiploid cells may be conferring some advantage to the neurons allowing them to proliferate. The cells displayed mature neuronal morphology with long, extensively branched processes decorated with spines and varicosities. A further exploration of the neurobiology of the neurons in HM using both in vivo and in vitro methods may lead to an elucidation of the nature and role of the growth factors that control neuronal proliferation. Such insight would have profound implications for the treatment of neurodegenerative disease.
5
6~
This study was supported by grants from the National Center of Neurology and Psychiatry of the Ministry of Health and Welfare, and from the Ministry of Education of Japan.
I 0
lOO '2.60 Distance along dendrites
300
pill
Figure 5. Distribution of spines on basal dendrites of large and moderate sizes of neurons in the visual cortex (Patient 7). 0 = large neurons, ~ = moderate neurons, and • = controls.
References
[1] Bignami A, Palladini G, Zappella M. Unilateral megalencephaly with nerve cell hypertrophy. An anatomical and quantitative histochemical study. Brain Res 1968;9:103-14.
Takashima et ah Hemimegalencephaly 279
[2] Shah MD, Merchant RH, Nagar PG. Unilateral macrencephaly. Indian Pediatr 1986;23:304-7. [3] George RE, Hoffman HJ, Hwang PA, Becker LE, Chuang SH. Management of intractable seizures in unilateral megalencephaly. J Neurosurg, in press. [4] Takashima S, Chan F, Becker LE, Armstrong DE Morphology of the developing visual cortex of the human infant. A quantitative and qualitative Golgi study. J Neuropathol Exp Neurol 1980;39:487-501. [51 Dambska M, Wisniewski K, Sher JH. An autopsy case of hemimegalencephaly. Brain Dev 1984;6:60-4. [6] Laurence KM. A case of unilateral megalencephaly. Dev Med Child Neurol 1964;6:585-90. [7] Manz HJ, Phillips TM, Rowden G, McCullough DC. Unilateral megalencephaly, cerebral cortical dysplasia, neuronal hypertrophy, and heterotopia: Cytomorphometric, fluorometric cytochemical, and biochemical analyses. Acta Neuropathol 1979;45:97-103. [8] Robain O, Floquet C, Heldt N, Rosenberg F. Hemimegalencephaly: A clinicopathological study of four cases. Neuropathol Appl Neurobiol 1988; 14:125-35. [9] Townsend JJ, Nielsen SL, Malamud N. Unilateral megalencephaly: Hamartoma or neoplasm? Neurology 1975;25:448-53.
280 PEDIATRIC NEUROLOGY
Vol. 7 No. 4
[10] Barkovich AJ, Chuang SH, Norman D. MR of neuronal migration anomalies. AJR 1988:150:179-87. [11] Kalifa GL, Chiron C, Sellier N, et al. Hemimegalencephaly: MR imaging in five children. Radiology 1987;165:29-33. [121 Mikhael MA, Mattar AG. Malformation of the cerebral cortex with heterotopia of the gray matter. J Comput Assist Tomogr 1978:2: 291-6. [13] Takashima S, Becker LE, Chart F, Takada K. A Golgi study of the cerebral cortex in Fukuyama-type congenital muscular dystrophy, Walker-type lissencephaly, and classical lissencephaly. Brain Dev 1987; 9:621-6. [14] Fitz CR, Harwood-Na~sh DC, Boldt JH. The radiographic teatures of unilateral megalencephaly. Neuroradiology 1978;15:145-8. [15] King M, Stephenson JB, Ziervogel M, Doyle D, Galbraith S. Hemimegalencephaly-A case for hemispherectomy. Neuropediatrics 1985; 16:46-55. [16] Ronnett GV, Hester LD, Nye JS, Connors K, Snyder SH. Human cortical neuronal line: Establishment from a patient with unilateral megalencephaly. Science 1989;248:603-4.
Immunohistochemical and Goigi studies were performed on 6 patients with hemimegalencephaly. Immunohistochemical staining demonstrated glial, neuronal, and myelin heterotopia in the leptomeninges, cortex, and white matter with glial fibrillary acidic protein, myelin basic protein, and synaptophysin antisera. Golgi studies revealed small and deformed neurons in the superficial layers around abnormal sulci, and hypertrophic neurons with an increased number of dendrites and spines in the deeper cortex. The coexistence of a cell migration disorder, proliferation, and hypertrophy in each patient may imply a growth factor disturbance that controls cell proliferation. These unilateral cerebral malformations suggest that early surgical excision may be beneficial. Takashima S, Chart F, Becker LE, Kuruta H. Aberrant neuronal development in hemimegalencephaly: Immunohistochemical and Golgi studies. Pediatr Neurol 1991;7: 275-80.
Methods Clinical data are described in Table 1 [3]. Brain tissue was obtained from 6 patients at surgical resection or autopsy. The formalin-fixed and paraffin-embedded specimens were cut, deparaffinized, and stained with hematoxylin and eosin, luxol-fast blue, Holzer, and Bodian stains. Peroxidase and antiperoxidase immunohistochemistry using antisera against glial fibrillary acidic protein (GFAP), myelin basic protein (MBP), and synaptophysin was applied to brain sections. Fresh brain tissue from 3 patients was placed in Golgi fixative and stained by the rapid Golgi method [4]. The specimens were observed under light microscopy and camera lucida drawings prepared.
Results
Histology. In all 6 patients, histologic examination revealed abnormal gyration, poor gray-white matter differentiation, disturbed lamination, enlarged neurons (Fig 1), and increased neuronal heterotopia (subcortical and deep white matter).
Introduction Hemimegalencephaly or unilateral megalencephaly is a congenital malformation caused presumably by abnormal neuronal proliferation and migration during the second through fifth month of gestation, resulting in overgrowth and polymicrogyria of one cerebral hemisphere [1]. Patients with unilateral megalencephaly typically present with a triad of clinical findings: intractable seizures, developmental delay, and progressive hemiparesis. The etiology and pathogenesis are unknown. Because of the intractable seizure disorder, total or partial hemispherectomy has been advocated as a preferred treatment [2]. In this report, neuropathologic, immunohistochemical, and somatodendritic observations are described in the megalencephalic hemisphere of 6 patients.
Figure 1. Enlarged neurons with disturbed lamination in the cerebral cortex. Hematoxylin and eosin stain, original magnification x400.
From the *Department of Pathology, Division of Neuropathology; University of Toronto and The Hospital for Sick Children; Toronto, Canada; and tDivision of Mental Retardation and Birth Defect Research; National Institute of Neuroscience; National Center of Neurology and Psychiatry; Tokyo, Japan.
Communications should be addressed to: Dr. Takashima; Division of Mental Retardation and Birth Defect Research; National Institute of Neuroscience; NCNP; 4-1-1 Ogawahigashicho; Kodaira, Tokyo 187, Japan. Received January 14, 1991; accepted February 28, 1991.
Takashima et al: Hemimegalencephaly 275
Table 1.
Patients and neuropathology
1
2
3
Patients 4
5
6
7
M
M
F
F
M
M
1::
Seizure onset
18 mos PM G MC
4 days PM G MC
2 days PM G CPS
! day IS PM G
3 days PM G
14 days IS PM MC
Psychomotor
MR
DD
MR
DD
NA
DD
DD
Hemiparesis
+
+
+
+
-
+
+
8 yrs
10 mos
10 yrs
6 mos
3 days
5 mos
9 mos
Surgery/autopsy
S
S
S
S
A
SA
S
Laterality right/left
R
L
R
L
L
R
R
Focal/diffuse
D
D
D
D
D
D
F
Abnormal gyral pattern
+
+
+
+
+
+
+
Irregular neuron lamination
+
+
+
+
+
+
+
Submerged gyri
+
+
+
+
-
-
+
Subcortical heterotopia
+
+
+
+
+
+
+
Heterotopia in deep W
+
+
Rare
+
+
+
+
Neuronal radial pattern
-
+
-
Focal
-
Focal
+
Calcification CAV
-
-
-
C
C,W
Myelination into cortex
+
+
+
+
-
--
+
Poor myelination at C/W margin
+
+
+
+
+
+
+
Neurons increased in number
+
+
+
+
+
+
+
Neurons increased in size
+
+
+
+
+
+
+
Glial enlargement
-+
+
-
-
-+
Meningeal glioneurohal heterotopia
+
+
+
+
-
Sex Symptoms and signs
A g e at examination
+_
Abbreviations: C CPS DD G 1S MC MR
= = = = = = =
Cortex Complex partial seizure Developmental delay Gener',dized Infantile spasm Myoclonic Mental retardation
NA PM W + _+
= = = = = -
Not applicable Partial motor White matter Present Very slightly Absent
A spectrum of pathologic changes was observed; some brains exhibited only mild histologic distortion. In others
276
PEDIATRIC NEUROLOGY
Vol. 7 No. 4
(Patients (LGH)
1-4),
leptomeningeal
was found in association
glioneuronal
heterotopia
with submerged
gyri and
Table 2.
lmmunohistochemistry results Patients 1
2
3
4
5
6
7
Cerebral white matter
+
+
+
+
++
++
+
Cerebral cortex
+
+
+
+
++
++
+
Leptomeninges
+
+
+
+
--
--
--
Cerebral cortex
+
+
+
+
--
--
+
Molecular layer
+
-+
+
+
--
--
_
Leptomeninges
-
+
-I-
+
--
--
--
Cerebral white matter
+
+
+
+
+
+
+
Leptomeninges
+
+
+
+
--
--
+
Glial fibrillary acidic protein
Myelin basic protein
Synaptophysin
Abbreviations: = Negative + = Slight + = Moderate ++ = Marked
-
irregular myelination into the gray matter. In the cortical areas with LGH, there were many shallow sulci resembling polymicmgyria. The cortex was variable in thickness but consisted o f 6 cellular layers with numerous large pyramidal neurons identified predominately in the deeper layers. Patients 2 and 6 demonstrated marked neuronal enlargement and Patient 5 had neuronal multinucleation. A persistent, immature neuronal radial pattern, glial enlargement, and focal calcification were present in several patients (Table 1). lmmunohistochemistry. F i n d i n g s are s u m m a r i z e d in Table 2. G F A P was identified within astrocytes in the
cerebral cortex and white matter of all patients (Fig 2). In the 4 brains with LGH, positive astrocytes were present within these heterotopia. MBP-positive cells and processes were found in the cortical molecular layer and LGH. Synaptophysin staining was demonstrated in neurons of the cerebral cortex and in heterotopia of the white matter. In the areas of cerebral cortex with abnormally shallow sulci, there were protrusions of myelin-sheathed bundles which were synaptophysin-negative and MBP-positive, oriented perpendicular to the pial surface (Fig 3). Golgi Study. In Golgi-impregnated sections, most pyramidal neurons were arranged radially but some were orien-
Figure 2. Astrocytes are increased in the cerebral white matter and cortex. Enlarged neurons are also found in the deep cortex. GFAP immunohistochemical staining, original magnification xlO0.
Takashima et al: Hemimegalencephaly 277
/
II
ql,
o
) i
.i
r
J
Figure 3. Protrusion of myelin sheaths in the cerebral cortex with abnormal gyral formation. MBP immunohistoehemical staining, original magnification .v40.
tated obliquely and others horizontally (Fig 4). A small number of neurons were inverted with axons directed toward the pial surface. The somata were variable in size and basal dendrites were short in small neurons and their ramifications irregular in most of the pyramidal and stellate neurons. Particularly, adjacent to shallow sulci, there were deformed pyramidal and stellate neurons with irregularity of the somata and clustering of the basal dendrites. Spines were decreased on some neurons and abnormally thin on others. Occasionally, there were fusiform neurons with spines located on the soma similar to immature neurons. Identified in the deeper cortex were giant pyramidal and stellate neurons with large amounts of cytoplasm and thick dendrites. The large neuronal soma had a rounded contour or occasionally protrusions into many small processes. The dendrites disclosed complex ramifications and were covered with many spines (Fig 5). Pyramidal and stellate neurons with short dendrites and a small number of spines were observed in the heterotopia.
Discussion The gross pathology of hemimegalencephaly is characterized by cerebral hemihypertrophy with polymicrogyria and pachygyria. Irregular cortical laminations, cortical thickening, chaotically oriented neurons, and neuronal heterotopia in the white matter are evident histologically [1,5-8]. In this study, all brains had abnormal gyri, poor gray-white matter differentiation, loss of normal cortical lamination, enlarged neurons, increased number of neu-
278 PEDIATRIC NEUROLOGY Vol.7 No. 4
rons, and heterotopic neurons. In addition, LGH associated with abnormal shallow sulcal formation was lound in 4 of 7 patients, hnmunostaining with antiserum to MBP demonstrated abnormal cells and processes in the cortex and LGH in these patients. Synaptophysin-positive reactions were demonstrated in neuronal heterotopias of various sizes as well as in irregular cortical neuronal arrangements associated with the pial protrusions of MBP-positive myelin sheaths. Townsend et al. commented on the wide spectrum of pathologic changes encountered in hemimegalencephaly [9]. Bignami et al. reported polymicrogyria with prominent fusion of molecular cortical layers [11. Laurence described disorganization of the cytoarchitecture of gray matter with swollen, distorted neurons arranged in irregular layers with large vacuolated neurons [61. Numerous reports have documented various degrees of lissencephaly and pachygyria [110-12,14,15]. Similarly, we observed a spectrum of pathologic changes, ranging from mild disruption of cortical lamination with small increases in neuronal size and number to marked disorganization of the cortex with numerous, large, misaligned neurons dispersed throughout the cortex and white matter. Two patients demonstrated marked hemispheral enlargement with striking increases in neuronal size and number bordering on neoplastic proportions and one patient exhibited neuronal multinucleation. By using Golgi stains, Robain et al. found that the increased size of the giant neurons is associated with an increased size of the dendritic tree, an increased number of dendritic branches, and prominent perisomatic processes [81. The large size of the neurons may be due to an increased amount of DNA I1]. In our patients, small and deformed neurons were found in the superficial layers around abnormal sulci and giant neurons coexisted laminarly or diffusely in the deeper cortex of each patient. In the cortex, irregular orientation of small neurons associated with a few abnormally large neurons is well described in the polymicrogyria found in the Fukuyama type of congenital muscular dystrophy and in Walker-Warburg lissencephaly [13]; however, these dysplasias reveal marked disorganization of the cortical neuronal arrangement with extensive proliferation of glioneuronal tissue engulfing adjacent leptomeninges. The pathogenetic mechanism producing unilateral cerebral hypertrophy is unknown; however, Bignami et al. [1 I and Manz et al. [71 reported an increase in DNA, RNA, and protein content in the affected hemisphere, thus implicating heteroploidy of chromosomal DNA and increased transcription and translation in the hemimegalic hemisphere. In addition, cell morphometry 14] has demonstrated an increased number of neurons, suggesting an increase in proliferation or a decrease in neuronal cell death. Furthermore, Golgi studies reveal hypertrophic cortical neurons with an increased number of dendrites [8] and spines. It is unknown why the disturbance of cell proliferation is restricted to one hemisphere. Of great in-
A
B
C
Figure 4. Camera lucida drawing of neurons in the visual cortex stained by the Golgi method. Most neurons are large with an increased number of dendrites. (C) Control (6 months of age).
terest is the recent development of the first neuronal cell line established from cultures of human cerebral cortex
Number of s 3ines
©
10
[]
•
(A,B) Hemimegalencephaly (9 months of age).
[ 16]. The successful cell line was developed from a patient with HM suggesting that the hyperdiploid cells may be conferring some advantage to the neurons allowing them to proliferate. The cells displayed mature neuronal morphology with long, extensively branched processes decorated with spines and varicosities. A further exploration of the neurobiology of the neurons in HM using both in vivo and in vitro methods may lead to an elucidation of the nature and role of the growth factors that control neuronal proliferation. Such insight would have profound implications for the treatment of neurodegenerative disease.
5
6~
This study was supported by grants from the National Center of Neurology and Psychiatry of the Ministry of Health and Welfare, and from the Ministry of Education of Japan.
I 0
lOO '2.60 Distance along dendrites
300
pill
Figure 5. Distribution of spines on basal dendrites of large and moderate sizes of neurons in the visual cortex (Patient 7). 0 = large neurons, ~ = moderate neurons, and • = controls.
References
[1] Bignami A, Palladini G, Zappella M. Unilateral megalencephaly with nerve cell hypertrophy. An anatomical and quantitative histochemical study. Brain Res 1968;9:103-14.
Takashima et ah Hemimegalencephaly 279
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