Glossary in Congenital Malformations
NeuroLearn NeuroHelp Malformations @ General Syndromes
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
#Hemimegalencephaly: This is a condition in which there is an abnormal
hemisphere that is larger than the other, normal hemisphere, most likely a
combination of proliferative and migration disorder.
·
Clinical features:
There is variable degree of mental retardation, not infrequently infantile
spasms or the so-called Ohtahara syndrome (early infantile epileptic
encephalopathy). In the vast majority of caes seizures are severe and cannot be
controlled adequately by anticonvulsant medications. The onset of seizures is
early, usually in the first days or weeks of life. Hemispherectomy may control
the seizures in up to 85% of cases. Affected individuals have variable
psychomotor retardation and hemiparesis.
·
Pathology:
It may involve only the cerebrum or both cerebellum and cerebrum. The gyral
pattern of the enlarged hemisphere is abnormal, resembling pachygyric or
polymicrogyric cortex. Cortical architecture may be abnormal. There are
considerable numbers of abnormally large neurons, some larger than Betz cells,
scattered through the cortex and also in the subcortical white matter.
Hippocampal pyramidal cells and granule cells may also be abnormally large. The
may be cytoskeletal abnormalities in these giant neurons; silver staining
reveals tangle-like formation reminiscent of Alzheimer tangles. Ballon cells
with both features of neurons and glia are present; these cells express both
GFAP and synaptophysin.
#Heterotopia: Displacement or misplacement of parts; the
presence of a normal tissue in an abnormal location.
#Heterotopic gray matter
(neuronal heterotopia): Refers
to collections of neurons that lie between the ependymoma of the lateral
ventricle and the cortex. They come in four major patterns: diffuse, nodular,
laminar, and leptomeningeal.
·
Diffuse neuronal heterotopia: Heterotopic neurons scattered haphazardly through
the gyral andcentral white matter. They may be associated with nodular
heterotopia and other CNS malformation.
·
Subcortical band heterotopia (double cortex):
They are frequently seen in
female (heterozygous) carrier of X-linked lissencephaly (doublecortin gene on
Xq22.3). They may give a so-called "double cortex" on gross section
and MRI. Pathologically, there is laminar, or diffuse and symmetrical
heterotopia, consists of a single or interrupted nodular band of gray matter
that lies between ventricle and cortex, separated from both the cortex and the
ventricle by myelin. Extensive involvement is extensive but striate, cingulated,
fusiform and medial temporal gyri are spared.
·
Ventricular nodular heterotopia: Nodular heterotopia occurs commonly. Heterotopic
grey matter can be seen in anywhere within the brain but most the ventricular
surface is the most common site. There is a female predominance. It may consist
of a single nodule of gray matter at the ventricular surface or a row of nodules
at the ventricular wall creating an irregular ventricular surface. They may not
be well demarcated in the myelinating white matter in fetus and infants. These
nodules are frequently positive for synaptophysin.
Bilateral
periventricular nodular heterotopia may be related to a gene on Xq28. Pathologically, there are bilateral and symmetric
subependymal (periventricular) heterotopia. Clinically, most patients have
normal intelligence and epilepsy with multiple seizures types that may or may
not be difficult to control. Asymptomatic individuals may be seen. Male patients
are more severely affected but female patients are more common.
·
Leptomeningeal glial and glioneuronal heterotopias:
·
Infratentorial:
Usually takes the form of small round masses, occasionally as sheets, of
fibrillar glial tissue beside the brain stem. Rarely, neurons are present.
·
Supratentorial:
Can occur with or without the presence of neurons. They can be seen in a variety
of malformations. They may be associated with abnormalities in the underlying
cortex. One of the possible embryogenesis is that the migrating neurons breache
the glia-limitans. In the brain stem, there is no outer rim of neurons analogous
to cerebral cortex, which no doubt accounts for the lack of neurons in the
subpial-glial nodules in those sites.
#Holoprosencephaly: (holo-, Greek, whole; pro-, Greek, in front)
·
"A
median holosphere with a single ventricular cavity instead of two hemispheres
with symmetrical lateral ventricles" (Yakovlev 1959). This is a
developmental failure of cleavage of the proencephalon with a deficit in midline
facial development (Critical event: the evagination of the cerebral hemispheres
via sagittal cleavage of the prosencephalon occurs at approximately 35 days of
gestation). Timing: Critical event
must have happened no later than the 5th and 6th weeks of gestation.
·
The
olfactory bulbs and tracts are almost always absent. It is frequently associated
with cyclopia in the severe form; sometimes due to trisomy 13-15. The most
severe form is aprosencephaly.
·
The
cardinal features include a single telencephalic ventricle and continuity of the
cerebral hemisphere across the midline. Corpus callosum is usually absent
(olfactory bulbs and tracts are not discernible until 42 days in the normal
developing brain).
·
Can be
further divided into alobar, semilobar and lobar type.
#Hydromyelia:
Dilation
of the central canal of the spinal cord with an abnormal accumulation of fluid.
The hydromyelic cavity is at least partially covered by ependymal cells and
connected with the central canal. Pathogenesis:
There is an undoubted association between hydromyelia and neural tube
malformations. Hydromyelia may be
resulted from incomplete fusion of the posterior columns or as a persistence of
the primitive large canal of the embryo. [Ikenouchi
J. et al., Acta Neuropathol 2002 103: 248-254]
#Hydranencephaly: Complete destruction of the cerebral hemispheres
resulting in fluid filled bubble-like hemispheres. Absence of the cerebral
hemispheres, their normal site being occupied by cerebrospinal fluid. The
membrane encasing the CSF has an outer connective tissue layer with and inner
irregular layer of glial and glial-neuronal tissue admixed with hemosiderin-laden
macrophages and mineralized debris. This is regarded as a destructive process
and one of the pathogenesis include compromised blood supply by the internal
carotid arteries. Depending on the time of onset of the original insult, the
preserved cortex may show cytoarchitectonic abnormalities such as polymicrogyria.
#Hydrocephalus: Increased volume of CSF within the head without a
definition of its location. However, usually considered synonymous with
enlargement of at least the lateral ventricles.
NeuroLearn NeuroHelp Malformations General Syndromes For Comment: KarMing-Fung@ouhsc.edu