Last Updated : 7/6/2010
What are various
abnormalities of the brain?
There are several abnormalities of brain that can occur in a child. Some may be present right from birth such as neuronal heterotropia, lissencephaly (pronounced as lis-n-kaph-a-lee), pachygyria, schizencephaly (pronounced as she-zen-kaph-a-lee), agenesis of corpus callosum holoprosencephaly and anencephaly. Some abnormalities of brain can occur over a period of time such as microcephaly, craniosynostosis (pronounced as cray-ni-o-sin-os-toe-cis), porencephaly and macrocephaly.
The brain cells are called neurons when the brain is developing in the fetus, (baby in the womb) these neurons migrate towards the periphery of the brain. When these neurons are unable to migrate, they remain within the substance of the brain. Heterotropias can lead to fits and learning disability.
The normal brain is shaped like a walnut with creases (known as gyri) and crevices (known as sulci). When there is absence of sulci and gyri, it is known as lissencephaly. The surface of the brain thus appears smooth. In most patients, why lissencephaly occurs is not known but in 15-20%, a genetic cause in chromosome 17 is suspected. Patients have mental retardation and seizures.
Figure 1: Lissencephaly
Normally, the gyri and sulci in brain are at typical distances. When the gyria are widened, it is called as pachyguria. Patients have stiff limbs, mental retardation and fits.
When there is a cleft in the brain either on one side or on both the sides, it is called as schizencephaly. Patients have mental retardation.
What is agenesis of corpus callosum?
There is a structure in the brain called as corpus callosum. Absence of corpus callosum is called as agenesis of corpus callosum. Patients may have varied presentation. Most of the patients have no symptoms whereas few may have fits (seizures) to mental retardation. Patients may have associated brain anomalies such as genetic syndromes, hydrocephalus and neuronal heterotopias.
Figure 2: Absence of corpus callosum (typical bat wing appearance)
What is porencephaly?
Presence of cysts or cavities in the brain is called as porencephaly. This may be present right from birth or may occur post trauma or surgery. Patients may have delayed development.
Figure 3: Porencephalic cyst
other brain malformations?
Just as malformations can occur in the brain, other malformations can occur in the spine and spinal cord such as meningocele, meningomyelocele and spina bifida.
What is encephalocele?
Encephalocele (pronounced as N-ceph-a-low-seal) is a condition where brain, or its outer lining - the meninges protrude out due to a defect in the skull bone. Patients have a fluctuant swelling over the skull. Depending on the part of the brain that is involved, patients may have visual problems, seizures or mental retardation. If only meninges are protruding, prognosis is good.
Anencephaly (pronounced as N-N-ceph-a-lee) is a fatal brain malformation in which the brain lobes are absent. Infant is born with a defect in the skull bones with soft rudimentary brain seen from the defect. Most infants are still born or die shortly after birth. Commonest cause of anencephaly is Folic Acid deficiency and if mother takes folic acid supplement during pregnancy, the risk significantly decreases.
What is holoprosencephaly?
Holoprosencephaly (pronounced as holo-pro-zen-ceph-a-lee) is a condition in which brain fails to divide into two lobes and only a single lobe is present. This condition is common in patients with genetic syndromes. Most patients have severe delayed development, spasticity and seizures.
Figure 4: Holoprosencephaly
What is megelencephaly?
Large brain is called megelencephaly. Large head is called macrocephaly. Large head does not necessarily mean large brain. Large head can occur due to variety of causes such as large brain, increase in fluid in brain (hydrocephalus) or due to bleed in the head. Megelencephaly occurs with various genetic disorders in which abnormal substance is stored in the brain such as in Canavan and Alexander leukodystrophy. Sometimes large brains can run in families without any pathological abnormality. In patients with genetic disorders and large head, they can have seizures and mental retardation.
What is the
treatment of brain malformations?
Most of the brain malformations cannot be corrected as they are due to abnormal development of brain. Seizures will be controlled by anti-fit medications and spasticity will require physiotherapy. Conditions such as spina bifida and encephalocele can be treated surgically whereby the skull defect or spine defect is closed and brain or spinal cord is pushed back into the space it occupies. However prognosis would depend on the amount of brain damage that is already present.
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