There was a H/O seizures and mental retardation.
There is thickening of the cortex in both cerebral hemispheres. The sulci are shallow and sparse and the gyri are flat and broad based. There is slight ventricular dilatation and the brainstem appears a little smaller in size. The cerebellum also appears to be dysplastic.
Lissencephaly means smooth brain and refers to a paucity of gyral and sulcal development on the surface of the brain. Smooth brain results from many causes like congenital infections (CMV), impaired stem cell formation and abnormal neuronal migration. Children with lissencephaly are severely disabled physically and intellectually. Agyria is defined as absence of gyri on the surface of the brain, synonymous with complete lissencephaly, while pachygyria is defined as few broad flat gyri, synonymous with incomplete lissencephaly. Two major pathological subtypes of lissencephaly exist :-
Classical Lissencephaly:
This results from arrest of migration of neurons. Children with classical lissencephaly always have global developmental delay and seizures, although the age of onset and severity of symptoms may vary. Some patients have chromosome 17 defects or X chromosome defect. Children with classical complete lissencephaly are hypotonic at birth gradually developing spasticity and those with incomplete lissencephaly have less severe motor abnormalities with hypertonia. Medically refractory epilepsy with increasing complex seizure disorder over time is characteristic. Most patients have areas of agyria and pachygyria. Systemic abnormalities of the eyes, ears, heart and kidney are also present.
Microscopically, the cerebral cortex is composed of a thin outer layer of neuron, a cell sparse zone and a thick inner layer of neurons. This inner layer represents young neurons that were stopped prematurely from their migration to the cortex or some abnormality of fetal ependymia.
The MR imaging appearance of classical lissencephaly reveals a smooth brain surface with diminished white matter and shallow vertically oriented Sylvian fissure. The cerebrum has a "figure of eight" appearance with corpus callosal hypogeneis with large ventricular trigones and occipital horns. The small brain stem results from maldevelopment of corticospinal and corticobulbar tracts.
Cobblestone Lissencephaly:
This results from overmigration of neurons. These patients suffer from associated muscular dystrophy and hypotonia, myelination delay, hydrocephalus and ocular abnormalities.
The MR appearance shows a thickened cortex with few shallow sulci, an irregular gray-white matter junction, pontine hypogenesis, vermian hypogenesis with cerebellar polymicrogyria, hydrocephalus, micro-opthalmia and callosal hypogenesis and an occasional occipital cephalocele. When the abnormality is seen in the frontal cortex, frontal polymicrogyria is seen as an irregularity of the cortical surface and cortical white matter junction. The temporo-occipital abnormality is seen as a thickened cortex with a smooth outer surface but an irregular inner surface. Dysplasia of the cerebellar cortex manifests as dysplastic folia with subcortical cysts located predominantly in the dorsal portion of the cerebellar hemisphere. Myelination is often delayed.