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Megalencephaly is defined as enlargement of part of or all of the cerebral hemispheres. It could be bilateral or unilateral.
Often polymicrogyria or agyria is found on the affected side.
It can occur in a variety of syndromes including
MRI may show a thickened cortex with ipsilateral ventricular dilatation on the side of the megalencephaly and this feature allows differential diagnosis between congenital hemimegalencephaly from other causes, such as a lesion obstructing the foramen of Monro.
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