Last revised by Joshua Yap on 24 May 2023

Megalencephaly is a disorder characterized by an abnormally large brain. It is primarily a proliferative disorder of embryonic origin. It may involve all or part of the cerebral hemispheres and can be bilateral or unilateral. It is often associated with polymicrogyria or agyria

This slightly differs from the term macrocephaly which means an increase in size of the cranial vault.

It can occur in a variety of syndromes including:

It may be apparent as abnormal head circumference measurements, especially noted in the first four months of life.

Mental retardation, seizures, and other neurological abnormalities have been reported. It is important to emphasize that there is no classical pattern of symptoms 2

Megalencephaly is a complex abnormal cell proliferation process representing excessive amount of normal brain constituents, cellular proliferation, inadequate physiologic apoptosis, and/or storage of metabolites 1

MRI may show a thickened cortex with ipsilateral ventricular dilatation on the side of the megalencephaly. This feature allows differential diagnosis of congenital hemimegalencephaly from other causes, such as a lesion obstructing the foramen of Monro.

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