Megalencephaly is primarily a proliferative disorder of embryonic origin, macroscopically defined as enlargement of part of or all of the cerebral hemispheres. It could be bilateral or unilateral. Often polymicrogyria or agyria is found in association. 

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

  • content pending 

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 emphasise that there is not a 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


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.

Malformations of the central nervous system
Share article

Article information

rID: 1654
Tags: cases, refs
Synonyms or Alternate Spellings:

Support Radiopaedia and see fewer ads

Updating… Please wait.

Alert accept

Error Unable to process the form. Check for errors and try again.

Alert accept Thank you for updating your details.