Megalencephaly

Megalencephaly (MEG) 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. 

Terminology 

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

Clinical features

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 not a classical pattern of symptoms ². 

Pathology

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. 

Associations

It can occur in a variety of syndromes including

• achondroplasia
• Beckwith-Wiedemann syndrome
• neurofibromatosis type 1 (NF1)
• tuberous sclerosis (TS)
• Klippel-Trenaunay-Weber syndrome
• epidermal nevus syndrome

Radiographic features

MRI

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.

See also 

• differential diagnosis of bilateral megalencephaly and hemimegalencephaly
• macrocephaly