General
- AKA
- Macrencephaly
- Megalencephaly
- Large brain
- Not to be confused with macrocephaly, which is enlargement of the skull.
- Brains may weigh up to 1600–2850 grams.
Aetiology: Not a single pathologic entity.
- Hypertrophy of
- Gray matter alone
- Gray and white matter
- Presence of additional structures (glial overgrowth, diffuse gliomas, heterotopias, metabolic storage diseases…).
Associated conditions:
- Neurocutaneous syndromes (especially neurofibromatosis)
- Megalencephaly-capillary malformation syndrome (MCAP):
- An overgrowth syndrome with megalencephaly (often with hydrocephalus,
- Chiari malformation, polymicrogyria and seizures)
- Capillary malformations in the skin (usually on the face)
Clinical features
- IQ may be normal, but developmental delay, retardation, spasticity and hypotonia may occur.
- Head circumference is 4–7cm above mean.
- The usual signs of hydrocephalus (frontal bossing, bulging fontanelle, “setting sun” sign, scalp vein engorgement) are absent.
Imaging studies
- CT or MRI
- Show normal-sized ventricles
- Can be used to rule out extraaxial fluid collections.
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