Occipitofrontal circumference > 2 SD above the mean for age and sex.
Aetiology
Megalencephaly:
- Benign familial
- Neurocutaneous syndromes:
- Neurofibromatosis, tuberous sclerosis, Sturge-Weber, Klippel-Trenaunay-Weber, linear sebaceous nevus
- Others:
- Sotos, Fragile X syndrome
- Leukodystrophies:
- Alexander, Canavan, megalencephalic leukoencephalopathy
- Lysosomal storage diseases:
- Tay-Sachs, mucopolysaccharidosis, gangliosidosis
Increased cerebrospinal fluid:
- Hydrocephalus
- Benign enlargement of subarachnoid space
- Hydranencephaly, choroid plexus papilloma
Enlarged vascular compartment:
- Arteriovenous malformation
- Subdural, epidural, subarachnoid or intraventricular hemorrhage
Increase in bony compartment:
- Bone disease:
- Achondroplasia, osteogenesis imperfecta, osteopetrosis, hyperphosphatasia, cleidocranial dysostosis
- Bone marrow expansion:
- Thalassemia major
Miscellaneous causes:
- Intracranial mass lesions:
- Cyst, abscess or tumor
- Raised intracranial pressure:
- Idiopathic pseudotumor cerebri, lead poisoning, hypervitarninosis A, galactosemia