Macrocephaly

Macrocephaly (from the ancient Greek μακρό- macro- long- + -κέφαλος -kephalos -head), occurs when the head is abnormally large; this includes the scalp, the cranial bone, and the contents of the cranium.

Causes

Macrocephaly may be due to megalencephaly (enlarged brain), to hydrocephalus (water on the brain), cranial hyperostosis (bone overgrowth), and other conditions. It is called "syndromic" when it is associated with any other noteworthy condition, and "non-syndromic" otherwise. It can be caused by genetic conditions or by environmental events.

Many genetic conditions are associated with macrocephaly, including familial macrocephaly, autism, PTEN mutations such as Cowden disease, neurofibromatosis type 1, and tuberous sclerosis; overgrowth syndromes such as Sotos syndrome (cerebral gigantism), Weaver syndrome, Simpson-Golabi-Behmel syndrome (Bulldog syndrome), and macrocephaly capillary malformation (M-CMTC) syndrome; neuro-cardio-facial-cutaneous syndromes such as Noonan syndrome, Costello syndrome, and cardiofaciocutaneous syndrome; Fragile X syndrome; leukodystrophies (brain white matter degeneration) such as Alexander disease, Canavan disease, and megalencephalic leukoencephalopathy with subcortical cysts; and glutaric aciduria type 1 and D-2-hydroxyglutaric aciduria.

Environmental events associated with macrocephaly include infection, neonatal intraventricular hemorrhage (bleeding within the infant brain), subdural effusion (collection of pus beneath the outer lining of the brain), and arachnoid cysts (cysts on the brain surface).

Diagnosis

Macrocephaly is customarily diagnosed if head circumference is greater than 2 standard deviations (SD) above the mean. Relative macrocephaly occurs if the measure is less than 2 SD above the mean but is disproportionately above that when ethnicity and stature are considered. In research, cranial height or brain imaging are also used to determine intracranial volume more accurately.

See also

• Microcephaly

References