Makrocephalia

Makrocephalia, often rendered macrocephaly in English, refers to an abnormally large head as defined by head circumference that is significantly above the normal range for age and sex. In clinical practice, this is commonly described as a head circumference above the 97th percentile or more than two standard deviations above the mean for the child’s age and sex. The condition can result from various underlying causes and may reflect either an enlarged brain (megalencephaly), a thickened skull, or an increased intracranial volume from other sources.

Causes and classification include benign familial or idiopathic macrocephaly, where head size is inherited and development is typically normal. Secondary macrocephaly arises from conditions that increase intracranial volume or skull size, such as hydrocephalus, intracranial masses, or brain overgrowth syndromes. Syndromic forms associated with macrocephaly include certain overgrowth disorders and PTEN-related conditions, as well as neurocutaneous or genetic syndromes in which large head size is part of the phenotype. Distinguishing among these etiologies requires a careful clinical assessment and often imaging and genetic testing.

Evaluation typically begins with accurate measurement of head circumference and plotting on growth charts, followed by assessment of development, neurological status, and growth trajectory. If head growth is rapid or accompanied by signs of increased intracranial pressure (such as vomiting, lethargy, or developmental regression), imaging is indicated. In infants with open fontanelles, cranial ultrasound can be a first step; MRI offers detailed information about brain structure. Management depends on the underlying cause: benign familial macrocephaly usually requires observation, while hydrocephalus, tumors, or syndromic conditions may need medical or surgical intervention, therapy for associated developmental issues, and ongoing follow-up. Prognosis varies with etiology and associated conditions.