Microcephalus

Microcephalus, also known as microcephaly in modern terminology, is a condition in which an individual has a smaller head circumference than would be expected for age and sex. It is typically defined as a head circumference more than two standard deviations below the mean, or below the third percentile, and can be present at birth or develop in early childhood.

The condition reflects reduced brain growth and is often associated with varying degrees of neurodevelopmental impairment. Individuals with microcephalus may experience developmental delays, learning difficulties, motor problems, and, in some cases, seizures. The severity and functional outcome are highly dependent on the underlying cause and the degree of brain involvement.

Causes of microcephalus are diverse. They include genetic mutations (including autosomal recessive and X-linked patterns), chromosomal abnormalities, congenital infections (such as Zika virus, toxoplasmosis, rubella, cytomegalovirus, and others), teratogenic exposures during pregnancy (for example, alcohol and certain medications), and severe malnutrition or metabolic disorders. In many cases, no single cause is identified, and microcephalus occurs as part of a broader syndrome or due to multifactorial factors.

Diagnosis relies on newborn and pediatric head circumference measurements over time, compared with standardized growth charts. Imaging with MRI or CT can reveal brain size reduction and sometimes associated structural abnormalities. Genetic testing and infectious disease screening are often pursued to identify an underlying etiology.

Management is multidisciplinary and supportive, focusing on maximizing development through early intervention, physical and occupational therapy, speech therapy, management of seizures if present, and educational planning. Prognosis varies widely, ranging from relatively mild impairment to severe disability, depending on etiology and brain involvement.