= clinical syndrome characterized by a head circumference below the normal range

Incidence: 1.6÷1,000 or 1÷6,200 to 1÷8,500 births

Etiology:

1. Undiagnosed intrauterine infection (toxoplasmosis, rubella, CMV, herpes, syphilis), toxic agents, drugs, hypoxia, irradiation, maternal phenylketonuria
2. Premature craniosynostosis
3. Chromosomal abnormalities (trisomies 13, 18, 21)
4. Meckel-Gruber syndrome

Often associated with:

microencephaly, macrogyria, pachygyria, atrophy of basal ganglia, decrease in dendritic arborization, holoprosencephaly

• AC÷HC discrepancy
• head circumference <3 SD below the mean
• apelike sloping of forehead
• dilatation of lateral ventricles
• poor growth of fetal cranium
• intracranial contents may not be visible (rare)

Prognosis: normal to severe mental retardation (depending on degree of microcephaly)