DEFINITION:

A congenital anomaly of the central nervous system (CNS) where the head circumference is > 3 standard deviations below the mean for age and sex.

EPIDEMIOLOGY:

• incidence: common
• age of onset:
  • birth (genetic) or first 2 years of life (nongenetic)
• risk factors:
  • see differential diagnosis - two main groups:
    • primary (genetic) vs secondary (nongenetic)

DIFFERENTIAL DIAGNOSIS:

PATHOGENESIS:

• most often occurs as a result of a small brain (micrencephaly) but also due to a poorly growing skull (i.e., craniosynostosis)
• micrencephaly may be due to:
  • abnormal neuronal migration during fetal development
    • heterotropias of neuronal cells
    • cytoarchitectural derangements
• if insult to brain occurs beyond 2 years of age less likely to produce severe microcephaly

HISTORY:

• genetic vs nongenetic
• family history (for genetic etiology)
• exposure to risk factors: radiation, infection, drugs, maternal
• DM or PKU, significant fever during first 4-6 weeks of life, HIE
• head circumference curve characteristics - if small at birth in utero problems
• dysmorphic features, seizures, developmental delay

CLINICAL FEATURES:

• look for dysmorphic features
• sequential assessment of head circumference

INVESTIGATIONS:

MANAGEMENT: