Approach Considerations

Microcephaly can be diagnosed prenatally via ultrasound conducted late in the 2nd trimester or early in the third.

Postnatally, microcephaly is determined via physical examination. Measure the infant's head circumference and compare it against population standards. If the child's head circumference is less than 2 standard deviations (SD) below the average, microcephaly is indicated.

Congenital microcephaly

Congenital microcephaly is present either prenatally or at the time of birth or delivery. It can develop as a result of abnormal brain development or disruption in the normal development of the brain.

If the infant has clinical features suggesting a specific disease or syndrome, conduct specific testing for that condition. An MRI should be obtained, particularly if the child's development is delayed. Results may show a specific malformation or pattern of injury. If the MRI is normal or non-specific, consider testing for infectious (e.g., toxoplasmosis, cytomegalovirus, HIV), toxic, genetic, or metabolic disorders.^[3]

Postnatal-onset microcephaly

Acquired microcephaly can develop after birth due to hypoxic-ischemic injury or a post-natal insult such as trauma or infection. In this instance, the head circumference is normal at birth but becomes comparatively smaller as the baby grows in length. An MRI may be helpful in these cases to rule in or out specific conditions, particularly if the microcephaly is severe (< -3SD) or if there are neurological signs or symptoms present. Consider testing girls for Rett syndrome if other typical findings are present such as loss of purposeful hand movements and loss of language, appearance of compulsive movements such as hand wringing, and appearance of breathholding or apnea.^[3]