Primer on microcephaly

Microcephaly can present in the newborn period, either at birth or postnatally. In large cohorts, genetic factors and perinatal brain damage secondary to maternal exposures and prenatally acquired infections are the leading causative factors. However, in up to ~40% of children with microcephaly, no etiology is identified. Although many classifications exist, it is important to remember that both congenital microcephaly and postnatalonset microcephaly can be due to genetic or “acquired” causes. Careful history and physical examination is the initial step in evaluating a neonate with microcephaly. Diagnostic evaluation should be tailored based on these findings. In all-comers with microcephaly, neuroimaging proves to have the highest diagnostic yield, with magnetic resonance imaging providing the highest sensitivity. Genetic testing has the next highest diagnostic yield, and if presentation does not suggest a specific genetic disorder, comparative genomic hybridization would be the recommended first-line genetic testing. Definitive treatment for microcephaly does not exist, but supportive treatment aimed at preventing further damage or mitigating untoward effects of existing comorbidities may be available. Overall prognosis relates to severity of disease, underlying diagnosis, and comorbid conditions identified. Zika virus is emerging as an infectious pathogen leading to congenital microcephaly. Given its potentially devastating effects, a low threshold of suspicion is warranted at this time for women presenting with a fever and rash during pregnancy with a personal history or sexual contact with a person who has a history of travel to affected regions, or with findings of microcephaly on prenatal ultrasonography.