Microcephaly is a head circumference < 2 standard deviations below the mean for age.
(See also Overview of Congenital Craniofacial Anomalies.)
In microcephaly, the head is disproportionately small in relation to the rest of the body.
Microcephaly has many chromosomal and environmental causes, including prenatal drug, alcohol, or radiation exposure, prenatal infections (eg, TORCH [toxoplasmosis, other pathogens, rubella, cytomegalovirus, and herpes simplex], Zika virus), and poorly controlled maternal phenylketonuria. Microcephaly also is a feature of > 400 genetic syndromes.
The consequences of microcephaly itself include neurologic and developmental disorders (eg, seizure disorders, intellectual disability, spasticity).
Diagnosis of Microcephaly
Prenatally, ultrasound
Postnatally, physical examination, including measurement of head circumference and cranial imaging
Genetic testing
Prenatally, the diagnosis of microcephaly sometimes is made with ultrasound done in the late second or early third trimester.
Postnatally, evaluation should include detailed prenatal history to identify risk factors, developmental and neurologic assessment, and brain MRI or CT. Primary isolated autosomal recessive microcephaly refers to microcephaly that is not associated with other extracerebral malformations. There are several different genes that can cause it.
A clinical geneticist should evaluate affected patients even in cases of apparent isolated congenital anomaly.
Chromosomal abnormalities can occur with microcephaly. Among the genetic syndromes to be considered are Seckel syndrome, Smith-Lemli-Opitz syndrome, syndromes due to defective DNA repair (eg, Fanconi and Cockayne syndromes), and Angelman syndrome. For parents of an affected child, risk of the disorder appearing in subsequent offspring may be as high as 25%, depending on which syndrome is present, and thus clinical genetic assessment is necessary. A gene panel test specific for microcephaly is available through several diagnostic laboratories. Chromosomal microarray analysis, or broader gene panel tests also should be considered in the evaluation of patients with microcephaly. If the results of these tests are nondiagnostic, whole exome sequencing analysis may be recommended.
Treatment of Microcephaly
Symptomatic treatment
Symptoms resulting from brain damage are treated. Some disorders causing microcephaly can be treated.
In general, management is based on symptoms, and developmental services are maximized (1).
Treatment reference
1. Ashwal S, Michelson D, Plawner L, Dobyns WB; Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society. Practice parameter: Evaluation of the child with microcephaly (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology and the Practice Committee of the Child Neurology Society. Neurology. 2009;73(11):887-897. doi:10.1212/WNL.0b013e3181b783f7
