Microcephaly is a head circumference < 2 standard deviations below the mean for age and sex.
In microcephaly, the head is disproportionately small in relation to the rest of the body. The prevalence of microcephaly at birth is estimated at 1.5 to 3.0 per 10,000 (1–3). (See also Overview of Congenital Craniofacial Anomalies.)
Microcephaly has many chromosomal and environmental causes (4, 5), including prenatal medication, 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 hundreds of genetic syndromes.
The consequences of microcephaly itself include neurologic and developmental disorders (eg, seizure disorders, intellectual disability, spasticity).
This photo shows a child with microcephaly with a head circumference < 2 standard deviations for his age. He also has other deformities including sloping forehead, micrognathia, relatively large ears, and severe contractures of all limbs.
General references
1. Morris JK, Rankin J, Garne E, et al. Prevalence of microcephaly in Europe: population based study. BMJ. 2016;354:i4721. Published 2016 Sep 13. doi:10.1136/bmj.i4721
2. Messinger CJ, Lipsitch M, Bateman BT, et al. Association Between Congenital Cytomegalovirus and the Prevalence at Birth of Microcephaly in the United States. JAMA Pediatr. 2020;174(12):1159-1167. doi:10.1001/jamapediatrics.2020.3009
3. Orioli IM, Dolk H, Lopez-Camelo JS, et al. Prevalence and clinical profile of microcephaly in South America pre-Zika, 2005-14: prevalence and case-control study. BMJ. 2017;359:j5018. Published 2017 Nov 21. doi:10.1136/bmj.j5018
4. Farrar DS, Knowles RL, Nunez C, et al. Etiology of Severe Microcephaly in Infants: A Multinational Surveillance Study. Pediatrics. 2026;157(2):e2025072700. doi:10.1542/peds.2025-072700
5. 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) [RETIRED]: 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
Diagnosis of Microcephaly
Prenatally, ultrasound
Postnatally, physical examination, including measurement of head circumference and cranial imaging brain imaging
Sometimes genetic testing
Prenatally, the diagnosis of microcephaly sometimes is made with ultrasound performed 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. If maternal infection is suspected as a cause, serology or nucleic acid antibody testing in the neonate may be diagnostic, depending on the specific organism (1). Primary isolated autosomal recessive microcephaly refers to microcephaly that is not associated with other extracerebral malformations.
A clinical geneticist should evaluate affected patients even in cases of apparent isolated congenital anomaly.
Chromosomal abnormalities can also occur with microcephaly. Among the genetic causes to be considered are Seckel syndrome, Smith-Lemli-Opitz syndrome, syndromes due to defective DNA repair (eg, Fanconi and Cockayne syndromes), and Angelman syndrome. Depending on which cause is present, risk of the disorder appearing in subsequent offspring may be as high as 25%, and thus clinical genetic assessment is necessary (2, 3). 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. Clinical exome sequencing analysis or clinical genome sequencing may be recommended.
Diagnosis references
1. Devakumar D, Bamford A, Ferreira MU, et al. Infectious causes of microcephaly: epidemiology, pathogenesis, diagnosis, and management. Lancet Infect Dis. 2018;18(1):e1-e13. doi:10.1016/S1473-3099(17)30398-5
2. Verloes A, Drunat S, Passemard S. ASPM Primary Microcephaly. 2020 Apr 2. In: Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026.
3. Verloes A, Ruaud L, Drunat S, et al. WDR62 Primary Microcephaly. 2022 Feb 17. In: Adam MP, Bick S, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2026.
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 and early intervention services should be maximally utilized (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
