Microcephaly !

Malformation

The baby's head is much smaller than expected because the brain did not grow well; Zika put it in the news in Colombia in 2016.

Updated 2026-11-01

See it in 3D: Frontal lobe · Parietal lobe · Lateral ventricles

What it is

Microcephaly is a head circumference far below what is expected for age and sex. Because the skull grows as the brain pushes it, it reflects a small brain. It can be genetic or acquired through prenatal infections, alcohol, malnutrition or poor blood supply; the 2015–2016 Zika epidemic put it at the center of birth defect surveillance in Colombia.

Key facts

Skull size depends on brain growth: the underlying defect is in the brain.
Genetic causes: autosomal recessive forms that reduce neural progenitor proliferation.
Acquired causes: Zika, toxoplasmosis, CMV, rubella, alcohol, maternal or infant malnutrition, blood supply problems.
It can be present at birth or appear later (postnatal microcephaly).
Colombia: on 14 April 2016 the INS confirmed the first two cases of Zika-associated microcephaly (Norte de Santander and Cundinamarca).

Embryological cause

The ventricular zone of the neural tube makes too few neurons: neural progenitor proliferation or survival fails.
In genetic forms, spindle and centrosome genes shorten the period in which progenitors divide.
Zika virus infects neural progenitors and kills them, leaving a thin cortex and calcifications.
Without the push of the brain the skull grows little; in severe Zika the skull may look collapsed with redundant scalp.

Markers

ASPM
MCPH1
CDK5RAP2

How it presents

Low head circumference, ideally measured within the first 24 hours and compared with charts (CDC or INTERGROWTH-21st).
Seizures, developmental delay, intellectual disability, movement and balance problems.
Feeding difficulty, hearing loss and vision problems.
In congenital Zika, retinal lesions, joint contractures and hypertonia may accompany it.

Diagnosis

Prenatal ultrasound: usually detected late in the second or early in the third trimester.
Head circumference at birth against reference charts.
MRI or CT: calcifications, cortical abnormalities, ventriculomegaly.
In Colombia the INS Zika protocol included molecular tests, genetics, brain imaging and eye and hearing evaluation.

Test yourself

Think of the answer, then tap the question to see it.

Why does microcephaly reflect a brain problem rather than a skull problem?

Because the skull grows as the brain grows; if the brain grows little, so does the skull.

Which cells does Zika virus infect to cause microcephaly?

The neural progenitors of the developing brain, whose death reduces neuron production.

When did Colombia confirm its first cases of Zika-associated microcephaly?

On 14 April 2016 the INS announced two confirmed cases, in Norte de Santander and Cundinamarca.

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See it in 3D

The structures of Durgical's 3D anatomy where it is found.

Microorganisms

← All of embryology

Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.

Sources: Microcephaly (Centers for Disease Control and Prevention, 2024); Colombia confirmó dos primeros casos de microcefalia asociados a zika (Instituto Nacional de Salud (Colombia), 2016); CMV in Newborns (Centers for Disease Control and Prevention, 2024); Langman's Medical Embryology, 13th ed., ch. 18: Central Nervous System (Wolters Kluwer, 2015).

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Representative model, for educational purposes only.