Rare. By definition, a microcephaly is present when the head circumference is less than at least 3 standard deviations from the average circumference for age and sex.

There are many possible causes:

• chromosomal aberrations: trisomy 13, 18, partial 4p10q; deletions 4p, 5p, 13q
• polymalformative syndrome:  Bloom, Coffin-Sirs, Cornelia de Lange, Seckel, Lempli-Opitz syndromes
• abnormalities of brain development: craniosynostosis,  autosomal recessive or X-linked primary microcephaly
• disorder of neurulation: encephalocele
• holoprosencephaly
• disorder of neuronal migration: lissencephaly, pachygyria, agenesis of the corpus callosum
• affections during the second half of pregnancy: infections (CMV, rubella), hemorrhage, ischemia in utero
• environmental causes: alcoholism, diabetes, maternal phenylketonuria, CO poisoning, maternal hyperthermia
• delayed intrauterine development

Anesthetic implications:

based on associated anomalies;  laryngotracheal growth is generally not affected by the microcephaly: choose the endotracheal tube according to  age.

References:

Updated: August 2016