Microcephaly

Alternative names:

microcephalia; microcephalic; microcephalus

Definition:

Having a head size (measured as the distance around the top of the head), significantly below the median for the infant's age and sex. Significantly below is generally considered to be smaller than 3 standard deviations below the mean, or less than 42 cm in circumference at full growth.

Considerations:

Microcephaly most often occurs because of failure of the brain to grow at a normal rate. Skull growth (which occurs along the suture lines) is determined by brain expansion, which takes place during the normal growth of the brain. Conditions and disease that affect brain growth cause microcephaly.

Microcephaly is often associated with some degree of mental retardation.

Microcephaly may occur following brain-damaging infections in the extremely young infant (such as meningitis and meningoencephalitis).

Common causes:

Primary Causes:

• Down's syndrome
• cri du chat syndrome
• Seckel's syndrome
• Rubinstein-Taybi syndrome
• trisomy 13
• trisomy 18
• Smith-Lemli-Opitz syndrome
• Cornelia de Lange syndrome

Secondary Causes:

• uncontrolled maternal phenylketonuria (PKU)
• methylmercury poisoning
• congenital rubella
• congenital toxoplasmosis
• congenital CMV
• maternal drug use
• malnutrition

Note: There may be other causes of microcephaly. This list is not all inclusive, and the causes are not presented in order of likelihood. The causes of this symptom can include unlikely diseases and medications. Furthermore, the causes may vary based on age and gender of the affected person, as well as on the specific characteristics of the symptom such as quality and associated complaints. Use the Symptom Analysis option to explore the possible explanations for microcephaly, occurring alone or in combination with other problems.

Update Date: 02/09/00
Updated by: J. Gordon Lambert, MD, Associate Medical Director, Utah Health Informatics and adam.com editorial