Microcephaly is a condition in which a person's head size is much smaller than that of others of the same age and sex. Head size is measured as the distance around the top of the head. A smaller than normal size is determined using standardized charts.

Skull of a newborn

The "sutures" or anatomical lines where the bony plates of the skull join together can be easily felt in the newborn infant. The diamond shaped space on the top of the skull and the smaller space further to the back are often referred to as the "soft spot" in young infants.


Microcephaly is 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. It most often occurs because of failure of the brain to grow at a normal rate.

Ultrasound, normal fetus - ventricles of brain

This is a normal fetal ultrasound performed at 17 weeks gestation. The development of the brain and nervous system begins early in fetal development. During an ultrasound, the technician usually looks for the presence of brain ventricles. Ventricles are spaces in the brain that are filled with fluid. In this early ultrasound, the ventricles can be seen as light lines extending through the skull, seen in the upper right side of the image. The cross hair is pointing to the front of the skull, and directly to the right, the lines of the ventricles are visible.


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