Microcephaly has generally been equated with mental retardation. However, not all children with head circumference less than 2 standard deviations are mentally retarded. Twenty-five percent of hypopituitary dwarfs with normal IQ were microcephalic. It can also be classified as congenital or acquired. Congenital microcephaly may follow intrauterine infections with rubella, CMV, Toxoplamosis.
Congenital microcephaly is also a part of many chromosomal abnormalities and other syndromes.
The condition may be autosomal recessive or associated with chromosomal disorders. The infants are abnormal at birth. They not only have a small head but also have characteristic facial and cranial configurations. Their rounded heads, with small or absent anterior fontanel and recessed or sloped forehead indicative of the shallow anterior cranial fossa, readily identify them as infants with severe morphologic cerebral abnormalities. Some demonstrate immediate signs of neurologic dysfunction such as hypotonicity, hypertonicity, or an abnormal cry, whereas others function surprisingly normally for the first few months of life.