microcephaly /mī′krōsef″əlē/ [Gk, mikros + kephale, head] , a congenital anomaly characterized by abnormal smallness of the head in relation to the rest of the body and by underdevelopment of the brain, resulting in some degree of intellectual disability. The head is more than two standard deviations below the average circumference size for age, sex, race, and period of gestation. It has a narrow, receding forehead; a flattened occiput; and a pointed vertex. The facial features are generally normal. The condition may be caused by an autosomal-recessive disorder, a chromosomal abnormality, a toxic stimulus such as irradiation or chemical agents, maternal infection during prenatal development, or any trauma, especially during the third trimester of pregnancy or early infancy. There is no treatment, and care is primarily supportive and educational. Also called microcephalia, microcephalism. Compare macrocephaly. −microcephalic, microcephalous, adj., −microcephalus, microcephalic, n.
