Colpocephaly is a congenital brain abnormality in which the occipital horns - the posterior or rear portion of the lateral ventricles (cavities) of the brain -- are larger than normal because white matter in the posterior cerebrum has failed to develop or thicken.  Colpocephaly, one of a group of structural brain disorders known as cephalic disorders, is characterized by microcephaly (an abnormally small head) and impaired intellect. Other features may include movement abnormalities, muscle spasms, and seizures. Although the cause of colpocephaly is unknown, researchers believe that the disorder results from some kind of disturbance in the fetal environment that occurs between the second and sixth months of pregnancy. Colpocephaly may be diagnosed late in pregnancy, although it is often misdiagnosed as hydrocephalus (excessive accumulation of cerebrospinal fluid in the brain). It may be more accurately diagnosed after birth when signs of impaired intellect, microcephaly, and seizures are present.