This is an enlargement of the occipital horns of the ventricular system due to underdevelopment of the white matter in the posterior cerebrum. Embryologically, the lateral ventricles arise as a simple out pouching of the telencephalon. As the temporal lobes develop they form a U shape. The occipital projections follow, and are moulded by development of the adjoining structures, including the corpus callosum. Reduction in white matter mass in the region of the posterior poles due to some insult to the developing brain between 4 and 16 weeks will result in the occipital horns remaining relatively prominent (hydrocephalus ex vacuo). Colpocephaly may result from metabolic, chromosomal or multifactorial causes. Maternal diabetes, valproic acid and alcohol have also been implicated.


This will be made by finding characteristic enlargement of the occipital horns of the lateral ventricles in association with an increased lateral atrial diameter. Microcephaly may also be observed. A careful search for the cause and any associated anomalies should then be undertaken.

Differential Diagnosis

Any process in which abnormal development of adjacent structures occurs has the potential to exhibit colpocephaly, thus: Agenesis of the corpus callosum is the most common associated intracerebral anomaly; an elevated and enlarged third ventricle appearing as a midline cyst may be observed. Absence of the cavum septi pellucidi would also be characteristic. In septo-optic dysplasia, where the cavum septi pellucidi is absent in 50% of cases, there is microphthalmia, and there is an association with midline facial defects. In lissencephaly, agyria will be noted; hypoplasia of the corpus callosum is also present. In degenerative disorders such as porencephaly, cystic replacement of adjacent parenchyma may cause enlargement of the lateral ventricles. Communication with the ventricular system is characteristic of schizencephaly, and may aid the diagnosis.

Sonographic Features

Disproportionate enlargement of the occipital horns of the lateral ventricles and of the lateral atrial diameter.

Associated Syndromes


  1. Vergani P, Ghidini A, Strobelt N, Locatelli A, Mariani S, Bertalero C, Cavallone M Prognostic indicators in the prenatal diagnosis of agenesis of corpus callosum Am J Obstet Gynecol 170: 753-758
  2. Joffe GM, Del Valle GO, Izquierdo LA, Curet LB Colpocephaly Fetus 2: 7422.5
    Bertino RE, Nyberg DA, Cyr DR, Mack LA Prenatal diagnosis of agenesis of the corpus callosum J Ultrasound Med 7: 251-260