Agenesis of the corpus callosum.

Agenesis of the corpus callosum is an uncommon congenital anomaly which causes dilatation of the posterior horns of the lateral ventricles and a falsely high ventricular/hemispheric ratio on antenatal ultrasound scans with an incidence on studies of air encephalograms of 0.7% (Grogono, 1968). It may be confused with hydrocephalus and lead to unnecessary intervention. The characteristic features on both ante- and postnatal ultrasound are: (1) Absence of the corpus callosum. (2) Marked separation of the slit-like anterior horns of the lateral ventricles and dilatation of the posterior and inferior horns creating the typical “rabbit's ear” or “devil's horn” appearance. (3) Visualization of both medial and lateral walls of the anterior horns of the lateral ventricles which are displaced from the midline. (4) Variable dorsal and superior displacement of the third ventricle. (5) Loss of the normal parallel sulcal pattern above the third ventricle. A case of congenital absence of the corpus callosum is described...