[Commissural agenesis associated with inter hemispheric cyst].

The Objectives of this study were to Report a rare malformation and to try to understand the embryological origin of such lesion. We reported the case of an eight-month-old female infant, without any particular past medical history, who was refered for seizures and vomiting. The examination revealed normal anthropometric constants, a soft painless and renitent tumefaction of the vertex and a psychomotor delay. Skull x-ray showed a parietal lacuna opposite to an opacity. Ultrasound scan showed an encephalocystocele communicating with dilated ventricles. CT x-ray revealed a single ventricle with an important back and upper extension, which evokes a cystic formation of the centre line. The existence of this cystic formation suppose an agenesis of diencephalic and telencephalic structures notably commissural. Interest of such observation is in its rarity, its complexity, the possibility of its antenatal diagnosis and in the etiopathogenic discussions that she gives rise to.