Hypoplasia of the basi-occipital bone and persistence of the spheno-occipital synchondrosis in a patient with transitory supplementary fissure of the basi-occipital.

The author had the opportunity to observe the progressive development of a special form of basilar impression characterized by transitory supplementary fissure of the basi-occipital bone, persistence of the spheno-occipital synchondrosis and hypoplasia of the basi-occipital. He proposes to dissociate the general concept of basilar impression and to consider anatomo-clinical entities such as the example described in this paper.