[The pterygoclival trihedron: its 3D reconstruction, stability and possible variations during growth]

The growth's study, from skull's radiographics, needs the use of superposition's structures. Three X-ray radiographics pictures from the front, from profile and from under are retalling by a soft. This orthogonalization's step has been realized for every child at two different ages. The reconstruction of the "clivus" straight and "pterygoïde" straights from three views gives the "pterygo-clivus triedre" which stability is studied for time.