[MRI observation on Arnold-Chiari I malformation].

Craniocerical junction of 42 patients with Arnold-Chiari I malformation (ACM-1) and 41 normal controls were studied. In addition to the decendent tonsil, all the components in the posterior cranial fossa including the 4th ventricle, oblongata medulla and the sinus confluence of patients with ACM- 1 were decended. Although the spinal foramen magnum anterior -posterior diameter was smaller but not statistically different from the control. The results suggest that the main pathology of ACM- 1 is the shallow and small posterior cranial fossa and the resulted organ decendent as a whole.