[Atlantoaxial dislocation in neurofibromatosis.--Report of three cases--].

Atlantoaxial dislocation has received little attention in many studies of spinal deformity in neurofibromatosis. The only four cases of atlantoaxial dislocation associated with neurofibromatosis has been previously reported in the literature. We reported three rare cases of atlantoaxial dislocation associated with neurofibromatosis. These characteristics in roentgenogram were as follows; (1) marked narrowing of sagittal diameter at C1 level without instability (instability index 0%) (2) association with other mesodermal dysplasia, such as posterior vertebral body scalloping, vertebral body dysplasia, dural ectasia etc. Neurofibromatous tissue was found around the anterior region of the odontoid process in one of our three patients. We speculate that atlantoaxial dislocation in neurofibromatosis may be due to mesodermal dysplasia. On the other hand, a neurofibroma was found around the anterior region of the odontoid process in our third case. Therefore, there is a possibility that atlantoaxial dislocation in the instance was caused by the neurofibroma involving transverse atlantal ligament.