Basilar Impression (Platybasia)

Basilar impression, sometimes spoken of as platybasia, is a deformity of the occipital bone and upper end of the cervical spine resulting from anomalous development. It may produce marked pressure effects upon the medulla and adjacent parts of the central nervous system. These pressure effects may simulate syringomyelia, disseminated sclerosis, or progressive spastic paralysis so closely as to be indistinguishable from them. It is, therefore, of paramount importance that every practicing neurologist and radiologist be thoroughly familiar with the clinical manifestations and roentgen findings, especially as surgical reconstruction of the foramen magnum and upper spinal canal may prove of marked benefit to the patient (vide infra, Case I). In spite of the fact that the anatomic changes are bizarre and, once they are appreciated, striking, the condition is easily overlooked. Our own experience suggests that typical examples could be gleaned from the current x-ray film files of many large medical centers, by reviewing all cases of syringomyelia, multiple sclerosis, and progressive spastic paralysis. The morphologic changes shown by roentgenograms give the impression of softening of the base of the skull and moulding through the force of gravity. It is as though the weight of the head has caused the ears to approach the shoulders, while the cervical spine, refusing to be shortened, has pushed the floor of the posterior fossa upward into the brain space. The resultant changes in relationships and shapes of such parts as the clivus, petrous portions of temporal bones, and foramen magnum are shown by the roentgenograms (Figs. 1 and 2) and drawing (Fig. 3).