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JMS Pearce

Platybasia is a spinal disease of a malformed relationship between the occipital bone and cervical spine.

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Virchow coined the term "platybasia" to describe an abnormal flattening of the skull base, a defect which he attributed to abnormal bone development. He observed that the association of platybasia, occipitalization of the atlas, and fusion of cervical vertebrae in both groups suggested a common developmental origin. Neurologically, platybasia is not usually of any consequence. However, Virchow in 1876 reported that basilar impression was occasionally seen in association with platybasia. In addition to flattening of the base of the skull, there is upward displacement (impression) of the basilar and condylar portions of the occipital bone which caused infolding or invagination of the foramen magnum, reduction of the posterior fossa, and consequent protrusion of the upper cervical spine into the anterior brainstem, with neurological signs. Basilar invagination of the skull, the commonest malformation of the craniocervical junction. is a well recognised cause of lower cranial nerve palsies, ataxia, hydrocephalus andcervical cord compression with pyramidal weakness. It is associated with other malformations of the notochord and craniovertebral junction, such as occipitalization of the atlas, Klippel-Feil anomaly, Chiari type I malformation, and syringomyelia . The neurological signs may vary considerably because of the closely packed neural structures and the secondary effects of vascular and CSF disruption. After careful clinical and radiological tests, surgical decompression may be needed in patients with progressing symptoms.