Platybasia and basilar invagination.

Descriptions of the flattening (platybasia) of the skull base and the upward displacement(impression) of the basilar and condylar portions of the occipitalbone by the upper cervical spine date to the late 18th and early 19th centuries. Anatomical measurements to display these abnormalities were begun in 1865, but the full clinical significance was not appreciated until Homen's work in 1901. Subsequent refinement of radiology facilitated diagnosis and the later advent of surgical treatment.