Nonrheumatoid cranial settling.

Cranial settling is a condition in which erosive changes of the atlantal lateral masses result in downward telescoping of the atlas onto the axis body, anterior displacement of the atlantal posterior arch, and subsequent ventral and dorsal cervicomedullary compression. Cranial settling is described in conjunction with rheumatoid basilar invagination and atlanto-axial instability, possibly representing the most life-threatening abnormality associated with rheumatoid arthritis. The authors describe a case of symptomatic cranial settling in a nonrheumatoid patient with chronic, severe, spasmodic torticollis resulting in erosive changes in the occipito-atlanto-axial complex.