Lateral compression of the foramen magnum with the Chiari I malformation: case illustrations

Excerpt

The morphometry and size of the foramen magnum play an important role in the pathophysiology of various disorders of the skull base. Elongation of the clivus and hence the anterior aspect of the foramen magnum results from, for example, growth of the spheno-occipital synchondrosis. Descent of the occiput via growth from the petro-occipital and sphenopetrosal junctions is important in the formation of the bone around the foramen magnum while the primary determinants of foramen magnum size and area are the basi-exoccipital and exo-supraoccipital synchondroses and the three enchondral parts of the basiocciput, exocciput, and supra-occiput [22]. In contrast to the majority of cranial and facial bones, which develop from intramembranous ossification, the cranial base takes the intermediate step of calcification of a cartilaginous model [9]. We review the literature regarding anomalies of the foramen magnum related to various disease processes and present two illustrative cases demonstrating lateral compression of the foramen magnum that resulted in complications related to posterior fossa decompression procedures in children with Chiari I malformation. …