Normal and pathological growth of the foramen occipitale magnum shown in the plain radiography.

The transverse diameter fo the foramen occipitale magnum (f. o. m.) in the semiaxial skull X-ray was measured and evaluated statistically in 174 cerebrally healthy children of different ages. These normal values are contrasted with the foramen diameters of 35 children with verified Arnold-Chiari malformation as well as children with macrocephaly and microcephaly. The values in children with Arnold-Chiari malformation are all above the norm, irrespective of whether or not there is a concomitant hydrocephalus.