Definition for Arnold-Chiari malformation type 1

The Chiari I malformation (CMI) is a disorder of uncertain origin that has been traditionally defined as downward herniation of the cerebellar tonsils of a distance of at least 3-5 mm through the foramen magnum (Dyste and Menezes, 1988; Dyste et al., 1989; Pillay et al., 1991) .The anomaly is a leading cause of syringomyelia (Banerji and Millar, 1974; Dyste et al., 1989; Milhorat et al., 1995) and occurs in association with osseous abnormalities at the craniovertebral junction. more

The Chiari I malformation (CMI) is a disorder of uncertain origin that has been traditionally defined as downward herniation of the cerebellar tonsils of a distance of at least 3-5 mm through the foramen magnum (Dyste and Menezes, 1988; Dyste et al., 1989; Pillay et al., 1991) .The anomaly is a leading cause of syringomyelia (Banerji and Millar, 1974; Dyste et al., 1989; Milhorat et al., 1995) and occurs in association with osseous abnormalities at the craniovertebral junction. In contrast to other Chiari malformations, CMI tends to present in the second or third decade of life and is sometimes referred to as the "adult-type" Chiari malformation. CMI is distinguished from the more familiar Chiari II (Arnold-Chiari) malformation, which is present at birth and consists of downward herniation of the lower cerebellum and medulla into the spinal canal, in association with myelodysplasia and complex anomalies of the brain such as aqueductal forking and polymicrogyria (14,60) .The comparatively rare Chiari III malformation is also present at birth and is defined as cerebellar herniation into a cervical encephalocele (26,60). less