Arnold Chiari, or “Cruveilhier Cleland Chiari” malformation

In 1891, Hans Chiari (1851-1916) wrote his first paper on ectopia of cerebellar tissue.1 He described a malformation of the cerebellum and brainstem with varying descent through the foramen magnum into the cervical canal. He related the changes to congenital hydrocephalus, because he had not observed the deformities in late onset or acute hydrocephalus. The malformation is not described in Kinnier Wilson's Neurology, and presumably was long regarded as a rare curiosity until the surgery of dysraphism and hydrocephalus began. Unfortunately, some English translations of Chiari's work2 contained inaccuracies, but Koehler has corrected these.3 Chiari described three grades:

Type 1 showed “elongation of the tonsils and medial parts of the inferior lobes of the cerebellum into cone shaped projections, which accompany the medulla oblongata into the spinal canal.”

In most cases the cerebellum itself appeared normal, but in some instances there was softening or sclerosis. The fourth ventricle was normal or slightly elongated; the medulla appeared flattened. Chiari was uncertain whether these changes cause symptoms or not, but he was inclined to believe bulbar symptoms might result.

He recorded type 2 changes in a 6 month old child who had paraplegia, a paralysed bladder, and had …