Arnold-Chiari Malformation With Normal Spine

Abstract

There has been considerable discussion of the etiology of the Arnold-Chiari malformation, and many elaborate hypotheses have been advocated to explain the almost constant association of this anomaly of the hindbrain with spina bifida. The report of the following case in which a typical Arnold-Chiari malformation occurred without any abnormality of the spinal cord or vertebral column is therefore important in refutation of some of these theories. Chiari,¹ in 1891, described the anomalies of the hindbrain that he found in cases of congenital hydrocephalus, and divided these into four types of which types I and II are pertinent to this paper. Type I showed a variable displacement of the cerebellar tonsils into the upper cervical canal. Type II showed a downward displacement of the inferior vermis of the cerebellum accompanied by a similar caudal dislocation of the lower pons and medulla together with the fourth ventricle into the