Early descriptions of the Arnold-Chiari malformation

✓ John Cleland described an unusual congenital anomaly of the brain stem in 1883 in which the medulla was elongated, the fourth ventricle extended into the cervical canal, and the inferior vermis distorted caudally. In 1891 Chiari described two types of brain stem malformation; in one the cerebellar tonsils extended into the cervical canal without medullary deformation, while in the other there was caudal extension of the brain stem and cerebellum and prolongation of the inferior vermis into the cervical canal. The second type was termed the “Arnold-Chiari” malformation by other authors in 1907, and corresponds to the condition described earlier by Cleland. The anatomical features and differences between the types of malformation are tabulated.