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Chiari malformations

Dr Frank Gaillard and Dr Jeremy Jones et al.

The Chiari malformations are a group of defects associated with congential caudal 'displacement' of the cerebellum and brainstem.

Initial descriptions were based on autopsy observations. Three types were described, with a forth added later. Types II and III are likely to be related to each other ¹.

Chiari I malformation
- most common
- peg-like cerebellar tonsils displaced into the upper cervical canal through the foramen magnum
Chiari II malformation
- displacement of the medulla, fourth ventricle and cerebellum through the foramen magnum
- usually with associated with a lumbosacral spinal myelomeningocoele
Chiari III malformation
- features similar to Chiari II but with an occipital and / or high cervical encephalocoele
Chiari IV malformation
- severe cerebellar hypolasia without displacement of the cerebellum through the foramen magnum
- probably a variation of cerebellar hypoplasia

Etymology

First described by Hans Chiari, Austrian pathologist, (1851 - 1914) in 1891 ³. In this and subsequent papers Chiari also credited Julius Arnold (1835 - 1915) Professor of Anatomy at Heidelberg, on the grounds of a previous publication by Arnold believed by him to be of a Chiari II malformation. It appears that this is not actually the case, and as such the term Arnold-Chiari to denote Chiari II malformations is no longer advocated ⁴.