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
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.
- 1. Ketonen L, Hiwatashi A, Sidhu R. Pediatric brain and spine, an atlas of MRI and spectroscopy. Springer Verlag. (2005) ISBN:3540213406. Read it at Google Books - Find it at Amazon
- 2. Elster AD, Chen MY. Chiari I malformations: clinical and radiologic reappraisal. Radiology. 1992;183 (2): 347-53. Radiology (abstract) - Pubmed citation
- 3. Chiari H. Uber veranderungen des kleinhirns infolge von hydrocephalie des grosshimns. Dtsch Med Wochenschr 1891; 17: 1172-i 175
- 4. Pearce JM. Arnold chiari, or "Cruveilhier cleland Chiari" malformation. J. Neurol. Neurosurg. Psychiatr. 2000;68 (1): 13. doi:10.1136/jnnp.68.1.13 - Free text at pubmed - Pubmed citation