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| Arnold Chiari Malformation |
| Etiology •Both Chiari type l and ll may be due to a malformed posterior fossa. |
| Pathogenesis •There many theories related to the causes of Arnold Chiari type ll including pulling of the brainstem and lower cerebellum into the foramen magnum by anchoring of the spinal cord by the meningomyelocoele. None really explains all the malformations. •Chiari l may be due to a small posterior fossa., |
| Epidemiology •Both Arnold Chiari l and ll are sporadic although type l can be inherited |
| General Gross Description •Arnold Chiari type ll is almost always associated with a meningomyelocoele. •Consists of malformation of the brainstem and cerebellum leading to extension of the medulla and cerebellum through the foramen magnum where the cervical spinal cord should rest. •Usually associated with hydrocephalus •Arnold Chiari type l is not related to spina bifida, is often seen in adults and consists of herniation of the cerebellar tonsils through the foramen magnum around the cervical spinal cord. |
| General Microscopic Description •Arnold Chiari ll shows variable malformations and repositioning of nuclei in the brainstem with disorganization and atrophy of the herniated cerebellum. •Arnold Chiari l shows some loss of neurons and gliosis of the herniated cerebellar tonsils. |
| Clinical Correlation •Chiari ll is almost always seen with meningomyelocoele and hydrocephalus with all their clinical problems. It may cause brainstem or cervical cord compression. •Seen in children and adults. •Chiari l is sporadic or occasionally inherited. It can cause headaches, brainstem compression and rarely sudden death. •Usually becomes manifest during middle life. |
| References • Cotran RS, Kumar V, Robbins SL: Robbins Pathologic Basis of Disease. 5th ed. Philadelphia, W.B. Saunders, 1994, pp. 1302-3 • Poirer J et.al. Manual of basic neuropathology. Philadelphia: Saunders, 1990, pp. 203-4. |
| Arnold Chiari Malformation |
| Synopsis by: M.L. Grunnet M.D. (TX2000M20150)[64] |
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