NINDS

Chiari malformations (CMs) are structural defects in the base of the skull and the cerebellum, the part of the brain that controls balance. When part of the cerebellum extends through the opening at the base of the skull, the cerebellum and brain stem can be pushed downward. The resulting pressure on the cerebellum can block the flow of cerebrospinal fluid (CSF, the liquid that surrounds and protects the brain and spinal cord) and can cause a range of symptoms including dizziness, muscle weakness, numbness, headache, and problems with hearing, balance, and coordination. Symptoms may change for some individuals depending on buildup of CSF and any resulting pressure on tissue and nerves. CMs are classified by the severity of the disorder and the parts of the brain that protrude into the spinal canal. The most common is Type I, which may not cause symptoms and is often found by accident during an examination for another condition. Type II (also called classic CM and Arnold-Chiari malformation) is usually accompanied by a myelomeningocele--a form of spina bifida that occurs when the spinal canal and backbone do not close before birth, causing the spinal cord to protrude through an opening in the back. This can cause partial or complete paralysis below the spinal opening. Symptoms of Type III--the most serious form of CM--include those seen in Type II, in addition to additional severe neurological defects. In CM Type IV, parts of the creebellum are missing, and portions of the spinal cord may be visible. Other conditions sometimes associated with CM include hydrocephalus, syringomyelia (a fluid-filled cyst in the spinal cord), and spinal curvature.

MalaCards based summary

Chiari Malformation Type Ii, also known as arnold-chiari malformation, is related to craniosynostosis-hydrocephalus-arnold-chiari malformation type i-radioulnar synostosis syndrome and chiari malformation type i, and has symptoms including ataxia, cyanosis and opisthotonus. An important gene associated with Chiari Malformation Type Ii is FUZ (Fuzzy Planar Cell Polarity Protein). The drugs Benzocaine and Nimodipine have been mentioned in the context of this disorder. Affiliated tissues include skin, brain and testes.

NIH Rare Diseases

Chiari malformation type 2 (CM type II) is a type of Chiari malformation in which both the cerebellum and brain stem tissue extend into the foramen magnum (the hole at the skull base for passing of the spinal cord). CM type II is usually accompanied by a myelomeningocele (a form of spina bifida that occurs when the spinal canal and backbone do not close before birth), which can result in partial or complete paralysis of the area below the spinal opening. While the severity of CM type II can vary greatly, it can potentially cause severe, life-threatening complications during infancy or childhood. The exact cause of CM type II is not known but it appears to be due to defects in the brain and spinal cord that occur during fetal development. Treatment includes surgery to ease symptoms and/or stop the progression of damage to the nervous system. For most people, surgery improves or stabilizes symptoms. Some people may require more than one surgery. Last updated: 9/11/2017

OMIM

Chiari malformation type II (CM2), also known as the Arnold-Chiari malformation, consists of elongation and descent of the inferior cerebellar vermis, cerebellar hemispheres, pons, medulla, and fourth ventricle through the foramen magnum into the spinal canal. CM2 is uniquely associated with myelomeningocele (open spina bifida; see 182940) and is found only in this population (Stevenson, 2004). It is believed to be a disorder of neuroectodermal origin (Schijman, 2004). For a general phenotypic description of the different forms of Chiari malformations, see Chiari malformation type I (CM1; 118420). (207950)