ARNOLD CHIARI TYPE II MALFORMATION

2 months baby with a large meningocele


Sagittal T2 images revealed small posterior fossa with herniation of elongated cerebellar tonsil.
Large meningomyelocele in the lumbar region with a neural placode within it.
Axial T2 image of brain showed dilated atrium and occipital horn of left ventricle- s/o colpocephaly.





•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

Arnold chiari type II malformation:

• Usually accompanied by a lumbar myelomeningocele leading to partial or complete paralysis below the spinal defect.  
• As opposed to the less pronounced tonsillar herniation seen with Chiari I, there is a larger cerebellar vermian displacement.
• Low lying torcular herophili, tectal beaking, and hydrocephalus with consequent clival hypoplasia are classic anatomic associations.
• The position of the torcular herophili is important for distinction from Dandy-Walker syndrome in which it is classically upturned.
•  This is important because the hypoplastic cerebellum of Dandy-Walker may be difficult to distinguish from a Chiari malformation that has herniated or is ectopic on imaging.
• Colpocephaly may be seen due to the associated neural tube defect.

Reference : Pediatric brain and spine, an atlas of MRI and spectroscopy. Springer Verlag. (2005) ISBN:3540213406