Table 2. Types of Chiari malformations.

CM: Chiari malformation

Sr No.	Type of Chiari malformation (CM)	Findings
1	CM0	A syrinx within the spinal cord without herniation of cerebellar tonsillar or brain stem through the foramen magnum.
2	CM0.5	The ventral tonsillar wrapping around the medulla in the absence of a cerebellar tonsillar descent in the upper spinal canal.
3	CM1	The descent of cerebellar tonsils (more than 6 mm) into the upper cervical spinal canal.
4	CM1.5	The caudal descent of cerebellar tonsils and brainstem through the foramen magnum greater than 12 mm.
5.	CM2	The medulla, fourth ventricle, and cerebellum are pushed downward into the upper cervical spinal canal with lower spinal myelomeningocele.
6	CM3	A high cervical-occipital encephalocele and protruding cerebellum and/or brainstem.
7	CM3.5	An occipitocervical encephalocele communicating with the foregut.
8	CM4	The severe cerebellar hypoplasia without displacement of the cerebellum through the foramen magnum.
9	CM5	The absent cerebellum with occipital lobe herniation through the foramen magnum.