Table 2.

Pathogenesis of Chiari-like malformation and syringomyelia: summary of the existing knowledge base—craniocervical junction and cervical changes.

Anatomical feature	Study finding(s)	Possible implication
Proximity of atlas to skull (atlanto-occipital overlapping)	SM risk increases with decreased distance between atlas and occipital bones (39, 62–64)	Reduced distance between the skull and the cervical vertebrae increases risk of SM
	Greater distance between atlas and basioccipital bone is protective against SM (39)
	CKCS with SM have shorter distance between the spheno-occipital synchondrosis and atlas (40)
Odontoid peg impingement of ventral subarachnoid space/neural tissue	Commonly seen in association with CM (40, 56, 65)	Contributes to overcrowding and conformation change of craniospinal junction with loss of cisterna magnum
	Greater distance between atlas and odontoid peg is protective against SM (40)
	Odontoid peg is more acutely angled, contributing to craniospinal disproportion, medullary elevation and cervical flexure (40)
Proximity of dens to atlas	SM risk increases with decreased distance between odontoid peg and atlas in Affenpincher (40)
Dorsal impingement subarachnoid space/spinal cord (atlantoaxial bands) at C1-C2	Commonly seen in association with CM and more prominent in extended than flexed positions (56, 62, 63, 65, 66)	Significance undetermined
Width of spinal canal	Increased width of spinal canal at C2-C3 and C3 in CKCS with SM (67)	Questionable clinical significance
Atlantoaxial subluxation	Occasional comorbidity with CM (68)	No significant association with SM
Size of C2 spinous process	Significantly smaller in CKCSs than in non-CKCS breeds (68)
Angulation at C2-C3	No correlation (67)