Figure 4.

MRI and CT of a two-year-old female Chihuahua with hydrocephalus, quadrigeminal cistern expansion, and syringomyelia. (a) T2-weighted midsagittal brain and cervicothoracic spine. Yellow star, dilated lateral ventricle; green star, dilated third ventricle; blue star, quadrigeminal cistern expansion with compression of the cerebellum, which is herniated into the spinal canal. White arrow, craniocervical junction abnormality with cervical flexure, angulation of the odontoid peg, and compression of the craniospinal junction. Red arrow, developing cervicothoracic syrinx. (b) Mid-sagittal reformatted CT of the skull and cranial cervical spine. White arrow, craniocervical junction abnormality with cervical flexure, angulation of the odontoid peg, and compression of the craniospinal junction (images created by C. Rusbridge and S.P. Knowler).