Figure 8.

Morphometric changes in CMSM. Mid-sagittal T2-weighted brain MRI of three CKCS: normal (A), CM-pain affected (B), and SM-affected (C). The left column compares the CSF spaces. There is effacement of the cranial subarachnoid spaces evidenced by reduced definition of the sulci filled with high signal CSF in affected dogs (B,C). A Red asterisk highlights the cruciate sulcus for comparison. In addition there is ventriculomegaly with dilatation of the lateral ventricle (purple asterisk), third ventricle and quadrigeminal cistern (green asterisk) and fourth ventricle (aqua asterisk). The right column compares the neuro-anatomical changes and also the direction in which the neuroparenchyma has been deformed and crowded by the bony restrictions. Compared to the normal CKCS (A), the affected CKCS (B,C) are more brachycephalic with shortening of the basicranium and prephenoid bone (orange shading) with reduced and more ventrally orientated olfactory bulbs (green shading). The rostral forebrain is flattened in (B,C) and the rostrotentorial neuroparenchyma is displaced dorsocaudally giving increased height to the cranium particularly in (B). This reduces the functional caudotentorial space contributing to the hindbrain herniation. The atlas is closer to the skull and supraocciptal bone is flattened, particularly in (C), the SM-affected dog which also has a reduction of the occipital crest (orange asterisk). In addition to the brachycephaly, the SM affected dog has further compromise of the craniocervical junction by a cervical flexure and acute angulation of the odontoid peg resulting in kinking/ elevation of the craniospinal junction. The syrinx is indicated by the dark blue asterisk (Siemens Magnetom Symphony, A Tim System, 1.5 T, Erlangen, Germany).