Abstract
Chiari-like malformation (CM) and syringomyelia (SM) is a frequent diagnosis in predisposed brachycephalic toy breeds since increased availability of MRI. However, the relevance of that MRI diagnosis has been questioned as CM, defined as identification of a cerebellar herniation, is ubiquitous in some breeds and SM can be asymptomatic. This article reviews the current knowledge of neuroanatomical changes in symptomatic CM and SM and diagnostic imaging modalities used for the clinical diagnosis of CM-pain or myelopathy related to SM. Although often compared to Chiari type I malformation in humans, canine CM-pain and SM is more comparable to complex craniosynostosis syndromes (i.e., premature fusion of multiple skull sutures) characterized by a short skull (cranial) base, rostrotentorial crowding with rostral forebrain flattening, small, and ventrally orientated olfactory bulbs, displacement of the neural tissue to give increased height of the cranium and further reduction of the functional caudotentorial space with hindbrain herniation. MRI may further reveal changes suggesting raised intracranial pressure such as loss of sulci definition in conjunction with ventriculomegaly. In addition to these brachycephalic changes, dogs with SM are more likely to have craniocervical junction abnormalities including rostral displacement of the axis and atlas with increased odontoid angulation causing craniospinal junction deformation and medulla oblongata elevation. Symptomatic SM is diagnosed on the basis of signs of myelopathy and presence of a large syrinx that is consistent with the neuro-localization. The imaging protocol should establish the longitudinal and transverse extent of the spinal cord involvement by the syrinx. Phantom scratching and cervicotorticollis are associated with large mid-cervical syringes that extend to the superficial dorsal horn. If the cause of CSF channel disruption and syringomyelia is not revealed by anatomical MRI then other imaging modalities may be appropriate with radiography or CT for any associated vertebral abnormalities.
Highlights
Chiari-like malformation (CM) is a complex skull and craniocervical junction disorder associated with brachycephaly with skull base shortening, low volume caudal fossa and rostrotentorial, caudotentorial and craniospinal crowding
Limited “low cost” imaging of CM or SM with a 3-sequence protocol of the hindbrain and cranial cervical spinal cord is offered by some institutions for dog breeders that wish to screen their breeding stock [33, 106], this minimal protocol does not provide information about the brain or syrinx involvement of the thoracic and lumbar regions and is not recommended for the dog presented to a veterinarian for a diagnostic work of suspected CM or SM
If the cause of CSF channel disruption is not apparent, balanced steady-state free precession sequences such as FIESTA (Fast Imaging Employing Steady-state Acquisition) or 3D-CISS (Three-Dimensional Constructive Interference in steady state) should be employed to improve detection of arachnoid webs and diverticulae [109, 124]. These are a three dimensional gradient echo sequence that produces high contrast between the CSF and structures within the subarachnoid space. They have less flow void artifact associated with turbulent CSF and allow higher detection rates of arachnoid webs and other adhesions [102, 125] (Figure 6) and for low field Magnetic Resonance Imaging (MRI) where obtaining good signal-to-noise and spatial resolution is a challenge, it is recommended that a Balanced steady-state free precession sequences (bSSFP) sequence be included in any protocol that evaluates the CSF channels [109]
Summary
Chiari-like malformation (CM) is a complex skull and craniocervical junction disorder associated with brachycephaly with skull base shortening, low volume caudal fossa and rostrotentorial, caudotentorial and craniospinal crowding. SM development may be associated with subarachnoid space narrowing and/or change in the angulation of the vertebral canal Increased axial stress at the site of spinal curvature may explain the syrinx distribution in the CKCS In CKCS MRI imaging of the cranial cervical region only has high sensitivity for detection of SM the extent of the disease may be underestimated Dogs with a wider asymmetrical SM more likely to experience pain
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
