Syringomyelia (SM) MRI Screening Protocol
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Basic
MRI Screening Protocol - Proposed BVA KC Syringomyelia MRI screening scheme
- Related Links
- Veterinary Resources
Dr. Clare Rusbridge, BVMS DipECVN MRCVS, of the Stone Lion Veterinary Centre in Wimbledon, UK, published the following protocol in October 2009, for veterinarians who perform magnetic resonance imaging (MRI) scanning to diagnose dogs suspected of having syringomyelia (SM) or Chiari-like malformation (CM).
Basic MRI Screening Protocol
for SM -- COMS -- OH
copyright by Clare Rusbridge, BVMS DipECVN MRCVS PhD.
Positioning:
The dog’s head should be in extension as mild flexion can “improve” a chiari malformation. This is often easiest to achieve by having the dog in sternal recumbency (prone) with the head elevated on a small foam cushion. If the dog is positioned in either dorsal or lateral recumbency then care must be taken to ensure that the head in extension especially in brachycephalic dogs as the head tends to flop forward especially when in dorsal recumbency.
How head position affects apparent chiari malformation. The dog on the left, positioned in dorsal recumbency (supine) may have a mild chiari malformation however it is difficult to be sure.
It is also essential that the head and neck are straight and in line with each other.
TW1 MRI images from a dog positioned with the head slightly rotated with respect to the neck. The images on the left were obtained for assessment of the cervical spinal cord and demonstrate a cervical syrinx (midsagittal cervical spine). However the section though the bran is slightly oblique giving an impression that the dog has only a mild herniation of cerebellum through the foramen magnum. The image on the right indicates the true appearance of the cerebellar herniation (midsagittal brain).
The images above illustrate how difficult it is to make assessments of severity of cerebellar herniation using isolated "snap shots" especially the person interpreting the MRI scan is not aware of how the dog was positioned. It also illustrates how important it is to position the dog accurately. A study on the effect of positioning on apparent severity of the chiari malformation was funded by the UK CKCS club.
Minimum area covered:
The minimum required images are
1) Sagittal T1W from intra thalamic adhesion to as far caudal as possible – The images must include a mid sagittal section of spinal cord visible in one section from the cisterna magna to the C4/C5 intervertebral disc space. If this cannot be achieved because the dog has scoliosis secondary to syringomyelia then a dorsal image of the spinal cord must be included in addition.
2) Sagittal T2W as above
3) T1W Transverse images though the maximum width of the syrinx if there is syringomyelia or as a block centred on C2/C3 and extending from at least mid point of the vertebral body of C2 and reaching the mid point of the vertebral body of C3
In addition transverse images though the lateral ventricles and tympanic bullae are preferred (the latter can be low quality images).
I image from ~ level of the thalamus / corpus callosum to as far caudal as possible. For minimum (i.e. low cost) imaging, three (3) sequences are done. If paying full price for a scan, I would expect a full study of the areas covered.
Example of a good quality “mini” MRI scan.
Does quality matter?
In the UK low cost MRI screening for SM is performed in many cases on ESOVATE MRI machines. Images of excellent quality can be obtained but operators should beware of taking short cuts either for time or economic reasons. Subtle SM may be missed. The images above are taken from the same dog with a narrow syringomyelia (arrow). The image on the left is taken with a short acquisition times and the SM is not appreciable. The image on the right is a longer acquisition time. The consequence to the breeder of missing subtle disease may be devastating as his or her whole breeding program may be based on the assumption that the dog in question is unaffected.
For more information about MRI scanning for Chiari-like malformation and syringomyelia, including examples of settings for ESOVATE machines, see Dr. Rusbridge's SM MRI screening webpage for veterinarians, from which the foregoing information has been excerpted.
Proposed BVA KC Syringomyelia MRI screening scheme
On October 24, 2008, a panel of veterinary neurologists met at the British Veterinary Association in London, England to discuss a proposed new syringomyelia MRI screening protocol. At this point -- October 2009 -- it is subject to further review and approval, but here is the gist of it at this preliminary stage:
Proposed BVA KC Syringomyelia MRI screening scheme
SUMMARY (October 24, 2008)
Members of Panel
Members of the panel must be board certified in neurology or radiology and have the capacity to read DICOM images i.e. have E Film ™ or similar.
Certification
Breeders will receive a YES / NO answer on whether the dog has central canal dilatation or syringomyelia.
If the dog has a syringomyelia then certificate will also detail the maximum transverse width of the syrinx on a T1W image cranial to the C4-5 disc space.
Imaging
The minimum required images are:
1) Sagittal T1W from intra thalamic adhesion to as far caudal as possible – The images must include a mid sagittal section of spinal cord visible in one section from the cisterna magna to the C4/C5 intervertebral disc space.
If this cannot be achieved because the dog has scoliosis secondary to syringomyelia then a dorsal image of the spinal cord must be included.
2) Sagittal T2W as above.
3) T1W Transverse images though the maximum width of the syrinx if there is SM or as a block centred on C2/C3 and extending from at least mid point of the vertebral body of C2 and reaching the mid point of the vertebral body of C3.
Identification of dogs and labeling of images
Dogs presented for scanning must have permanent identification in the form of microchip / tattoo and Kennel Club Registration number. [NOTE: This identification requirement does not apply to dogs suspected of having syringomyelia.]
The microchip / tattoo and the Kennel Club Registration number together with the name, sex, breed and date of birth should be incorporated onto the DICOM images.
Age of dogs
The wording of the certificate will clearly state that this is the MRI status of the dog at the current time and that the situation may change.
The minimum screening age is 12 months. [NOTE: This age limitation does not apply to dogs suspected of having syringomyelia.]
It is also recommended that breeders determine the MRI status of their breeding stock at 2-3 years and again when 6 years of age. This will provide further information about that individual dog’s estimated breeding value EBV (and therefore the EBV of that individual dog’s offspring).
Proposed Procedure
DICOM files on a CD are submitted together with the appropriate documentation to the BVA
BVA will check documentation and DICOM images before sending on to 2 members of the panel.
Those 2 panel members will reach a consensus decision – if they disagree then the images will be referred to the arbitrator.
Results are submitted to the BVA.
Certificate is issued to the owner.
Results are submitted to the Kennel Club and can be accessed by appropriate individuals e.g. Canine Genetics Unit at the Animal Health Trust.
Appeals will be submitted to the arbitrator of the panel.
Procedure for non-diagnostic images
An image is designated non-diagnostic by a consensus opinion from the 2 panel members.
In the case of conflict (i.e. one panel member considers acceptable and the other not) then the arbitrator will make the final decision.
If images are non-diagnostic then the veterinarian concerned will be informed in writing as to why the images are unacceptable, together with constructive advice for improving them.
Inclusion of breeds other than CKCS
This scheme is not breed specific i.e. any breeder may participate providing the dog has permanent identification in the form of tattoo or microchip.
Inclusion of dogs from other countries
This scheme is also not limited to the UK i.e. images and appropriate documentation may also be submitted from other countries.
Dogs scanned before the scheme comes into effect
Breeders are encouraged to submit result certificates for SM and mitral valve dysplasia, together with the Kennel Club registered name and number of the dog or a 5-generation pedigree to Dr Sarah Blott, CKCS Health Breeding Programme, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU. PDF copies of the certificates can also be sent to sarah.blott@aht.org.uk
It is likely that it will be many months before an official scheme can be started. This is because of the lengthy consultation and preparation process that is involved.
Prior to the scheme coming into effect it is recommend that from January 2009:
1) The approved protocols for imaging are followed – this will include permanent identification of dogs with microchip or tattoo;
2) That the images are reviewed by a board certified radiologist or neurologist.
Related Links
Syringomyelia
SM
Breeding Protocol
Board Certified Veterinary Neurologists
Questions for Cavalier Breeders
Dr.
Rusbridge's Website
Dr. Rusbridge's Doctoral Thesis
Dr. Rusbridge's Syringomyelia News Winter 2007 Research Update
Dr. Rusbridge's Syringomyelia News Autumn 2007 Research Update
Dr. Rusbridge's Syringomyelia News 2007 Research Update
A SM support group is
http://uk.groups.yahoo.com/group/ArnoldChiari_dogs/
A SM discussion group is
http://groups.yahoo.com/group/CKCS-SM/
A website devoted to syringomyelia in Cavaliers is Karlin Lillington's
SM.CavalierTalk.com
Veterinary Resources
Neurological signs and results of magnetic resonance imaging in 40 cavalier King Charles spaniels with Chiari type 1-like malformations. Lu D, Lamb CR, Pfeiffer DU, Targett MP. Vet Rec. Aug 2003;153(9):260-3.
The Use of Ultrasonography to Diagnose “Caudal Occipital Malformation Syndrome” in Dogs – a Prospective Study in 12 Dogs. B Levitin, JJ McDonnell, D Faissler, AS Tidwell. J Vet Intern Med; May/June 2005;19(3) (ACVIM 23rd Ann. Vet. Med. Forum Abstract Program: Abstract 209).
Brain Stem Auditory Evoked Response (BAER) Testing in Cavalier King Charles Spaniels with Caudal Occipital Malformation Syndrome. CW Dewey, KS Bailey, G Barone, J Stefanacci. J Vet Intern Med; May/June 2006;20(3) (ACVIM 24th Ann. Vet. Med. Forum Abstract Program: Abstract 270).
Syringomyelia in cavalier King Charles spaniels: the relationship between syrinx dimensions and pain. C Rusbridge, H Carruthers. M-P Dubé, M Holmes, N D Jeffery. J Small Anim. Pract. 2007 Aug;48(8):432-6. Quote: "Objectives: This study was designed to test the hypothesis that pain associated with syringomyelia in dogs is dependent upon size and involvement of the dorsal part of the spinal cord. Methods: Masked observers determined syrinx dimensions and precise location within the spinal cord on magnetic resonance images of 55 cavalier King Charles spaniels with syringomyelia. After removal of masking, syrinx size and location were compared between the cohorts of dogs that exhibited pain with those that did not. Results: Maximum syrinx width was the strongest predictor of pain, scratching behaviour and scoliosis in dogs with syringomyelia. Both pain and syrinx size were positively correlated with syrinxes located in the dorsal half of the spinal cord. Clinical Significance: Large syrinxes associated with damage to the dorsal part of the spinal cord are associated with persistent pain suggesting that the pain behaviour expressed by this group of patients is likely to be 'neuropathic pain', resulting from disordered neural processing in the damaged dorsal horn. As such it is likely that conventional analgesic medication may be ineffective."
Magnetic resonance imaging - unravelling the mystery. J. Fraser McConnell. J Small Anim. Pract. 2007 Aug;48(8): 421-422. Quote: "With evidence based medicine in vogue the study by Claire Rusbridge and colleagues (Rusbridge and others 2007) is to be congratulated and is of particular value as it contains a cohort of dogs with no clinical signs. Obtaining MR images of neurologically normal animals can be difficult as it is often not possible to justify anaesthesia in such animals. The use of MRI screening prior to breeding gives valuable information from a group of clinically normal animals. ... Reliance on statistical analyses alone can be misleading when it comes to determining the significance of MRI changes for an individual animal. While the diagnosis of syringohydromyelia in cavalier King Charles spaniels is straightforward with MRI, the problem is one of interpreting what the changes will mean for an individual. It has long been recognised that there is a poor correlation between severity of MRI abnormalities and whether the dog will show clinical signs with syringomyelia. This was shown by Lu and others (2003) who found no correlation between the severity of the syrinx and presence of neurological signs relating to the spine; some dogs with marked syringomyelia having no spinal signs (Lu and others 2003). The study by Rusbridge and colleagues in this issue reports different results and found, not surprisingly, that the larger the syrinx the more likely the individual will show clinical signs. While the study suggests that assessing syrinx size based on transverse plane images may be a more useful method than length of syrinx this does not give all the answers to the problem of interpretation. The data shows that while there is a good correlation between size of syrinx and pain there is an almost complete overlap of the range of syrinx size between the two groups. The significance of this is that it is still not possible to state with certainty, based on the MRI findings, whether a dog will develop clinical signs. It is likely that functional imaging such as CSF flow studies will be required to unpick the complexity of syringomyelia in cavalier King Charles spaniels. Similar findings have been reported in other areas of neuroimaging such as degenerative lumbosacral stenosis and intervertebral disk disease (Penning and others 2006, Mayhew and others 2002, Suwankong and others 2006) It is clear that with all the advances in imaging techniques there are still no easy answers. Imaging findings must be interpreted in light of the clinical findings and support rather than replace the neurologist or neuropathologist!"
Radiographic morphology of the cranial portion of the cervical vertebral column in Cavalier King Charles Spaniels and its relationship to syringomyelia. Stalin CE, Rusbridge C, Granger N, Jeffery ND. Am J Vet Res. 2008 Jan;69(1): 89-93. Quote: "Results suggested that radiographic morphology of the atlantoaxial region in CKCSs differs from morphology of that region in dogs of other breeds, but that these differences do not account for why some CKCSs develop syringomyelia and others do not."
