View Full Version : New research about head position for MRIs
14th August 2011, 03:55 PM
Influence of head positioning on the assessment of Chiari-like malformation in Cavalier King Charles spaniels
J. J. Upchurch, BVetMed, MRCVS1,
I. M. McGonnell, PhD2,
C. J. Driver, BSc, BVetMed, MRCVS1,
L. Butler, BSc1 and
H. A. Volk, DVM, PhD, DipECVN, FHEA, MRCVS1
+ Author Affiliations
Department of Veterinary Clinical Sciences, Royal Veterinary College, Hatfield, Hertfordshire AL9 7TA, UK
Department of Veterinary Basic Sciences, The Royal Veterinary College, Royal College Street, London NW1 0TU, UK
Correspondence to Dr Volk, e-mail: firstname.lastname@example.org
Chiari-like malformation (CM) is almost omnipresent in the Cavalier King Charles spaniels (CKCS), often leading to syringomyelia (SM). Morphometric studies have produced variable results concerning relationship between the brain parenchyma within the caudal cranial fossa (CCF) and SM. The present study assesses the effect of head position, one potential confounder. Magnetic resonance images of CKCS with CM were reviewed in extended and flexed head positions. Volumes were calculated from transverse T2-weighted brain images. Mid-sagittal images were used for measurement of cerebellar herniation and CSF space between cerebellum and brainstem. Fourteen CKCS were included into the study, seven dogs with CM and seven with CM/SM. There was no difference between the relative brain parenchyma within the CCF in extended position and flexed position, or the brain parenchyma within the rostral and middle cranial fossae proportion. Cerebellar herniation and CSF space between cerebellum and brainstem were significantly increased in the flexed position. Cerebellar herniation and CSF space differed significantly between CM and CM/SM in a flexed head position. Volumetric measurements did not vary with head position. Cerebellar herniation and CSF space between the cerebellum and the brainstem were larger in a flexed head position.
14th August 2011, 07:50 PM
What does all of this mean? I luckily am not a breeder or have a cavalier needing an MRI but some do have CM or other reasons. I'm just confused and I think others are too. Somethings regarding herniation etc. Goes way over my head.
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14th August 2011, 07:52 PM
You explained the recent CM study being progressive in laymans terms, can you do the same? So much for taking break from message boards :)
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14th August 2011, 08:21 PM
It means that when the head is in one position–flexed–it pushes the brain down further towards the foramen magnum and makes the herniation more prominent and obvious. If the head isn't flexed, the herniation is less obvious. Researchers have been aware of this for a while. It makes sense–I imagine you might get a similar situation with the human head if it was bent backwards and then bent forwards in an MRI.
It would not change the grade for breeders on MRIs, so from that point of view, it doesn't actually matter very much. There are many different degrees of herniation as well and neurologists sometimes have to make a call on whether they believe they see herniation or not. I had a discussion about this with Geoff Skerritt in the UK at couple of years ago and I am sure breeders have raised the issue before as well because most breeders would prefer a scan certificate not to state that the dog has herniation. So one would assume breeders would actually prefer not to have the head sharply flexed!
The point of picking a consistent head position for MRIs is not to accentuate or decentuate herniation, but to have a standard point for reading MRIs so that breeders have as consistent results across different neurologists, across the world, as possible. It is my understanding from neurologists that a very flexed head position can possibly create some health risks when scanning–so I don't know whether anyone would actually want a markedly flexed head.
There is actually a new standard waiting to be published as part of the BVA/KC MRI scheme so at the moment, we don't know what neurologists have concluded is the ideal head position and what they have agreed upon–and keep in mind that the researchers involved with this paper would be in discussion with other neurologists focused on this issue so one would presume it might influence any new standard. One would also presume that there might be a new standard, given that more is now known and that time has passed. It's a shame that we have no idea what the current standard might be but…
Unfortunately, the Cavalier Club in the UK has objected to the publication of results of this scheme, despite the fact that every single other health program of this sort run by the Kennel Club mandates publication of results and this would be the only exception (with no logical reason for there to be an exception, except that club cavalier breeders –or at least, their new committee, which would not necessarily reflect the beliefs of the membership–would apparently like to keep the results secret)– and the Kennel Club has been unable to mediate a resolution–a situation which the British Veterinary Association has already raised as an alarming and disappointing issue, given that the MRI scheme has been in gestation for eons and was supposedly something that the breed club wanted. See: http://www.cavaliertalk.com/forums/showthread.php?39133-News-on-the-BVA-KC-Official-Scheme-for-CMSM
Meanwhile, the horrific and widespread problem of CM and SM grows steadily more obvious and of greater concern in the breed and no doubt, more widespread due to lack of scanning and lack of sharing results. No wonder Jemima Harrison has said that a return to an examination of what has happened since Pedigree Dogs Exposed with cavaliers, is a priority: http://pedigreedogsexposed.blogspot.com/2011/08/cavaliers-agony-and-agony.html
A recently published study of 555 Cavaliers with no clinical symptoms, showed that about 70% have SM–not just CM, but SM–by the time they reach age 6 or older, and given that that is only the percentage that breeders and owners felt were not showing symptoms, you can assume the rate of affected dogs in the breed is considerably higher for older dogs, so it is appalling that the breed club is holding up a significant action they could take to try to help push research forward and address & minimise this terrible problem in the breed.
Meanwhile, of course, the dog shows continue… I wish as much energy could be put towards resolving this state of limbo, which has effectively shelved a major health initiative for the breed and the breeders.
Separately from this -- Anne, if you wish to ask Rod questions directly, which happens in a lot of threads, perhaps PM him for a private discussion? I am sure if he wishes to comment, he will in his own time :) (he almost always does if he reads a thread and doesn't really need constant prompting), but if you wish to raise issues directly with him more urgently and feel you need to draw his attention to something, please do so by email or PM. :thmbsup:
14th August 2011, 09:04 PM
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15th August 2011, 03:16 AM
Okay, okay. Karlin covered this much more adequately than what I'm about to cut&paste, but here goes:
They have found the degree of cerebellar herniation was significantly worse in dogs with a flexed compared to an extended head position. When cerebrospinal fluid (CSF) space between the cerebellum and brainstem was compared in CKCS with and without SM, there was a significant increase in CSF space in CKCS with CM alone compared to those with CM/SM when head position was flexed. Based upon their findings, they state that it may be appropriate to position patients in a more flexed head position for optimal imaging in order to identify morphologic changes more accurately. They stated that this is important to consider for imaging CKCS with CM especially when studying the pathogenesis of CM/SM.
The current screening protocol calls for "the dog's head should be "in extension, as mild flexion can 'improve' a chiari malformation." If "improve" means "lessen", then this study appears to reach the opposite conclusion.
This new study does not conclude that if the extended position is utilized, it would appear that the dog does not have CM, while in the flexed position, it does show CM. It does however, recommend that the flexed position be used in the future.
There are more details from the report at http://www.cavalierhealth.org/sm-mri-screeningprotocol.htm#Influence_of_head_positionin g
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