CM/SM – diagnosis
MRI scan of a Cavalier with syringomyelia (asterixis) secondary to foramen magnum obstruction. Although the cerebellum is not obviously herniated though the foramen magnum it is compressed and indented by the supraoccipital bone (arrow).
What is a “mini” MRI?
A “mini” MRI is a limited study MRI of the brain and cervical region provided at low cost by veterinary practices and intended as an economical screening test for breeders. The disadvantage of using it to diagnose spinal disease such as syringomyelia is that neurological examination and consultation before the MRI is important for determining if a MRI scan is indeed appropriate and which regions to image. Scanning a small predestined area may mean that the cause or the full extent of the dog’s problem is missed. In addition the opportunity to discuss MRI results with the neurologist is a valuable opportunity to ask questions and determine the optimum treatment plan.
Will taking radiographs (x-rays) help?
Computed tomography and radiographs have limited value. CM is appreciable on radiographs and, in the Griffon Bruxellois, a ratio of the height to the length of the caudal skull can be used to predict CM (sensitivity 87%, specificity of 78%). However this is likely to be more of value in predicting the breeding value of a dog rather than as a diagnostic test for syringomyelia (Rusbridge and others 2009). In cases with severe syringomyelia cervical images may suggest widening of the vertebral canal especially in the upper neck. Radiographs can also be used to confirm that abnormal head posture is due to scoliosis. They are of greatest value in ruling out other vertebral abnormalities such as atlantoaxial subluxation and for an indication of the likelihood of intervertebral disc disease. Other abnormalities of the craniocervical regions which may be seen in dogs with CM/SM are occipital dysplasia i.e. wide foramen magnum (Rusbridge and Knowler 2006), atlantoaxial subluxation (Stalin and others 2008) and dens abnormalities (Bynevelt and others 2000). Myelography is not recommended for animals suspected to have CM/SM.
Radiographic abnormalities which may be seen with CM/SM. 1. Lateral skull of a normal Griffon Bruxellois 2. Griffon Bruxellois with CM. The back of the skull has a sloped in appearance (black arrow). By comparison the parietal bone is longer (white arrow) 3. Skull and cervical vertebral column in a Cavalier with CM and wide syringomyelia. The vertebral canal is wider than normal particularly in the C1-C2 region (arrow). 4. Cavalier with atlantoaxial subluxation (this dog did not have syringomyelia) 5. Scoliosis in a Cavalier with a wide syringomyelia 6. Occipital dysplasia in a Griffon Bruxellois – there is incomplete ossification of the supraoccipital bone and the foramen magnum is wider with a dorsal keyhole notch (outlined).
Would ultrasound help obtain a diagnosis?
Ultrasonography through the space between the head and neck can be used to confirm CM however as this malformation is common in Cavaliers and may not be associated with clinical signs this information has limited value. Likewise a syrinx may be identified if within the upper part of the neck; however, failure to detect a syrinx does not eliminate the possibility of there being one further down the spine.
Is there a risk to general anaesthesia in a dog with syringomyelia?
CM/SM does not appear to increase risk of anaesthesia. Depending on the severity, mitral valve disease (heart disease) may be a precluding factor and this is normally assessed and discussed prior to anaesthesia.
What conditions could have similar signs or be confused with syringomyelia?
The most important diseases are other causes of pain and spinal cord dysfunction such as intervertebral disc disease; CNS inflammatory diseases such as granulomatous meningoencephalomyelitis; vertebral abnormities such as atlantoaxial subluxation; neoplasia; and discospondylitis. When scratching or facial/ear rubbing is the predominant clinical sign, ear and skin disease should be ruled out. The scratching behaviour for syringomyelia is classically to one distinct area.
My Cavalier has been diagnosed with PSOMS – what is this?
Mucoid material within the middle ears (arrows) is a common incidental finding in the Cavalier and is similar to “glue ear” in children. Typically the material has soft tissue intensity on MRI and there is no evidence of associated inflammation or infection (despite this, the condition is commonly and confusingly referred to a primary secretary otitis media or PSOMS). The most common explanation is that the material produced normally by the middle ear it is not drained out by the eustachian tube either because of the skull conformation or because of extra soft tissue in the eustachian tube and pharyngeal area. It is difficult to ascertain how much problem this material causes, as for many animals it is an incidental finding however it is reasonable to assume that some dogs have discomfort and/or hearing loss. The material can be removed however if the underlying problem is not resolved, e.g. poor eustachian tube drainage, then the material will reform. In most cases the problem is minor and is not treated. In some cases using tympanostomy tubes (Corfield and others 2008) or eustachian tube surgery has been suggested.
My dog had fly catching behaviour – is this caused by syringomyelia?
No – there is no evidence that this condition is associated with CM/SM although the two conditions could occur simultaneously. Fly catching is thought to be a compulsive disorder. Classically the dog acts as if watching / catching a fly. Some may also behave as if their ears or feet are irritated and some can also tail chase. Compulsive disorders are compared to obsessive compulsive disorders in humans and are poorly understood; it has been suggested in the Cavalier that there is an underlying neurochemical and/or metabolic imbalance. Diagnosis is typically made on the basis of clinical history and elimination of other behavioural, medical, metabolic, and neurological disorders. Compulsive disorders are managed with a programme of training to interrupt the behaviour sometimes combined with drugs such as selective serotonin re-uptake inhibitors. High protein diets, i.e. high meat content, tend to make compulsive behaviours worse and conversion to a low protein diet can result in improvement of signs although in some dogs this may be only temporary.
My dog has been diagnosed with episodic collapse - what is this and is it related to syringomyelia?
Episodic collapse or falling is more correctly known as hyperexplexia and characterised by limb cramping triggered by excitement and exercise. It is not related to syringomyelia. For more information visit http://www.episodicfalling.com/first.html
My dog’s MRI report said that there was also a quadrigeminal cyst – what is this?
A quadrigeminal cyst is a fluid-filled space located in front of the fourth ventricle. Cavaliers have a higher incidence of quadrigeminal cysts. By occupying space within an already crowded caudal fossa this may aggravate the obstruction at the foramen and increase the likelihood of syringomyelia.
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