Canine Chiari malformation (CM) and syringomyelia (SM) Frequently Asked Questions

Chiari-like malformation (CM), pronounced "kee-ah-ree," is a condition where the skull and the junction between the head and neck are improperly formed. Essentially, the skull is too small to accommodate the brain, leading to overcrowding in the upper spinal cord area at the neck. This condition is frequently found in dogs with shorter skulls and muzzles, and in some breeds, like Pomeranians and Chihuahuas, it is also linked to their smaller body size.

More information here.

Syringomyelia (SM), pronounced "sir-rin-go-my-ee-lia," is a condition of the spinal cord where fluid-filled spaces, called syrinxes, form inside the spinal cord itself.

More information here.

Dogs with CM/SM usually come from breeds or mixes that were bred to be small and have "baby-like" features, such as a rounded forehead, short muzzle, a flat back of the head, and a noticeable angle between the forehead and nose (deep stop).

The brain and spinal cord are surrounded by a protective covering called the meninges and float in a fluid known as cerebrospinal fluid (CSF). This fluid helps shield the nervous system from pressure and makes the nervous tissue more flexible under pressure. Syringomyelia happens when the flow of CSF is blocked, causing the fluid to build up in spaces within the spinal cord. This buildup can harm the delicate nervous tissue. There are different ideas about how syringomyelia develops. In dogs, it often occurs due to obstruction to CSF flow at the base of the skull and top of the neck, like in Chiari-like malformation. It can also happen when there is scarring or adhesions between the meninges and spinal cord, such as in Pug dog myelopathy or after bleeding for example after trauma.

These are the signs of pain associated with Canine Chiari-like malformation. The most common clinical signs include vocalization (spontaneous or when picked up under the chest or changing position, especially at night), head scratching or rubbing, reduced activity, difficulty with stairs or jumping, spinal pain, changes in behavior (becoming more timid, anxious, or aggressive), disturbed sleep, and sensitivity to touch.

This is a group of clinical signs of spinal cord disease (myelopathy) that happens when the central syrinx is large (4mm or more in width in a Cavalier). The clinical signs depend on where the syrinx forms. For example, a dog with a syrinx in the neck may have phantom scratching and a curved spine with head tilt (scoliosis), while a dog with a large syrinx in the lower neck and upper back may have weakness in the limbs and spine. The most common clinical signs of SM-S are phantom scratching, scoliosis, weakness, and trouble with limb coordination.

The most common clinical signs include vocalization (spontaneous or when picked up under the chest or changing position, especially at night), head scratching or rubbing, reduced activity, difficulty with stairs or jumping, spinal pain, changes in behavior (becoming more timid, anxious, or aggressive), disturbed sleep, and sensitivity to touch. Chiari check can be used to give a Chiari-pain score.

More information on clinical signs here.

Syringomyelia can have no clinical signs, especially when the cavity is small and stays in the center of the spinal cord without causing it to expand. However, if the syrinx grows, it can damage the spinal cord. In CKCS dogs, this is usually reported when the syrinx is 4mm or larger in diameter. The most common clinical signs of syringomyelia are phantom scratching, scoliosis (curved spine), weakness, and postural deficits (difficulty knowing where the limb is, causing the paw to stay in awkward positions). Chiari check can be used to give a SM-S score.

More information on clinical signs here.

Syringomyelia can show no clinical signs or be discovered by chance during an MRI. This is more likely when the syrinx is small, symmetrical, and doesn’t cause the spinal cord to expand.

If your dog has epilepsy, fly catching, facial nerve paralysis, balance problems (vestibular disease), or severe hind limb weakness, these are not likely caused by CM or SM. Syringomyelia can sometimes be found by chance on an MRI, but conditions like epilepsy, vestibular disease, facial nerve paralysis, fly catching, and degenerative myelopathy don't cause visible changes on an MRI. A veterinary surgeon unfamiliar with this might mistakenly over-interpret the MRI results.

SM-associated “phantom” scratching is a specific but not universal sign of syringomyelia. It involves a rhythmic scratching motion without actually touching the skin, often with the body and neck curving towards the foot. The scratching usually targets the shoulder or neck area, often starting on one side and progressing to both sides in severe cases. It can be triggered by lightly rubbing the skin, usually on the neck, which can make walking on a collar difficult. Phantom scratching can also be triggered by excitement or anxiety. It's linked to a large syrinx in the middle of the neck's spinal cord, affecting an area called the superficial dorsal horn on the same side as the scratching. Syringomyelia-related scratching can be elicited by rubbing a specific area of skin, typically on the neck but sometimes the chest or belly.
Phantom scratching doesn’t always indicate pain or abnormal sensations. Dogs with CM/SM may also scratch or rub their heads and ears, but this is not phantom scratching—it may be a sign of CM-related pain (CM-P). Syringomyelia does not cause general itching. If your dog is scratching its belly or nibbling its back feet, it's more likely due to allergies or a skin infection. For a video showing the difference types of scratching here.

No – this is more likely due to a skin condition like allergies, fleas, or yeast infection (Malassezia), and your dog should be checked and treated for these. Syringomyelia can sometimes be found by chance on an MRI, and a dog can have more than one medical condition. Syringomyelia does NOT cause general itchiness.

No – this may be fly catching syndrome. Fly catching is a behaviour where a dog acts as if it's watching or catching an invisible fly. Some dogs also act like their ears or feet are irritated, and others may chase their tails. This behaviour appears compulsive, happening continuously especially when emotionally aroused, and may be linked to an imbalance in brain chemicals or metabolism. Diagnosis is based on the dog's history and ruling out other behavioral, medical (especially gut-related), metabolic, and neurological conditions. In many cases there appears to be a link to gastrointestinal issues or food intolerance, so it's important to rule these out, even if the dog doesn’t have diarrhoea. If gut issues are ruled out, it’s best to see both a neurologist familiar with the condition and possibly a veterinary behaviour specialist. Many cases are managed with a selective diet, in some behaviour training to interrupt the behaviour may be recommended and rarely medications like selective serotonin re-uptake inhibitors (SSRIs) may be recommended. More information here.

No – syringomyelia affects the spinal cord, while seizures are caused by forebrain issues. There is no known link between seizures or epilepsy and Chiari-like malformation. Your dog should be checked and treated specifically for epilepsy or seizures.

This behaviour is common in brachycephalic dogs and is often thought to be related to gastroesophageal pain. Many dogs improve with treatment for gastroesophageal reflux. There is no known link to syringomyelia, except that both conditions are commonly seen in brachycephalic breeds.

No – syringomyelia affects the spinal cord, while facial nerve paralysis happens when the facial nerve, which controls the facial muscles, is damaged. There is no known link between facial nerve paralysis and Chiari-like malformation in dogs. The most common cause of facial nerve paralysis in dogs is idiopathic, similar to Bell's palsy in humans. It often improves on its own, although recovery can take months or even years.

No – syringomyelia affects the spinal cord, while vestibular disease is caused by damage to the inner ear, brainstem, or the nerve connecting them. Although it’s theoretically possible that Chiari malformation could cause balance problems, this is rare. The most common cause of vestibular disease is an idiopathic syndrome affecting the inner ear, which usually has a good prognosis. If there are signs of brain disease, a referral to a neurologist is recommended.

It would be very unusual for syringomyelia to cause severe weakness or paralysis, so it’s more likely to be another spinal condition. The most common cause of sudden paralysis is intervertebral disc disease, while slowly progressing paralysis in Cavaliers is often caused by inherited degenerative myelopathy (genetic test SOD-1 mutation) and in Pug dogs by Pug dog myelopathy.

The most important conditions to consider are other causes of pain and spinal cord problems, such as intervertebral disc disease, CNS inflammatory diseases like meningoencephalomyelitis of unknown origin (e.g., granulomatous meningoencephalomyelitis), vertebral issues like atlantoaxial subluxation, tumours, and discospondylitis. If scratching or rubbing the face/ears is the main clinical sign, ear and skin diseases should be ruled out first. Syringomyelia-related scratching can be elicited by rubbing a specific area of skin.

The diagnosis of CM-P is based on clinical signs, medical history, the appearance of the condition on an MRI, and ruling out other causes of head and spinal pain. Chiari Check can be used to generate a Chiari-pain score and likelihood of disease. More information on the MRI appearance is here.

Syringomyelia is diagnosed using magnetic resonance imaging (MRI), which shows fluid-filled cavities in the spinal cord that have a similar signal to cerebrospinal fluid. Chiari Check can be used to generate a SM-S score and likelihood of disease. More information on the MRI appearance is here.

The diagnosis of SM-S is based on clinical signs, medical history, the appearance on MRI, and ruling out other causes of spinal disease. Chiari Check can be used to generate a SM-S score and likelihood of disease. More information on the MRI appearance is here.

It’s definitely worth seeing a specialist before getting an MRI. The MRI should be customized to check for CM-P, SM-S, or your dog’s specific clinical signs. Many non-specialists may not request the same detailed imaging a neurologist would. You could end up paying the same price for an MRI that’s of lower diagnostic quality or too limited. Plus, the interpretation may not fully consider your dog’s signs. Getting an MRI elsewhere is unlikely to "help" your neurologist.

An MRI protocol for syringomyelia (for full details see here)
Sagittal imaging of brain and spinal cord:

• To the caudal extent of the pre-syrinx/syrinx.
• HASTE provides a single-slice MR myelogram sequence, allowing rapid assessment of CSF spaces and the syrinx's full length, which can reduce scanning time.
• The entire brain and at least one region of the spinal cord (typically cervical but ideally the entire spinal cord)
• Static T1W and T2W sequences:
• Confirm fluid-filled cavity signal matches CSF.
• Eliminate other causes of T2W hyperintensity, e.g., MUO.

Transverse imaging:

• Focus on widest syrinx in the C1-C5, C6-T2, T3-L3, and L4-S3 spinal segments.
• Measure the maximum transverse width and position of the syrinx, including dorsal horn involvement.

Paramagnetic contrast enhancement: Use if:

• There's evidence of a mass to distinguish cystic intramedullary tumours.
• The cause of CSF channel obstruction isn't clear.
• There is a pre-syrinx, and other causes of spinal cord oedema need to be ruled out.

Steady-state sequences: Use if the cause of CSF channel disruption is unclear.

• E.g., FIESTA, 3D-CISS.
• Improves detection of arachnoid webs and diverticula.

If a purebred dog:

• Include the confirmed microchip number and Kennel Club registration number on DICOM images.
• For submission to health schemes if needed later.

The central canal is a narrow space filled with cerebrospinal fluid that runs along the entire spinal cord and is connected to the brain’s ventricles. It’s a leftover structure from the neural tube and is usually less than 0.5mm wide and barely visible on an MRI. If it's abnormally enlarged, it will be noted in MRI reports. However, small enlargements (less than 2 millimetres) usually don't cause problems for the dog. Still, it is part of the CM/SM spectrum, and some young dogs with a dilated central canal have later developed syringomyelia. Additionally, dogs with central canal dilation have produced offspring with syringomyelia, so it may be more important for breeding decisions.

The first stage of syrinx development seems to involve fluid buildup (interstitial oedema or glymphoedema) within the spinal cord, usually around an enlarged central canal—this is known as a pre-syrinx or presyringomyelia. At this stage, the fluid is spread within the spinal cord tissue rather than forming distinct cavities.

The ventricles are four connected cavities in the brain that continue into the central canal of the spinal cord. These include two lateral ventricles, the third ventricle, and the fourth ventricle, all filled with cerebrospinal fluid (CSF). If there’s a blockage in the CSF flow, the fluid can build up and enlarge the ventricles. When this enlargement is seen on an MRI without causing problems, it’s often called ventriculomegaly. Severe enlargement that affects the brain is called hydrocephalus. Hydrocephalus caused by CM is rare, and most cases of ventricular enlargement don't cause any clinical signs. Ventriculomegaly is also common in brachycephalic (dome-headed) breeds and can occur for reasons unrelated to CM.

PSOMS or OME is a buildup of thick, mucoid material in the middle ears, commonly seen in brachycephalic breeds like Cavalier King Charles Spaniels, French Bulldogs, and Boxers. It is similar to "glue ear" in children. On an MRI, this material appears as fluid, with no signs of inflammation or infection. The most common reason for this is that the material in the middle ear doesn’t drain properly due to the shape of the skull and the soft tissue in the throat area (like the tonsils).
It can be hard to tell how much of a problem PSOMS causes, as it is often found by chance. One recent study found no link to ear rubbing in Cavaliers, though other studies suggest it may cause ear pain, which improves after the material is drained. Some dogs may have hearing loss. While the material can be removed, it may return if the underlying issue, such as poor Eustachian tube drainage, isn’t fixed. In most cases, the condition is minor and doesn't require treatment. In some situations, using tympanostomy tubes (grommets) or performing myringotomy (drainage) may be recommended.

A supracollicular fluid accumulation is an increase in cerebrospinal fluid in the space in front of the cerebellum and above the colliculus. It's typically associated with an enlarged third ventricle or an expanded quadrigeminal cistern (a fluid filled space which connects to the subarachnoid space) but is not a true cyst. In most dogs, this is an incidental finding seen with ventriculomegaly. However, because it occupies space in an already crowded skull, it can worsen the blockage at the craniocervical junction, raising the risk of Chiari-related pain and syringomyelia. In brachycephalic cats, like Persians, it can grow larger and cause balance problems.

Dogs can show signs of the disease at any age, but the majority (around 45%) develop their first signs within the first year of life. About 40% of cases show signs between 1 and 4 years old, while around 15% develop signs later, between 6 and 8 years old.

Some dogs with syringomyelia may show no or only mild clinical signs. However, syrinxes can gradually enlarge, and a dog that is asymptomatic early in life may develop signs later on. However, for clinically affected dogs the syringomyelia can remain remarkably unchanged over years – the original expansion occurs quickly and then the syrinx achieves a hydrodynamic equilibrium and clinical signs stabilise. Scoliosis may slowly improve even if the syrinx remains.

Unlike mitral valve disease, Chiari-like malformation and syringomyelia (CM/SM) are rarely fatal. However, this doesn’t lessen the impact of the condition, as it can be extremely painful, and many dogs are eventually euthanized due to uncontrolled pain. This is more common in dogs with a wide syrinx or those showing clinical signs before 4 years of age. A study of 14 Cavaliers with neuropathic pain managed conservatively showed that 36% were eventually euthanized due to pain, while 43% lived beyond 9 years (the average life expectancy for a Cavalier is 10.7 years). Most dogs remain able to walk, although some may experience significant weakness and wobbliness.

Your dog's activity doesn't need to be restricted, but you should be aware that they may avoid certain activities and may not tolerate grooming in specific areas (like one ear). Simple adjustments, such as raising the food bowl, removing neck collars, and providing short, frequent walks, can be helpful. For more information see here.

The most common surgery to treat Chiari malformation and syringomyelia is cranial/cervical decompression. In this procedure, the surgeon removes part of the back of the skull (the supraoccipital bone) and the top portion of the first vertebra. Sometimes, the meninges (the protective covering around the brain and spinal cord) are cut, and a patch may be placed using graft material.
A technique from human surgery, called cranioplasty, has also been adapted for dogs. This involves placing a plate made of titanium mesh, PEEK, or PMMA over the area where the bone was removed.
For dogs with ventriculomegaly or hydrocephalus along with syringomyelia, a tube (shunt) may be inserted to drain excess fluid from the brain's enlarged cavities.
Another option for managing syringomyelia is inserting a shunt directly into the fluid-filled cavity in the spinal cord. However, this method is less commonly used in humans due to the risk of the shunt becoming blocked or causing other complications over time. More information here.

Cranial/cervical decompression surgery helps reduce pain and improve neurological problems in about 80% of cases, and around 45% of dogs still have a good quality of life two years after surgery. However, the surgery may not fully fix the causes of syringomyelia, and the fluid-filled cavities (syrinx) often remain. Most of the improvement is likely due to better CSF flow through the foramen magnum, meaning the surgery is more helpful for Chiari malformation pain (CM-P) rather than syringomyelia signs like phantom scratching (SM-S).

Surgery is most needed and likely to work best for dogs that are in pain (due to CM-P) and aren't getting enough relief from medication.

After surgery, dogs stay in the hospital until they are comfortable enough to stop receiving pain injections. Once they go home, it usually takes 2 to 6 weeks for them to return to a more normal activity levels.

After surgery, dogs don't need to be kept in a crate or cage. For the first 2 weeks, their exercise should be limited to short walks of 5-10 minutes, 2-4 times a day. After that, you can slowly increase the exercise over the next 4-8 weeks, depending on how the dog is doing.

In some cases, scar tissue can form over the foramen magnum, causing a blockage again. This leads to about 25% to 50% of dogs getting worse over time, sometimes as soon as 2 months after surgery.

Even after successful surgery it is possible that your neurologist may recommend continuing some medication because the damage to the nervous tissue has resulted in a neuropathic pain syndrome or because the syringomyelia persists.

Yes - Chiari malformation (CM) is a complex trait with a moderately high heritability. It likely involves genes that regulate skull development from embryo to adult, particularly those in pro-osteogenic (bone forming) signalling pathways. Syringomyelia (SM) involves additional genetic factors. As multiple genes are likely involved, a simple genetic (DNA) test for CM is unlikely. In fact, the genetic tendency for CM is likely to be fixed, meaning it could be present in all individuals of the breed. This means that while MRI screening for syringomyelia (SM) can help reduce the incidence of clinical disease in the breed, the genetic tendency for the problem will not go away without introducing new genes through a cross-breeding program. This approach would also require a shift in mindset, acknowledging that some brachycephalic head shapes are not healthy.
References:

1. Kibar, Z.; Dubé, M.P.; Knowler, S.P.; Rusbridge, C.; Rouleau, G. Preliminary results from syringomyelia (SM) genome wide scans in cavalier King Charles spaniel kindred and directions for future research. Chiari-like malformation and Syringomyelia in the Cavalier King Charles Spaniel 2007, 179.
2. Lemay, P.; Knowler, S.P.; Bouasker, S.; Nedelec, Y.; Platt, S.; Freeman, C.; Child, G.; Barreiro, L.B.; Rouleau, G.A.; Rusbridge, C.; et al. Quantitative Trait Loci (QTL) Study Identifies Novel Genomic Regions Associated to Chiari-Like Malformation in Griffon Bruxellois Dogs. PloS one 2014, 9, e89816, doi:10.1371/journal.pone.0089816.
3. Ancot, F.; Lemay, P.; Knowler, S.P.; Kennedy, K.; Griffiths, S.; Cherubini, G.B.; Sykes, J.; Mandigers, P.J.J.; Rouleau, G.A.; Rusbridge, C.; et al. A genome-wide association study identifies candidate loci associated to syringomyelia secondary to Chiari-like malformation in Cavalier King Charles Spaniels. BMC genetics 2018, 19, 16, doi:10.1186/s12863-018-0605-z.

The estimated heritability of symptomatic SM was found to 0.81 whereas symptomatic and asymptomatic syringomyelia is 0.37. This means that the likelihood of passing on symptomatic syringomyelia (SM) from one generation to the next is 81%. This indicates a very strong genetic influence in dogs that show clinical signs of SM (i.e. breeding with dogs that show clinical signs is risky and irresponsible). On the other hand, when both symptomatic and asymptomatic cases of syringomyelia are considered together, the heritability drops to 37%. This suggests that while genetics still play a role in both symptomatic and asymptomatic cases, environmental or other factors are also likely contributing. Also, although there is moderately high heritability, the late onset nature means that screening for SM is challenging because the breeder may not know that a dog is affected unless they MRI screen the dog at least 3 years of age.
References:

1. Thofner, M.S.; Stougaard, C.L.; Westrup, U.; Madry, A.A.; Knudsen, C.S.; Berg, H.; Jensen, C.S.; Handby, R.M.; Gredal, H.; Fredholm, M.; et al. Prevalence and heritability of symptomatic syringomyelia in Cavalier King Charles Spaniels and long-term outcome in symptomatic and asymptomatic littermates. Journal of veterinary internal medicine / American College of Veterinary Internal Medicine 2015, 29, 243-250, doi:10.1111/jvim.12475.
2. Lewis, T.; Rusbridge, C.; Knowler, P.; Blott, S.; Woolliams, J.A. Heritability of syringomyelia in Cavalier King Charles spaniels. Vet J 2010, 183, 345-347, doi:10.1016/j.tvjl.2009.10.022.

Brachycephalism (a shortened skull) in toy breeds is the main risk factor for CM and SM. Any breed or cross with brachycephalism and/or miniaturization could be predisposed to these conditions. CM/SM has been reported in breeds such as Cavalier King Charles Spaniels and their crosses, King Charles Spaniels, Griffon Bruxellois, Affenpinschers, Chihuahuas, Yorkshire Terriers, Maltese, Boston Terriers, French Bulldogs, Pugs, Pomeranians, and brachycephalic cats. Less commonly affected breeds include Havanese, Miniature Dachshunds, Miniature/Toy Poodles, Bichon Frisé, Shih Tzus, Staffordshire Bull Terriers, Pekingese, and Miniature Pinschers.

To better understand the genetics of CM, we measured different parts of the skull and spine in 74 dogs (50 with CM and 24 without). We found six traits related to CM and studied the dogs' genes to look for connections. We identified specific areas on five chromosomes that were linked to CM. Two of these areas, on chromosomes CFA2 and CFA14, were especially important. They found a gene in one area (CFA2) that is linked to a similar condition in humans, making it a strong candidate for further study ( Sall-1 gene orthologue in humans is mutated in Townes-Brocks syndrome which has previously been associated to Chiari malformation I).
References:

1. Lemay, P.; Knowler, S.P.; Bouasker, S.; Nedelec, Y.; Platt, S.; Freeman, C.; Child, G.; Barreiro, L.B.; Rouleau, G.A.; Rusbridge, C.; et al. Quantitative Trait Loci (QTL) Study Identifies Novel Genomic Regions Associated to Chiari-Like Malformation in Griffon Bruxellois Dogs. PloS one 2014, 9, e89816, doi:10.1371/journal.pone.0089816.

Genetic studies have identified two regions on the chromosomes (loci on CFA22 and CFA26) that were associated with the syrinx diameter. These traits were associated with reduced volume and altered orientation of the back of the skull. However, the inheritance is also complex i.e., there are more genetic influences.
References:

1. Ancot, F.; Lemay, P.; Knowler, S.P.; Kennedy, K.; Griffiths, S.; Cherubini, G.B.; Sykes, J.; Mandigers, P.J.J.; Rouleau, G.A.; Rusbridge, C.; et al. A genome-wide association study identifies candidate loci associated to syringomyelia secondary to Chiari-like malformation in Cavalier King Charles Spaniels. BMC genetics 2018, 19, 16, doi:10.1186/s12863-018-0605-z.
2. Knowler, S.P.; Cross, C.; Griffiths, S.; McFadyen, A.K.; Jovanovik, J.; Tauro, A.; Kibar, Z.; Driver, C.J.; La Ragione, R.M.; Rusbridge, C. Use of Morphometric Mapping to Characterise Symptomatic Chiari-Like Malformation, Secondary Syringomyelia and Associated Brachycephaly in the Cavalier King Charles Spaniel. PloS one 2017, 12, e0170315, doi:10.1371/journal.pone.0170315.

Chiari malformation (CM) is considered ubiquitous in Cavalier King Charles Spaniels (CKCS), with studies showing at least a 92% incidence. CKCS without CM typically have a different appearance, being larger and having a longer muzzle with a more tapered stop, often referred to as the "traditional" look. This head shape was common in dogs bred during the 1960s and 70s, compared to the more modern and fashionable appearance seen today, which is preferred both in the show ring and by pet owners.
A 2011 prevalence study for Cavalier King Charles Spaniels (CKCS) in the UK and Netherlands found an overall syringomyelia (SM) prevalence of 46% across all age groups. The study revealed a 1.3 increase in odds ratio per year, meaning that out of 100 CKCS without SM, 30 would likely develop the condition each year. The prevalence was 25% in one-year-old CKCS and 70% in those over 6 years old.
A Dutch study in 2017 with 1020 dogs showed similar results, with a 39% prevalence rate, with 79.3% of the dogs aged between 1-3 years, and it also found that SM prevalence increased with age. A 2009 USA study of 64 dogs found an SM prevalence of 42% (mean age 2.7 years). A 2018 German study reported an overall SM prevalence of 48.1% (mean age 3.72 years) and an odds ratio of 1.27, consistent with the UK/Netherlands study.
References:

1. overlapping in dogs. Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association 2009, 50, 264-268.
2. Stenning, E.M. Cavalier King Charles Spaniels W. & G. Foyle Ltd London, Great Britiain 1964.
3. Knowler, S.P.; Gillstedt, L.; Mitchell, T.J.; Jovanovik, J.; Volk, H.A.; Rusbridge, C. Pilot study of head conformation changes over time in the Cavalier King Charles spaniel breed. The Veterinary record 2019, 184, 122, doi:10.1136/vr.105135.
4. Parker JE, Knowler SP, Rusbridge C, et al. Prevalence of asymptomatic syringomyelia in Cavalier King Charles spaniels. The Veterinary Record 2011;168:667.
5. Wijnrocx K, Van Bruggen LWL, Eggelmeijer W, et al. Twelve years of chiari-like malformation and syringomyelia scanning in Cavalier King Charles Spaniels in the Netherlands: Towards a more precise phenotype. PloS One 2017;12
6. Schulze S, Refai M, Deutschland M, et al. Prevalence of syringomyelia in clinically unaffected Cavalier King Charles Spaniels in Germany (2006-2016). Tierarztliche Praxis Ausgabe K, Kleintiere/Heimtiere 2018;46:157-162.

Studies in other predisposed breeds are much smaller and with a possible selection bias.

• Griffon Bruxellois have estimated prevalence of 61-80% and 45-74% for Chiari-like malformation and syringomyelia respectively.
• Pomeranians have estimated prevalence of 54.9- 89.5% and 23.9-52.6% for Chiari-like malformation and syringomyelia respectively.
• Chihuahuas (apple-headed) have estimated prevalence of 100% and 37.7-65.7% for Chiari-like malformation and syringomyelia respectively.

References:

1. Freeman, A.C. et al. (2014) ‘Chiari‐Like Malformation and Syringomyelia in American Brussels Griffon Dogs’, Journal of Veterinary Internal Medicine, 28(5), pp. 1551–1559. Available at: https://doi.org/10.1111/jvim.12421.
2. Harcourt‐Brown, T.R. et al. (2015) ‘Prevalence of Chiari‐like Malformations in Clinically Unaffected Dogs’, Journal of Veterinary Internal Medicine, 29(1), pp. 231–237. Available at: https://doi.org/10.1111/jvim.12477.
3. Kiviranta, A. et al. (2021) ‘Persistent fontanelles in Chihuahuas. Part II Association with craniocervical junction abnormalities, syringomyelia, and ventricular volume’, Journal of Veterinary Internal Medicine, 35(4), pp. 1848–1856. Available at: https://doi.org/10.1111/jvim.16123.
4. Kiviranta, A. ‐M. et al. (2017) ‘Syringomyelia and Craniocervical Junction Abnormalities in Chihuahuas’, Journal of Veterinary Internal Medicine, 31(6), pp. 1771–1781. Available at: https://doi.org/10.1111/jvim.14826.
5. Knowler, S.P. et al. (2014) ‘Quantitative Analysis of Chiari-Like Malformation and Syringomyelia in the Griffon Bruxellois Dog’, PLoS ONE, 9(2), p. e88120. Available at: https://doi.org/10.1371/journal.pone.0088120.
6. Knowler, S.P. et al. (2017) ‘Craniometric Analysis of the Hindbrain and Craniocervical Junction of Chihuahua, Affenpinscher and Cavalier King Charles Spaniel Dogs With and Without Syringomyelia Secondary to Chiari-Like Malformation’, PLOS ONE, 12(1), p. e0169898. Available at: https://doi.org/10.1371/journal.pone.0169898.
7. Rusbridge, C. et al. (2009) ‘Chiari‐like malformation in the Griffon Bruxellois’, Journal of Small Animal Practice, 50(8), pp. 386–393. Available at: https://doi.org/10.1111/j.1748-5827.2009.00744.x.
8. Santifort, K.M. et al. (2023) ‘Phenotypic characterization of Pomeranians with or without Chiari-like malformation and syringomyelia’, Frontiers in Veterinary Science, 10. Available at: https://doi.org/10.3389/fvets.2023.1320942.
9. Santifort, K.M., Carrera, I. and Mandigers, P.J.J. (2024) ‘Longitudinal assessment of syringomyelia in Pomeranians’, Frontiers in Veterinary Science, 11. Available at: https://doi.org/10.3389/fvets.2024.1364464.
10. Wiles, B.M. et al. (2017) ‘Large-scale survey to estimate the prevalence of disorders for 192 Kennel Club registered breeds’, Canine Genetics and Epidemiology, 4(1), p. 8. Available at: https://doi.org/10.1186/s40575-017-0047-3.

Whilst the majority of CKCS can be regarded as “on the CM spectrum,” not all dogs have clinical signs. CM can result in two pathologies – a pain syndrome (Chiari-like malformation pain or CM-P) and syringomyelia (SM) (see under clinical signs).
However, this means that for some breeds the genetic tendency for the problem will not go away without introducing new genes through a cross-breeding program. This approach would also require a change in mindset from breeders, judges, and the pet-buying public, recognising that some brachycephalic (short-headed) shapes are not healthy.

Dogs predisposed to Chiari-like malformation and syringomyelia should be screened through an official scheme that has a minimal quality control and more than one scrutineer for example KC/BVA CMSM scheme. See Guide to finding a reputable Cavalier breeder. Dog breed health information is here.

The minimum age for screening is 12 months. It's also recommended that breeders check the MRI status of their breeding dogs at 3 years old and again at 5 years old. This gives more information about the dog's estimated breeding value (EBV), which can also help predict the EBV of the dog's offspring.

At this time, it's not recommended to breed dogs with early onset syringomyelia. In the future, a mate select system using estimated breeding values might help find a suitable mate, but this will only work if most breeders perform health screenings.

Your dog's activity doesn't need to be restricted, but you should be aware that they may avoid certain activities and may not tolerate grooming in specific areas (like one ear). Simple adjustments, such as raising the food bowl, removing necHopefully, he will stay happy and healthy. The main concern with dogs that show no clinical signs is that their puppies are more likely to develop the condition and show clinical signs.

The official BVA/KC Chiari Malformation and Syringomyelia (CMSM) health scheme was launched in 2011 following a long consultation period during which Cavalier King Charles Spaniel breeders requested an official program. In 2012, the Breeding Guidelines were updated based on a 2011 study showing the effectiveness of the 2006 guidelines. The official scheme was connected to an Estimated Breeding Value (EBV) system called "Mate Select," with plans to develop further breeding advice from it. However, for this to work, breeders needed to participate in the scheme (or a similar one), which unfortunately did not happen.
It is likely too late for an effective Estimated Breeding Value (EBV) scheme. For an EBV system to work, most breeders must participate, and the scheme requires evaluation of many dogs and their relatives to accurately assess traits. For Cavalier King Charles Spaniels (CKCS), this means assessing common and serious health issues like Chiari malformation, syringomyelia, mitral valve disease, dry eye, and the SOD1 mutation (similar to ALS in humans).
A major concern for CKCS is their already high level of inbreeding, with a coefficient of 40—where a value of 25 is equivalent to breeding full siblings. The breed is described as "heavily bottlenecked," with a greater accumulation of mutations related to mitral valve disease compared to other breeds. Additionally, CKCS have the highest "mean cluster membership proportions," meaning they are more genetically similar than other breeds.
Although an EBV scheme would be the safest method for breeding healthier CKCS, it may further strain the breed's limited genetic diversity, potentially leading to the emergence of other diseases. Sadly, we've already seen degenerative myelopathy linked to the SOD1 mutation appear in CKCS, even in dogs that were thought to be free of syringomyelia and heart issues and recently a "new" inherited metabolic disease has been discovered in Cavalier King Charles Spaniels (CKCS), leading to seizures and epilepsy (MCADD - Medium-chain Acyl-CoA Dehydrogenase Deficiency.). Researchers tested 162 Swiss and German Cavaliers and found a variant allele frequency of 23.5%, meaning that the mutant gene responsible for the disease was present in 23.5% of all the genes tested. Further selection pressure is likely to result in other diseases emerging.
References:

1. Knowler SP, McFadyen AK, Rusbridge C. Effectiveness of breeding guidelines for reducing the prevalence of syringomyelia. Veterinary Record 2011;169:681-681
2. Axelsson E, Ljungvall I, Bhoumik P, et al. The genetic consequences of dog breed formation—Accumulation of deleterious genetic variation and fixation of mutations associated with myxomatous mitral valve disease in cavalier King Charles spaniels. PLoS genetics 2021;17:e1009726.
3. Berger B, Berger C, Heinrich J, et al. Dog breed affiliation with a forensically validated canine STR set. Forensic Sci Int Genet 2018;37:126-134.

Look at these resources: Guide to buying a puppy; Buying a Cavalier puppy; Puppy contract; The Standard for Dog breeding; Guide to finding a reputable Cavalier breeder
A good breeder will have screened their dogs for diseases common in the breed - for more information on which diseases in which breeds see here. Avoid breeders that are not able to provide official health scheme certificates and breeders that say “never heard of this in my lines”.

Dogs predisposed to Chiari-like malformation and syringomyelia should be screened through an official scheme that has a minimal quality control and more than one scrutineer for example KC/BVA CMSM scheme. See Guide to finding a reputable Cavalier breeder. Dog breed health information is here.

The terminology for syringomyelia has changed over the years. Syringohydromyelia and syringomyelia are now considered the same, as the anatomical differences between them are more theoretical than real. Most neurologists and neurosurgeons use the term syringomyelia but some, particularly veterinary radiologists, still prefer syringohydromyelia. For more information on nomenclature see here.

This term is sometimes used in the USA as an alternative for Chiari-like malformation. However, it's not anatomically accurate, as there is no "caudal occipital bone"—the occipital bones are caudal. Chiari-like malformation affects the entire skull and craniocervical junction. A working group decided to use the term "Chiari-like malformation" because, although it’s an eponym and not perfect, it isn't restricted by an anatomical description. However, this term is still “clunky” and many prefer the simpler “canine chiari”.

This term was used in early papers as an alternative for Chiari-like malformation but has since been discarded. Chiari-like malformation involves more than just occipital bone hypoplasia; it is a global skull and craniocervical junction abnormality. A working group decided to use the term "Chiari-like malformation" because, although not perfect and eponymous, it isn't limited by an anatomical description.

This term was first proposed in a paper as an alternative to Chiari-like malformation to address reviewer concerns that the eponymous term was outdated and unsuitable. The suggestion was that the veterinary community move away from the human nomenclature and redefine the condition based on current understanding. The new name highlights that the condition results from brachycephaly and that cerebrospinal fluid obstruction is a key part of its development.

Arnold-Chiari malformation is a historical term used to describe Chiari type II malformation in humans, which involves hindbrain herniation along with spina bifida and hydrocephalus. This term is entirely inappropriate for veterinary use, but some texts have mistakenly applied it to describe Chiari-like malformation in dogs.

The term "syrinx" means hollow tube or reed, and "myelia" or "myelo" refers to marrow, which was an old medical term for the spinal cord. Therefore, "syringomyelia" refers to a hollow spinal cord. In Greek mythology, Syrinx was a nymph pursued by Pan. To escape his advances, she was transformed into reeds by water nymphs. When Pan embraced the reeds, his sigh produced a melancholic sound. Amused by the melody, he fashioned the reeds into an instrument called the "Syrinx" in her honour. From this, we get the terms syringomyelia, syrinx, syringes, and even pan pipes!