Canine Chiari-Like Malformation and Syringomyelia: Diagnosis and Management

At a Glance

Chiari-like malformation (CM) and syringomyelia (SM) represent a progressive neurological disease complex in small-breed dogs, particularly Cavalier King Charles Spaniels. CM involves a mismatch between the caudal cranial fossa volume and the hindbrain, leading to herniation of the cerebellum through the foramen magnum. SM develops when cerebrospinal fluid (CSF) flow is obstructed at the craniocervical junction, causing fluid accumulation within the spinal cord parenchyma. This article provides veterinarians with a comprehensive framework for diagnosis, medical and surgical management, and long-term monitoring of affected dogs.

Pathophysiology and Anatomic Basis

CM in dogs is characterized by a shallow or flattened caudal cranial fossa, resulting in overcrowding of the cerebellum and brainstem. The cerebellar vermis herniates through the foramen magnum, obstructing CSF flow at the craniocervical junction. This obstruction leads to altered CSF dynamics, including increased pulsatile pressure within the spinal cord central canal. Over time, these pressure changes cause dilation of the central canal and accumulation of CSF within the spinal cord parenchyma, forming a syrinx. The syrinx most commonly develops in the cervical spinal cord but can extend into the thoracic or lumbar segments.

The Chiari-like Malformation review published in The Veterinary Clinics of North America: Small Animal Practice (2016) describes the morphologic features of CM, including reduced caudal cranial fossa volume, cerebellar herniation, and associated ventriculomegaly. The relationship between CM and SM is well established, with SM developing secondary to CSF flow obstruction at the foramen magnum.

The Surgical modeling of Chiari-like malformation in rats: Insights from canine morphology study (PloS one, 2024) used a rat model to investigate the biomechanical consequences of CM, providing insights into how the morphologic changes in the canine skull and brain contribute to CSF flow obstruction and syrinx formation. This experimental work supports the clinical observation that the severity of CM correlates with the risk of developing SM.

Breed Predisposition and Epidemiology

Cavalier King Charles Spaniels have the highest reported prevalence of CM and SM among dog breeds. The Chiari-like malformation and syringomyelia in American Brussels Griffon dogs study (Journal of Veterinary Internal Medicine, 2014) documented CM and SM in that breed, confirming that the condition is not limited to Cavaliers. The Incidence of Chiari-like Malformation/Syringomyelia in a Cohort of Small Dog Breeds Scanned Using MRI over a Period of 8 Years in the Netherlands (Pets, 2024) reported that CM and SM occur across multiple small breeds, including Chihuahuas, Pomeranians, and Yorkshire Terriers. The Chiari-like Malformation and Syringomyelia in Pomeranians: A Longitudinal Study (Veterinary Sciences, 2025) further characterized the condition in Pomeranians, demonstrating that breed-specific presentations exist.

Other breeds with documented CM and SM include Brussels Griffons, Maltese, Miniature Dachshunds, and French Bulldogs. The condition is increasingly recognized in small-breed dogs undergoing MRI for neurologic evaluation. Breeders and veterinarians should be aware that CM and SM can occur in any small-breed dog with appropriate clinical signs.

The Ventriculomegaly in Cavalier King Charles Spaniels with Chiari-like malformation study (Journal of Veterinary Medical Science, 2022) found that ventriculomegaly is common in affected dogs and may correlate with clinical severity. This finding suggests that the structural abnormalities in CM extend beyond the caudal cranial fossa to include the entire ventricular system.

Clinical Signs and Examination Findings

Pain and Hyperesthesia

Cervical pain is the most consistent clinical sign in dogs with CM and SM. Affected dogs may exhibit yelping or crying spontaneously, particularly when rising, jumping, or being picked up. Owners often report that the dog appears uncomfortable when its neck is touched or when wearing a collar. Pain may be referred to the thoracic or lumbar spine, making localization challenging.

On physical examination, dogs with CM and SM may exhibit cervical hyperesthesia on palpation of the neck and shoulders. Some dogs resist neck manipulation and may guard the cervical region. A thorough orthopedic and neurologic examination is essential to differentiate CM and SM from other causes of cervical pain, such as intervertebral disc disease or meningitis.

Phantom Scratching

Phantom scratching, also known as air scratching or imaginary scratching, is a characteristic sign of SM. The dog scratches at the shoulder, neck, or flank without making contact with the skin. This behavior is often unilateral and may occur spontaneously or when the dog is excited, walking, or eating. The scratching is not associated with dermatologic disease and does not result in hair loss or skin lesions.

Phantom scratching is thought to result from dysesthesia or paresthesia caused by the syrinx compressing sensory pathways within the spinal cord. The behavior may be intermittent and can be triggered by specific activities, such as leash walking or being petted. Owners may misinterpret the scratching as a behavioral issue or a skin condition, leading to delayed diagnosis.

Scoliosis and Postural Abnormalities

Cervical scoliosis, with the head and neck held in a curved position, is common in dogs with SM. The scoliosis may be intermittent or persistent and is often accompanied by a head tilt. Some dogs adopt a "prayer position" with the forelimbs extended and the hindquarters elevated, similar to the posture seen in dogs with cervical disc disease.

Scoliosis in CM and SM is thought to result from asymmetric compression of the spinal cord or nerve roots by the syrinx. The curvature may be more pronounced when the dog is standing or walking and may resolve when the dog is lying down. Serial photographs or videos can help document the progression of scoliosis over time.

Neurologic Deficits

As SM progresses, neurologic deficits may develop. Thoracic limb weakness, proprioceptive ataxia, and conscious proprioception deficits are common. In severe cases, dogs may develop thoracic limb spasticity, pelvic limb weakness, or urinary incontinence. The Ventriculomegaly in Cavalier King Charles Spaniels with Chiari-like malformation study (Journal of Veterinary Medical Science, 2022) found that ventriculomegaly is common in affected dogs and may correlate with clinical severity.

Neurologic deficits in CM and SM are typically progressive, although the rate of progression varies among individuals. Some dogs remain stable for months or years, while others deteriorate rapidly. The presence of neurologic deficits is an indication for surgical referral, as medical therapy alone is unlikely to reverse established deficits.

Intermittent Signs

Some dogs with CM and SM exhibit intermittent signs that may be mistaken for other conditions. The Intermittent "greeting" due to Chiari-like malformation/syringomyelia and occipital dysplasia in a Cavalier King Charles Spaniel (Tierarztliche Praxis Ausgabe K Kleintiere Heimtiere, 2008) described a case where the dog displayed episodic "greeting" behavior, likely representing paroxysmal pain or dysesthesia. Veterinarians should consider CM and SM in dogs with episodic pain or behavioral changes.

Other intermittent signs include episodic yelping, hiding, or restlessness. These episodes may be triggered by excitement, exercise, or changes in barometric pressure. Owners should be encouraged to keep a diary of episodes, noting the frequency, duration, and triggers.

Diagnostic Imaging

Magnetic Resonance Imaging

MRI is the gold standard for diagnosing CM and SM. The study should include T1-weighted and T2-weighted sequences in sagittal and transverse planes through the brain and cervical spinal cord. T2-weighted sequences are most sensitive for detecting syrinx fluid, which appears as a hyperintense signal within the spinal cord. The syrinx may be central or eccentric and can extend from the cervical region into the thoracic or lumbar spinal cord.

The Assessment of cerebellar pulsation in dogs with and without Chiari-like malformation and syringomyelia using cardiac-gated cine magnetic resonance imaging (Veterinary Journal, 2013) demonstrated that cardiac-gated cine MRI can assess cerebellar pulsation and CSF flow dynamics. This technique may provide additional information about the severity of CSF flow obstruction and guide surgical planning.

MRI Findings in CM

MRI findings in CM include:

• Cerebellar herniation through the foramen magnum
• Flattened or indented caudal cranial fossa
• Ventriculomegaly (enlarged lateral ventricles)
• Obliteration of the cisterna magna
• Kinking or compression of the brainstem at the craniocervical junction

The degree of cerebellar herniation can be quantified by measuring the distance the cerebellum extends beyond the foramen magnum. Ventriculomegaly is assessed by measuring the height or volume of the lateral ventricles. These measurements can be used to monitor disease progression and to guide treatment decisions.

MRI Findings in SM

MRI findings in SM include:

• T2-weighted hyperintense fluid cavity within the spinal cord
• Syrinx most commonly in the cervical region
• Syrinx may be central or eccentric
• Syrinx may extend into the thoracic or lumbar spinal cord
• Septations or loculations within the syrinx may be present

The size and extent of the syrinx should be documented in the MRI report. The syrinx diameter, length, and location (cervical, thoracic, lumbar) are important for prognosis and surgical planning. Serial MRI studies can assess changes in syrinx size over time.

Differential Diagnoses

Differential diagnoses for CM and SM include:

• Cervical intervertebral disc disease
• Meningomyelitis
• Intracranial neoplasia
• Atlantoaxial instability
• Occipital dysplasia
• Hydrocephalus

A complete diagnostic workup, including CSF analysis and infectious disease testing, may be necessary to rule out other causes of cervical pain and neurologic deficits. MRI is essential for differentiating CM and SM from other structural diseases of the brain and spinal cord.

Medical Management

Corticosteroids

Corticosteroids are the mainstay of medical therapy for CM and SM. Prednisolone or dexamethasone reduces inflammation and edema within the spinal cord and may decrease CSF production. The goal is to use the lowest effective dose for the shortest duration to minimize adverse effects. Long-term corticosteroid use is associated with polyuria, polydipsia, panting, muscle wasting, and immunosuppression.

Corticosteroid therapy should be tapered gradually to avoid adrenal suppression and rebound inflammation. The tapering schedule depends on the duration of therapy and the dose used. Dogs receiving long-term corticosteroids should be monitored for signs of hyperadrenocorticism, urinary tract infections, and gastrointestinal ulceration.

Gabapentin and Pregabalin

Gabapentin is commonly used as an adjunctive analgesic for neuropathic pain in dogs with CM and SM. The mechanism of action involves modulation of voltage-gated calcium channels in the central nervous system. Pregabalin, a related compound, may be used when gabapentin is ineffective or poorly tolerated. Both drugs require dose adjustment in dogs with renal impairment.

Gabapentin and pregabalin are generally well tolerated, but adverse effects can include sedation, ataxia, and gastrointestinal upset. These effects are often dose-dependent and may resolve with continued use. The dose should be increased gradually to achieve the desired analgesic effect while minimizing adverse effects.

Omeprazole

Omeprazole, a proton pump inhibitor, has been proposed as a treatment for CM and SM based on the hypothesis that reducing CSF production may decrease syrinx size. Evidence for this approach is limited, and omeprazole is not considered a primary therapy. Some clinicians use omeprazole as an adjunctive treatment in dogs with concurrent gastrointestinal signs.

Adjunctive Analgesics

Nonsteroidal anti-inflammatory drugs (NSAIDs) may be used for acute pain episodes but should be used cautiously in dogs receiving corticosteroids due to the risk of gastrointestinal ulceration. Acetaminophen, amantadine, and tramadol are sometimes used as adjunctive analgesics, although evidence for their efficacy in CM and SM is limited.

Multimodal analgesia, combining drugs with different mechanisms of action, may provide better pain control than any single agent. The choice of analgesic should be based on the severity of pain, the presence of adverse effects, and the individual dog's response to therapy.

Activity Modification

Dogs with CM and SM should avoid activities that increase intracranial pressure, such as jumping, rough play, and wearing collars. A harness should be used instead of a collar for leash walking. Stairs should be minimized, and ramps should be provided for accessing furniture or vehicles.

Environmental modifications can reduce the risk of exacerbating clinical signs. Soft bedding, non-slip flooring, and elevated food and water bowls may improve comfort. Owners should be advised to avoid activities that involve neck manipulation, such as pulling on a leash or lifting the dog by the scruff.

Surgical Management

Foramen Magnum Decompression

Foramen magnum decompression (FMD) is the primary surgical treatment for CM and SM. The procedure involves removing the dorsal rim of the foramen magnum and the dorsal lamina of the first cervical vertebra (C1) to decompress the craniocervical junction. The dura may be opened to allow CSF drainage and to inspect for arachnoid adhesions. Some surgeons place a dural graft to prevent scar formation.

The Outcomes of 87 small-breed dogs surgically treated for Chiari-like malformation and syringomyelia (Veterinary Surgery, 2026) reported that FMD can improve clinical signs in a majority of dogs, although recurrence of signs is possible. The study emphasized that surgical outcomes depend on patient selection, surgeon experience, and postoperative management.

Ventriculoperitoneal Shunting

Ventriculoperitoneal (VP) shunting is an alternative surgical approach for dogs with severe ventriculomegaly and hydrocephalus. The shunt diverts CSF from the lateral ventricle to the peritoneal cavity, reducing intracranial pressure. VP shunting is less commonly performed than FMD and carries risks of shunt infection, obstruction, and failure.

VP shunting may be considered when FMD is not feasible or when ventriculomegaly is the predominant abnormality. The decision to perform VP shunting should be made in consultation with a veterinary neurosurgeon.

Postoperative Care

Postoperative care includes:

• Strict confinement for 4-6 weeks
• Corticosteroids and analgesics as needed
• Monitoring for surgical site infection
• Gradual return to normal activity
• Long-term follow-up with MRI to assess syrinx size

Postoperative pain management should include multimodal analgesia, with opioids, NSAIDs, and gabapentin as needed. The surgical site should be monitored for signs of infection, such as swelling, discharge, or dehiscence. Neurologic status should be assessed daily during the postoperative period.

Surgical Complications

Complications of FMD include:

• Surgical site infection
• CSF leakage
• Meningitis
• Scar formation and recurrence of signs
• Neurologic deterioration
• Anesthesia-related complications

The risk of complications can be minimized by careful patient selection, meticulous surgical technique, and appropriate postoperative care. Owners should be informed of the potential risks and benefits of surgery before proceeding.

Monitoring and Follow-Up

Clinical Assessment

Dogs with CM and SM should be assessed regularly for changes in clinical signs. Owners should be educated to recognize signs of pain, phantom scratching, and neurologic deterioration. A pain scoring system, such as the Canine Brief Pain Inventory or the Glasgow Composite Measure Pain Scale, can be used to quantify pain severity.

Serial neurologic examinations should be performed at each follow-up visit. The presence of new neurologic deficits, worsening of existing deficits, or changes in pain severity should be documented. Owners should be encouraged to keep a diary of clinical signs between visits.

MRI Follow-Up

Repeat MRI is indicated when clinical signs worsen or when surgical intervention is being considered. The timing of follow-up MRI depends on the clinical course. Dogs with stable signs may not require repeat imaging, while dogs with progressive signs should be imaged to assess syrinx size and to rule out other causes of deterioration.

MRI follow-up after surgery is recommended to assess the adequacy of decompression and to monitor for recurrence of the syrinx. The timing of postoperative MRI varies among surgeons but is typically performed 3-6 months after surgery.

Quality of Life Assessment

Quality of life assessment is essential for dogs with CM and SM. Owners should be asked about the dog's ability to perform normal activities, such as walking, eating, and interacting with the family. The presence of pain, the need for medication, and the impact of the condition on the dog's behavior should be documented.

A quality of life questionnaire can be used to standardize the assessment. Questions should cover pain, mobility, appetite, behavior, and overall well-being. The results can be used to guide treatment decisions and to determine when euthanasia should be considered.

Common Failure Patterns

Inadequate Pain Control

Inadequate pain control is a common failure pattern in dogs with CM and SM. Owners may underreport pain, or veterinarians may underestimate the severity of pain. Regular pain assessment and adjustment of analgesic therapy are essential. Dogs with persistent pain despite medical therapy should be evaluated for surgical intervention.

Pain in CM and SM can be difficult to recognize, as dogs may not exhibit obvious signs of pain. Subtle signs, such as changes in behavior, decreased activity, or reluctance to be touched, may indicate pain. Owners should be educated to recognize these signs and to report them promptly.

Medication Noncompliance

Medication noncompliance, particularly with corticosteroids, can lead to clinical deterioration. Owners should be educated about the importance of consistent medication administration and the risks of abrupt discontinuation of corticosteroids. A medication schedule and pill organizer can improve compliance.

Noncompliance may result from adverse effects, cost, or difficulty administering medications. Veterinarians should discuss these issues with owners and offer solutions, such as changing the medication, adjusting the dose, or using a different route of administration.

Delayed Surgical Referral

Delayed surgical referral is a common failure pattern in dogs with progressive CM and SM. Veterinarians should refer dogs to a veterinary neurologist or neurosurgeon when medical therapy fails to control signs, when neurologic deficits develop, or when the dog's quality of life is compromised.

Early surgical referral may improve outcomes by preventing irreversible neurologic damage. Dogs with large syrinxes, rapid progression, or severe pain are more likely to benefit from surgery than dogs with mild or stable signs.

Concurrent Conditions

Concurrent conditions, such as cervical intervertebral disc disease, otitis media, or dental disease, can complicate the diagnosis and management of CM and SM. A thorough diagnostic workup, including MRI, is essential to identify all contributing factors.

Treatment of concurrent conditions may improve clinical signs and reduce the need for medication. For example, treating otitis media may reduce head shaking and pain, while treating dental disease may improve appetite and overall well-being.

Welfare and Safety Context

Pain and Suffering

CM and SM are painful conditions that can significantly impair a dog's quality of life. The World Organisation for Animal Health (WOAH) Animal Health and Welfare guidelines emphasize the importance of recognizing and treating pain in animals. Veterinarians have a responsibility to provide adequate analgesia and to consider euthanasia when pain cannot be controlled.

Pain in CM and SM is often chronic and progressive, requiring long-term management. Owners should be prepared for the financial and emotional costs of caring for a dog with CM and SM. Support groups and online resources can provide valuable information and support.

Breeding Considerations

CM and SM have a genetic component, and breeding affected dogs is discouraged. The American College of Veterinary Internal Medicine (ACVIM) and the American Animal Hospital Association (AAHA) recommend that dogs with CM and SM not be used for breeding. Breeders should screen breeding stock with MRI to identify affected dogs and to reduce the prevalence of the condition.

Breeding programs should prioritize the selection of dogs with normal cranial conformation and no evidence of CM or SM on MRI. The use of MRI screening in breeding stock has the potential to reduce the incidence of CM and SM in future generations.

Euthanasia

Euthanasia should be considered when a dog's quality of life is unacceptable despite medical and surgical therapy. Signs that may indicate a poor quality of life include:

• Persistent pain that is unresponsive to medication
• Inability to perform normal activities
• Progressive neurologic deficits
• Urinary or fecal incontinence
• Weight loss or anorexia

The decision to euthanize a dog with CM and SM is difficult and should be made in consultation with the owner and a veterinary neurologist. Quality of life assessment tools can help guide this decision.

Professional Escalation Criteria

Urgent Referral

Urgent referral to a veterinary neurologist or neurosurgeon is indicated for:

• Acute onset of severe pain
• Rapid progression of neurologic deficits
• Development of thoracic limb spasticity or pelvic limb weakness
• Suspected spinal cord compression
• Failure of medical therapy to control signs

Dogs with these signs require immediate evaluation and may benefit from surgical intervention. Delaying referral can result in irreversible neurologic damage and a poor outcome.

Routine Referral

Routine referral is indicated for:

• Dogs with confirmed CM and SM on MRI
• Dogs with persistent pain despite medical therapy
• Dogs with progressive clinical signs
• Dogs being considered for surgical intervention
• Breeders seeking screening MRI for breeding stock

Routine referral allows for a comprehensive evaluation by a specialist and the development of a long-term management plan. Owners should be encouraged to seek referral early in the disease course to optimize outcomes.

Practical Decision Framework for Medical Versus Surgical Management

Selecting between continued medical therapy and surgical intervention in dogs with Chiari-like malformation and syringomyelia requires a structured, evidence-based approach. The decision is rarely straightforward, as individual dogs respond differently to treatment and disease progression varies. This section provides a practical decision framework, record system, and troubleshooting method that veterinarians can implement in clinical practice.

Clinical Decision Algorithm

The decision to pursue surgical management should be based on a combination of clinical severity, response to medical therapy, and MRI findings. The following algorithm provides a stepwise approach to decision-making.

Step 1: Assess Clinical Severity

Grade the dog's clinical signs using a standardized scoring system. The following categories can be used:

• Mild: Intermittent phantom scratching, occasional cervical pain, no neurologic deficits. The dog maintains normal activity levels and quality of life.
• Moderate: Frequent phantom scratching, persistent cervical pain, mild scoliosis, no or minimal neurologic deficits. The dog may have reduced activity but can still perform normal functions.
• Severe: Constant pain, marked scoliosis, neurologic deficits (thoracic limb weakness, proprioceptive ataxia, spasticity), urinary or fecal incontinence. The dog has significantly impaired quality of life.

Step 2: Evaluate Response to Medical Therapy

Document the dog's response to a standardized medical trial. A minimum trial of 4-6 weeks of optimal medical therapy should be completed before considering surgery, unless the dog presents with severe signs at initial diagnosis.

Response categories:

• Good response: Clinical signs reduced by more than 50 percent. The dog is comfortable, pain-free, and maintaining normal activity. Medical therapy can be continued.
• Partial response: Clinical signs reduced by 25 to 50 percent. The dog has some improvement but continues to show signs of pain or discomfort. Consider dose adjustment or addition of adjunctive analgesics before proceeding to surgery.
• Poor response: Clinical signs reduced by less than 25 percent or worsening despite medical therapy. The dog continues to show significant pain or neurologic deficits. Surgical referral is indicated.

Step 3: Interpret MRI Findings

MRI findings that support surgical intervention include:

• Large syrinx (diameter greater than 50 percent of spinal cord diameter)
• Syrinx extending into the thoracic or lumbar spinal cord
• Septations or loculations within the syrinx
• Significant cerebellar herniation (greater than 5 mm beyond the foramen magnum)
• Obliteration of the cisterna magna
• Ventriculomegaly with compression of surrounding brain parenchyma

The Ventriculomegaly in Cavalier King Charles Spaniels with Chiari-like malformation study (Journal of Veterinary Medical Science, 2022) found that ventriculomegaly is common in affected dogs and may correlate with clinical severity. Dogs with severe ventriculomegaly may benefit from earlier surgical intervention.

Step 4: Consider Breed and Individual Factors

Breed-specific considerations may influence the decision to pursue surgery. The Chiari-like Malformation and Syringomyelia in Pomeranians: A Longitudinal Study (Veterinary Sciences, 2025) suggested that Pomeranians may have a different clinical course than Cavalier King Charles Spaniels. Individual factors such as age, overall health, and owner commitment to postoperative care should also be considered.

Step 5: Make a Recommendation

Based on the above factors, the following recommendations apply:

• Mild signs with good response to medical therapy: Continue medical management. Reassess every 3-6 months.
• Moderate signs with partial response to medical therapy: Optimize medical therapy. Consider referral for surgical evaluation if signs persist after 8-12 weeks.
• Moderate signs with poor response to medical therapy: Refer for surgical evaluation.
• Severe signs at initial diagnosis: Refer for surgical evaluation immediately.
• Severe signs despite medical therapy: Refer for surgical evaluation urgently.

Record System for Monitoring Disease Progression

A standardized record system is essential for tracking disease progression and treatment response. The following system can be implemented in clinical practice.

Clinical Sign Diary

Owners should be provided with a structured diary to record clinical signs daily. The diary should include:

• Date and time of each episode
• Type of sign (phantom scratching, yelping, head shaking, scoliosis, weakness)
• Duration of episode
• Severity (mild, moderate, severe)
• Trigger (if identifiable)
• Medication administered and dose
• Any other observations (activity level, appetite, behavior)

The diary should be reviewed at each follow-up visit. Trends in the frequency and severity of signs can guide treatment decisions.

Pain Scoring System

A validated pain scoring system should be used at each visit. The Canine Brief Pain Inventory or the Glasgow Composite Measure Pain Scale can be used. The following components should be assessed:

• Pain severity at rest
• Pain severity during activity
• Pain severity during handling
• Impact of pain on quality of life
• Response to analgesic therapy

Pain scores should be recorded in the medical record and compared at each visit. A consistent increase in pain scores over time indicates disease progression and may warrant surgical referral.

Neurologic Examination Form

A standardized neurologic examination form should be used to document findings at each visit. The form should include:

• Mental status
• Gait and posture
• Cranial nerve function
• Postural reactions (conscious proprioception, hopping, hemiwalking)
• Spinal reflexes (patellar, withdrawal, perineal)
• Pain perception
• Scoliosis assessment (degree and direction of curvature)
• Cervical hyperesthesia assessment

The form should be completed at each visit and compared to previous examinations. Changes in neurologic status should be documented and communicated to the owner.

MRI Follow-Up Schedule

Repeat MRI should be considered based on clinical progression. The following schedule is recommended:

• Dogs with stable signs: Repeat MRI every 12-24 months, or sooner if clinical signs change.
• Dogs with progressive signs: Repeat MRI at the time of clinical deterioration.
• Dogs after surgery: Repeat MRI at 3-6 months postoperatively to assess decompression and syrinx size.
• Dogs with recurrent signs after surgery: Repeat MRI at the time of recurrence.

The MRI report should include measurements of syrinx diameter, length, and location, as well as assessment of cerebellar herniation and ventriculomegaly. Changes in these measurements over time can guide treatment decisions.

Troubleshooting Method for Treatment Failure

When a dog with CM and SM fails to respond to medical therapy, a systematic troubleshooting approach can identify the cause and guide corrective action.

Step 1: Confirm the Diagnosis

Before assuming treatment failure, confirm that the diagnosis is correct. Review the MRI findings to ensure that CM and SM are present and that no other structural abnormalities are contributing to clinical signs. Consider the possibility of concurrent conditions, such as cervical intervertebral disc disease, meningitis, or intracranial neoplasia.

The Chiari-like Malformation review published in The Veterinary Clinics of North America: Small Animal Practice (2016) emphasizes that CM and SM can coexist with other neurologic conditions. A complete diagnostic workup, including CSF analysis and infectious disease testing, may be necessary to rule out other causes of clinical signs.

Step 2: Assess Medication Compliance

Medication noncompliance is a common cause of treatment failure. Ask the owner about the medication schedule, any missed doses, and any difficulties administering medications. Consider the following:

• Is the owner giving the correct dose at the correct frequency?
• Is the owner using the correct route of administration?
• Has the owner discontinued any medications without consulting the veterinarian?
• Is the owner experiencing difficulty administering medications due to the dog's behavior or adverse effects?

If noncompliance is identified, work with the owner to develop a plan to improve compliance. This may include changing the medication formulation, using a pill organizer, or setting reminders.

Step 3: Optimize Medical Therapy

If compliance is adequate, optimize the medical regimen. Consider the following adjustments:

• Increase the dose of gabapentin or pregabalin within the therapeutic range.
• Add an adjunctive analgesic, such as amantadine or tramadol.
• Consider switching from prednisolone to dexamethasone or vice versa.
• Add omeprazole if not already prescribed.
• Consider adding a nonsteroidal anti-inflammatory drug for acute pain episodes, but use cautiously with corticosteroids.

The goal is to achieve the best possible pain control with the fewest adverse effects. Dose adjustments should be made gradually and monitored closely.

Step 4: Evaluate for Concurrent Conditions

Concurrent conditions can complicate the management of CM and SM. Consider the following:

• Otitis media or interna: Can cause head shaking, pain, and vestibular signs.
• Dental disease: Can cause oral pain and reluctance to eat.
• Orthopedic conditions: Can cause lameness and pain that may be mistaken for neurologic signs.
• Gastrointestinal disease: Can cause vomiting, diarrhea, and abdominal pain.
• Urinary tract infection: Can cause dysuria and behavioral changes.

A thorough physical examination, including otoscopic examination, oral examination, and orthopedic examination, should be performed at each visit. Additional diagnostic tests, such as radiography, ultrasound, or urinalysis, may be indicated.

Step 5: Consider Surgical Referral

If medical therapy has been optimized and the dog continues to show significant clinical signs, surgical referral should be considered. The decision to refer should be based on the following criteria:

• Persistent pain despite optimal medical therapy
• Progressive neurologic deficits
• Large or expanding syrinx on MRI
• Poor quality of life despite medical management
• Owner request for surgical evaluation

The Outcomes of 87 small-breed dogs surgically treated for Chiari-like malformation and syringomyelia (Veterinary Surgery, 2026) reported that foramen magnum decompression can improve clinical signs in a majority of dogs. Early surgical referral may improve outcomes by preventing irreversible neurologic damage.

Common Failure Patterns and Corrective Actions

The following table summarizes common failure patterns in the management of CM and SM and provides corrective actions.

Welfare and Safety Context

The decision to pursue surgical management carries significant welfare implications. The World Organisation for Animal Health (WOAH) Animal Health and Welfare guidelines emphasize the importance of recognizing and treating pain in animals. Veterinarians have a responsibility to provide adequate analgesia and to consider euthanasia when pain cannot be controlled.

Surgery is not without risks. The Outcomes of 87 small-breed dogs surgically treated for Chiari-like malformation and syringomyelia (Veterinary Surgery, 2026) reported that complications can occur, including surgical site infection, CSF leakage, meningitis, and scar formation. Owners should be informed of these risks and the potential for recurrence of signs after surgery.

The decision to pursue surgery should be made in consultation with a veterinary neurologist or neurosurgeon. The specialist can provide a detailed assessment of the risks and benefits of surgery for the individual dog and can perform the procedure with the highest level of expertise.

Professional Escalation Criteria

The following criteria indicate the need for escalation of care to a veterinary neurologist or neurosurgeon:

• Acute onset of severe pain that is unresponsive to medical therapy
• Rapid progression of neurologic deficits over days to weeks
• Development of thoracic limb spasticity or pelvic limb weakness
• Suspected spinal cord compression with loss of pain perception
• Failure of medical therapy to control signs after 8-12 weeks
• Large or expanding syrinx on MRI
• Owner request for surgical evaluation

Dogs with these signs require immediate evaluation by a specialist. Delaying referral can result in irreversible neurologic damage and a poor outcome.

Frequently Asked Questions

What is the difference between Chiari-like malformation and syringomyelia?

Chiari-like malformation is a structural abnormality of the skull and brain where the cerebellum herniates through the foramen magnum due to a shallow caudal cranial fossa. Syringomyelia is a secondary condition where fluid accumulates within the spinal cord, forming a syrinx. CM can occur without SM, but SM almost always develops secondary to CM.

Which dog breeds are most commonly affected by CM and SM?

Cavalier King Charles Spaniels have the highest reported prevalence. Other affected breeds include Brussels Griffons, Pomeranians, Chihuahuas, Yorkshire Terriers, Maltese, Miniature Dachshunds, and French Bulldogs. The condition can occur in any small-breed dog.

What are the earliest signs of CM and SM in dogs?

The earliest signs include cervical pain, phantom scratching (air scratching), and intermittent yelping. Owners may notice the dog crying when picked up, avoiding collar use, or scratching at the shoulder without making contact with the skin. Scoliosis of the neck may also be an early sign.

How is CM and SM diagnosed definitively?

MRI is the gold standard for diagnosis. T2-weighted sequences show the syrinx as a hyperintense fluid cavity within the spinal cord. MRI also reveals cerebellar herniation, ventriculomegaly, and other structural abnormalities. CT is not adequate for diagnosis.

Can CM and SM be treated without surgery?

Yes, many dogs are managed medically with corticosteroids, gabapentin, and activity modification. Medical therapy aims to reduce inflammation, control pain, and slow progression. Surgery is reserved for dogs with progressive signs despite medical therapy or those with severe pain or neurologic deficits.

What is the prognosis for dogs with CM and SM?

The prognosis is variable. Many dogs with mild signs can be managed medically for years with acceptable quality of life. Dogs with progressive signs or large syrinxes have a guarded prognosis. Surgical decompression can improve signs in a majority of dogs, but recurrence is possible.

Should dogs with CM and SM be bred?

No, dogs with CM and SM should not be used for breeding. The condition has a genetic component, and breeding affected dogs perpetuates the problem. Breeders should screen breeding stock with MRI to identify affected dogs.

When should euthanasia be considered for a dog with CM and SM?

Euthanasia should be considered when a dog's quality of life is unacceptable despite optimal medical and surgical therapy. Signs that may indicate a poor quality of life include persistent pain unresponsive to medication, inability to perform normal activities, progressive neurologic deficits, and urinary or fecal incontinence.

Related Veterinary Guides

• Dog
• Arthritis In Dogs Symptoms And Diagnosis
• Canine Hyperadrenocorticism Cushings Diagnostic Management
• Dog Pregnancy Symptoms
• Dog Shedding Management

References and Further Reading

• www.merckvetmanual.com
• www.aaha.org
• www.acvim.org
• Merck Veterinary Manual. Merck Veterinary Manual.
• Animal Health and Welfare. World Organisation for Animal Health.
• Chiari-like Malformation.. The Veterinary clinics of North America. Small animal practice, 2016.
• Understanding and Treating Chiari-like Malformation and Syringomyelia in Dogs.. Topics in companion animal medicine, 2018.
• Surgical modeling of Chiari-like malformation in rats: Insights from canine morphology.. PloS one, 2024.
• Outcomes of 87 small-breed dogs surgically treated for Chiari-like malformation and syringomyelia.. Veterinary surgery : VS, 2026.
• Ventriculomegaly in Cavalier King Charles Spaniels with Chiari-like malformation: relationship with clinical and imaging findings.. The Journal of veterinary medical science, 2022.
• Chiari-like malformation and syringomyelia in American Brussels Griffon dogs.. Journal of veterinary internal medicine, 2014.
• Incidence of Chiari-like Malformation/Syringomyelia in a Cohort of Small Dog Breeds Scanned Using MRI over a Period of 8 Years in the Netherlands. Pets, 2024.
• Intermittent "greeting" due to Chiari-like malformation/ syringomyelia (CM/SM) and occipital dysplasia in a Cavalier King Charles Spaniel. Tierarztliche Praxis Ausgabe K Kleintiere Heimtiere, 2008.
• Assessment of cerebellar pulsation in dogs with and without Chiari-like malformation and syringomyelia using cardiac-gated cine magnetic resonance imaging. Veterinary Journal, 2013.
• Chiari-like Malformation and Syringomyelia in Pomeranians: A Longitudinal Study. Veterinary Sciences, 2025.

This article is educational and is not a substitute for veterinary diagnosis or treatment. Contact a veterinarian for advice about an individual animal.