Chiari-Like Malformation (CM) in Dogs
Chiari-like malformation (CM) is a condition where the skull is too small for the brain, causing the cerebellum to herniate through the foramen magnum at the base of the skull. This obstructs cerebrospinal fluid (CSF) flow and frequently leads to syringomyelia — fluid-filled cavities within the spinal cord.
MRI is the only way to diagnose Chiari-like malformation. At Sage Veterinary Imaging, our 3-Tesla MRI provides detailed visualization of the craniocervical junction, cerebellar herniation, CSF flow obstruction, and any associated syringomyelia — guiding decisions about medical management or surgical decompression.
SVI offers advanced mri services at our centers in Round Rock, Texas; Spring, Texas; and Sandy, Utah.
Chiari-Like Malformation at a Glance
What Is Chiari-Like Malformation?
In Chiari-like malformation, the caudal fossa (the bony compartment at the back of the skull housing the cerebellum) is abnormally small relative to the brain structures it contains. This overcrowding forces the caudal cerebellum and brainstem to herniate through the foramen magnum — the opening at the base of the skull where the spinal cord exits.
This herniation obstructs the normal pulsatile flow of cerebrospinal fluid between the brain and spinal cord. The resulting abnormal CSF dynamics create pressure differentials that force fluid into the spinal cord, forming syrinx cavities (syringomyelia). The CM/SM complex is the primary cause of neuropathic pain, phantom scratching, and progressive neurological dysfunction in affected breeds.
CM is overwhelmingly a condition of Cavalier King Charles Spaniels, where decades of selective breeding for a domed, shortened skull have made the condition nearly universal in the breed. The severity of clinical signs does not always correlate with the degree of herniation on MRI — some dogs with significant herniation remain asymptomatic while others with mild herniation develop severe pain.
Signs & Symptoms of Chiari-Like Malformation
CM itself may cause direct pain from compression at the craniocervical junction, while associated syringomyelia causes additional neuropathic signs. Many dogs show signs between 6 months and 4 years of age.
How MRI Diagnoses Chiari-Like Malformation
MRI is essential for CM/SM diagnosis because the craniocervical junction, cerebellum, and spinal cord cannot be evaluated by any other imaging modality with sufficient detail.
What Our 3T MRI Reveals
Cerebellar herniation — MRI shows the degree to which the cerebellum extends through the foramen magnum, the presence of indentation or compression of the herniated cerebellum, and crowding of the brainstem.
CSF flow assessment — MRI sequences evaluate whether CSF is flowing normally across the craniocervical junction or is obstructed by the herniated cerebellum. Significant obstruction drives syringomyelia development.
Associated syringomyelia — The entire cervical and cranial thoracic spinal cord is evaluated for syrinx cavities, with measurements of syrinx width that correlate with clinical severity.
Additional findings — MRI identifies other concurrent conditions including atlantoaxial instability, dorsal compression bands, and ventricular enlargement (hydrocephalus) that may contribute to clinical signs.
MRI vs. Other Imaging for CM
MRI
Essential and only diagnostic tool. Shows cerebellar herniation, CSF obstruction, and syringomyelia in detail.
CT
Shows skull bone anatomy and caudal fossa size. Cannot evaluate soft tissues (cerebellum, spinal cord, CSF flow).
X-Ray
Cannot evaluate the brain, cerebellum, or spinal cord. Not useful for CM/SM diagnosis.
Which Breeds Are Most at Risk?
Breeds at Highest Risk
Cavalier King Charles Spaniels are affected at rates estimated above 95% for CM and 70%+ for SM on MRI, making it nearly universal in the breed. Brussels Griffons are the second most affected breed. King Charles Spaniels (English Toy Spaniels), Chihuahuas, Pomeranians, and Maltese are also at elevated risk. Breeders of affected breeds are encouraged to use MRI screening as part of responsible breeding programs.
What to Expect During a CM/SM MRI Evaluation
A comprehensive CM/SM MRI evaluation includes imaging of the brain (to assess the caudal fossa and cerebellar herniation) and the cervical/cranial thoracic spinal cord (to detect and measure any syringomyelia). The study takes approximately 60–90 minutes under general anesthesia.
Results are interpreted by a board-certified veterinary radiologist the same day. Reports include detailed measurements of cerebellar herniation, CSF flow assessment, syrinx dimensions, and a comprehensive evaluation of any associated findings. These measurements serve as a baseline for future comparison and guide treatment planning.
Dr. Jaime Sage, DVM, MS, DACVR
Dr. Jaime Sage is the founder of Sage Veterinary Imaging and a board-certified veterinary radiologist (DACVR) with advanced expertise in diagnostic MRI for companion animals. Dr. Sage personally interprets complex cases and works closely with referring veterinarians to ensure every imaging study delivers clear, actionable diagnostic answers.
Her published research on MRI in veterinary medicine — co-authored with Dr. Patrick Gavin, a pioneer in the field — has contributed to advancing the standard of care for pets requiring advanced diagnostic imaging.
Why Choose Sage for CM/SM Evaluation
Schedule a CM/SM Evaluation
If your Cavalier or other at-risk breed has neck pain, phantom scratching, or neurological signs, MRI is the essential first step toward diagnosis and effective treatment.
Chiari-Like Malformation FAQ
Get Answers for Your Pet
MRI is the essential diagnostic tool for Chiari-like malformation and syringomyelia. Accurate diagnosis is the first step toward effective pain management and improved quality of life. Visit one of our locations to get started.