Chiari-like Malformation in Dogs

According to experts, almost 95% of Cavalier King Charles Spaniels have Chiari-like malformation, but only a quarter of these dogs will have any symptoms. This disorder creates the production of cysts in the spinal cord that triggers pain in the shoulders, base of the neck, ears, and sternum and may even cause fainting and coma in severe cases. The cause of Chiari-like malformation is not fully understood, but is thought to be hereditary in some toy breeds.

A Chiari-like malformation (caudal occipital malformation syndrome) is a condition that retards the growth of the hollow places in your dog’s skull, making the posterior fossa too small or deformed. This causes syringomyelia, which is the compression of the brain, forcing it down through the opening in the base of the skull and the cerebrospinal fluid (CSF) is unable to flow through.

The signs of Chiari-like malformation depend on how severe the malformation is and the age of your dog.

• Neck pain (holding neck stiff)
• Headache (head pressing)
• Blurry vision (bumping into things)
• Crying out while moving
• Air scratching (scratching at the space beside or behind neck)
• Hearing loss
• Head tilting
• Walking in circles
• Dizziness or fainting
• Rapid involuntary movement of the eyeballs
• Eyes looking in two different directions
• Instability or stumbling
• Weakness
• Absent reflexes
• Involuntary muscle movements
• Falling over while walking
• Rolling to one side when lying down
• Paralysis that comes and goes (in one limb or all over)

 Types

Chiari-like malformation is graded between 0-2, as is syringomyelia.

Chiari-like malformation

• Grade 0 - No malformation at all
• Grade 1 - Indented cerebellum
• Grade 2 - Impacted or actually herniated by being pushed through the gap at the base of the skull

Syringomyelia

• Grade 0 - Normal with no canal dilation, presyrinx, or syrinx
• Grade 1 - Dilation of under two millimeters
• Grade 2 - Dilation of more than two millimeters.

The grade for syringomyelia is also followed by a letter because it is progressive.

• A - More than five years old
• B - Three to five years old
• C - One to three years old

Chiari-like malformation is thought to be caused by the malformation of the skull, which veterinary experts believe is abnormally small. Another theory is that some breeds (most often King Charles Spaniels) have larger than normal brains, causing it to be pushed out through the base of the skull. However, it is not completely understood, but it is most often diagnosed in certain breeds, such as:

• Brussels Griffon
• Cavalier King Charles Spaniel

Diagnosing your dog with Chiari-like malformation is usually as simple as running a few blood tests and magnetic resonance imaging (MRI), especially if your dog is a King Charles Spaniel or Brussels Griffon. However, your veterinarian will need your dog’s medical file and history as well as immunization records. Also, be sure to let the veterinarian know if your pet is on any kind of medication. You should also mention what symptoms you have seen and when they symptoms started. Afterward, a complete physical examination will be done. This usually includes height, weight, reflexes, body temperature, breath sounds, respirations, pulse rate, blood pressure, and oxygen level. 

A neurological test done by checking the vision and a detailed check of the reflexes can help determine whether your dog has a Chiari-like malformation, syringomyelia (SM), and can tell how severe the malformation is. However, an MRI (magnetic resonance imaging) is the only way to truly see the severity of the disease by differentiating between the cerebrospinal fluid and extracellular fluid. A radiograph (x-ray) or CT scan cannot show these differences, so they are unable to help in the diagnosis, treatment, and prognosis. In addition, an ultrasound may also be helpful in getting a detailed look at the neck and spinal cord for any lesions or abnormalities. Laboratory tests that are usually performed during diagnosis are urinalysis, biochemistry profile, CBC (complete blood count), electrolyte and glucose levels, and a cerebrospinal fluid retrieval (spinal tap). This procedure is done while your dog is under general anesthesia (asleep). The veterinarian or an anesthesiologist will use a syringe to draw a small amount of the fluid from your dog’s spine between two of the vertebrae and it will be microscopically examined for bacteria and other organisms.

Treatment for Chiari-like malformation is mainly just pain relief. There are surgical options that can be performed, but they are expensive and not always successful.

Medications

The medications your veterinarian chooses will depend on the severity of the malformation and symptoms your dog is showing. The most common drugs prescribed in dogs with Chiari-like malformation are gabapentin (analgesic), naproxen (NSAID), pregabalin (anticonvulsant), omeprazole (antacid), prednisolone (corticosteroid), and amitriptyline (antidepressant).

Surgical Treatment

There are several surgical options that can help the cerebrospinal fluid to flow as it is supposed to, reducing pain and deterioration although most veterinarians will not recommend them unless the condition is severe. The costs, reliability, and risks are just not worth it in most cases. Some of these surgical options are:

• Cranioplasty
• Duraplasty
• Syringosubarachnoid shunt

Prognosis is guarded depending on the severity of your dog’s case and the age it is found. If the signs are evident before four years old, the disease will most often progress to a serious level before age six, causing unbearable pain. Most owners find that humanely euthanizing their pet rather than letting them suffer is the best way to handle this painful and progressive disorder. However, your veterinarian can give you more detailed information about your dog’s situation.