Chiari-like malformation (CM) the most common cause of
foramen magnum
The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
obstruction and
syringomyelia
Syringomyelia is a generic term referring to a disorder in which a cyst or cavity forms within the spinal cord. Often, syringomyelia is used as a generic term before an etiology is determined. This cyst, called a syrinx, can expand and elongate ...
in dogs. Syringomyelia (SM) is a disease of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...
typified by fluid filled cavities, or
syrinxes, within the spinal cord substance but it can cause pain by disrupting the
cerebrospinal fluid
Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates.
CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the bra ...
(CSF), in the brain
CM is a condition characterized by the mismatch of size between the brain and the skull. CM is very widespread in many Toy breed dogs and has been studied in the
Cavalier King Charles Spaniel
The Cavalier King Charles Spaniel is a British breed of toy dog of spaniel type. Four colours are recognised: Blenheim (chestnut and white), tricolour (black/white/tan), black and tan, and ruby; the coat is smooth and silky. The lifespan is usual ...
and the
Griffon Bruxellois
The Griffon Bruxellois or Brussels Griffon is a breed of toy dog, named for their city of origin of Brussels, Belgium. The Griffon Bruxellois may refer to three different breeds, the Griffon Bruxellois, the Griffon Belge and the Petit Brabanço ...
(Brussels Griffon) and Chihuahua. As many as 95% of Cavalier King Charles Spaniels may have CM.
It is worldwide in scope and not limited to any country, breeding line, or kennel, and experts report that it is believed to be inherited CM is so widespread in the Cavalier that it may be an inherent part of the CKCS's breed standard. This disease not only affects thousands of dogs, but a similar
condition affects over three hundred thousand children yearly.
[ ] Therefore, canines are an appropriate model for the treatment of the human condition.
Symptoms
Clinical signs for CM include behavioural signs of pain- vocalization, head scratching/rubbing, reduced activity, reduced stairs / jumping ability, spinal pain, altered emotional state (behavioural change to more timid, anxious or aggressive), sleep disturbance and touch aversion.
Common symptoms in human patients include, severe headache and neck pain, dizziness, vertigo, disequilibrium, visual disturbances, ringing in the ears, difficulty swallowing, palpitations, sleep apnea, muscle weakness, impaired fine motor skills, chronic fatigue and painful tingling of the hands and feet, pruritus.
Diagnosis
Diagnosis of CM alone is challenging and identified by anatomical characteristics and ruling out other disorders.
Whole spine MR imaging may be used to evaluate the extent of syrinx formation (fluid filled cavity within the spinal cord) in CM dogs, developing a thermal camera-based screening test for the disorder and a method of measuring the actual syrinx volume from MR images.
Before the introduction of MRI, the diagnosis of CM and SM were commonly confused with that of allergic skin disorders,
disk disease, ear infections and
epilepsy
Epilepsy is a group of non-communicable neurological disorders characterized by recurrent epileptic seizures. Epileptic seizures can vary from brief and nearly undetectable periods to long periods of vigorous shaking due to abnormal electrical ...
.
After CM was reported in human patients, the initial research was provided for the diagnosis of animals.
MRI in animals is safe, however, to ensure that the patient remains motionless, light general anesthesia is required.
According to recent studies,
thermography
Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are ...
may be a useful tool in the diagnosis of CM and SM.
Thermography
Infrared thermography (IRT), thermal video and/or thermal imaging, is a process where a Thermographic camera, thermal camera captures and creates an image of an object by using infrared radiation emitted from the object in a process, which are ...
requires no sedation or clipping of hair for a dog to be imaged by the infrared camera. After the image is captured, computer software is used to assess changes in the temperature and color pattern to detect abnormality.
Treatment
The type of treatment needed for dogs diagnosed with CM/SM depends on the severity of the condition and the age of the dog. Young dogs with clinical signs should be considered for surgical removal to minimize the progression of the disease as the dog ages. Older dogs with little or no clinical signs may be treated medically, rather than surgically. However, severe cases of CM/SM may require surgery regardless of age. The goal of surgery is syrinx decompression through restoration of normal cerebrospinal fluid circulation.
The surgical treatment of CM in dogs is described as "foramen magnum decompression FMD".
Despite an approximately 80% success rate with this surgical technique, there is a 25% to 50% relapse, primarily due to excessive scar tissue formation at the decompression site.
A cranioplasty may be performed instead, in which a plate, constructed using titanium mesh and bone cement, is fixed to the back of the skull following a standard FMD procedure. The procedure had been effective in humans. The postoperative relapse rate associated with the titanium cranioplasty procedure is less than 7%.
History
The name "Chiari-like" derives from one of the early scientists who diagnosed a similar structural
condition in children, Dr.
Hans Chiari
Hans Chiari (4 September 1851 − 6 May 1916) was an Austrian pathologist, who was a native of Vienna. He was the son of gynecologist Johann Baptist Chiari (1817–1854), and brother to rhinolaryngologist Ottokar Chiari (1853–1918).
Biograp ...
.
References
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Chiari-like malformation