Structure and Function of the Brain and Spinal Cord in Dogs

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Structure and Function of the Brain and Spinal Cord in Dogs

By: Virginia Wells

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What Are the Common Diseases of the Brain?

Brain disorders can be subdivided into congenital abnormalities, infections, inflammations, degenerative diseases, metabolic disorders, vascular conditions, tumors, traumatic injuries, nutritional disorders, toxic conditions, and diseases of unknown cause. Some examples of brain diseases that occur in dogs are listed below:

Hydrocephalus is the accumulation of cerebrospinal fluid within the ventricular system of the brain. As a result, the ventricles become enlarged and the brain matter shrinks from the fluid pressure. It may be primary and congenital, resulting from either increased production of CSF or failure of absorption. Hydrocephalus may also develop secondary to obstruction of the ventricles. Congenital cases most commonly occur in toy and brachycephalic breeds of dogs, such as the pug, Chihuahua, toy poodle, Lhasa apso, etc.

Peripheral vestibular disease is a condition that affects both the brain and the nerves that control equilibrium. Dogs with vestibular disease have difficulty with balance and orientation. Signs include head tilt, falling and falling over. Canine idiopathic vestibular disease (also called "old dog vestibular disease") is a common form of the disease.

Infectious encephalitis is inflammation of brain tissue caused by infectious organisms. In dogs it may be caused by viral diseases (canine distemper, infectious canine hepatitis, rabies), parasitic infestations, protozoal infections (toxoplasmosis, neosporosis, encephalitozoonosis), numerous bacteria, rickettsial organisms (ehrlichiosis, Rocky Mountain spotted fever, salmon poisoning), and fungal infections (blastomycosis, cryptococcosis, coccidioidomycosis).

Seizures are abnormal brain activity that may result in convulsions that manifest as odd behaviors, tremors, muscles contractions, salivation and defecation. There are many causes of seizures such as epilepsy, which is a condition characterized by recurrent seizures. Epilepsy is found in many pure bred and mixed breed dogs. The Belgian tervuren is listed among the breeds for which a genetic factor is either proved or highly suspected. Other breeds with increased prevalence of epilepsy include the beagle, dachshund, German shepherd dog, boxers, collie, and Labrador retriever.

Narcolepsy is a neurological disorder that induces extreme daytime sleepiness. It may be accompanied by cataplexy, which is characterized by sudden episodes of muscular weakness. Dogs are one of the few animals that suffer from narcolepsy.

Brain tumors may be primary and arise from brain tissues, or they may be secondary and develop from either surrounding or distant tissues. Many different tumors can metastasize to the brain.

Head trauma is a fairly common injury in dogs that are hit by cars or receive either blunt or penetrating injuries to the head. Clinical signs can vary widely depending upon the type of injury, but may include stupor, loss of consciousness, abnormalities in pupil size and the function of other cranial nerves, seizures, weakness, inability to walk, and head tilt.

What Are the Common Diseases of the Spinal Cord?

Spinal cord disorders generally cause dysfunction of one or more limbs and/or the tail. Spinal cord disorders may occur alone or in combination with disorders of the brain. Like brain disorders, spinal cord diseases can be subdivided into congenital abnormalities, infections, inflammations, degenerative diseases, vascular conditions, tumors, traumatic injuries, nutritional disorders, toxic conditions, and diseases of unknown cause. Some examples of spinal cord diseases that occur in dogs are listed below:

Spina bifida is a rare developmental anomaly characterized by defective closure of the two halves of the vertebra (back bone) through which the spinal cord may or may not protrude. It usually results in dysfunction of the tail and anus, incontinence and sometimes pelvic limb weakness. It is seen most commonly in "screw-tailed" breeds such as the English bulldog, but has also been reported in Rhodesian ridgebacks.

Infectious meningitis is inflammation of the meninges of the brain or spinal cord, arising from some sort of infection. The most common causes of meningitis in dogs are bacterial infections, canine distemper virus infection, infectious canine hepatitis virus, and toxoplasmosis.

Spinal tumors can occur in the vertebrae, the meninges, nerve roots and/or the spinal cord itself. Tumors that arise from cells within or covering the spinal cord are called primary tumors. Tumors arising from nearby tissues that invade or impinge upon the spinal cord are referred to as secondary tumors.

Degenerative myelopathy is a slowly progressive disease characterized by loss of muscle coordination, weakness and thinning of the muscles, and eventual paralysis of the hind limbs. It is common in German shepherd dogs.

Intervertebral disc disease arises with degenerative changes that result in protrusion of the discs of the vertebral column. As the discs put pressure on the spinal cord, certain clinical signs may be seen. These include pain, muscle weakness, partial or complete paralysis, and other neurologic deficits.

What Types of Diagnostic Tests Are Used to Evaluate the Brain and Spinal Cord?

A complete neurologic examination including the testing of various reflexes provides valuable information on the function of the brain and spinal cord.

Cerebrospinal fluid (CSF) analysis is the microscopic examination of CSF retrieved via a spinal tap. The analysis often provides valuable information as to the presence of infection, inflammation, and other abnormalities.

X-rays provide information about the bony skull around the brain, and the vertebrae that surround the spinal cord. The brain and spinal cord themselves do not show up well on X-rays, but a special procedure called a myelogram can help highlight various areas of the spine.

Computed tomography (CT scan or CAT scan) is a special X-ray technique that provides serial images of the brain and spinal cord using enhanced computer processing.

Magnetic resonance imaging (MRI) uses the properties of certain tissues subjected to extremely powerful magnetic fields to generate detailed images of body organs. MRI is a very useful tool in evaluating both the brain and spinal cord.

Various electrodiagnostic tests are available to assess different functions of the brain and spinal cord. Such tests include the brain stem auditory evoked response (BAER), which is used to detect deafness; the electroencephalogram (EEG), which may detect abnormalities in brain activity during a seizure disorder; and nerve conduction velocity (NCV), which assesses the function of peripheral nerves.

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