A tumor is formed when abnormal cells grow out of control. A brain tumor can grow within the skull, inside the brain, in the cranial nerves, or even in the pituitary and pineal gland.
Two types of canine brain tumors can occur: primary and metastatic brain tumors.
Primary brain tumors are those that arise from the brain cells that have started to grow uncontrollably.
Common primary brain tumors in dogs include Meningioma, Glioma, and others.
Metastatic brain tumors are those that arise when cancer cells located primarily in other organs spread to the brain.
Common metastatic brain tumors in dogs include hemangiosarcoma, mammary carcinoma and melanoma.
Brain tumors occur very commonly in older dogs, regardless of gender or breed. In fact, it has been found that 95% of older dogs over the age of 7 suffer from some form of brain tumors.
In recent years, there has been an increasing incidence of brain tumors occurring in younger dogs as well. Some breeds such as brachycephalic breeds (e.g. Boxers, English Bulldogs, and Boston Terriers) are more susceptible to brain tumors when they are younger.
Causes of Canine Brain Tumors
The exact causes of brain tumors in dogs are not known.
Possible triggers may include:
- Serious injuries to the head
- Exposure to radiation and electromagnetic field
- Exposure to some chemicals such as pesticides
General Symptoms of Canine Brain Tumors
Brain tumours in dogs can cause numerous signs and symptoms depending on the part of the brain affected.
In older dogs the symptoms are progressive. They may start very suddenly or quite slowly, and they can get better and then worsen again.
Typical signs and symptoms of brain tumors in dogs include:
- Unsteady gait or or staggering
- Sudden unexplained aggressiveness
- Failure to recognize family members and friends
- Getting lost in familiar places
- Head shaking
- Hearing loss
- Loss of eyesight
- Urinary incontinence
- Change in appetite (either eating a lot or refusing to eat)
Of course, not all dogs with brain tumors show all of the above signs and symptoms.
Symptoms and Part of Brain Affected
As mentioned earlier, the symptoms to a large extent depend on the part of the brain that is affected. For example:
In the Forebrain
Cancer in the forebrain (which is responsible for cognitive behavior and integration of sensory information) will cause cognitive changes in a dog, such as:
- Seizures (new onset of seizures is a typical sign of cancer in the forebrain. These seizures can occur in association with some of the above symptoms, or they may just be the only symptom)
- Loss of learned behavior
- An increase or decrease in both appetite and thirst
- Failure to recognize familiar faces
- Problems with awareness and vision (e.g. misjudgement of openings to doorways)
- Urinary incontinence (having “accidents” in the house)
- Constant pacing or circling
In the Brainstem
Cancer in the brainstem will affect the balance, respiratory and cardiovascular functions of a dog. This is because the brainstem is responsible for regulating and controlling motor function; maintaining a sense of balance; controlling movement of and sensation to the face, the eyes, the throat, larynx and tongue, and the muscles of mastication (chewing and biting).
Typical symptoms of cancer in the brainstem include:
- Loss of balance (ataxia)
- Weakness on one side of the body
- Head tilt
- Irregular movement of the eyes (nystagmus)
- Loss of appetite
If the tumor affects the muscles responsible for chewing, the dog will have difficulty eating and swallowing.
If the tumor affects the respiratory system, the dog will have difficult breathing.
Dogs with tumors in the brainstem usually end in paralysis, coma and death.
In the Cerebellum
Finally, tumors may arise in the cerebellum, which controls coordination of movements and, together with the vestibular system, controls balance and posture.
A dog with a tumor in the cerebellum shows such symptoms as:
- Body swaying
- Uncoordinated gait
- Head tremors that occur when the dog wants to do something, but disappear when the dog is relaxed (intention tremors)
- Head tilt
Diagnosis of Canine Brain Tumors
Diagnosis of brain tumors in dogs is made based on clinical signs as well as brain scanning using CT scan or MRI.
To determine if the tumor is malignant or benign, the vet will do a biopsy.
The vet will also do chest and abdominal x-rays and sometimes abdominal ultrasound to see if the cancer has metastasize and, if so, to what extent.
Conventional Treatment of Canine Brain Tumors
Treatment options for dog brain tumors include surgical removal, radiation, chemotherapy, and palliative treatment.
Surgery is possible only for primary brain tumors that are located in an area that can be reached safely. For example, tumors that are close to the surface of the brain. Since most canine brain tumors are metastatic tumors, surgery is not an option for such cases.
In cases where surgery is impossible, such as metastatic tumors or tumors that are located too deep inside the brain, radiation therapy is one way to slow down the growth of the tumor.
Sometimes, after surgery, the dog will also receive radiation treatment. Radiation can result in dramatic and rapid improvement of signs.
Unfortunately, radiation by itself usually cannot destroy the tumor and average remission times are 8 to 14 months before the tumor recurs. Depending on the location of the tumor, radiation may cause some side-effects, such as ear infections, nausea, or ulcers in the mouth.
As the brain is protected from circulating substances in the blood by a barrier called the blood brain barrier (BBB), there are not too many drug choices that are effective in treating brain tumors. One drug that may be effective in treating gliomas is temozolomide.
Palliative treatment means using drugs to treat the symptoms only. Dogs whose brain tumors are in such a stage that other treatments are not possible usually receive palliative treatment.
For example, the vet may give a combination of anti-inflammatory medication (corticosteroids such as prednisone) to reduce the swelling and pressure caused by the tumor. He may also prescribe anti-seizure drugs such as Phenobarbital to reduce the severity and frequency of seizures.
Palliative treatment will keep the dog alive for an average of 2 to 3 months while maintaining a reasonable quality of life for the dog.
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