By Dr. Becker
Brain cancer is unfortunately a relatively common disease in older pets. Brain tumors in animals vary a great deal in terms of their level of malignancy, and some can be treated effectively.
Tumors originating from the membranes covering the brain, called meningiomas, are seen more often in dogs with long heads and noses like the Collie. Brachycephalic breeds, with their short noses and flat faces, more often develop pituitary tumors.
Brain tumors are more common in dogs than cats, especially dogs over five years of age. Predisposed breeds include the Boxer, Boston Terrier, and Golden Retriever.
Primary and Secondary Brain Tumors
A tumor is an abnormal growth of cells, and is classified as either primary or secondary. A primary brain tumor means the cancer originated within the cells of the brain and its membranes.
Types of primary brain tumors include meningioma, glioma, choroid plexus papilloma, and pituitary adenoma or adenocarcinoma.
A secondary brain tumor is either cancer that has metastasized to the brain from a primary tumor somewhere else in the animal’s body, or it’s a tumor affecting the brain by extending into brain tissue from a nearby, non-nervous system location, such as a bone.
Examples of tumors that may spread to the brain include hemangiosarcoma, mammary carcinoma, and melanoma. Unfortunately, these tumors have a very poor prognosis because they’ve already spread through the body.
Symptoms of a Brain Tumor
Symptoms of a brain tumor arise from the mass either compressing or invading the brain, and depend on what area is affected. Brain tumors typically cause progressive signs in older animals. The symptoms often start off mild and progress in severity, but not always. They can start quite suddenly, for example, an older pet may just start having seizures, or they can occur more subtly and gradually. They can also wax and wane in severity.
If the tumor is affecting the forebrain, which is the area responsible for thought and behavior, symptoms can include behavioral changes, an increase or decrease in thirst or hunger, constant pacing or circling, decreased awareness and vision on one side of the body, pain or head pressing, and seizures.
In fact, the sudden onset of seizures is the most common symptom of the presence of a tumor of the forebrain, and is what I see as the most common, in terms of symptoms, in clinical practice.
If the tumor is affecting the brainstem, the animal’s ability to walk, mental alertness, and respiratory and cardiovascular systems may be impacted. The most common symptoms of a brainstem tumor are loss of balance and weakness on one side of the body.
There can also be head tilting, drunken gait or staggering, circling, difficulty swallowing, loss of appetite, and vomiting. There may also be a change in the bark or voice, inability to move the eyes, and paralysis. In some cases, an affected pet may lapse into a coma and die.
A tumor of the cerebellum, which controls coordination of movements, can have symptoms including uncoordinated gait, head tremors, and swaying of the trunk.
Diagnosing Brain Cancer
Generally speaking, any pet over five years of age who presents with a new onset of neurologic symptoms should be suspected for a brain tumor. Diagnosis will include a complete physical and neurologic exam, routine blood work, and chest and abdominal X-rays to check for the spread of cancer.
Since most soft tissue brain tumors can’t be seen on X-rays of the skull, it’s necessary to do a magnetic resonance imaging (MRI) or computerized tomography (CT) scan of the brain. Most neurologists prefer MRIs.
The type of tumor can often be determined from its appearance on CT or MRI images, but the mass can only be definitively diagnosed by taking a sample, either during surgery to remove it or with a biopsy. This can prove challenging, since many tumors lie very deep within the skull and are not good candidates for surgical removal.
Brain masses caused by infections can look like tumors on brain images, so it’s critically important that a sample of the tumor is evaluated to identify the cell types involved. This procedure not only identifies the type of tumor, but also grades the malignancy of it.
The traditional treatment for brain tumors in dogs and cats is what you might expect – surgery, radiation therapy, chemotherapy, and palliative treatment of symptoms.
The aim of surgery, which is the best option, is to hopefully completely remove the tumor, but sadly, this is a rare outcome. Meningiomas tend to develop on the surface of the brain, and are the best candidates for surgical removal. Gliomas are typically found deep within the brain and are much more difficult or even impossible to remove.
Often, surgery is useful primarily to alleviate the animal’s symptoms by decompressing the brain.
Radiation therapy can slow the progression of most types of brain tumors in pets. But in order to have this therapy safely, the animal must be healthy enough to undergo general anesthesia for each dose of radiation. If the mass is large, it’s better to surgically remove as much of it as possible first, which will decompress the brain and make the pet better able to endure a course of radiation.
Chemotherapy isn’t a common choice of treatment for brain tumors, because the blood-brain barrier limits the effectiveness of the drugs. There are a few chemo drugs that can cross the barrier, so it may be offered as an option to treat a glioma when radiation isn’t a possibility. However, chemotherapeutic agents can have devastating side effects, especially on the liver and bone marrow, and must be closely monitored during treatment. I don’t ever recommend chemotherapy for patients with brain tumors.
The goal of palliative treatment for a brain tumor is to alleviate the animal’s symptoms. For example, if your dog or cat is seizing or has fluid accumulation in the brain, we want to get those things under control.
In most pets, brain tumors can be treated, but not cured. I see dozens of patients a year for adjunctive therapy for brain tumors. I strongly recommend you connect with an integrative or holistic veterinarian who can provide additional, all natural therapies to reduce pain and inflammation. Sometimes we can actually slow tumor growth with complimentary therapies, and we have lots of options to offer for improving your pet’s quality of life.