Brain Tumors in Dogs

PetMD Editorial
Aug 12, 2008
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A tumor is defined as an abnormal growth of cells, and may be classified as primary or secondary. A primary brain tumor originates from cells normally found within the brain and its surrounding membranes. A secondary brain tumor, on the other hand, is either cancer that has spread to the brain (a process known as metastasis) from a primary tumor elsewhere in the body, or is a tumor that affects the brain by extending into brain tissue from an adjacent non-nervous system tissue, such as bone or the nasal cavity..

Dogs older than five years are more susceptible to developing brain tumors; the median age of affected pets is nine years. Certain breeds of dogs are at higher risk for developing primary brain tumors than others. Brain tumors that originate from the membranes covering the brain (known as meningiomas) are found more frequently in dolichocephalic breeds of dogs, which are characterized by long heads and noses, such as the Collie. Conversely, brachycephalic breeds of dogs, which are characterized by their short-nosed and flat-faced appearance, are more likely to develop gliomas, which are tumors of the interstitial tissue of the central nervous system.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this in the petMD health library.

Symptoms and Types

The most common indication of a brain tumor in dogs is seizure, especially seizures that begin for the first time in a dog older than five years of age. Other signs suggestive of a brain tumor include abnormal behavior (e.g., increased aggression), altered consciousness, hypersensitivity to pain or touch in the neck area, vision problems, propulsive circling motions, uncoordinated movement, and a “drunken,” unsteady gait. Non-specific signs such as inappetance, lethargy, and inappropriate urination may also be seen.


The causes and risk factors that may cause brain tumors in dogs are unknown. It is speculated that various dietary, environmental, genetic, chemical, and immune system factors may be involved, but this is uncertain.


A tissue biopsy is the only available method for definitively diagnosing brain tumors in dogs. Imaging tests such as radiographs (x-rays) or ultrasound of other anatomical sites can be used to locate or to rule out primary tumors in other areas that may have spread to the brain. Magnetic resonance imaging (MRI) or computed tomography (CT) of the brain are the recommended tests for confirming the diagnosis of primary or secondary brain tumors.


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