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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 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.

Brain tumors appear to be more common in dogs than other pets. Dogs older than five years are more susceptible, and some breeds of dogs seem to be at higher risk 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 tumors in the pituitary gland near the brain.

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 page in the PetMD health library.

Symptoms and Types

The most common indication of a brain tumor in dogs is seizures, especially seizures that begin to occur after the animal has reached at least five years of age. There are other signs which may suggest a brain tumor, including abnormal behavior and mental status, over-sensitivity to pain or touch in the neck area, and vision problems that lead to circling motions, uncoordinated movement and a “drunken” gait.

Causes

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.

Diagnosis

A tissue biopsy is the only available method for definitively diagnosing brain tumors in dogs. X-Rays and ultrasounds elsewhere in the body can be used to locate or to rule out primary tumors in other areas, while a magnetic resonance imaging (MRI) scan can reveal tissue irregularities in the brain.