One of the less common cancers I’m asked to consult on are brain tumors. Though such tumors occur with fair frequency in both cats and dogs, optimal diagnostic and treatment plans are not well established. Thus brain tumors are considered a challenging disease for both veterinary neurologists and oncologists.
Brain tumors are either primary or secondary, with about equal chance of either of them being the diagnosis. Primary brain tumors originate from cells normally found within the brain tissue itself, or the thin membranes lining its surface. The most common primary tumors are meningiomas, astrocytomas, oligodendrogliomas, choroid plexus tumours, central nervous system (CNS) lymphoma, glioblastoma, histiocytic sarcomas, and ependymomas.
Secondary brain tumors occur when either a primary tumor located elsewhere in the body spreads to the brain (a process known as metastasis) or extends into the brain via invasion from adjacent tissue (e.g., bones of the skull, nasal cavity, eye, etc.).
Brain tumors occur most often in older pets, with the median age of affected dogs and cats being 9 and 11 years, respectively. Certain breeds show a predisposition for developing primary brain tumors: Boxers, Golden retrievers, and domestic shorthair cats are at increased risk.
Brain tumors that originate from the membranes covering the brain (known as meningiomas) occur more often in dolichocephalic breeds—those with long heads and noses—such as Collies. Conversely, brachycephalic breeds, with their short-nosed, flat-faced appearance, are more likely to develop gliomas, which are tumors of the interstitial tissue of the central nervous system.
The most common clinical sign of a brain tumor in dogs is seizures. Cats are more likely to show a sudden onset of aggression. Other signs suggestive of a brain tumor include behavioral changes, 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 loss of appetite, lethargy, and inappropriate urination are also seen.
There are several recommended staging tests for pets suspected to have brain tumors. These tests are designed to examine for widespread disease in the body, are considered part of a general health screen, and can establish baseline information with which we can compare to in the future.
Staging tests include complete blood count (CBC), chemistry panel, thoracic radiographs, and abdominal ultrasonography. These tests are used rule out an extracranial primary tumor that has metastasized to the brain, or the possibility of another primary tumor located in a distant site. These tests provide owners with peace of mind for moving forward with advanced imaging (MRI/CT) of their pets’ brains. In approximately 8% of cases, results from such tests will ultimately lead to a change in the anticipated diagnostic and treatment plan.
When a brain tumor is suspected, and staging tests are considered clear, the recommended next test is typically magnetic resonance imaging (MRI). The exception would be cases where a pituitary tumor is suspected, as these tumors are better visualized using CT scan.
The only way to definitively diagnose a brain tumor and determine its exact tissue of origin would be through biopsy. While it is ideal to have a diagnosis before proceeding with therapy, veterinarians often recommend treatment based on a presumptive diagnosis from the imaging characteristics of an intracranial mass This is due to the increased risk associated with the procedure and the negative impact the clinical signs seen in affected patients has on their overall quality of life.
There are three primary treatment options for dogs that have been diagnosed with brain tumors: surgery, radiation therapy, and chemotherapy. The objectives of such therapies are to or reduce the size of the tumor and to control secondary effects, such as fluid build-up in the brain. Surgery may be used to completely or partially remove tumors, while radiation therapy and chemotherapy may help shrink tumors or reduce the chance of regrowth following surgery. Medications are also often prescribed to manage the side effects of brain tumors, such as seizures.
The prognosis for dogs with brain tumors is considered guarded to fair. Survival times of 2-4 months are expected with supportive care alone, 6-12 months with surgery alone, 7-24 months with radiation therapy alone, 6 months to 3 years with surgery combined with radiation therapy, and 7-11 months with chemotherapy alone.
As is typical for many aspects of veterinary oncology, accurate prognostic information for cats with brain tumors is lacking.
If your veterinarian suspects your pet has a brain tumor, please consider seeking a consult with a board certified veterinary neurologist or oncologist in your area to understand your options for both diagnosis and treatment.
You can find more information at the website for the American College of Veterinary Internal Medicine.