Brain Tumors in Dogs The most common forms of brain tumors in dogs are known as Glioma and Meningioma. Glioma is a type of cancer that starts in the brain or spine. It is called a glioma because it arises from glial cells. Glial cells provide support and protection for neurons, the other main type of cell in the nervous system. Although other types of brain tumors occur, there seems to be an increased incidence of gliomas in short-nosed (bradycephalic) dog breeds, like Pugs, Boston Terriers and Boxers. Glioma tumors in dogs are among the common primary tumors of the central nervous system (CNS), and they tend to occur in aged patients, with the brachycephalic breeds being more predisposed. Canine astrocytomas (central nervous system tumors that arise primarily in and rarely spread away from the CNS) and oligodendrogliomas (a rare form of brain tumors) each have about the same occurrence of about 10% of all primary tumors. Astrocytomas usually involve the cerebral hemispheres, predominantly in the temporal-pyriform region, and the diencephalon, but they may be located in almost any area of the CNS. Optic pathway gliomas in animals are extremely rare, and they almost always adopt an anaplastic form which means they are cancer cells which divide rapidly and have little or no resemblance to normal cells. Meningiomas arise from the arachnoidal cap cells of the meninges (the system of membranes which envelops the central nervous system) and represent about 15% of all primary brain tumors).Brain tumors often have some identifiable clinical symptoms since they often damage nerves exiting the brain or the centers that control these nerves. Often the words “brain tumor” lead us to conjure an image of a growth deep and inaccessible inside the brain but this is not what a meningioma is. Because the meningioma is a tumor of the meninges (the outer membranes) these tumors grow from the skull inward. This makes them much more accessible surgically (depending on their size) than one might have at first thought. Meningiomas are generally benign, meaning that they do not create “cancer.” They do not spread to other areas of the body or invade and destroy tissue local to them. The reason they are a problem is that there is a limited amount of space within the skull. The brain and its bath of cerebrospinal fluid takes up almost all the room and when a tumor begins to grow, the brain tissue is compressed. Inflammation can result leading to more swelling and soon nerves of the brain are damaged. Signs of Meningioma In the dog, seizures are the most common sign. In cats, signs are more vague and consist of listlessness and behavior changes. The following signs have been reported with meningiomas (largely depending on the brain area involved):
Here are some things we know:
What Kind of Testing is Done for Possible Brain Tumor? A basic blood panel (and urinalysis if possible) is the foundation for virtually every medical work up as this will help us assess the patient’s general health. Obviously, it is important to identify if any other problems are present to contend with. Chest radiographs are important to screen for cancer spread. Often times, brain tumors are the result of spread from a malignancy that developed somewhere else. In one study, 55% of brain tumors had not actually started in the brain but had spread there from some other location. The central test for a brain tumor is imaging of the brain: either CT (sometimes called “CAT scan”) or MRI (magnetic resonance imaging). These techniques allow imaging of the actual brain so that the tumor can be located specifically and distinguished from areas of blood clot or inflammation. Radiographs simply cannot penetrate the skull bone and it is only since these more advanced technologies have become available that imaging the brain is possible. The MRI is preferred over CT as it is better able to identify fluid build up, swelling, cysts, bleeding and other subtle soft tissue changes inside the brain. Treatment Medication If the goal is “palliation,” in other words just keeping the pet comfortable and minimizing seizures, prednisone can be used to relieve swelling in the brain tissue and anti-seizure medication such as phenobarbital or potassium bromide A more definitive therapy involves surgical removal of the tumor and/or radiation therapy, both very expensive treatments. Surgery Surgery alone has produced median survival times of 7 months for dogs. For cats, where tumors are somewhat more easily removed, median survival is 26 months. About one cat in five will have a recurrence of the tumor after surgery. Radiation There are many different schedules used for radiation treatments: some weekly, some daily, some on alternate days. Radiation can be done instead of surgery or in combination with surgery and what protocols yield the longest survival times is not clear. Currently, the philosophy on treatment is that a combination of surgery plus radiation yields the best results for dogs. Cats seem to do so well with surgery that recommendations lean away from radiation. |