Overview
Brain tumors are generally divided into two main categories: those that start in the brain itself, called primary brain tumors, and those that develop outside the brain but press against it, called brain-associated tumors. Primary brain tumors arise from the brain’s own tissues and include types like meningiomas, which are often slow-growing and treatable, and gliomas, such as astrocytomas and oligodendrogliomas, which originate from the brain’s supportive cells.
On the other hand, brain-associated tumors originate from nearby structures but can compress and interfere with normal brain function. Common brain-associated tumors include pituitary tumors, which form near the base of the brain and peripheral nerve sheath tumors, commonly affecting the trigeminal nerve, a major nerve in the face. Additionally, cancers that begin in other parts of the body can spread to the brain, known as metastatic cancers.
Meningiomas are the most common type of primary brain tumor in both dogs and cats. These tumors develop from the protective layers that cover the brain and can press on the brain itself, causing neurological symptoms. They make up about 50% of all brain tumors in pets. Meningiomas are most often seen in older animals, especially large-breed dogs and cats, but they can occur in any breed. These tumors typically grow slowly, which means there are often multiple treatment options available, depending on the tumor’s location and size.
Gliomas are the second most common type of primary brain tumor. Unlike meningiomas, gliomas develop from the brain tissue itself. They are especially common in brachycephalic breeds, such as Boston Terriers, Boxers, French Bulldogs, and English Bulldogs. Gliomas tend to be more aggressive than meningiomas, though their severity can vary. MRI is an important tool in evaluating how aggressive a glioma might be. Because gliomas come from within the brain and are usually more invasive, they often carry a poorer prognosis and fewer treatment options.
Pituitary tumors develop from the pituitary gland, a small but important gland located just beneath the brain. These tumors often cause signs of brain dysfunction by taking up space and putting pressure on surrounding brain tissue. Although some pituitary tumors can affect hormone levels (as seen in conditions like Cushing’s disease), many cause problems simply due to their size. Fortunately, pituitary tumors usually grow slowly and often respond well to radiation therapy.
Peripheral nerve sheath tumors most commonly affect the trigeminal nerve, which is responsible for facial sensation and jaw movement. Tumors in this area often lead to severe muscle loss on one side of the head and may cause facial pain or discomfort. Although these tumors tend to grow slowly, they can be invasive and may press on nearby brain structures, leading to additional neurological signs. Similar to pituitary tumors, they are often highly responsive to radiation therapy.
Clinical Signs
One of the most common signs of a brain tumor or structural issue in pets is a change in behavior or the onset of seizures. Depending on which part of the brain is affected, other neurological symptoms may also be present. These can include walking in circles, pressing the head against walls, difficulty walking, balance problems (vestibular signs), blindness, and other neurological deficits. These signs can vary in severity depending on the size of the tumor and the part of the brain that is affected.
Diagnosis
MRI is the most effective tool for diagnosing brain tumors. In certain cases, a spinal tap may provide additional information to help identify the specific type of tumor and distinguish it from other conditions with similar MRI characteristics.
Treatment and Prognosis
While there is currently no cure for brain tumors in dogs and cats, there are treatments that can help control symptoms and improve your pet’s quality of life. The best treatment depends on the type of tumor and where it is located in the brain.
Surgery
Some meningiomas can be partially surgically resected since they are on the surface of the brain. Because these tumors are closely connected to the brain tissue, it’s not possible to remove every tumor cell completely. This means the tumor may grow back over time. For this reason, surgery is often combined with radiation therapy afterward to help kill any remaining tumor cells and extend survival.
Survival times can vary greatly, but on average, dogs treated with surgery alone live about 12 to 18 months, while those receiving both surgery and radiation may live 18 to 24 months or longer. Cats often respond very well to surgery alone and can live for several years afterward, even without additional radiation treatment.
Other tumors, like gliomas, are located deeper within the brain and are usually too risky to remove surgically. Tumors such as pituitary masses and nerve sheath tumors are also rarely removed by surgery because of their location, but they often respond well to radiation therapy.
Radiation Therapy
Radiation therapy uses focused, high-energy beams to target and shrink tumors by destroying cancer cells. The treatment is carefully planned to minimize damage to the healthy brain tissue around the tumor. While radiation usually doesn’t cure the tumor, it often helps reduce its size and relieve symptoms.
Radiation therapy usually requires multiple short sessions, often spread out over one to several weeks. Because brain tumors are difficult to biopsy safely, it’s not always possible to know in advance how well a tumor will respond to radiation. Unfortunately, most tumors will eventually grow back over time.
Tumor response to radiation therapy can vary significantly depending on the type. For instance, the average prognosis for meningiomas is typically 12 to 18 months, while gliomas generally range from 6 to 12 months. However, these time frames are approximate and can be shorter or longer depending on the the specific tumor. Pituitary gland tumors and nerve sheath tumors often respond very well to radiation, and dogs with these tumors can live significantly longer, sometimes more than two years after treatment.
Radiation can have side effects, which may include temporary or, rarely, permanent worsening of neurological symptoms, hair loss in the treated area, and possible damage to the eyes.
Palliative Care
Palliative care is a gentle, less invasive approach that focuses on keeping your pet comfortable and attempting to improve their quality of life. This often involves medications like anti-inflammatory steroids to reduce swelling around the tumor, as well as treatments to manage symptoms like seizures, discomfort, anxiety, or dizziness—depending on your pet’s specific signs.
While these treatments can help relieve symptoms and make your pet feel better, they don’t stop the tumor from growing. The amount of time this care can buy varies depending on the size, type and location of the tumor. For dogs and cats with tumors, the average survival time with palliative care ranges from about 1 to 6 months, with gliomas often carrying a worse prognosis than meningiomas.