Brain Tumors in Dogs

What Is a Brain Tumor in a Dog?

A tumor is an abnormal growth of body tissue. Tumors can occur in nearly any part of a dog’s body, including the brain. There are two broad categories of tumors:  benign (not cancer) and malignant (cancer). Brain tumors are classified as primary or secondary.

Primary brain tumor: A primary brain tumor is one that originated in the brain or in one of the layers covering the brain, called the meninges.

Secondary brain tumor: A secondary brain tumor is one that has spread to or invaded the brain after starting in another location. This can happen either by metastasis or by invasion. Metastasis occurs when tumor cells break off from a primary tumor, travel through the body, and establish themselves elsewhere. Invasion occurs when a tumor extends into neighboring bodily tissues.

Symptoms of Brain Tumors in Dogs

• Seizures (the most common symptom)

• Sensitivity to touch on the head or neck area

• Issues with vision

• Uncoordinated or unsteady movement

• Abnormal behaviors, such as repetitive circling

• Increased reactivity

• Lethargy or excessive tiredness

• Lack of appetite

• Head tilt

• Inability to control urination or bowel movements

Causes of Brain Tumors in Dogs

There are no known direct causes of brain tumors in dogs. Research suggests that a combination of factors, such as diet, surrounding environment, genetics, and immune system health, may be involved. Brain tumors can occur at any age but typically happen in dogs over the age of 5.

Certain breeds with particular head and nose shapes appear to be more at risk for developing brain tumors than others, including:

Dolichocephalic dog breeds: These are breeds with an elongated head and nose. Examples include the Collie, Greyhound, Dachshund, Italian Greyhound, and Great Dane. These breeds are more likely to develop meningioma, a type of brain tumor that develops in the membranes surrounding the brain.

Brachycephalic dog breeds: These are breeds with a shorter nose and flatter face. Examples include the Pug, Shih Tzu, Bulldog, Boxer, Boston Terrier, Pekingese, and Mastiff, among others. These breeds are more likely to develop glioma, a type of tumor that originates in the brain or spinal cord.

How Veterinarians Diagnose Brain Tumors in Dogs

A brain tumor may be suspected in older dogs based on abnormal neurological signs. The veterinarian will start with a thorough physical examination and will test for any sign that something may be affecting your dog’s brain, spinal cord, and nerves.

Bloodwork such as a complete blood count and serum blood chemistry will likely be performed to rule out other causes of seizures or abnormal behavior. Routine bloodwork cannot diagnose a brain tumor but can eliminate other possible causes of your dog’s symptoms. 

Chest X-rays and abdominal ultrasound will likely be recommended to see if the cancer has spread. Approximately 55% of brain tumors do not start in the brain, but instead spread there from another location. Even if the brain tumor is a primary tumor, it may have spread to other locations.

Imaging of the brain is needed to confirm that a brain tumor is present. X-rays cannot penetrate the skull bone enough to visualize the brain. Computed tomography (CT) or magnetic resonance imaging (MRI) are needed to image the brain and locate the tumor. Dogs will be given general anesthesia for CTs or MRIs to make sure they do not move during the procedure. CTs and MRIs are typically performed by a veterinary neurologist.

The veterinarian may suspect the type of tumor present based on the appearance of a mass on the CT or MRI, but a biopsy is necessary to identify the type of tumor. Other diseases can look like tumors or cancer on a CT or MRI include abscesses, parasites ( such as toxoplasmosis), cysts, blood clots, and inflammatory lesions.

Treatment of Brain Tumors in Dogs

Your veterinarian or veterinary neurologist will discuss the best treatment plan for your dog if they are diagnosed with a brain tumor, depending on the type of tumor and whether it has metastasized. 

There are three primary treatment options: surgery, radiation therapy, and chemotherapy.

Surgery: The goal of surgery is to remove the brain tumor. This is often not possible unless it is located on the brain’s surface. Surgery is more likely to be successful for dogs diagnosed with meningioma; however, it is likely that the tumor will recur. This is a highly specialized procedure performed only by a veterinary neurosurgeon.  Dogs with tumors located deeper in the brain are not good candidates for surgery because of complications that can arise from cutting through healthy brain tissue to reach the tumor site.

Radiation therapy: Radiation therapy is commonly used to target and shrink brain tumors. Radiation can cause negative side effects such as nausea, mouth ulcers, and ear infections, but these can be treated with medication. Radiation can quickly improve your dog’s condition, but it rarely destroys the entire tumor. On average, brain tumors treated with radiation will recur in eight to 14 months.

Chemotherapy: Chemotherapy is not a common option for treating brain tumors in dogs.

The brain is protected by a network of blood vessels that serve as a barrier to keep dangerous substances out. The body interprets chemotherapy drugs as being harmful and prevents them from reaching the brain, and therefore the tumor, in large amounts.

Medication: Medications may be used as a solo treatment to keep your dog comfortable and increase their quality of life or they may be used with surgery, radiation therapy, or chemotherapy. Common medications may include steroids to help slow the growth of the tumor and decrease swelling in the brain, as well as anti-seizure medications to control seizures secondary to the brain tumor.

Recovery and Management of Brain Tumors in Dogs

Dogs diagnosed with a brain tumor will need ongoing care with their veterinary neurologist. This is because a brain tumor can rarely be cured and will likely recur even when fully removed with surgery or destroyed with radiation.

Routine exams are important for increasing your dog’s lifespan while maintaining their quality of life. These exams often include imaging and an evaluation of symptoms common for dogs with brain tumors, such as seizures.

Dog parents also need to be on the lookout for other complications. For example, brain tumors can increase pressure on your dog’s skull and make it more difficult for them to swallow. This can cause them to accidentally inhale food or water into the lungs, which can lead to an infection in the lungs called aspiration pneumonia.

Medications will likely be prescribed for the remainder of your dog’s life. These can help to manage symptoms as well as the brain tumor itself. For example, anti-inflammatory medication can help reduce swelling and pressure, and anti-seizure medication can help control and prevent seizures.