CNS tumors can involve the brain or the spinal cord. A tumor is defined as an abnormal growth of cells, and may be classified as primary or secondary. A primary CNS tumor originates from the nervous tissue or its surrounding membranes. A secondary CNS tumor, is either cancer that has spread to the brain (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.
Animals older than 8 years are more susceptible to developing CNS tumors; the median age of affected pets is nine years. Certain breeds of dogs are at higher risk for developing primary CNS tumors than others. Cats are also known to get certain types of tumors.
Common Dog Tumor Types:
- Primary: Meningioma, glioma, choroid plexus
- Secondary: Hemangiosarcoma, osteosarcoma, pituitary tumors, lymphoma
Common Feline Tumor Types:
- Primary: Meningioma
- Secondary: Lymphoma
The most common indication of a brain tumor is seizure, especially seizures that begin for the first time in a dog/cat older than five years of age. Other signs suggestive of a brain tumor include abnormal behavior (e.g., increased aggression), 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 inappetance, lethargy, andinappropriate urination may also be seen. The most common symptoms associated with a spinal cord tumor is weakness or paralysis either in the back legs or all 4 legs depending on the tumor location.
A strong presumptive diagnosis can be made by advanced imaging (usually MRI) of the brain or spinal cord. A definitive diagnosis can only be made from a biopsy.
Treatment options can range from minimal palliative measures to more aggressive definitive measures (i.e. surgery, radiation therapy and chemotherapy). Palliative measures typically involve steroids (prednisone) to decrease peritumoral inflammation and edema. Anticonvulsants are required in some animals to control seizures. Depending on the individual patient, these drugs may be discontinued following definitive treatment. The primary goal of definitive therapy for tumors is to improve or even eliminate when possible the adverse secondary effects and resulting clinical signs and include a combination of medical management, surgery, radiation therapy, and chemotherapy.
Surgery has the advantage of removing the structural mass which immediately relieves CNS pressure in addition to providing a tissue sample for definitive diagnosis—however, surgery is not without risk and post-surgical complications include infection, edema, and hemorrhage. The location, size, and invasiveness of the tumor will determine the possibility for both surgical removal and completeness of surgical margins.
Radiation therapy (RT) can be used alone or in combination with other treatment modalities and is well established for the treatment of intracranial neoplasms. Cyberknife radiation allows very pinpoint high doses to tumor with minimal affects to the normal surrounding tissue.
Chemotherapy may be employed depending on the tumor type. The type of blood vessels in the brain act as a “blood-brain barrier” and prevent entrance of toxic or foreign substances, including most chemotherapy drugs, into the CSF. CCNU and Cytosar are chemotherapeutic agents that can penetrate the blood-brain barrier and have been shown to improve clinical signs and reduce tumor size in some instances. The benefit of chemotherapy for dogs with incompletely excised brain tumors is currently unknown. True data in a large group of patients is lacking however, anecdotal reports of benefits exist.
There are many variables that determine the prognosis with CNS tumors. In all cases, the prognosis is at least guarded, but some are more easily treated than other. With palliative measures alone survival times are typically in the realm of weeks to months, while the combination of surgery and radiation therapy can provide survival times around 2.5+ years.