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Canine brain tumors
CANINE BRAIN TUMORS
What are brain tumors?
Primary brain tumors are relatively uncommon in dogs. Gliomas and meningiomas are
most common. They occur most frequently in older dogs (over 5 years) with no breed
or sex predilection. The most common secondary tumors in dogs include local
extension of nasal tumors, metastases from mammary, prostatic or lung carcinoma and
hemangiosarcoma. Skull tumors that may affect the brain by local extension include
osteosarcoma, chondrosarcoma, and multilobular osteochondroma.
How are brain tumors diagnosed?
The signs of brain tumors will depend on the location, extent, and rate of growth of the
tumor. Many dogs with brain tumors will have a long history of vague symptoms such
as behavior alterations that are often overlooked by owners until significant brain
dysfunction develops. The most frequently recognized clinical sign is seizures,
particularly in dogs over the age of 4 years. Other signs may include weakness, head
tilt, circling, and ataxia. A complete blood cell count, chemistry panel, and urinalysis are
necessary to rule out metabolic causes of seizures. Advanced imaging such as CT
scan or MRI is necessary to identify a brain tumor. Ultimately a biopsy would be
necessary to definitively diagnosis the type of brain tumor; however this is not usually
performed. MRI and CT imaging characteristics for certain tumors have been
described which may help differentiate tumor types. Chest X-rays are useful to evaluate
for metastases or secondary tumors prior to consideration of treatment.
What are the treatment options?
Surgery The precise location, size, and extent of the tumor determine the possibility of
surgical removal. Meningiomas, particularly those located in the frontal lobes often may be excised. Tumors of the caudal fossa and brain stem have significant morbidity and mortality associated with surgery. If the tumor is not able to be completely removed with surgery, additional therapy such as radiation or chemotherapy may be warranted.
Radiation therapy The use of radiation therapy for dogs with brain tumors has been well
established. Radiation therapy may be used as a sole treatment for nonresectable brain tumors or as an adjuvant to surgery. The CT or MRI image is used to plan the radiation therapy in order to minimize radiation effects on surrounding normal brain tissue. Radiation therapy is performed Monday through Friday daily for 3-4 weeks. General anesthesia is required for treatment. See radiation handouts for more detailed information.
Chemotherapy Little information is available regarding the efficacy of chemotherapy for brain
tumors in dogs. Few chemotherapy drugs are capable of penetrating the blood-brain barrier. CCNU is one drug with limited use in canine brain tumors. This is an oral chemotherapy agent that is administered on an every 3 week schedule. Recent attention has been given to hydroxyurea in the treatment of meningiomas in humans. Hydroxyurea is an oral chemotherapy agent that is administered daily. In humans, administration of hydroxyurea appears to slow or arrest the progression of the tumor based on serial MRI imaging. Because of the financial investment, it is often not feasible to perform serial imaging examinations (MRI or CT) in dogs, making it difficult to evaluate the efficacy of these therapies.
Palliative therapy Palliative therapy involves the use of phenobarbital or other anticonvulsants to
control seizure activity and prednisone to reduce tumor associated swelling or edema.
What is the prognosis?
The prognosis of brain tumors depends on several factors including the tumor
type, and method of treatment. With palliative therapy only, the prognosis is poor, with an average survival time of between 2-4 months. The prognosis for dogs with primary brain tumors is significantly improved by surgical removal, irradiation, and chemotherapy either alone or in combination. Surgical removal of brain tumors yields an average survival of 6-10 months. Many brain tumors are not able to be completely excised and postoperative radiation therapy is warranted. If radiation is performed following surgery, the average survival time is improved to 14-18 months. For nonresectable brain tumors treated with radiation therapy, the average survival is 12 months. Little data exists on survival times for dogs with brain tumors receiving chemotherapy as the sole treatment or chemotherapy as an adjuvant to surgery.
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