Diagnosis and Treatment Options in Dogs
The diagnosis of a brain tumor is devastating news for most pet owners. It may be hard to make a decision on what to do during this time. The term “brain tumor” simply means a mass within the skull. Due to their location brain tumors – whether they are benign or malignant – will have malignant biological behavior to them. The brain is surrounded by a rigid skull which gives little space for volume expansion. A growing or invading tumor adds more tissue to this closed space. Initially the patient can compensate for the volume increase, but overtime, as the mass continues to grow, the rising pressure on the brain compromises its function. Brain herniation, or physical displacement of a portion of the brain into an adjacent compartment within the skull, is a rare but serious life threatening complication of increased intracranial pressure.
About 60% of all brain masses are meningiomas. This tumor arises from the meninges rather than from the brain itself, and are usually benign and slow growing. However, malignant or invasive forms of meningioma that infiltrate the brain tissue do sometimes occur. Other primary brain tumors include astrocytoma, oligodendroglioma, choroid plexus papilloma, pituitary adenoma or adenocarcinoma, and rarely primary lymphoma. These tumors have the potential to metastasize or cross normal tissue barriers. Various malignancies may also metastasize to the brain. In these instances, the brain manifestations may be overlooked since many of the obvious clinical signs are typically related to other organ systems.astrocytomaThe average age brain tumors are diagnosed in older dogs is, on average is 9.4 years but can also range between 3 months to 16 years. Most dogs diagnosed with a meningioma are 10 years of age or older. As a general rule, brain tumors progress slowly, however, an acute onset is sometimes possible. The physiological function of the affected area determines the neurological examination findings. About 75% of all brain tumors are supratentorial, causing forebrain signs. The most common abnormality in dogs is seizures. A brain tumor should be on the list of differentials for dogs 5 years and older that present for a recent onset of seizures or for other neurological signs related to the brain. Other forebrain-related symptoms include circling, pacing, aimless wandering, abnormal behavior,,blindness and aggression. Approximately 25% of brain tumors are located in the brainstem or the cerebellum. Clinical signs of tumors in this region include head tilt, leaning or falling to one side, incoordination or inability to walk, severe dullness, rapid eye movements, inability to close the eyes, abnormal eye position and occasionally head tremors.
Middle aged or older dogs may have comorbidities. In addition, a recent study showed that approximately 25% of dogs with meningiomas have multiple lesions.In order to determine if a patient is a good candidate for advanced treatment options a complete physical and neurological examination is crucial. Since many older dogs present with heart murmurs, a consultation with a cardiologist is often required to assess the risk of anesthesia. Routine blood work including CBC, platelet count, chemistry profile and urinalysis are essential to evaluate the function of vital organs such as the liver, kidney and bone marrow .It is also recommended to perform chest radiographs to check for evidence of metastatic spread of any potential brain tumor, along with an ultrasound of the abdomen to rule out concurrent disorders.An MRI is reliable for documenting the size and location of brain tumors, and can demonstrate edema formation and potential brain herniation, but does not provide a specific tissue diagnosis which is vital to obtain a sample by either a CT-guided, ultrasound-guided or surgical biopsy. Hisopathology will not only reveal the tumor type, but will also establish the grade of the tumor, which is important for treatment and prognosis.
The major goal of all of potential therapies is to prolong life as long as possible and to get as close as possible to a normal lifespan without compromising the quality of life. An additional 1-3 years of life can bring an older dog with a meningioma close to a normal lifespan. Since a long-term cure is often not the major goal, treatment strategies are not as aggressive as those used in human brain cancer treatment protocols.The purpose of surgery for canine meningioma is to obtain a complete resection including the tumor, meninges and adjacent bone structures. Unfortunately, complete resection of the tumor is not always possible. In some cases debulking (partial removal) and reduction of intracranial pressure are the goals of surgery. Healthy brain tissue should be spared as much as possible, since brain cells cannot regenerate. Since bleeding can be difficult to stop in brain tissue, damage of larger blood vessels must be avoided. Advanced equipment like the ultrasonic aspirator helps to overcome some of the difficulties of brain surgery.Potential complications following brain surgery include damage of healthy brain tissue, bleeding into the surgical site, infection, and in very rare cases an elevation in the blood sodium level of unknown cause. Life-threatening post-surgical complications are seen in under 10% of patients undergoing brain surgery at Tufts Foster Hospital for Small Animals.Conventional radiation therapy and stereotactic radiation surgery are options for tumors that are incompletely excised or inoperable. The degree of control depends largely on the total dose of radiation that is delivered to the mass. Division of the total radiation dose into small fractions reduces the risk of undesirable side effects.Chemotherapy has not proven to be very effective in the treatment of canine meningiomas. Although Hydroxyurea is thought to have activity against meningiomas, there is no published data to date. Supportive care with anticonvulsive medications and corticosteroids may help alleviate clinical signs but will not change tumor growth rate.
The outcome of the treatment of canine meningioma depends on many factors including age at diagnosis, symptoms, tumor location, size, concurrent disorders, treatment protocol, and the level of experience of the surgical and medical team. To date, no single approach has proven to be best for every situation. Typically, the longest survival time can be achieved with a combination of two or more treatment options. The best option has to be determined for each individual patient based on location of tumor, condition and age of the patient, and the owner’s expectations and financial situation. Unfortunately, most studies focus on the patient’s total survival vs. symptom-free survival time which is rarely assessed. Canine frontal lobe meningiomas are common, and are challenging to manage due to anatomical reasons which makes complete surgical removal difficult. Surgical resection alone results in a median survival time of 7 months and a combination of surgery and radiation therapy in a median of 17-18 months. For meningiomas in more surgically-accessible areas, such as, the convexities or the cerebellum,the median survival time with surgery alone is 16 months, and a combination of surgery and radiation results in a median symptom free survival time of 30 months. Reported median survival times following radiation therapy exclusively are highly variable, ranging from 12 to 24 months.In summary, clinical signs of canine cerebral meningiomas can often be alleviated for prolonged periods, providing an excellent quality of life. Tumor size and location, treatment modality, and the patient’s age and comorbidities are major determinants of outcome.