Brain Tumors in Pets
Tumors within the skull come in many shapes and sizes. In the veterinary world, unlike the human world, we rarely have a confirmed diagnosis from a biopsy. Without extensive surgery, very specialized equipment would be required and is just too cost prohibitive in most veterinary settings. Instead, we often rely on advanced imaging like magnetic resonance imaging (MRI) or computed tomography (CT). While these tests are not perfect for diagnosing these tumors, they tend to give us a very strong idea about the type of tumor we are seeing. Meningiomas, gliomas and pituitary tumors each have a unique look and this helps us to distinguish between them. The different types of tumors may require different treatment modalities and carry a different prognosis.
MRI is considered the best test for diagnosing brain tumors in dogs. This test uses very strong magnets to alter the “spin” of the cells. Different cell types have different changes and this helps to tell one type from another. While people are usually awake for these tests, our pets need to be anesthetized so that they remain perfectly still. It is not uncommon for this test to require more than an hour of anesthesia time. There are very few facilities that have MRI available within the veterinary community so it may be necessary to have this test done off site.
While CT scans of the brain are not as sensitive as MRI for soft tissues, they often will reveal changes inside the brain quite well. CT scans are considered better for looking at lesions in the bone and are required for radiation treatment planning in many cases. Pets need to be anesthetized for this procedure as well, again, so that they remain perfectly still. If the CT scan is to be used for stereotactic radiotherapy planning, a device to immobilize the patient so they remain in the same exact position on the CT table and the treatment table may be required. CT scans are often completed in a much shorter amount of time, typically under 30 minutes.
Brain tumors in dogs and cats typically fall into one of three categories. Meningiomas are tumors of the covering of the brain or spinal cord. These tumors can occur anywhere along the outside of the brain or between the two hemispheres along the falx cerebri. Changes that are often seen with dogs and cats with meningiomas include seizures, circling, or a change in attitude or mentation. It is more common for cats to have a meningioma in the cranial (front) and dorsal (top) part of the brain and they are often more amenable to surgery because of this. Gliomas are tumors of the brain tissue itself. Gliomas can occur anywhere within the brain. While these tumors can cause seizures, often mentation changes or changes in the fine motor control are seen. Pituitary tumors affect the pituitary gland. This gland lies within the floor of the skull below the brain. The pituitary gland is involved with the endocrine function in mammals. The endocrine system controls many of the hormones that regulate our normal body functions. Pituitary tumors in dogs can lead to Cushing’s Disease (hyperadrenocorticism). These dogs produce too much endogenous steroid and are often pot-bellied, losing hair in a symmetrical pattern on their bodies, have thin skin, and have changes in the bloodwork including dramatic elevations in the alkaline phosphatase. Cats with pituitary tumors may develop acromegaly. This condition leads to the production of too much growth hormone. Acromegalic cats often start to grow (even later in life) and have classic features like lengthening of the lower jaw and uncontrolled diabetes.
If the tumor cannot be surgically removed, radiation therapy is the next best option. Conventionally fractionated radiation therapy (CFRT) has been used for many years for these tumors. With this treatment, the animals come in daily for about 3 weeks and receive a treatment each day. The side effects are minimal with this treatment but it does require lots of visits and lots of anesthesia.
Recently, Arizona Veterinary Oncology added the ability to perform stereotactic radiosurgery on not only brain tumors, but many other tumor types as well. This type of radiation allows us to deliver a much more precise beam of radiation to the tumor while doing a better job of sparing the normal tissues. This allows treatment to be done in a smaller number of treatments, meaning less anesthesia for your pet as well. Since the radiation does not affect the normal tissues, we also do not see the side effects typically associated with radiation therapy (hair loss, blister like lesions of the skin). The larger doses that can be delivered hopefully will lead to longer survival times for these patients too.
Chemotherapy has rarely been used in animals for brain tumors. The brain is very good at preventing “outsiders” from getting in. As such, many of our chemotherapy medications are not able to penetrate the brain. CCNU (Lomustine) is one chemotherapy that is believed to be able to get into the brain and is sometimes recommended as one piece of the treatment for meningiomas.
With the advanced treatment options, only available at our hospital, the future seems a little brighter for dogs and cats with brain tumors.