John H. Rossmeisl DVM, MS, Diplomate ACVIM (SAIM and Neurology)
What is a Meningioma?
Meningiomas are among the most common brain tumors in dogs, accounting for about 40% of all canine primary brain tumors. Meningiomas are more common in large breed dogs, and frequently occur in dogs older than 10 years. Boxers, Golden Retrievers and Miniature Schnauzers are predisposed to the development of meningiomas. Meningiomas are classified into three types: benign (Grade I), atypical (Grade II), and anaplastic (Grade III or malignant). In dogs, the incidence of Grade I tumors is 50-60%, 40-45% for Grade II tumors, and < 5% for Grade III tumors.
The symptoms associated with brain tumors will usually reflect the location of the tumor within the brain. While the signs associated with brain tumors can often indicate where the problem is located within the brain, they are not specific for what is causing those symptoms. Thus, the symptoms caused by brain tumors can be the same as those caused by other common disorders of the brain, such as brain inflammation (encephalitis) or stroke. Seizures and behavioral changes are the most common clinical signs of tumors located in the front of the brain, while a loss of equilibrium (vertigo) is the most frequent symptom of tumors affecting the brainstem. Meningiomas also frequently cause swelling of the brain adjacent to the tumor, which can cause or contribute to symptoms.
Definitive diagnosis of any type of brain tumor can only be done following microscopic examination of tumor tissue obtained by biopsy, during surgical removal, or from a post-mortem examination. Given the non-specific nature of the symptoms associated with brain tumors, performing an MRI of the brain is the preferred method of presumptive diagnosis of brain tumors in dogs and cats. Meningiomas have some characteristic features that allow an accurate presumptive diagnosis of meningioma based on abnormalities seen on MRI (Figure 1). Meningiomas arise from cells within the lining of the surface of the brain and usually appear along the outer edges of the brain adjacent to the skull, and can form in numerous locations. The different grades of meningiomas cannot be differentiated using current MRI techniques.
There are several methods commonly used to treat brain tumors in dogs, including palliative therapies, surgery, radiation therapy, and chemotherapies. Use of various combinations of these approaches is often necessary to improve the pet’s quality of life, as well as to prolong survival.
- Palliative, or symptomatic, treatments are designed to relieve some of the secondary effects resulting from the presence of the tumor. Frequently used palliative treatments include steroids, which treat brain swelling and inflammation, and anti-convulsant drugs for those animals that are experiencing seizures. The goal of palliative treatment is to make the patient feel better, but these treatments do not usually have any specific or significant anti-cancer effects.
- Surgical removal of meningiomas is often possible, especially for those tumors located in the forebrain.
- Radiation therapy using a variety of dose prescriptions and techniques has been used safely and successfully for the treatment of meningiomas. Radiation has been shown to be beneficial if used as a primary treatment in those cases in which surgery is not possible, or in combination with surgery.
- There have been no large controlled studies clearly demonstrating the benefits of systemically administered chemotherapies to animals with meningiomas.
Dogs with meningiomas treated exclusively with palliative therapy have been shown to have median survivals in the 1-3 month range, although longer survivals can be often be noted with tumors located in the front of the brain.
Results from studies examining surgical treatment of canine meningiomas are highly variable and heavily dependent on surgeon experience and operative techniques used. However, surgical resection is generally considered beneficial, and has been associated with survivals ranging from approximately 5 to 70 months.
Radiation treatments administered to dogs as a sole primary therapy typically result in survival times ranging from 12-24 months. When radiation treatment is performed in addition to surgical resection, survivals range from 16-30 months.