Brain Tumors in Dogs

Figure 1 - MRI and Pathology of Canine Glioblastoma Multiforme
These transverse MRI images (panels T1, T2, and T1+Gad) were obtained from a 7-year-old, spayed female Boston terrier with seizures. A large cystic mass lesion is located in the parietotemporal region of the brain and is causing significant compression of the surrounding brain tissue (arrows on top right panel). On the bottom left panel labeled T1+Gad, intravenously administered contrast material has leaked out of abnormal vasculature within the tumor, creating the appearance of a lighter (white) colored ring predominantly around the periphery of the tumor, when compared to the top left panel. This characteristic is called ring enhancement, and is a common feature in high-grade gliomas. The bottom right panel is a microscopic section from a biopsy from this high-grade tumor, which was a glioblastoma mutliforme (WHO Grade IV astrocytoma).

Brain tumors are a significant problem in the canine population, but are not often definitively diagnosed because of the need for advanced imaging (magnetic resonance imaging - MRI) studies of the brain and ultimately pathologic examination of representative brain tissue (Figure 1). Primary brain tumors can arise from any of the resident cells within the brain tissue itself, or the protective lining surrounding the brain. Brain tumors cause clinical signs primarily by compressing or invading the brain tissue. Seizures, behavioral changes, visual disturbances, and vestibular signs (vertigo) are common abnormalities observed by owners of dogs with brain tumors. Although these signs may often indicate where in the brain the problem is arising from, they are rarely specific for what disease is causing the problem.

The brain tumor clinical trials being offered at VMRCM are focused on improving the treatment of brain tumors called gliomas. Gliomas are the second most frequent type of primary canine brain tumor encountered in clinical practice, and arise from the supporting cells of the brain, namely the astrocytes (astrocytoma) and oligodendroglia (oligodendroglioma). Gliomas typically affect middle-aged to older dogs (7-10 years), and are common in short-nosed (brachycephalic) breeds of dogs, such as the Boxer, Boston Terrier, and English and French Bulldogs. The biological behavior of canine gliomas is quite diverse and currently poorly understood, but all types of gliomas include slow-growing (low-grade) and aggressive, highly malignant (high-grade) variants.