Brain: Glioma, poorly differentiated, malignant
This dog has a malignant glioma. Gliomas are common in the dog, especially in certain dog breeds (brachycephalic breeds are overrepresented as well as golden retriever). The incidence of intracranial neoplasia in the dog, based on necropsy studies, is approximately 2-5% with gliomas representing approximately 40% of the total number of cases. Histologically, oligodendrogliomas outnumber astrocytomas when large necropsy studies are performed even though some older studies seem to suggest that their numbers are roughly equal. Recent advanced immunohistochemical and molecular studies have confirmed that oligodendrogliomas outnumber the cases of astrocytoma.
The grading scheme for veterinary gliomas is poorly defined and dated and increasing reliance is being given to the human World Health Organization grading system. In this grading system there are four grades of astrocytoma (ranging from lowest grade (grade I; pilocytic astrocytoma) to grade IV (glioblastoma)). Oligodendrogliomas are graded either as a grade II or grade III with the higher grade reserved for cases with glomeruloid blood vessels and serpiginous tracts of necrosis. Although this case lacks glomeruloid vasculature and tracts of necrosis, it has a high mitotic rate and is quite invasive highlighting its aggressive nature. This case is a good example to not overly rely on the human criteria for diagnosing canine gliomas. While there is some overlap, a true veterinary grading scheme is needed.
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