Anaplasic Ependymoma in a Dog

Abstract

Background: Anaplastic ependymoma is a rare primary intracranial neoplasm in dogs and cats, which originates from ependymal cells that line the ventricular system of the brain and spinal cord. Normally, this neoplasm occurs as a single, expansive mass that develops mainly in the lateral ventricles, and neurological changes are due to local tissue impairment and peritumoral tissue compression. This article reports a case of anaplastic ependymoma in a dog treated at the Veterinary Hospital of the Federal University of Mato Grosso do Sul (UFMS), emphasizing and describing the neurological signs and histopathology of this tumor.

Case: This article reports the case of a 11-year-old mongrel dog with a history of butting its head against obstacles, of compulsive walking, and altered proprioception of the right side limbs. The condition evolved to positional strabismus of the left eye, left lateral deviation of the head, vertical nystagmus, decreased level of consciousness, and constant lateral decubitus.  Due to the suspicion of intracranial neoplasia and worsening of its clinical condition, the animal was euthanized. Necropsy of its body revealed a mass of approximately 3 cm in diameter in the third ventricle (in the left lateral region). A histological examination revealed random clusters of ependymal cells with a few rosettes and pseudorosettes. The cells were cuboid to cylindrical in shape, with moderate eosinophilic cytoplasm with indistinct borders, and round to oval moderately hyperchromatic nuclei with 1-2 visible nucleoli. Based on these findings, the tumor was characterized as anaplastic ependymoma.

Discussion: Intracranial tumors occur more frequently in older animals, and usually neurological signs tend to evolve progressively. Most affected dogs are mongrels, like the dog described in this report, but Golden Retrievers, Boxers, Labrador Retrievers, German Shepherds, Bullmastiffs and Rottweillers are breeds that can also be affected by this type of tumor. The main differential diagnoses for masses in the ventricles of the brain are choroid plexus papilloma, ependymoma, medulloblastoma, epidermoid cyst or dermoid cyst.  Considered a rare tumor, ependymoma typically affects the ventricular system, which may impair CSF drainage, with consequent development of prosencephalic symptoms such as seizures and compulsive walking. The vestibular signs that were also observed were attributed to the proximity of the affected site to brainstem. Ependymomas are well-defined, soft, with a smooth surface, pale to reddish, and usually larger than 2 cm. When sectioned, they may exhibit cystic, necrotic and hemorrhagic areas. Histopathologically, they are densely cellular and highly vascularized, characteristically forming rosettes and pseudorosettes. In this reported case, the neurological signs were attributed to the presence of a tumor in the third left lateral ventricle. A definitive diagnosis can only be made based on a histopathological analysis of the tumor, using biopsy or necropsy specimens. Treatment consists of reducing the size of the tumor with chemotherapy or radiotherapy or removing it completely and controlling the side effects through palliative therapy. However, in this case, a lack of diagnostic resources such as advanced imaging and brain biopsy did not allow for the diagnosis of ependymoma in the third ventricle of the live animal, thus precluding therapeutic attempts.