Brain Neoplasms in Elderly Dogs

Background: The prevalence of intracranial neoplasms in dogs represents 2.1 to 4.0% of the cases. Brain tumors may be primary or metastatic. The objective of this study was to describe two cases of intra encephalic neoplasia in elderly dogs received for necropsy by the Veterinary Oncology Service in the Federal University of Pelotas.Cases: Case 1: A 12-year-old female canine, without breed and medium size, was received for necropsy. The animal has had behavioral changes. Macroscopic examination of the encephalus revealed asymmetry and congestion. The organs were collected and fixed in 10% formalin. In the brain cleavage we noticed an extensive brown-gray mass with reddish areas, expansive, moderately demarcated, soft to cut and discrete hydrocephalus. Serial fragments of the brain and fragments of the organs were sent for processing. The slides were stained with the hematoxylin and eosin technique for histopathological analysis. At the microscopic examination, cuboidal cells were observed in the encephalus sometimes in acinar arrangements, of extensive and very limited pattern, diagnosed as ependymoma. Case 2: It is a 15-year-old, female poodle dog, with several tumors. During necropsy multiple subcutaneous nodules, mesentery, intestinal serosa, stomach and liver were noticed. At the cut these were firm and whitish. No macroscopic changes were observed in the other organs. Fragments of organs and brain were collected and a serial section of the encephalus was performed for further processing and histological analysis. In the histopathological analysis the masses were constituted by proliferation of sometimes rounded cells, elongated, with rounded nuclei and eosinophilic cytoplasm, allowing the diagnosis of mesothelioma. The same cell pattern was observed in other organs. In the frontal cortex of the encephalus there were small foci of cells similar to those observed in the mesentery, as well as metastatic emboli in the meningeal and encephalic vessels, characterizing the diagnosis of metastatic mesothelioma.Discussion: Neoplasms of the central nervous system may be primary or metastatic. The ependymoma observed in case 1 was only diagnosed after visualization of the encephalic mass during necropsy, pointing to the importance of postmortem examination. Brain neoplasms in dogs occur with a frequency and variety similar to that of humans. Most of these are found in older dogs, and 95% of those affected are over five years of age. One situation that may occur in ependymomas is the development of obstructive hydrocephalus by the expansion of the neoplasm into the ventricular system. The animal studied in case 1 presented behavioral changes for weeks before death, and at necropsy ventricular dilation was evidenced, suggesting that hydrocephalus had occurred and the behavioral changes due to tumor localization. Metastatic brain neoplasms occur due to the hematogenous spread of many tumors. The species in which the metastatic neoplasms are most commonly described is the canine. Metastases of mesotheliomas in the central nervous system are rare, which reinforces the need for a thorough postmortem examination, as evidenced in the second case of this study, since the animal did not manifest clinically signs of neurological involvement and the metastasis was only identified microscopically by serial cuts of the encephalon. It can be concluded that detailed, systematic and serial post-mortem examination of the central nervous system should be part of the diagnostic routine even if no clinical neurological signs are evident. The reports presented here are of importance since they are considered rare diagnoses of primary and metastatic brain tumors.