Gangliogliomas are thought to originate from glioneural precursor cells, like neural stem cells and are not usually malignant, but if they are, they evolve toward glioblastoma or primitive neuroectodermal tumor formation.
Gangliogliomas form part of the heterogeneous group of brain tumors which contains neuronal components such as dysembryoplastic neuroepithelial tumors, medulloblastomas, supratentorial primitive neuroectodermal tumors, and medulloepitheliomas. If there are neuronal cells alone, it is named gangliocytoma. The glial component is ordinarily astrocytic, but rarely, it may have oligodendroglial differentiation.
The most frequent location of gangliogliomas is the cerebrum, but it can develop elsewhere in the central nervous system, including the brainstem, cerebellum and spinal cord locations.
Affected dogs usually present with acute onset neurological or visual symptoms such as ataxia, blindness, depressed mentation and intermittent seizures. Both young and old dogs have been affected.
Diagnosis requires specialist imaging such as CT or MRI, with biopsy taken during exploratory craniotomy. Gangliogliomas are hypo or isointense in T1-weighted images and hyperintense in the T2-weighted MRI sequence. In general, although not as a rule, heterogeneous or at least some degree of contrast enhancement is seen in imaging studies.
Histopathologically, these tumors consist of irregularly arranged well-differentiated neuronal and glial cells, and multifocal mineral deposits. Neuronal cells have large clear nuclei and various amount of Nissl substances in the cytoplasm.
The current WHO histologic classification system differentiates the primarily neuroblastic olfactory neuroblastoma (esthesioneuroblastoma) and the more differentiated gangliocytomas and gangliogliomas. Gangliocytomas are an almost uniform proliferation of well-differentiated neuronal cells, whereas gangliogliomas include an additional population of neoplastic glial cells.
Immunostaining for glial fibrillary acidic protein, S-100, neurofilament, microtubule-associated protein-2 and neuron-specific enolase are usually positive.
The recommended treatment for gangliogliomas is surgical excision.
Treatment is usually curative, but adjunct radiation therapy is recommended to prevent recurrence. Although the results of radiotherapy for gangliogliomas are not well established, it is generally used for patients with postoperative residual tumor, in cases with malignant degeneration and in case of recurrence, principally if another surgical resection is not possible.
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