CNS microgliomatosis: pathological findings in a dog

AIM OF THE STUDY: To characterize a case of multifocal microgliomatosis (MCGs) in a dog. MCGs is a CNS tumor of the white matter described in humans and dogs. In the WHO classification MCGs has been included among hystiocytic disorders. However, it\u2019s derivation from the phagocytic microglia has never been fully demonstrated. MATERIALS AND METHODS: A 13 years old, male castrated, Boxer presented with ataxia and behavioural disorders progressing into seizures. Thomograpy revealed two lesions in the left and right cerebral emyspheres. The dog was humanely killed, the brain was removed and examined grossly and microscopically. Immunohistochemistry with anti-canine CD18 and CD45RA and antibodies recognizing vimentin, cytokeratin(AE1/AE3), GFAP, S-100, NSE, CD3 and CD79a was performed. RESULTS: Gross CNS findings were unremarkable. Histology revealed a multifocal mixed proliferative disorder substituting and blending into the white matter of composed of short interlacing and arborizing bundles of atypical spindle cells admixed with gitter cells, mature lymphocytes and granulocytes. No ground substance was present. No angiocentric pattern was evidenced. Spindle cells were vimentin and CD18 positive suggesting a leukocyte origin. All other markers were negative excluding the differential diagnoses such as lymphoma, meningioma, astrocytoma and neuroendocrine tumors. CD18 positive gitter cells and neutrophils were evidenced. Lymphocytes within lesion were mostly CD3 positive mature T cells. CONCLUSION: Our findings suggest tha MCGs is an immunoproliferative disorder resembling the mixed patter of reactive hystiocytoses where the spindle cells bear a phenotype indicative of a leukocyte (non-lymphoid) origin most likely of the CNS microglia