A 2-year-old female spayed mixed-breed dog presented with seizures, neck pain, and vestibular ataxia. The CSF protein concentration is 187 mg/dl (normal <20) and the WBC count was 253 cells/ul with 0 RBC/ul. See the images of the CSF below.

The smears are composed mainly of lymphoid cells with few scattered lysed cells and rare erythrocytes in a light pink proteinaceous background. The lymphoid cells consist of a monotypic population of large neoplastic lymphocytes (lymphoblasts). These large cells measure 15-25 um in diameter, with a moderate amount of basophilic cytoplasm with occasionally a perinuclear clear halo, round to ovoid to occasionally indented nuclei with a finely stippled chromatin pattern and 1 or more prominent nucleoli. Occasional atypical mitotic figures are present. Microorganisms are not seen.

Microscopic interpretation:
Marked lymphocytic pleocytosis with a predominance of immature atypical lymphocytes (most likely lymphoblasts), most consistent with lymphoma.

Read about two similar cases with treatment described by clicking on the link below.