PRIMARY ENCEPHALIC PLASMA-CELL TUMOR IN A DOG

A 5-year-old female spayed Spitz dog had a 5-week history of right hea d tilt, seizures, and progressive quadriplegia. Analysis of cerebrospi nal fluid revealed 27,600 white blood cells per microliter with 63% mo nonuclear phagocytes, 27% lymphocytes, 6% neutrophils, 3% plasmacytoid cells, and 1% eosinophils, and over 2000 mg/dl protein. On contrast-e nhanced magnetic resonance images, a focal 1-cm oval lesion was identi fied in the right ventral brainstem. There was also marked contrast en hancement of the meninges in the following areas: surrounding the brai nstem, outlining cerebellar folia, along the ventral floor of the brai n and extending to the falx cerebri, and partially outlining the left frontal lobe. At necropsy, the areas of contrast enhancement correspon ded to the presence of compact cellular sheets of pleomorphic, anisocy totic, oval to polygonal neoplastic cells with plasmacytoid differenti ation. The smaller of these plasmacytoid cells stained predominantly f or cytoplasmic immunoglobulin A using immunoperoxidase methodology. Ul trastructurally, the neoplastic cells had morphologic features typical of plasma cells, with large amounts of predominantly rough endoplasmi c reticulum with variably prominent Golgi formation. This is the first report of a canine primary intracranial malignant plasma cell tumor.