Malignant lymphoma of the meninges in two dogs

Two cases of malignant lymphoma of the leptomeninges in dogs are described. Both involved the subarachnoid space overlying the cerebrum and cerebellum and in one dog there was infiltration of neoplastic lymphocytes into the leptomeninges of the cervical spinal cord and nerve roots. These cases appeared to represent primary meningeal lymphoma, except that lymphoma was present in an ovary of one of the dogs and here the meningeal lymphocytes were demonstrated to be B cells by the peroxidase-antiperoxidase method for cytoplasmic immunoglobulin. Meningeal lymphoma, primary or metastic, is rare in dogs. The differential diagnosis is discussed and includes reticulosis, sarcomatosis of the meninges, and the diffuse spread of an oligodendroglioma in the subarachnoid space. A tentative diagnosis of meningeal lymphoma in these cases could be made by examination of the cerebrospinal fluid cells.