Pathological examination revealed aggressive infiltration of lymphocytes destroying the parenchyma, which was surrounded by a sparsely infiltrated area (Figure 2A). Infiltrating small lymphocytes were positive for CD3. The pattern of infiltration was only partially perivascular, and vessel walls were basically intact (Figure 2B). Well-formed granulomas were not observed. There was a small population of B-cells positive for CD20 or CD79a. EBER and EBNA were both negative in all of the cellular components. Neutrophils and acidophils were rarely observed. Damaged tissue contained an abundance of histiocytes, along with reactive astrocytes. MIB-1 labeling index was less than one percent.