Figure 7. Dural (subdural) lymphoma. Operative photograph shows the dura mater (arrows). Under this tough connective tissue membrane is a soft cream-colored mass of lymphoma cells. The next membrane layer is the arachnoid, and much of the lymphoma is above it. Note, however, the few small areas with milky or cloudy discoloration, which can be seen through the arachnoid (arrowheads): These areas are subarachnoid lymphoma. Extraaxial lymphoma, such as this case, is almost invariably metastatic to the CNS, whereas primary lymphoma is typically intraaxial within the brain.