Primary central nervous system lymphoma (PCNSL) mimicking a falx meningioma with increasingly massive intracerebral hemorrhage.

When using imaging to diagnose brain tumors, it is important to determine whether the tumor is intra- or extra-parenchymal. An 80-year-old man was found on magnetic resonance imaging to have an enhanced mass that appeared to be in the falx and a massive hematoma in the left frontal lobe; the provisional diagnosis was falx meningioma. However, the tumor and hematoma were found intraoperatively to be completely intraparenchymal. Additionally, the falx was intact and not adherent to brain tissue. Malignant lymphoma was diagnosed histologically on the basis of abnormal proliferation of atypical CD20-positive lymphocytes. Cerebral hemorrhage is an extremely rare presentation of primary central nervous system lymphoma. To the best of our knowledge, only 7 cases have been reported. All the reported cases had enhancement in the hematoma; however, in our case, there was definite enhancement outside the hematoma, making the correct diagnosis of lymphoma difficult.