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Imaging of Primary Central Nervous System Lymphoma before and after Radiotherapy

The imaging studies of seven patients (two of whom had acquired immunodeficiency syndrome) with histologically proven primary lymphoma of the central nervous system (PCNSL) were reviewed. Computed tomography (CT) and magnetic resonance imaging (MRI) scans were taken prior to and following radiotherapy. After radiotherapy, except in one case, all tumors rapidly decreased in size either partially or completely. The imaging features on MRI scans are not pathognomonic since intracerebral infections or gliomatosis cerebri may give similar findings. However, on T2-weighted images, homogeneous, slightly high-signal to isointense masses deep within the brain and in close proximity to the corpus callosum may give characteristic appearances. MRI findings assist in the differential diagnosis between PCNSL and toxoplasmosis, metastatic disease, gliomas and infarcts, especially if the tumor is situated in the brain stem and the posterior fossa. It is also useful in the follow-up of patients after radiotherapy in order to make management decisions related to adjuvant chemotherapy administration.