An instructive false diagnosis: steroid-induced complete remission of a CNS tumor--probably lymphoma.

In recent years the incidence of primary cerebral lymphomas has increased. Diagnosis by imaging techniques (CCT, angiography, MRT) and stereotactic biopsy are considered as reliable diagnostic tools. Therapeutically a combination of radio-, steroid- and chemotherapy is recommended. We report a case of space-occupying CNS lesion in which the radiopaque enhancing process completely disappeared after biopsy and steroid therapy. A year later the tumor recurred on the other side and again regressed after steroid therapy. The first biopsy showed signs of a papillar tumor, so a choroid plexus papilloma was suspected. On examination of the treatment history, however, this diagnosis had to be revised. A primary CNS lymphoma seems most probable. The phenomenon of a tumor remission under steroid administration and the problems related to the differential diagnosis are discussed.