Radiotherapy of head, neck and vertebral tumours is sometimes associated with central nervous system (CNS) tissue deterioration. Postradiation lesions are often interpreted - due to their analogy in the neuroradiological image - as recurrent or new tumour. We submit an observation of 5 patients, where in 4 the postradiation necrosis mimicked a CNS tumour. Both clinical units produce oedema- tous changes, a blood-brain-barrier disturbance and necrotic changes. We compare differential diagnostic difficulties with experience reported in the literature. Radiation necrosis may be one of the possible interpretations of a progressing finding on CT or MRI. The paper should stimulate detailed retrospective analyses of radiation technique in individuals, who reacted to therapy by exaggerated tissue damage.

        Key words: CNS tumour - radiation necrosis - blood-brain-barrier - recurrent tumour - radiation encephalopathy