[Treatment-induced tumor-like lesions in the course of neurooncological therapy]

The proper interpretation of imaging changes in the course of multimodal neurooncological therapy (neurosurgery, radiotherapy, chemotherapy, stereotactic radiosurgery) is crucial. The appearance of abnormal or new contrast-enhancing lesions does not indicate obvious tumor progression, in the contrary they are frequently induced by the oncological therapy itself. The differentiation of real tumor progression from therapy-induced lesions is essential, since the diagnosis of progressive disease results in the termination of the current regimen and initiation of second or third line therapy, if possible. The most common frequent therapy-induced tumor-like lesions include the followings: pseudoprogression seen at 1-3 months after the completion of concomittant radiochemotherapy of high-grade gliomas, real radiation necrosis which can develop even years after the completion of fractionated external beam radiotherapy of gliomas, and radiation necrosis seen after stereotactic radiosurgery delivered to metastatic brain tumors. The absorbable hemostatic materials applied to the wall of resection cavity during brain tumor surgery might cause delayed disturbancies in the blood brain barrier, inducing abnormal signal changes and contrast enhancement mimicking residual or recurrent tumor. Cerebrovascular ischemic lesions might cause cortical enhancement in the subacute stage, which may be misinterpreted as leptomeningeal tumor spread. The correct assessment of imaging findings requires special knowledge and multidisciplinary consultation, therefore the treatment and follow-up of brain tumor patients should be linked to brain tumor centers staffed by experts in the field of neurosurgery, neurooncology and brain tumor imaging.