Diagnosis and prognosis in neuro-oncology: contribution of positron emission tomography.

Positron emission, tomography (PET) assesses the uptake and distribution of a radiopharmaceutics labelling tissue metabolism, in tumour and in presuma bly healthy brain, respectively. This technique provides data which are com plementary from those obtained with anatomical imaging (CT-scanner, MRI) an d with histology performed on a biopsy sample. The most frequently used tra cers, in neuro-oncology, are 18FDG and 11C-methionine. However, for most of the applications of this technique, the latter tracer appears to be more e ffective than the former, both from the point of view of sensitivity and sp ecificity. The main applications of PET in clinical neuro-oncology are the following: 1) when establishing the, early diagnosis of a glioma, in order to differen tiate between cell lines (astrocytoma or oligodendroglioma) and grading; 2) during the follow-up of the tumour, in order to identify progression fro m a low grade towards an anaplastic lesion; 3) after surgical removal, to exhibit some residual tumour, 4) after radiation therapy or chemotherapy, for an early assessment of the response to therapy, 5) long after treatment, to differentiate between radiation necrosis and tu mour recurrence.