The role of PET-FDG when there is diagnostic doubt concerning relapse of radionecrosis of cerebral tumours

Introduction. Although CT and MR are sensitive techniques for the detection of cerebral rumours, both have limitations in distinguishing between tumour relapse (TR) and post-treatment radio necrosis (RN). Patients and methods. In this study we have determined the usefulness of metabolic imaging with PET-FDG in such situations. We assessed 70 patients with CNS tumours (22 low grade astrocytomas, 25 high grade astrocytomas, 3 oligodendrogliomas, 13 metastatic tumours and 7 other tumours. All had been treated with radiotherapy and other treatments such as radiosurgery, chemotherapy or different types of surgery, and presented clinical pictures which made it necessary to decide the differential diagnosis of relapse or radionecrosis. Results. In the PET-FDG study visual and semiquantitative analysis was done by SUV (Standardized Update Value). Confirmation of the findings was obtained in 44 cases (24 TR and 20 RN). MR was doubtful or inconclusive in most cases, whilst with PET correct diagnosis was made in all cases. Conclusions. Metabolic imaging with PET-FGD is better than anatomo-structural imaging techniques for differential diagnosis between tumour relapse and radionecrosis in CNS tumours which have been treated. Prospective studies are necessary for evaluation of SUV as a factor for prognosis of survival [REV NEUROL 1998, 27: 447-52].