FDG PET imaging in brain tumours: the WA PET/Cyclotron experience

Purpose: To determine the accuracy of FDG PET imaging in the assessment of brain tumours at our institution.

Methods: The first 49 FDG-PET scans in patients with either possible brain tumour or possible brain tumour recurrence, performed since the WA PET and Cyclotron Service became operational in 2002, were reviewed. There were 18 males and 31 females. FDG PET imaging was reported with reference to and in some instances coregistration and fusion with, the anatomic imaging. Based on the report the FDG study was classified as either positive or negative for the presence of tumour. 38 cases were included in the analysis, 21 having pathologic data and 17 with diagnostic clinical follow-up. 11 patients were excluded as they had no or inadequate follow-up data.

Results: Of the 21 cases with pathology, 18 were shown to have tumour. In the other three cases, the pathology was described as demyelinating in one, ischaemic with lymphocytic vasculitis in another and the last with white mater gliosis. Two of the three cases which where called positive on FDG imaging, the case of demyelination being a true negative. Of the 18 tumour cases there were 5 false negatives which included, one oligodendroglioma a ganglioglioma, a WHO 2 or 3 glioma and a highgrade astrocytoma and a glioblastoma. Thus of the false negatives only 2 cases can be explained by low grade pathology

17 cases were assessed by clinical follow-up. Of these cases 9 were considered positive, 8 being negative. There was one false positive in the clinical follow up group however the follow up duration was relatively short being only 4 months. There were 2 false negatives one being positive at 1 month and the second at 14 months following FDG. Sensitivity and specificity were calculated at Sens 74% and Spec 73%, PPV 87% and NPV 53%.

Conclusion: This study shows that the utility of FDG PET imaging in our hands is similar to the published literature. With a PPV of 87%, a positive FDG study indicates a high likelihood that there is brain tumour present and that it will progress.A negative study does not exclude the presence of tumour.