Is there a place for FET PET in the initial evaluation of brain lesions with unknown significance?

The aim of this study was to evaluate the clinical value of the use of O-(2-[18F]fluoroethyl)-l-tyrosine (FET) positron emission tomography (PET)/computed tomography (CT) in patients of a neurological clinic for evaluation of brain lesions newly diagnosed by magnetic resonance imaging (MRI). We evaluated 88 patients (44 women and 44 men) with a mean age of 50 ± 19 years who were sent consecutively for evaluation of an intracerebral mass or lesion observed by MRI from 2006 to 2008. Hospitalization was necessary due to neurological clinical symptoms. Images were obtained by PET/CT 30 min after i.v. injection of 185 MBq FET. Coregistration with MRI was done by HERMES workstation. FET uptake above the cortical level was observed in 60 patients. Neurosurgery was performed in 60 patients (51 with FET-positive imaging); 36 high-grade and 19 low-grade tumours were verified histologically. The sensitivity of FET PET for high-grade tumours (WHO III-IV) was 94% in this setting. Among the low-grade brain tumours (WHO I-II) 13 of 19 were FET positive, which indicates a sensitivity of 68%. Five of ten (50%) astrocytomas I and II could not be visualized by FET. Histological data were not provided for 28 of 88 patients, so the diagnostic approach is based upon longitudinal observation. Radiological and/or clinical control was done at a median of 7 months later. Three patients (all FET positive) died a few months after the examination because of rapid progression of the malignant brain tumour. A malignant entity could be excluded in the other 25 patients. Considering the whole cohort of 88 patients, 43 patients with malignant tumour could be identified, including high-grade glioma, intracerebral lymphoma (n = 1) and metastasis (n = 3). The sensitivity of FET PET for detecting a malignant tumour entity was 93%. We observed two false-positive cases with postischaemic lesions. Remarkably, the two patients with cerebral gliomatosis were false-negative on FET PET imaging. The negative predictive value for a malignant entity was calculated to be 89%. Our results indicate a high sensitivity of FET PET for detecting high-grade glioma in patients with neurological symptoms and recently observed brain lesions by MRI. In the setting of evaluating new brain lesions of unknown significance via FET PET a negative image can encourage a wait and see strategy - of course in accordance with the clinical picture and morphological imaging. (orig.)