This study aimed to analyse the characteristics of adrenal masses visible in the computerised tomography (CT) scans which have been also evaluated by 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography ( 18F-FDG PET), and to characterise the features of 18F-FDG PET scans associated with various adrenal endocrine tumours, especially benign functional tumours. 18F-FDG PET scans of 105 patients with adrenal masses on the CT scan were analysed. Positive uptakes in the 18F-FDG PET scans were seen in 60 malignant tumours (54 metastasic lesions, six primary adrenal cancers) and seven benign tumours. The positive predictive value of 18F-FDG PET imaging to characterise an adrenal mass as a malignant tumour was 90%; the corresponding negative predictive value to rule out malignancy was also 90%. Benign adrenal tumours were smaller than that of malignant lesions (p < 0.05). The mean standardised uptake value max (SUVmax) of the metastatic lesions [8.4 ± 6.5 (μCi/g)/μCi/kg] was significantly higher than that of the benign adrenal tumours [2.4 ± 1.2 (μCi/g)/μCi/kg, p < 0.001]. Examination of only the primary adrenal lesions revealed that all adrenocortical carcinomas, two of three cases of pheochromocytomas, three of five neuroblastomas and two of four cases of primary aldosteronism showed positive 18F-FDG uptake. In conclusion, for patients presenting adrenal masses with a high probability of malignancy, 18F-FDG PET can be used to differentiate malignant from benign adrenal lesions. However, the 18F-FDG PET uptake did not show an always consistent pattern for endocrine tumours, which was probably due to the variability inherent in 18F-FDG uptake. This study suggests that 18F-FDG PET scanning can offer supporting data to localise and characterise adrenal tumours.
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