18F-FDG PET/CT in the characterization and surgical decision concerning adrenal masses: a prospective multicentre evaluation.

PURPOSE: This prospective multicentre study assesses the usefulness of FDG PET/CT in characterizing and making the therapeutic decision concerning adrenal tumours that are suspicious or indeterminate in nature after conventional examinations (CE).

METHODS: Seventy-eight patients (37 men, 41 women, 81 adrenal lesions) underwent FDG PET/CT after CE including CT scan, biological tests and optionally (131)I-metaiodobenzylguanidine (MIBG) and/or (131)I-norcholesterol scans. FDG adrenal uptake exceeding that of the liver was considered positive. PET results were not decisive. Surgery was discussed when at least one of the following criteria was found during CE: size >3 cm, spontaneous attenuation value >10 HU, heterogeneous aspect, abnormal MIBG or norcholesterol scan or hormonal hypersecretion.

RESULTS: Following the gold standard (histology analysis or >or=9 months follow-up), 49 lesions potentially qualified for surgery (malignant = 27, benign secreting = 22) and 32 benign non-secreting lesions did not. PET was negative in 97% of non-surgical lesions and positive in 73% of potentially surgical ones which included all the malignant lesions, except 3 renal cell metastases, and 12 of 22 benign secreting lesions. The negative predictive value for malignancy was 93% (41/44) and positive predictive value for detecting surgical lesions was 97% (36/37). A high FDG uptake (maximum standardized uptake value >or= 10) was highly predictive of malignancy.

CONCLUSION: Adrenal FDG uptake is a good indicator of malignancy and/or of secreting lesions and should lead one to discuss surgery. If there is no prior history of poorly FDG-avid cancer, the absence of FDG uptake should avoid unnecessary removal of benign adrenal lesions.