The clinical consequences of functional adrenal uptake in the absence of cross-sectional mass on FDG-PET/CT in oncology patients

Abstract

Purpose: Oncology patients undergoing positron emission tomography/computed tomography (PET/CT) occasionally show discrete adrenal [18F]-fluorodeoxyglucose (FDG) uptake without an associated nodule on CT, leaving the clinician uncertain about the need to proceed with biopsy or surgical referral. This study aimed to identify the prevalence of this radiological finding and to evaluate the effectiveness of FDG uptake values in risk stratification for adrenal metastasis.

Methods: From 2014 to 2015, oncology patients who underwent FDG-PET/CT and demonstrated elevated FDG uptake in the adrenal gland without discrete nodularity on cross-sectional imaging were included in a retrospective cohort analysis. Clinical records and FDG-PET/CT scans were reviewed for clinicopathological data, follow-up data, SUVmax (highest SUV of either adrenal gland), and SUVratio (SUVmax/background liver uptake). A receiver operating characteristic analysis was conducted to evaluate the associations between SUV values and the progression to adrenal metastasis.

Results: Of 3040 oncology patients who underwent FDG-PET/CT scans, 92 (3.0%) showed elevated adrenal uptake without associated mass. From the final study cohort of 66 patients with comprehensive follow-up data, 5 patients (7.6%) developed evidence of adrenal metastasis. At SUVmax < 3.25 (AUC = 0.757) and SUVratio < 1.27 (AUC = 0.907), 34.8% and 60.6% of patients could be excluded with 100% negative predictive value, respectively.

Conclusions: Thresholds of SUVmax and SUVratio identified a significant proportion of patients who did not develop adrenal metastasis. In oncology patients who demonstrate increased adrenal FDG uptake without a discrete lesion on FDG-PET/CT, quantitative uptake values may be useful in selecting those not at risk of developing adrenal metastatic disease.

Keywords: Adrenal metastasis; Computed tomography; Positron emission tomography; Standardized uptake value; Tumor staging.