Background: 11C-Metomidate (MTO)-PET/CT has recently found utility as an alternative to adrenal vein sampling for lateralisation in primary aldosteronism. MTO binds with high affinity to 11b-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) and can be considered an adrenocortical-specific tracer. We and others have therefore hypothesised that combining MTO-PET/CT with 18F-FDG(FDG)-PET/CT would permit indeterminate adrenal lesions to be categorised in terms of (i) adrenocortical origin (MTO positive) or not (MTO negative) and (ii) malignant potential (as determined by extent of FDG positivity).
Method: Eight patients (4 male, 4 female) with a new indeterminate adrenal lesion were investigated using MTO-PET/CT and FDG-PET/CT (single centre, 20152019). Intensity and distribution of tracer uptake was independently assessed by two radiologists. Histological confirmation of the adrenal lesion was available for six patients.
Results: Benign and malignant lesions of adrenocortical and non-adrenocortical origin were correctly identified using dual PET studies. MTO uptake was only seen in lesions of adrenocortical origin, whereas high level FDG uptake reliably identified malignant lesions (Table 1).
|Side of lesion||Left||Left||Right||Right||Right||Left||Right||Right|
|Category||AdC Benign||Non-AdC Benign||AdC Malignant||Non-AdC Malignant||Non-AdC Malignant||Non-AdC Malignant||Non-AdC Malignant||Non-AdC Malignant|
|Key: ACA, adrenocortical adenoma; ACC, adrenocortical carcinoma; AdC, adrenocortical; FDG, 18F-FDG; GN, ganglioneuroma; Met, metastasis; MTO, 11C-metomidate; Phaeo, phaeochromocytoma; *histological confirmation of diagnosis not available; 1 patient with normal normetanephrine and borderline raised metanephrines levels.|
Conclusion: In this proof-of-concept study MTO- and FDG-PET-CT reliably distinguished between benign from malignant, and adrenocortical from non-adrenocortical, lesions. Further studies are required to confirm these findings.