Targeted Molecular Imaging in Adrenal Disease—An Emerging Role for Metomidate PET-CT

Abstract

Adrenal lesions present a significant diagnostic burden for both radiologists and endocrinologists, especially with the increasing number of adrenal ‘incidentalomas’ detected on modern computed tomography (CT) or magnetic resonance imaging (MRI). A key objective is the reliable distinction of benign disease from either primary adrenal malignancy (e.g., adrenocortical carcinoma or malignant forms of pheochromocytoma/paraganglioma (PPGL)) or metastases (e.g., bronchial, renal). Benign lesions may still be associated with adverse sequelae through autonomous hormone hypersecretion (e.g., primary aldosteronism, Cushing’s syndrome, phaeochromocytoma). Here, identifying a causative lesion, or lateralising the disease to a single adrenal gland, is key to effective management, as unilateral adrenalectomy may offer the potential for curing conditions that are typically associated with significant excess morbidity and mortality. This review considers the evolving role of positron emission tomography (PET) imaging in addressing the limitations of traditional cross-sectional imaging and adjunctive techniques, such as venous sampling, in the management of adrenal disorders. We review the development of targeted molecular imaging to the adrenocortical enzymes CYP11B1 and CYP11B2 with different radiolabeled metomidate compounds. Particular consideration is given to iodo-metomidate PET tracers for the diagnosis and management of adrenocortical carcinoma, and the increasingly recognized utility of 11C-metomidate PET-CT in primary aldosteronism.

11C‐Metomidate PET/CT is a useful adjunct for lateralization of primary aldosteronism in routine clinical practice

“…Surgery resulted in partial cure with improved BP on fewer agents (from six preoperatively to two postoperatively) and maintained at >2 years (Table ). Biochemistry remains suggestive of persistent PA, albeit confounded by beta‐blocker therapy …”

“…Pre‐imaging suppression of background adrenal CYP11B1 using low‐dose dexamethasone enhances the selectivity of metomidate for CYP11B2 and improves sensitivity and specificity for detection of unilateral APAs . Accordingly, 11 C‐Metomidate PET/CT has been proposed as an adjunctive or alternative lateralization modality in individuals for whom AVS and/or adrenal CT has not provided a clear answer in the clinical setting …”

“…22 Accordingly, 11 C-Metomidate PET/CT has been proposed as an adjunctive or alternative lateralization modality in individuals for whom AVS and/or adrenal CT has not provided a clear answer in the clinical setting. [22][23][24][25] Since 2014, we have used 11 C-Metomidate PET/CT as an adjunct and/or alternative lateralization modality for PA within the setting of a multidisciplinary hypertension clinic. Herein, we report our experience of using this imaging modality to guide clinical decision-making in routine clinical practice.…”

Accuracy of adrenal imaging and adrenal venous sampling in diagnosing unilateral primary aldosteronism

“…Furthermore, the interpretation of its results can be challenging [6,20]. The development of techniques to characterize phenotypes of primary aldosteronism based on the use of biomarkers or the availability of C-metomidate PET-CT may help to identify patients who will benefit from AVS in the future [25][26][27]. Moreover, major differences still exist regarding the standardization of AVS such as sequential or simultaneous catheterization or the significance of ACTH stimulation [20,23,24].…”

PET Imaging for Endocrine Malignancies: From Woe to Go

“…Adrenocortical adenomas and some adrenocortical carcinomas can also be imaged by radiolabeled metomidate, which targets the adrenocortical enzymes CYP11B1 and CYP11B2. This approach is increasingly recognized for its ability to localize aldosterone-producing adrenocortical adenoma, which can be millimetric in size (6). Although 11 C-metomidate has been the main agent in this regard, an iodinated ligand has also been described, opening the way for theranostic application (7).…”