Endocrine Abstracts

Background/aims/method: Evaluation/management of adrenal incidentalomas (AI) is an increasingly prevalent challenge. CT/MRI characteristics may be useful in determining whether a lesion is a benign adenoma and forthcoming ESE-ENSAT guidance suggests a role for ¹⁸F-FDG-PET/CT in distinguishing benign vs malignant lesions. We have previously demonstrated the utility of ¹¹C-metomidate (MTO), which binds CYP11B1/B2, in localising aldosterone-producing adenomas. A proposed European study (FAMIAN) suggests combining ¹⁸F-FDG-PET/CT with 131-iodometomidate imaging to distinguish tissue of adrenocortical origin as well as malignancy. In support of this hypothesis, we have used this dual imaging approach, with ¹¹C-MTO-PET/CT in conjunction with ¹⁸F-FDG-PET/CT, to investigate three patients with indeterminate adrenal pathology.

Results: (1) Double negative MTO and FDG in a benign ganglioneuroma. A 66-year-old woman presented with a non-functioning right AI (40 mm, heterogeneous features on CT, Fig. 1A), which was neither avid for FDG (1B) nor MTO (1C). She elected to have surgery; a benign ganglioneuroma (non-adrenocortical) was confirmed by histology.

(2) Double positive MTO and FDG in metastatic adrenocortical carcinoma (ACC). A 65-year-old woman with a history of right adrenalectomy (ACC) and liver lobectomy (solitary ACC metastasis) ten years previously, presented with tissue in the right adrenal bed/liver. This was avid for both FDG (suggesting malignancy, Fig. 2A) and MTO (suggesting adrenocortical origin, 2B). The diagnosis of recurrent ACC was supported.

(3) Positive FDG and negative MTO in primary adrenal lymphoma. A 66-year-old man presented with a non-functioning 30 mm right AI with indeterminate CT characteristics (baseline Hounsfield Units 40, Fig. 3A) which was FDG-avid (3B) but MTO-negative, with the adjacent normal adrenal showing physiological MTO uptake (3C). Histology demonstrated a rare primary adrenal lymphoma (non-adrenocortical).

Conclusions: Combining FDG and metomidate PET-CT can distinguish benign from malignant adrenal lesions and determine whether they are of adrenocortical origin. This novel approach may thus inform management in cases of indeterminate adrenal pathology.