PET/CT an Accurate Alternative to Adrenal Vein Sampling for Diagnosing Adrenal Tumors

A prospective within-patient comparison was conducted to determine whether the accuracy of postdexamethasone [¹¹C]metomidate ([¹¹C]MTO) PET/CT for diagnosing unilateral aldosterone-producing adrenal adenomas (APAs) is superior or noninferior to the accuracy of adrenal vein sampling (AVS) in predicting outcomes from unilateral adrenalectomy. The study, published in Annals of Internal Medicine, found that molecular imaging is an accurate and non-invasive alternative to AVS.

AVS has historically been the primary way of diagnosing unilateral PA, but it is invasive, difficult to perform, and has limited availability. As such, researchers from Queen Mary University of London sought to determine whether a molecular imaging diagnostic test ([¹¹C]MTO) for unilateral PA is comparable to the accuracy of AVS and whether [¹¹C]MTO is interchangeable with its longer-half-life analogue, para-chloro-2-[¹⁸F] fluoroethyletomidate ([¹⁸F]CETO).  They studied data for 169 patients aged 18 and older with primary aldosteronsim (PA) desiring surgery if unilateral PA was diagnosed between December 2016 and December 2022. The order of AVS or molecular imaging was determined by minimization. AVS was performed by one of three established radiologists and all molecular imaging scans were analyzed by a single radiologist who was blinded to the AVS result. AVS lateralization indices of less than three, three to four and greater than four were considered to indicate low, intermediate, and high probability, respectively, of unilateral PA. There were three requirements to determine high probability of unilateral PA from molecular imaging: 1) a focal adrenal nodule with characteristics of a benign adrenocortical adenoma, 2) uptake of [¹¹C]MTO into this nodule, and 3) a ratio of tumor maximum standardized uptake values (SUVmax) to contralateral gland SUVmax of more than 1.25. A multidisciplinary team reviewed and scored AVS and molecular imaging results. Thirty-one participants underwent both [¹¹C]MTO and [¹⁸F]CETO to determine if they are interchangeable procedures. The primary end point was the accuracy of [¹¹C]MTO and AVS at predicting biochemical and clinical outcomes six months after surgery in patients considered to have a high probability of unilateral PA.

The researchers found [¹¹C]MTO graded 89 of 169 (52.7%) participants as having high probability of unilateral PA compared with 78 of 169 (46.2%) participants graded as having high probability via AVS. 93 of these participants reached the primary outcome time duration of six months after surgery, and 92.3% of these participants achieved complete or partial biochemical success. They also found there was a high degree of agreement in the prediction of unilateral PA between [¹¹C]MTO and [18F]CETO.

The results suggest that [¹¹C]MTO is noninferior to AVS in diagnosing unilateral PA, providing clinicians a potential non-invasive, operator independent alternative to AVS.