11C-metomidate PET-CT scanning can identify aldosterone-producing adenomas after unsuccessful lateralisation with CT/MRI and adrenal venous sampling

Evaluation of Adrenal Incidentaloma

Adrenal incidentalomas have increased due to advanced and more sensitive imaging modalities, their increased utilization, and the aging population. Most adrenal incidentalomas are nonfunctional and benign, but a subset of patients has functional and/or malignant tumors. The evaluation of patients with an adrenal incidentaloma involves addressing 2 clinical questions: (1) Is the tumor functional? (2) Is the tumor malignant? A careful history and physical examination focused on signs and symptoms of adrenal functional tumors, biochemical testing, and imaging features are the cornerstone in the evaluation of patients with an adrenal incidentaloma.

A comparison of the performance of 68Ga-Pentixafor PET/CT versus adrenal vein sampling for subtype diagnosis in primary aldosteronism

Objective

To investigate the diagnostic efficiency and prognostic value of 68Ga-Pentixafor PET/CT in comparison with adrenal vein sampling (AVS) for functional lateralization in primary aldosteronism (PA). Histology and long-term clinical follow-up normally serve as the gold standard for such diagnosis.

Methods

We prospectively recruited 26 patients diagnosed with PA. All patients underwent 68Ga-Pentixafor PET/CT and AVS. Postsurgical biochemical and clinical outcomes of patients with unilateral primary aldosteronism (UPA), as diagnosed by PET/CT or AVS, were assessed by applying standardized Primary Aldosteronism Surgical Outcome (PASO) criteria. Immunohistochemistry (IHC) was performed to detect the expression of aldosterone synthase (CYP11B2) and CXCR4.

Results

On total, 19 patients were diagnosed with UPA; of these, 13 patients were lateralized by both PET/CT and AVS, four patients were lateralized by PET-only, and two by AVS-only. Seven subjects with no lateralization on AVS and PET received medical therapy. All patients achieved complete biochemical success except one with nodular hyperplasia lateralized by AVS alone. The consistency between PET/CT and AVS outcomes was 77% (20/26). Moreover, CYP11B2-positive nodules were all CXCR4-positive and showed positive findings on PET. Patients who achieved complete biochemical and clinical success had a higher uptake on PET as well as stronger expression levels of CXCR4 and CYP11B2.

Conclusion

Our analysis showed that 68Ga-Pentixafor PET/CT could enable non-invasive diagnosis in most patients with PA and identify additional cases of unilateral and surgically curable PA which could not be classified by AVS. 68Ga-Pentixafor PET/CT should be considered as a first-line test for the future classification of PA.

Investigation and assessment of adrenal incidentalomas

With the increasing volume of diagnostic imaging undertaken in an ageing population, adrenal incidentalomas (AIs) are increasingly commonly seen. These masses are most likely to be benign, but a small proportion may be malignant. Similarly, they are usually non-functional, but ∼14% are functional, ie hormone-secreting tumours. Clinical, biochemical and radiological assessment is mandated to stratify patients into those requiring radiological surveillance, medical management or surgical intervention or who can be discharged. Mass characteristics on cross-sectional (CT/MRI) imaging influence the need for radiological surveillance. Functional tumours where excess cortisol, aldosterone or catecholamine are secreted should be excluded, with mild autonomous cortisol secretion (MACS) and primary aldosteronism (PA) as the two most common functional states. MACS and PA are associated with an increased risk of cardiometabolic disease (eg hypertension, type 2 diabetes) and cardiovascular morbidity/mortality (eg coronary heart disease). Multidisciplinary management is critical for selected cases; the majority of adrenal incidentalomas only require a single assessment.

First-in-human evaluation of [18F]CETO: a novel tracer for adrenocortical tumours

PURPOSE

[11C]Metomidate positron emission tomography (PET) is currently used for staging of adrenocortical carcinoma and for lateralization in primary aldosteronism (PA). Due to the short half-life of carbon-11 and a high non-specific liver uptake of [11C]metomidate there is a need for improved adrenal imaging methods. In a previous pre-clinical study para-chloro-2-[18F]fluoroethyletomidate has been proven to be a specific adrenal tracer. The objective is to perform a first evaluation of para-chloro-2-[18F]fluoroethyletomidate positron emission computed tomography ([18F]CETO-PET/CT) in patients with adrenal tumours and healthy volunteers.

METHODS

Fifteen patients underwent [18F]CETO-PET/CT. Five healthy volunteers were recruited for test-retest analysis and three out of the five underwent additional [15O]water PET/CT to measure adrenal blood flow. Arterial blood sampling and tracer metabolite analysis was performed. The kinetics of [18F]CETO were assessed and simplified quantitative methods were validated by comparison to outcome measures of tracer kinetic analysis.

RESULTS

Uptake of [18F]CETO was low in the liver and high in adrenals. Initial metabolization was rapid, followed by a plateau. The kinetics of [18F]CETO in healthy adrenals and all adrenal pathologies, except for adrenocortical carcinoma, were best described by an irreversible single-tissue compartment model. Standardized uptake values (SUV) correlated well with the uptake rate constant K1. Both K1 and SUV were highly correlated to adrenal blood flow in healthy controls. Repeatability coefficients of K1, SUV65-70, and SUV120 were 25, 22, and 17%.

CONCLUSIONS

High adrenal uptake combined with a low unspecific liver uptake suggests that 18F]CETO is a suitable tracer for adrenal imaging. Adrenal SUV, based on a whole-body scan at 1 h p.i., correlated well with the net uptake rate Ki.

TRIAL REGISTRATION

ClinicalTrials.gov , NCT05361083 Retrospectively registered 29 April 2022. at,  https://clinicaltrials.gov/ct2/show/NCT05361083.

Repeat Adrenal Vein Sampling in Aldosteronism: Reproducibility and Interpretation of Persistently Discordant Results

CONTEXT

The reproducibility of adrenal vein sampling (AVS) is unknown.

OBJECTIVE

This work aimed to determine reproducibility of biochemical results and diagnostic lateralization in patients undergoing repeat AVS.

METHODS

A retrospective chart review was conducted of single-center, single-operator AVS procedures at a tertiary care center. Included were patients with confirmed primary aldosteronism (PA) undergoing repeat AVS because of concerns about technical success or discordant diagnostic results. Simultaneous AVS was performed by an experienced operator using a consistent protocol of precosyntropin and postcosyntropin infusion. Among successfully catheterized adrenal veins (selectivity index ≥ 2), the correlation of the adrenalaldosterone/cortisol (A/C) ratio was measured between the first and second AVS. The secondary outcome measure was diagnostic agreement on repeat AVS lateralization (lateralization index ≥ 3).

RESULTS

There were 46 sets of AVS from 23 patients at a median of 3 months apart. There was moderate correlation in A/C ratios in the adrenal veins and inferior vena cava (Spearman r = 0.49-0.59, P < .05) pre cosyntropin. Post cosyntropin, the correlation was better (Spearman r = 0.67-0.76, P < .05). In technically successful AVS, there was moderate correlation between the repeated lateralization indices (Spearman r = 0.53, P < .05). In 15 patients in whom repeat AVS was performed because of apparent lateralization discordance with computed tomography imaging, the final diagnosis was the same in the second AVS procedure. Initial failed AVS was successful 75% of the time on repeat attempt.

CONCLUSION

Repeat AVS was feasible and usually successful when an initial attempt failed. There was modest correlation between individual repeat adrenal A/C ratios and lateralization indices when AVS was performed twice. The final lateralization diagnosis was identical in all cases. This demonstrates that AVS is a reliable and reproducible localizing test in PA.

11C-Metomidate PET/CT Detected Multiple Ectopic Adrenal Rest Tumors in a Woman With Congenital Adrenal Hyperplasia

CONTEXT

Women with congenital adrenal hyperplasia (CAH) may present with androgen excess that is difficult to control with conventional suppressive doses of glucocorticoids. Clinical management is challenging, and the woman is at great risk of developing steroid-induced complications.

PATIENTS AND METHODS

A 32-year-old woman with salt-wasting CAH due to 21-hydroxylase deficiency underwent right-sided adrenalectomy because of a large myelolipoma. Over the years, androgens became increasingly difficult to suppress on prednisolone 5 + 0 + 2.5 mg daily, and at age 39 years the left adrenal with an enlarging myelolipoma was removed. A month later serum testosterone levels had increased from 4.1 preoperatively to 18.3 nmol/L (reference 0.2-1.8 nmol/L), and adrenocorticotropin levels from 32 to 283 pmol/L (reference < 14 pmol/L). No adrenal parenchyma was visualized on computed tomography (CT). In the further search for the source of the markedly elevated testosterone, positron emission tomography (PET) was performed with 2 different tracers, 18fluorodeoxyglucose (18FDG) reflecting glucose metabolism and 11C-metomidate, an inhibitor of 11-β-hydroxylase targeting adrenocortical tissue.

RESULTS

18FDG-PET/CT with cosyntropin stimulation showed ovarian/paraovarian hypermetabolism, suggestive of adrenal rest tumors. Further characterization with 11C-metomidate PET/CT showed uptakes localized to the ovaries/adnexa, behind the spleen, and between the right crus diaphragmaticus and inferior vena cava.

CONCLUSION

Adrenal rest tumors can give rise to high androgen levels in spite of suppressive supraphysiological glucocorticoid doses. This case illustrates, for the first time, the value of 11C-metomidate PET as a sensitive method in documenting adrenal rest tumors, currently considered rare in women with CAH.

11C-metomidate PET in the diagnosis of adrenal masses and primary aldosteronism: a review of the literature

BACKGROUND

Adrenal masses are commonly encountered in clinical practice, many of whom are incidental. Identifying malignancy, and excess hormone production is essential for appropriate management. Biochemical workup and imaging tests (dedicated adrenal CT and/or MRI) are used to determine the likelihood of excessive hormone function and malignancy, respectively. However, imaging cannot provide information about function and biochemical workup cannot localize the source. Furthermore, in primary aldosteronism, adrenal vein sampling, the gold standard for lateralization, has important limitations such as the technical expertise required, the elevated costs, and potential complications. Over the last decades, there has been a renewed interest in alternative noninvasive imaging techniques that provide information about adrenal function without the need for invasive procedures. In this review, we will evaluate the evidence and the potential role of ¹¹C-metomidate as a promising positron emission tomography (PET) tracer in clinical practice.

METHODS

A review of the English literature for articles describing the use of the tracer ¹¹C-metomidate in adrenal disorders.

RESULTS

A total of 12 studies were included in the systematic review, which altogether addressed the use of ¹¹C-metomidate in adrenal masses and the application of this tracer in primary aldosteronism.

CONCLUSIONS

¹¹C-metomidate, a selective inhibitor of 11-β-hydroxylase, demonstrated a high specificity for adrenocortical tissue. In addition, ¹¹C-metomidate is correlated with this enzyme activity making it a potentially useful PET tracer for the identification primary aldosteronism, in addition to detection of adrenocortical masses.

Using microwave thermal ablation to develop a subtotal, cortical-sparing approach to the management of primary aldosteronism

Objective: To investigate the feasibility and efficacy of localized, subtotal, cortical-sparing microwave thermal ablation (MTA) as a potential curative management for primary aldosteronism. The study investigated with equal importance the selected ablation of small volumes of adrenal cortex while sparing adjacent cortex. Method: An in-vivo study was carried out in swine (n = 8) where MTA was applied under direct visualization, to the adrenal glands at 45 W or 70 W for 60 s, using a lateral, side-firing probe and a non-penetrative approach. Animals were survived for 48 h post-procedurally. Animals were investigated for markers of histological, immunohistochemical and biochemical evidence of adrenal function and adrenal damage by assessing samples drawn intra-operatively and at the time of euthanasia. Results: Selected MTA (70 W for 60 s) successfully ablated small adrenocortical volumes (∼0.8 cm³) characterized by coagulative necrosis and abnormal expression of functional markers (CYP11B1 and CYP17). Non-ablated, adjacent cortex was not affected and preserved normal expression of functional markers, without increased expression of markers of heat damage (HSP-70 and HMGB-1). Limited adrenal medullary damage was demonstrated histologically, clinically and biochemically. Conclusion: MTA offers potential as an efficient methodology for delivering targeted subtotal cortical-sparing adrenal ablation. Image-guided targeted MTA may also represent a safe future modality for curative management of PA, in the setting of both unilateral and bilateral disease.

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

OBJECTIVE

To describe clinical practice experience of ¹¹ C-Metomidate PET/CT as an adjunct to adrenal vein sampling (AVS) in the lateralization of aldosterone-producing adenomas (APA) in primary aldosteronism (PA).

CONTEXT

Accurate lateralization of APA in the setting of PA offers the potential for surgical cure and improved long-term cardiovascular outcomes. Challenges associated with AVS, the current gold standard lateralization modality, mean that only a small proportion of potentially eligible patients currently make it through to surgery. This has prompted consideration of alternative strategies for lateralization, including the application of novel molecular PET tracers such as ¹¹ C-Metomidate.

DESIGN

Clinical Service Evaluation/Retrospective audit.

PATIENTS

Fifteen individuals with a confirmed diagnosis of PA, undergoing lateralization with ¹¹ C-Metomidate PET/CT prior to final clinical decision on surgical vs medical management.

MEASUREMENTS

All patients underwent screening aldosterone renin ratio (ARR), followed by confirmatory testing with the seated saline infusion test, according to Endocrine Society Clinical Practice Guidelines. Adrenal glands were imaged using dedicated adrenal CT. ¹¹ C-Metomidate PET/CT was undertaken due to equivocal or failed AVS. Management outcomes were assessed by longitudinal measurement of blood pressure, ARR, number of hypertensive medications following adrenalectomy or institution of medical therapy.

RESULTS

We describe the individual lateralization and clinical outcomes for 15 patients with PA.

CONCLUSION

¹¹ C-Metomidate PET/CT in conjunction with adrenal CT and AVS provided useful information which aided clinical decision-making for PA within a multidisciplinary hypertension clinic.

Diagnosis and treatment of primary aldosteronism: practical clinical perspectives

Primary aldosteronism (PA), the most common form of secondary hypertension, can be either surgically cured or treated with targeted pharmacotherapy. PA is frequently undiagnosed and untreated, leading to aldosterone-specific cardiovascular morbidity and nephrotoxicity. Thus, clinicians should perform case detection testing for PA at least once in all patients with hypertension. Confirmatory testing is indicated in most patients with positive case detection testing results. The next step is to determine whether patients with confirmed PA have a disease that can be cured with surgery or whether it should be treated medically; this step is guided by computed tomography scan of the adrenal glands and adrenal venous sampling. With appropriate surgical expertise, laparoscopic unilateral adrenalectomy is safe, efficient and curative in patients with unilateral adrenal disease. In patients who have bilateral aldosterone hypersecretion, the optimal management is a low-sodium diet and lifelong treatment with a mineralocorticoid receptor antagonist administered at a dosage to maintain a high-normal serum potassium concentration without the aid of oral potassium supplements.