Analysis of adrenal masses by 18F-FDG positron emission tomography scanning

Radiopharmaceuticals for Treatment of Adrenocortical Carcinoma

Adrenocortical carcinoma (ACC) represents a rare tumor entity with limited treatment options and usually rapid tumor progression in case of metastatic disease. As further treatment options are needed and ACC metastases are sensitive to external beam radiation, novel theranostic approaches could complement established therapeutic concepts. Recent developments focus on targeting adrenal cortex-specific enzymes like the theranostic twin [123/131I]IMAZA that shows a good image quality and a promising therapeutic effect in selected patients. But other established molecular targets in nuclear medicine such as the C-X-C motif chemokine receptor 4 (CXCR4) could possibly enhance the therapeutic regimen as well in a subgroup of patients. The aims of this review are to give an overview of innovative radiopharmaceuticals for the treatment of ACC and to present the different molecular targets, as well as to show future perspectives for further developments since a radiopharmaceutical with a broad application range is still warranted.

Adrenal functional imaging - which marker for which indication?

PURPOSE OF REVIEW

In recent years, a broad spectrum of molecular image biomarkers for assessment of adrenal functional imaging have penetrated the clinical arena. Those include positron emission tomography and single photon emission computed tomography radiotracers, which either target glucose transporter, CYP11B enzymes, C-X-C motif chemokine receptor 4, norepinephrine transporter or somatostatin receptors. We will provide an overview of key radiopharmaceuticals and determine their most relevant clinical applications, thereby providing a roadmap for the right image biomarker at the right time for the right patient.

RECENT FINDINGS

Numerous radiotracers for assessment of adrenal incidentalomas ([18F]FDG; [123I]IMTO/IMAZA), ACC ([123I]IMTO/IMAZA; [18F]FDG; [68Ga]PentixaFor), pheochromocytomas and paragangliomas ([123I]mIBG; [18F]flubrobenguane; [18F]AF78; [68Ga]DOTATOC/-TATE), or primary aldosteronism ([11C]MTO, [68Ga]PentixaFor) are currently available and have been extensively investigated in recent years. In addition, the field is currently evolving from adrenal functional imaging to a patient-centered adrenal theranostics approach, as some of those radiotracers can also be labeled with ß-emitters for therapeutic purposes.

SUMMARY

The herein reviewed functional image biomarkers may not only allow to increase diagnostic accuracy for adrenal gland diseases but may also enable for achieving substantial antitumor effects in patients with adrenocortical carcinoma, pheochromocytoma or paraganglioma.

Efficacy of PET-CT in the prediction of metastatic adrenal masses that are detected on follow-up of the patients with prior nonadrenal malignancy: A nationwide multicenter case-control study

Metastasis is the second most common type of adrenal gland mass. In patients undergoing follow-up for nonadrenal malignancy, adrenalectomy is performed when metastasis to adrenal gland is suspected on the basis of positron emission tomography-computed tomography (PET-CT) imaging. This study investigated the efficacy of PET-CT in the discrimination of metastatic lesions from nonmetastatic lesions in the adrenal glands. In this multicentric study, data was collected from enrolled centers. Forty-one patients who underwent surgery for suspected adrenal metastases were evaluated retrospectively. The following data types were collected: demographic, primary tumor, maximum standardized uptake value of adrenal mass (a-SUVx) and detectability in computed tomography and/or magnetic resonance imaging, and specimen size and histopathology. Six patients were excluded due to unavailability of PET-CT reports and 4 for being primary adrenal malignancy. The rest were divided into 2 groups (metastatic: n = 17, 55% and nonmetastatic: n = 14, 45%) according to histopathology reports. There was no statistical difference between the analyzed values, except the a-SUVx (P < .05). The a-SUVx cutoff value was defined as 5.50 by receiver operating characteristic curves and compared with literature. There was no statistical difference when each group was divided as low and high (P > .05). It was found that PET-CT was able to discriminate metastatic lesions from primary benign lesions (P = .022). PET-CT can discriminate primary benign lesions and metastatic lesions by cutoff 5.5 value for a-SUVx.

Adrenal functional imaging

Given the more widespread use of conventional imaging techniques such as magnetic resonance imaging or computed tomography, recent years have witnessed an increased rate of incidental findings in the adrenal gland and those adrenal masses can be either of benign or malignant origin. In this regard, routinely conducted morphological imaging cannot always reliably distinguish between cancerous and noncancerous lesions. As such, those incidental adrenal masses trigger further diagnostic work-up, including molecular functional imaging providing a non-invasive read-out on a sub-cellular level. For instance, [¹⁸F]FDG positron emission tomography (PET) as a marker of glucose consumption has been widely utilized to distinguish between malignant vs benign adrenal lesions. In addition, more adrenal cortex-targeted radiotracers for PET or single photon emission computed tomography have entered the clinical arena, e.g., Iodometomidate or IMAZA, which are targeting CYP11B enzymes, or Pentixafor identifying CXCR4 in adrenal tissue. All these tracers are used for diagnosing tumors deriving from the adrenal cortex. Furthermore, radiolabeled MIBG, DOPA, and DOTATOC/-TATE are radiotracers that are quite helpful in detecting pheochromocytomas originating from the adrenal medulla. Of note, after having quantified the retention capacities of the target in-vivo, such radiotracers have the potential to be used as anti-cancer therapeutics by using their therapeutic equivalents in a theranostic setting. The present review will summarize the current advent of established and recently introduced molecular image biomarkers for investigating adrenal masses and highlight its transformation beyond providing functional status towards image-guided therapeutic approaches, in particular in patients afflicted with adrenocortical carcinoma.

How to Differentiate Benign from Malignant Adrenocortical Tumors?

Simple Summary

Adrenocortical carcinoma is a rare cancer with a poor prognosis. Adrenal tumors are, however, commonly identified in clinical practice. Discrimination between benign and malignant adrenal tumors is of great importance to determine the appropriate treatment and follow-up strategy. This review summarizes the current diagnostic strategies and challenges to distinguish benign from malignant adrenal lesions. We will focus both on radiological and biochemical assessments, enabling diagnosis of the adrenal lesion preoperatively, and on histopathological and a wide variety of molecular assessments that can be done after surgical removal of the adrenal lesion. Furthermore, new non-invasive strategies such as liquid biopsies, in which blood samples are used to study circulating tumor cells, tumor DNA and microRNA, will be addressed in this review.

Abstract

Adrenocortical carcinoma (ACC) is a rare cancer with a poor prognosis. Adrenal incidentalomas are, however, commonly identified in clinical practice. Discrimination between benign and malignant adrenal tumors is of great importance considering the large differences in clinical behavior requiring different strategies. Diagnosis of ACC starts with a thorough physical examination, biochemical evaluation, and imaging. Computed tomography is the first-level imaging modality in adrenal tumors, with tumor size and Hounsfield units being important features for determining malignancy. New developments include the use of urine metabolomics, also enabling discrimination of ACC from adenomas preoperatively. Postoperatively, the Weiss score is used for diagnosis of ACC, consisting of nine histopathological criteria. Due to known limitations as interobserver variability and lack of accuracy in borderline cases, much effort has been put into new tools to diagnose ACC. Novel developments vary from immunohistochemical markers and pathological scores, to markers at the level of DNA, methylome, chromosome, or microRNA. Molecular studies have provided insights into the most promising and most frequent alterations in ACC. The use of liquid biopsies for diagnosis of ACC is studied, although in a small number of patients, requiring further investigation. In this review, current diagnostic modalities and challenges in ACC will be addressed.

Diagnostic accuracy of 18F-FDG PET or PET/CT for the characterization of adrenal masses: a systematic review and meta-analysis

OBJECTIVE

We aimed to explore the role of the diagnostic accuracy of ¹⁸F fluodeoxyglucose PET (¹⁸F-FDG PET) or PET/CT for characterization of adrenal lesions through a systematic review and meta-analysis.

METHODS

The MEDLINE, EMBASE, and Cochrane Library database, from the earliest available date of indexing through 30 April 2017, were searched for studies evaluating the diagnostic performance of ¹⁸F-FDG PET or PET/CT for characterization of adrenal lesions. We determined the sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR + and LR-), and constructed summary receiver operating characteristic curves.

RESULTS

Across 29 studies (2421 patients), the pooled sensitivity for ¹⁸F-FDG PET or PET/CT was 0.91 [95% CI (0.88-0.94)] with heterogeneity (χ² = 141.8, p = 0.00) and a pooled specificity of 0.91 [95% CI (0.87-0.93)] with heterogeneity (χ² = 113.7, p = 0.00). Likelihood ratio (LR) syntheses gave an overall positive likelihood ratio (LR+) of 9.9 [95% CI (7.1-13.7)] and negative likelihood ratio (LR-) of 0.09 [95% CI (0.07-0.13)]. The pooled diagnostic odds ratio was 105 [95% CI (63-176)]. In metaregression analysis, study design, publication year, study location (western vs others), interpretation criteria of PET or PET/CT images, quantification of PET or PET/CT [SUV_max (maximum standardized uptake value) vs SUV (standardized uptake value) ratio], patient group, and analysis method (patient-based vs lesion-based) were the sources of the study heterogeneity. However, in multivariate metaregression, no definite variable was the source of the study heterogeneity.

CONCLUSION

¹⁸F-FDG PET or PET/CT demonstrated good sensitivity and specificity for the characterization of adrenal masses. At present, the literature regarding the use of ¹⁸F-FDG PET or PET/CT for the characterization of adrenal masses remains still limited; thus, further large multicenter studies would be necessary to substantiate the diagnostic accuracy of ¹⁸F-FDG PET or PET/CT characterization of adrenal masses. Advances in knowledge: ¹⁸F- FDG PET or PET/CT showed good sensitivity and specificity for the characterization of adrenal masses and could provide additional information for that purpose.

Adrenal Imaging

Cross-sectional imaging can make a specific diagnosis in lesions, such as myelolipomas, cysts, and hemorrhage, and is often sufficient to distinguish benign from malignant adrenal processes. CT and MRI are useful studies to identify pheochromocytomas and cortisol-secreting or androgen-secreting tumors. In patients with primary aldosteronism, adrenal venous sampling remains the most accurate localizing study and should be performed in all patients older than 35. Radiolabeled isotope studies serve as second-line diagnostic tests for malignant adrenal tumors, primary or metastatic, as well as for pheochromocytoma. Nuclear imaging studies should follow a robust hormonal diagnosis and be correlated with findings on cross-sectional imaging.

Adrenocortical neoplasms in adulthood and childhood: distinct presentation. Review of the clinical, pathological and imaging characteristics

Adrenocortical tumors (ACT) in adulthood and childhood vary in clinical, histopathological, molecular, prognostic, and imaging aspects. ACT are relatively common in adults, as adenomas are often found incidentally on imaging. ACT are rare in children, though they have a significantly higher prevalence in the south and southeast regions of Brazil. In clinical manifestation, adults with ACT present more frequently with glucocorticoid overproduction (Cushing syndrome), mineralocorticoid syndromes (Conn syndrome), or the excess of androgens in women. Subclinical tumors are frequently diagnosed late, associated with compression symptoms of abdominal mass. In children, the usual presentation is the virilizing syndrome or virilizing association and hypercortisolism. Histopathological grading and ACT classification in malignant and benign lesions are different for adults and children. In adults, the described criteria are the Hough, Weiss, modified Weiss, and Van Slooten. These scores are not valid for children; there are other criteria, such as proposed by Wieneke and colleagues. In molecular terms, there is also a difference related to genetic alterations found in these two populations. This review discusses the imaging findings of ACT, aiming to characterize the present differences between ACT found in adults and children. We listed several differences between magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography-computed (PET-CT) and also performed a literature review, which focuses on studied age groups of published articles in the last 10 years regarding cortical neoplasm and imaging techniques. Published studies on ACT imaging in children are rare. It is important to stress that the majority of publications related to the differentiation of malignant and benign tumors are based almost exclusively on studies in adults. A minority of articles, however, studied adults and children together, which may not be appropriate.

Diagnostic performance of 18-F-FDG-PET-CT in adrenal lesions using histopathology as reference standard

PURPOSE

To determine the diagnostic performance of PET-CT in differentiating benign and malignant adrenal lesions when evaluating PET parameters individually as well as in combination with CT parameters, using histopathology as the reference standard.

METHODS

¹⁸F-FDG-PET-CT scans of patients undertaken within 6 months prior to pathologic evaluation of their adrenal lesion(s) were evaluated. PET assessments consisted individually of maximum standardized uptake value of the adrenal lesion (A-SUV_max) and its ("normalized") ratio to the liver (R-SUV_max). The diagnostic performances of these two PET parameters were also assessed when combined with the Hounsfield density from the non-contrast CT component of the PET-CT (A-HU). Diagnostic performance was assessed by area under the curve (AUC) of the receiver operating characteristics. Multiple logistic regression analysis was used to evaluate the individual and combined parameters.

RESULTS

The study cohort consisted of 61 adrenal lesions (59 patients). Malignant lesions (n = 52) had significantly higher median PET and CT parameters than benign lesions: A-SUV_max (11.4 vs. 6.1), R-SUV_max (3.3 vs. 1.7), and A-HU (37 vs. 24) [all p < 0.023]. AUC for the PET parameters individually was almost identical: 0.75 for A-SUV_max and 0.74 for R-SUV_max. On univariate analysis, thresholds of A-SUV_max >3.47 and R-SUV_max >0.83 yielded maximum accuracy (both 87%). The combination of these PET parameters individually with A-HU improved both AUC and accuracy (0.81% and 93%, respectively).

CONCLUSIONS

The individual PET parameters A-SUV_max and R-SUV_max have similar diagnostic performance for differentiating malignant and benign adrenal lesions; their performance and accuracy improve when combined with the CT component (A-HU).

5th International ACC Symposium: Imaging for Diagnosis and Surveillance of Adrenal Tumors--New Advances and Reviews of Old Concepts

Adrenocortical carcinoma (ACC) is often diagnosed incidentally. However, significant difficulties persist in diagnosing the rare ACC among the very common benign adrenal tumors, which are present in up to 5% of the population. Due to the very low prevalence of ACC, prospective studies are impossible to conduct. Two recent studies took the approach of reviewing preexisting adrenal tumors prior to the diagnosis of ACC. These data challenge current concepts of diagnosis and surveillance of incidentally discovered masses. Oncocytomas (benign and malignant) represent an entity that can be difficult to be diagnosed by radiographic characteristics and even histologically. However, some recent data provides insight into their appearance in imaging procedures. With regards to ACC specific imaging, which could be applied for differential diagnosis of adrenal tumors, surgery planning and surveillance several radionucleotides have been evaluated over the last decades showing promising results. Of particular interest, these substances can potentially be used for therapy as well.

123I-MIBG scintigraphy and 18F-FDG-PET imaging for diagnosing neuroblastoma

BACKGROUND

Neuroblastoma is an embryonic tumour of childhood that originates in the neural crest. It is the second most common extracranial malignant solid tumour of childhood.Neuroblastoma cells have the unique capacity to accumulate Iodine-123-metaiodobenzylguanidine (¹²³I-MIBG), which can be used for imaging the tumour. Moreover, ¹²³I-MIBG scintigraphy is not only important for the diagnosis of neuroblastoma, but also for staging and localization of skeletal lesions. If these are present, MIBG follow-up scans are used to assess the patient's response to therapy. However, the sensitivity and specificity of ¹²³I-MIBG scintigraphy to detect neuroblastoma varies according to the literature.Prognosis, treatment and response to therapy of patients with neuroblastoma are currently based on extension scoring of ¹²³I-MIBG scans. Due to its clinical use and importance, it is necessary to determine the exact diagnostic accuracy of ¹²³I-MIBG scintigraphy. In case the tumour is not MIBG avid, fluorine-18-fluorodeoxy-glucose ((18)F-FDG) positron emission tomography (PET) is often used and the diagnostic accuracy of this test should also be assessed.

OBJECTIVES

PRIMARY OBJECTIVES

1.1 To determine the diagnostic accuracy of ¹²³I-MIBG (single photon emission computed tomography (SPECT), with or without computed tomography (CT)) scintigraphy for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old.1.2 To determine the diagnostic accuracy of negative ¹²³I-MIBG scintigraphy in combination with (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old, i.e. an add-on test.

SECONDARY OBJECTIVES

2.1 To determine the diagnostic accuracy of (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old.2.2 To compare the diagnostic accuracy of ¹²³I-MIBG (SPECT-CT) and (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old. This was performed within and between included studies. ¹²³I-MIBG (SPECT-CT) scintigraphy was the comparator test in this case.

SEARCH METHODS

We searched the databases of MEDLINE/PubMed (1945 to 11 September 2012) and EMBASE/Ovid (1980 to 11 September 2012) for potentially relevant articles. Also we checked the reference lists of relevant articles and review articles, scanned conference proceedings and searched for unpublished studies by contacting researchers involved in this area.

SELECTION CRITERIA

We included studies of a cross-sectional design or cases series of proven neuroblastoma, either retrospective or prospective, if they compared the results of ¹²³I-MIBG (SPECT-CT) scintigraphy or (18)F-FDG-PET(-CT) imaging, or both, with the reference standards or with each other. Studies had to be primary diagnostic and report on children aged between 0 to 18 years old with a neuroblastoma of any stage at first diagnosis or at recurrence.

DATA COLLECTION AND ANALYSIS

One review author performed the initial screening of identified references. Two review authors independently performed the study selection, extracted data and assessed the methodological quality.We used data from two-by-two tables, describing at least the number of patients with a true positive test and the number of patients with a false negative test, to calculate the sensitivity, and if possible, the specificity for each included study.If possible, we generated forest plots showing estimates of sensitivity and specificity together with 95% confidence intervals.

MAIN RESULTS

Eleven studies met the inclusion criteria. Ten studies reported data on patient level: the scan was positive or negative. One study reported on all single lesions (lesion level). The sensitivity of ¹²³I-MIBG (SPECT-CT) scintigraphy (objective 1.1), determined in 608 of 621 eligible patients included in the 11 studies, varied from 67% to 100%. One study, that reported on a lesion level, provided data to calculate the specificity: 68% in 115 lesions in 22 patients. The sensitivity of ¹²³I-MIBG scintigraphy for detecting metastases separately from the primary tumour in patients with all neuroblastoma stages ranged from 79% to 100% in three studies and the specificity ranged from 33% to 89% for two of these studies.One study reported on the diagnostic accuracy of (18)F-FDG-PET(-CT) imaging (add-on test) in patients with negative ¹²³I-MIBG scintigraphy (objective 1.2). Two of the 24 eligible patients with proven neuroblastoma had a negative ¹²³I-MIBG scan and a positive (18)F-FDG-PET(-CT) scan.The sensitivity of (18)F-FDG-PET(-CT) imaging as a single diagnostic test (objective 2.1) and compared to ¹²³I-MIBG (SPECT-CT) (objective 2.2) was only reported in one study. The sensitivity of (18)F-FDG-PET(-CT) imaging was 100% versus 92% of ¹²³I-MIBG (SPECT-CT) scintigraphy. We could not calculate the specificity for both modalities.

AUTHORS' CONCLUSIONS

The reported sensitivities of ¹²³-I MIBG scintigraphy for the detection of neuroblastoma and its metastases ranged from 67 to 100% in patients with histologically proven neuroblastoma.Only one study in this review reported on false positive findings. It is important to keep in mind that false positive findings can occur. For example, physiological uptake should be ruled out, by using SPECT-CT scans, although more research is needed before definitive conclusions can be made.As described both in the literature and in this review, in about 10% of the patients with histologically proven neuroblastoma the tumour does not accumulate ¹²³I-MIBG (false negative results). For these patients, it is advisable to perform an additional test for staging and assess response to therapy. Additional tests might for example be (18)F-FDG-PET(-CT), but to be certain of its clinical value, more evidence is needed.The diagnostic accuracy of (18)F-FDG-PET(-CT) imaging in case of a negative ¹²³I-MIBG scintigraphy could not be calculated, because only very limited data were available. Also the detection of the diagnostic accuracy of index test (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma tumour and its metastases, and to compare this to comparator test ¹²³I-MIBG (SPECT-CT) scintigraphy, could not be calculated because of the limited available data at time of this search.At the start of this project, we did not expect to find only very limited data on specificity. We now consider it would have been more appropriate to use the term "the sensitivity to assess the presence of neuroblastoma" instead of "diagnostic accuracy" for the objectives.

Metabolic and anatomic characteristics of benign and malignant adrenal masses on positron emission tomography/computed tomography: a review of literature

PET/CT with (18)F-fluorodeoxyglucose (FDG) or using different radiocompounds has proven accuracy for detection of adrenal metastases in patients undergoing cancer staging. It can assist the diagnostic work-up in oncology patients by identifying distant metastases to the adrenal(s) and defining oligometastatic disease that may benefit from targeted intervention. In patients with incidentally discovered adrenal nodules, so-called adrenal "incidentaloma" FDG PET/CT is emerging as a useful test to distinguish benign from malignant etiology. Current published evidence suggests a role for FDG PET/CT in assessing the malignant potential of an adrenal lesion that has been 'indeterminately' categorized with unenhanced CT, adrenal protocol contrast-enhanced CT, or chemical-shift MRI. FDG PET/CT could be used to stratify patients with higher risk of malignancy for surgical intervention, while recommending surveillance for adrenal masses with low malignant potential. There are caveats for interpretation of the metabolic activity of an adrenal nodule on PET/CT that may lead to false-positive and false-negative interpretation. Adrenal lesions represent a wide spectrum of etiologies, and the typical appearances on PET/CT are still being described, therefore our goal was to summarize the current diagnostic strategies for evaluation of adrenal lesions and present metabolic and anatomic appearances of common and uncommon adrenal lesions. In spite of the emerging role of PET/CT to differentiate benign from malignant adrenal mass, especially in difficult cases, it should be emphasized that PET/CT is not needed for most patients and that many diagnostic problems can be resolved by CT and/or MR imaging.

Adrenocortical carcinoma: what the surgeon needs to know. Case report and literature review

Adrenocortical carcinoma is a rare and aggressive cancer and its prognosis is frequently unsatisfactory. Due to its rarity there's a lack of prospective randomized studies. Without experience in the approach of this kind of tumor, managing becomes challenging and, moreover, we have only few recommendations, based on weak evidence. We report a case that has some peculiarities and is an excellent food for thought. Then we deal with a literature review to highlight and summarize most significant aspects of epidemiology, clinic, diagnosis, therapy and prognosis in an exquisitely surgical point of view.

Characterization of lipid-rich adrenal tumors by FDG PET/CT: Are they hormone-secreting or not?

OBJECTIVES

The purpose of this study was to evaluate the diagnostic ability of FDG PET/CT to predict the hormone-secretion status of lipid-rich adrenal tumors.

METHODS

This study included 29 lipid-rich (CT number <10 HU) adrenal tumors 2 cm or larger in diameter in 28 patients who underwent FDG PET/CT. The diagnoses were based on endocrine examinations, including adrenal venous sampling and subsequent surgical resection, or on the endocrinological and morphological imaging follow-up during a period of at least 6 months. The FDG uptake of the adrenal tumors was evaluated semi-quantitatively using maximum standardized uptake values (SUVmax) and a ratio of the adrenal SUVmax compared to the liver SUVmax (SUVratio) was used for comparison. The statistical significance of differences was assessed using the Mann-Whitney U test, and a p value <0.05 was considered to be statistically significant.

RESULTS

The lipid-rich adrenal tumors were proved to be 16 non-hormone-secreting tumors (15 adenomas and one myelolipoma) and 13 hormone-secreting tumors (five subclinical cortisol-producing adenomas, six aldosterone-producing adenomas and two adenomas that produced both cortisol and aldosterone). None of the patients had pheochromocytoma or a malignant adrenal tumor. The SUVmax (median, range) of the hormone-secreting tumors (3.2, 2.0-8.3) was higher than that of the non-hormone-secreting tumors (2.4, 1.8-3.3) (p < 0.05). Similarly, the SUVratio of the hormone-secreting tumors (0.95, 0.70-3.10) was higher than that of the non-hormone-secreting tumors (0.72, 0.54-0.95) (p < 0.01). There was no significant difference in the tumor diameter between the two groups (p = 0.8). The sensitivity, specificity and accuracy of FDG PET/CT for differentiating hormone-secreting tumors from non-hormone-secreting tumors were 0.69, 0.81 and 0.76 for cutoff SUVratio of 0.8, and were 0.46, 1 and 0.76 for the cutoff SUVratio of 1.0, respectively.

CONCLUSIONS

A lipid-rich adrenal tumor presenting increased FDG uptake compared with that of the liver is likely to be a hormone-secreting adenoma. Therefore, additional endocrinological investigations are strongly recommended when an FDG-avid lipid-rich incidentaloma is detected on FDG PET/CT.

Clinical utility of FDG-PET for diagnosis of adrenal mass: a large single-center experience

OBJECTIVE

To examine the clinical utility of 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET) for diagnosing whether an adrenal mass is malignant, in contemporary clinical practice.

DESIGN

Retrospective medical record review of patients from 2 databases at a large hospital. The first database consisted of patients who underwent FDG-PET between the years 2009 to 2011 while the second database included patients who had histological diagnosis of adrenal mass between the years 1997 to 2011.

RESULTS

3.4% of 2921 patients had adrenal FDG uptake. Approximately 43% of them did not exhibit corresponding adrenal mass. FDG-PET performance parameters were better if a cutoff of SUV (standardized uptake value) ≥3 was used to define positivity. The imaging characteristics of malignant adrenal masses and pheochromocytoma were similar but differed remarkably compared to those of benign tumors. Serial imaging revealed that the malignant adrenal masses consistently exhibited high CT attenuation, while more than half of them initially exhibited SUV<3 and in some cases FDG uptake indistinguishable from the background. The FDG-PET results were confirmatory in 87% of patients, contributory in 11%, but definitely misleading in 2%.

CONCLUSIONS

FDG-PET is not required for adrenal mass diagnosis in most patients in contemporary practice but may help clinical decision making in specific situations.

Functional characterization of adrenal lesions using [123I]IMTO-SPECT/CT

CONTEXT

Adrenal tumors are highly prevalent and represent a wide range of different pathological entities. Conventional imaging often provides only limited information on the origin of these lesions. Novel specific imaging methods are, therefore, of great clinical interest.

OBJECTIVE

We evaluated [(123)I]iodometomidate ([(123)I]IMTO) imaging for noninvasive characterization of adrenal masses.

DESIGN/SETTING

This was a prospective monocentric diagnostic study in a tertiary care center.

PATIENTS AND INTERVENTION

A total of 51 patients with an adrenal lesion underwent [(123)I]IMTO imaging after injection of 185 MBq of [(123)I]IMTO. Sequential planar whole-body scans until 24 hours postinjection and single photon emission computed tomography (SPECT)/computed tomography imaging 4 to 6 hours postinjection were performed.

MAIN OUTCOME MEASURE

Sensitivity and specificity of [(123)I]IMTO imaging for the noninvasive characterization of adrenal lesions were measured.

RESULTS

Adrenocortical tissue showed high and specific tracer uptake with a short investigation time and low radiation exposure. Qualitative analysis of SPECT/computed tomography data resulted in a sensitivity of 89% and a specificity of 85% for differentiating adrenocortical tumors from lesions of nonadrenocortical origin. Receiver-operating characteristic analysis of semiquantitative data revealed a sensitivity of 83% and a specificity of 86% for identification of adrenocortical lesions at a cutoff value of tumor to liver ratio of 1.3.

CONCLUSIONS

[(123)I]IMTO is a highly specific radiotracer for imaging of adrenocortical tissue with a short investigation time and low radiation exposure. Because of the general availability of SPECT technology, [(123)I]IMTO scintigraphy has the potential to become a widely used tool to noninvasively characterize the biology of adrenal lesions.

Cross-sectional imaging work-up of adrenal masses

Advances in medical imaging with current cross-section modalities enable non-invasive characterization of adrenal lesions. Computed tomography (CT) provides characterization with its non-contrast and wash-out features. Magnetic resonance imaging (MRI) is helpful in further characterization using chemical shift imaging (CSI) and MR spectroscopy. For differentiating between benign and malignant masses, positron emission tomography (PET) imaging is useful with its qualitative analysis, as well as its ability to detect the presence of extra-adrenal metastases in cancer patients. The work-up for an indeterminate adrenal mass includes evaluation with a non-contrast CT. If a lesion is less than 10 Hounsfield Units on a non-contrast CT, it is a benign lipid-rich adenoma and no further work-up is required. For the indeterminate adrenal masses, a lipid-poor adenoma can be differentiated from a metastasis utilizing CT wash-out features. Also, MRI is beneficial with CSI and MR spectroscopy. If a mass remains indeterminate, PET imaging may be of use, in which benign lesions demonstrate low or no fluorodeoxyglucose activity. In the few cases in which adrenal lesions remain indeterminate, surgical sampling such as percutaneous biopsy can be performed.

Utility of F-18 FDG-PET in detecting primary aldosteronism in patients with bilateral adrenal incidentalomas

In patients with primary aldosteronism who have bilateral adrenal incidentalomas, it is important to identify which adrenal gland is secreting excess aldosterone. Traditionally, adrenal vein sampling (AVS) has been performed for lateralization despite its invasiveness. Here we report a case of bilateral adrenal incidentaloma in which 18-Fluorodeoxyglucose (FDG)-positron emission tomography (PET) was used to identify the functional adrenal mass. A 53-yr-old man was referred to our clinic due to bilateral adrenal incidentalomas (right: 1 cm, left: 2.5 cm) on computed tomography (CT). Given his history of colon cancer, FDG-PET/CT scanning was used to rule out metastasis. Although there was focal hot uptake lesion in the right adrenal gland, the patient was suspected primary aldosteronism clinically more than metastasis because of the patient's underlying hypertension with hypokalemia. It was consistent with the results of AVS. Based on these findings, we propose that FDG-PET/CT can be used instead of AVS to identify the source of primary aldosteronism between two bilateral adrenal incidentalomas.

Molecular imaging of adrenal neoplasms

The adrenal glands are complex structures from which a variety of benign and malignant tumors may arise and are a common site of metastatic disease. Several radiopharmaceuticals are used for imaging the adrenals, including I-123/I-131 metaiodobenzylguanidine (MIBG), norcholesterol derivatives, In-111 pentetreotide and Ga-68 somatostatin analogs, [F-18]fluorodeoxyglucose, [F-18]fluorodopa, [F-18]fluorodopamine, C-11 meta hydroxyephedrine, and C-11/F-18/I-123 Metomidate (MTO) or its analogs. In this review we focus on the role of these reagents in metastatic lesions, cortical neoplasms, pheochromocytoma/paraganglioma, and neuroblastoma (NB).

Imaging of adrenal masses with emphasis on adrenocortical tumors

Because of the more widespread and frequent use of cross-sectional techniques, mainly computed tomography (CT), an increasing number of adrenal tumors are detected as incidental findings (“incidentalomas”). These incidentaloma patients are much more frequent than those undergoing imaging because of symptoms related to adrenal disease. CT and magnetic resonance imaging (MRI) are in most patients sufficient for characterization and follow-up of the incidentaloma. In a minor portion of patients, biochemical screening reveals a functional tumor and further diagnostic work-up and therapy need to be performed according to the type of hormonal overproduction. In oncological patients, especially when the morphological imaging criteria indicate an adrenal metastasis, biopsy of the lesion should be considered after pheochromocytoma is ruled out biochemically. In the minority of patients in whom CT and MRI fail to characterize the tumor and when time is of essence, functional imaging mainly by positron emission tomography (PET) is available using various tracers. The most used PET tracer, [¹⁸F]fluoro-deoxy-glucose (¹⁸FDG), is able to differentiate benign from malignant adrenal tumors in many patients. ¹¹C-metomidate (¹¹C-MTO) is a more specialized PET tracer that binds to the 11-beta-hydroxylase enzyme in the adrenal cortex and thus makes it possible to differ adrenal tumors (benign adrenocortical adenoma and adrenocortical cancer) from those of non-adrenocortical origin.

Metomidate-based imaging of adrenal masses

Due to broader use of conventional imaging techniques, adrenal tumors are detected with increasing frequency comprising a wide variety of different tumor entities. Despite improved conventional imaging techniques, a significant number of adrenal lesions remain that cannot be easily determined. A particular diagnostic challenge are lesions in patients with known extra-adrenal malignancy because these patients frequently harbor adrenal metastases. Furthermore, adrenal masses with low fat content and no detectable hormone excess are difficult to diagnose properly. Fine needle biopsy is invasive, often unsuccessful, and puts patients at risk, e. g., in cases of pheochromocytoma or adrenal cancer. Noninvasive characterization using radiotracers has therefore been established in recent years. (18)F-FDG PET helps to differentiate benign from malignant lesions. However, it does not distinguish between adrenocortical or nonadrenocortical lesions (e.g., metastases or adrenocortical carcinoma). More recently, enzyme inhibitors have been developed as tracers for adrenal imaging. Metomidate is most widely used. It binds with high specificity and affinity to CYP11B enzymes of the adrenal cortex. As these enzymes are exclusively expressed in adrenocortical cells, uptake of labeled metomidate tracers has been shown to be highly specific for adrenocortical neoplasia. (11)C-metomidate PET and (123)I-iodometomidate SPECT imaging has been introduced into clinical use. Both tracers not only distinguish between adrenocortical and nonadrenocortical lesions but are also able to visualize metastases of adrenocortical carcinoma. The very specific uptake has recently led to first application of (131)I-iodometomidate for radiotherapy in ACC. In conclusion, metomidate-based imaging is an important complementary tool to diagnose adrenal lesions that cannot be determined by other methods.

Adrenal imaging

Adrenal masses are frequently encountered in imaging practices. Simple detection by radiologists is insufficient as many of these masses can now be characterized by imaging alone. Some masses can be characterized by their simple appearances, but most cannot. This article will describe the different principles used by imagers to lead them to the correct diagnosis for the overwhelming majority of lesions. Imagers should be familiar with these techniques to expedite treatment, especially in cancer patients and so prevent unnecessary biopsies, costs, and anxiety.

Characterization of adrenal masses by using FDG PET: a systematic review and meta-analysis of diagnostic test performance

PURPOSE

To perform a systematic review and meta-analysis of published data to determine the diagnostic utility of adrenal fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography (PET) for distinguishing benign from malignant adrenal disease.

MATERIALS AND METHODS

Data on FDG PET assessment in MEDLINE and other electronic databases (from inception to November 2009) and in subject matter-specific journals were evaluated and compared with histologic diagnoses and/or established clinical and imaging follow-up results. Methodologic quality was assessed by using Quality Assessment of Diagnostic Accuracy Studies criteria. Bivariate random-effects meta-analytical methods were used to estimate summary and subgroup-specific sensitivity, specificity, and receiver operating characteristic curves and to investigate the effects of study design characteristics and imaging procedure elements on diagnostic accuracy.

RESULTS

A total of 1391 lesions (824 benign, 567 malignant) in 1217 patients from 21 eligible studies were evaluated. Qualitative (visual) analysis of 841 lesions (in 14 reports) and quantitative analyses based on standardized uptake values (SUVs) for 824 lesions (in 13 reports) and standardized uptake ratios (SURs) for 562 lesions (in eight reports) were performed. Resultant data were highly heterogeneous, with a model-based inconsistency index of 88% (95% confidence interval [CI]: 79%, 98%). Mean sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, and diagnostic odds ratio values for differentiating between benign and malignant adrenal disease were 0.97 (95% CI: 0.93, 0.98), 0.91 (95% CI: 0.87, 0.94), 11.1 (95% CI: 7.5, 16.3), 0.04 (95% CI: 0.02, 0.08), and 294 (95% CI: 107, 805), respectively, with no significant differences in accuracy among the visual, SUV, and SUR analyses.

CONCLUSION

Meta-analysis of combination PET-computed tomography (CT) reports revealed that FDG PET was highly sensitive and specific for differentiating malignant from benign adrenal disease. Diagnostic accuracy was not influenced by the type of imaging device (PET vs PET/CT), but specificity was dependent on the clinical status (cancer vs no cancer).

Evaluation of incidentally discovered adrenal masses with PET and PET/CT

BACKGROUND AND PURPOSE

Incidentally discovered adrenal masses are commonly seen with high resolution diagnostic imaging performed for indications other than adrenal disease. Although the majority of these masses are benign and non-secretory, their unexpected discovery prompts further biochemical and often repeated imaging evaluations, sufficient to identify hormonally active adrenal masses and/or primary or metastatic neoplasms to the adrenal(s). In the present paper we investigate the role of PET and PET/CT for the detection of adrenal incidentalomas in comparison with CT and MRI.

MATERIALS AND METHODS

a systematic revision of the papers published in PubMed/Medline until September 2010 was done.

RESULTS

The diagnostic imaging approach to incidentally discovered adrenal masses includes computed tomography (CT), magnetic resonance imaging (MRI) and more recently positron emission tomography (PET) with radiopharmaceuticals designed to exploit mechanisms of cellular metabolism, adrenal substrate precursor uptake, or receptor binding.

CONCLUSION

The functional maps created by PET imaging agents and the anatomic information provided by near-simultaneously acquired, co-registered CT facilitates localization and diagnosis of adrenal dysfunction, distinguishes unilateral from bilateral disease, and aids in characterizing malignant primary and metastatic adrenal disease.

18F-FDG PET/CT in the characterization and surgical decision concerning adrenal masses: a prospective multicentre evaluation

PURPOSE

This prospective multicentre study assesses the usefulness of FDG PET/CT in characterizing and making the therapeutic decision concerning adrenal tumours that are suspicious or indeterminate in nature after conventional examinations (CE).

METHODS

Seventy-eight patients (37 men, 41 women, 81 adrenal lesions) underwent FDG PET/CT after CE including CT scan, biological tests and optionally (131)I-metaiodobenzylguanidine (MIBG) and/or (131)I-norcholesterol scans. FDG adrenal uptake exceeding that of the liver was considered positive. PET results were not decisive. Surgery was discussed when at least one of the following criteria was found during CE: size >3 cm, spontaneous attenuation value >10 HU, heterogeneous aspect, abnormal MIBG or norcholesterol scan or hormonal hypersecretion.

RESULTS

Following the gold standard (histology analysis or >or=9 months follow-up), 49 lesions potentially qualified for surgery (malignant = 27, benign secreting = 22) and 32 benign non-secreting lesions did not. PET was negative in 97% of non-surgical lesions and positive in 73% of potentially surgical ones which included all the malignant lesions, except 3 renal cell metastases, and 12 of 22 benign secreting lesions. The negative predictive value for malignancy was 93% (41/44) and positive predictive value for detecting surgical lesions was 97% (36/37). A high FDG uptake (maximum standardized uptake value >or= 10) was highly predictive of malignancy.

CONCLUSION

Adrenal FDG uptake is a good indicator of malignancy and/or of secreting lesions and should lead one to discuss surgery. If there is no prior history of poorly FDG-avid cancer, the absence of FDG uptake should avoid unnecessary removal of benign adrenal lesions.

18F-Fluorodeoxyglucose positron emission tomography for the diagnosis of adrenocortical tumors: a prospective study in 77 operated patients

CONTEXT

Most adrenal incidentalomas are nonfunctioning adrenocortical adenomas (ACAs). Adrenocortical carcinomas (ACCs) are rare but should be recognized at an early stage.

OBJECTIVE

The objective of the study was to evaluate the usefulness of (18)F-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) to predict malignancy in patients without a previous history of cancer.

DESIGN

This was a prospective, multicenter study from 2001 to 2006.

SETTING

The study was conducted at a network of seven university hospitals in Paris.

PATIENTS

Seventy-seven patients were included. All underwent surgery because of hypersecretory and/or growing benign lesions (n = 18), obvious ACCs (n = 21), or radiologically indeterminate lesions (n = 38).

MAIN OUTCOME MEASURE

The degree of (18)F-FDG PET uptake [maximum standardized uptake value (maxSUV)] was related to the pathological findings serving as a reference, and its diagnostic value was compared with that of computerized tomography (CT) scan.

RESULTS

Pathology eventually diagnosed 43 ACAs, 22 ACCs, and 12 nonadrenocortical lesions. Using a cutoff value above 1.45 for adrenal to liver maxSUV ratio, the sensitivity and specificity to distinguish ACAs from ACCs were, respectively, 1.00 (95% confidence interval 0.85-1.00) and 0.88 (95% confidence interval 0.75-0.96). Among the 38 indeterminate lesions at CT scan, we could analyze a subgroup of 16 adrenocortical tumors with high unenhanced density (>10 HU) and an inappropriate washout: (18)F-FDG PET correctly predicted the benignity in 13 of 15 ACAs.

CONCLUSIONS

In a multidisciplinary team approach, (18)F-FDG PET helps to manage suspicious CT scan lesions. An adrenal to liver maxSUV ratio less than 1.45 is highly predictive of a benign lesion.

PET/CT for the characterization of adrenal masses in patients with cancer: qualitative versus quantitative accuracy in 150 consecutive patients

OBJECTIVE

The objective of our study was to evaluate a large cohort of patients with PET/CT to determine whether qualitative (visual) assessment, quantitative standardized uptake value (SUV), or standardized uptake ratio (SUR) techniques should be used when attempting to characterize adrenal masses in patients with cancer.

MATERIALS AND METHODS

The study group was composed of 150 consecutive patients (78 men, 72 women; mean age, 60 years; range, 24-88 years) with documented adrenal lesions. All patients were known to have an underlying primary malignancy and were referred for PET/CT to evaluate the underlying primary and metastatic tumor burden. Definitive lesion characterization was determined by evaluating all histologic adrenal specimens and all relevant prior and follow-up CT scans, including unenhanced, contrast-enhanced, and delayed contrast-enhanced washout studies.

RESULTS

Of the 139 benign lesions, 109 were considered benign by CT densitometry measurements and 135 by qualitative PET data. Qualitative PET characterized 28 of 30 benign lesions that were considered indeterminate by unenhanced CT. All 26 malignant lesions were characterized by PET: All showed qualitative and quantitative signal intensity greater than the liver. By combining unenhanced and qualitative CT data with the retrospective PET data, the analysis yielded a sensitivity of 100% for the detection of malignancy, a specificity of 99%, a positive predictive value (PPV) of 93%, a negative predictive value (NPV) of 100%, and an accuracy of 99% (Table 1). Conversely, for the detection of benignity, the sensitivity, specificity, PPV, NPV, and accuracy were 99%, 100%, 100%, 93%, and 99%, respectively.

CONCLUSION

PET/CT is a highly accurate method for differentiating benign from malignant adrenal masses particularly when using qualitative, rather than quantitative, PET data. The routine use of quantitative mean or maximal SUV or SUR data may be unnecessary. Occasional benign lesions do show mild to moderate increased FDG uptake compared with that of the liver and may mimic some malignant lesions. Without evidence that these lesions are benign by unenhanced CT densitometry or adrenal mass stability or growth from previous CT scans, we recommend that these lesions be characterized using contrast-enhanced washout tests and that if those tests are inconclusive, using percutaneous biopsy if early lesion characterization is mandatory.

Clinical management of adrenocortical carcinoma

Adrenocortical carcinoma (ACC) is a rare and heterogeneous malignancy, and most of the diagnostic and therapeutic strategies are not fully established according to criteria of evidence-based medicine. However, recently collaborative efforts (e.g. International Consensus Conference 2003 and networks like the European Network for the Study of Adrenal Tumours (ENSAT)) have significantly advanced the field. This article summarizes current standards in the management of ACC. In patients with suspected ACC a thorough endocrine and imaging work-up is followed by complete (Ro) resection of the tumour by an expert surgeon and initiation of adjuvant mitotane. In advanced disease not amenable to radical resection, cytotoxic drugs will be added to mitotane. The most promising regimens (etoposide, doxorubicin, cisplatin plus mitotane and streptozotocin plus mitotane) are currently compared in an international phase-III trial. Several targeted therapies are under investigation (e.g. IGF-1 inhibitors, sunitinib, sorafenib) and may lead to new treatment options.

Endothelial cyst of the adrenal gland associated with adrenocortical adenoma: preoperative images simulate carcinoma

A 68-year-old woman was referred for characterization of a left adrenal incidentaloma. Endocrinological examinations indicated subclinical Cushing's syndrome, whereas the large volume (10 cm in diameter) and heterogeneous configuration of the tumor raised a strong suspicion of adrenal carcinoma. Hence, left adrenalectomy was performed. Histopathologically, this lesion was a thick hyaline-walled endothelial cyst, flanked with a compressed adrenocortical adenoma. The puzzling image resemblance of a variation of adrenal cyst to carcinoma necessitated histological examination for confirmative diagnosis. This is the first reported case of adrenal endothelial cyst associated with adrenocortical adenoma, the former of which alone is a rarity.

Computed tomography, magnetic resonance imaging and 11C-metomidate positron emission tomography for evaluation of adrenal incidentalomas

BACKGROUND

Given the higher sensitivity of modern computed tomography (CT) scanners, adrenal incidentalomas are being discovered increasingly often. This implies a growing quantitative diagnostic and clinical problem. CT and/or magnetic resonance imaging (MRI) and usually thorough hormonal testing are routinely used to determine the origin of these lesions. Recently, positron emission tomography (PET) using the tracer (11)C-metomidate (MTO) has been established as an alternative diagnostic method with high sensitivity for identifying adrenocortical lesions. The aim of this study was to evaluate the clinical use and value of MTO-PET compared to CT and MRI in the characterisation and work-up of adrenal incidentalomas.

METHODS

Initially, we retrospectively evaluated 20 adrenal incidentalomas in patients who had undergone CT, MRI and MTO-PET and from whom we had either histopathological diagnosis or clinical follow-up data. After this analysis we conducted a prospective study in order to compare the imaging modalities. In the latter study, 24 incidentalomas were imaged by CT, MRI and MTO-PET and the results were correlated to those from histopathology (n=8) and clinical diagnosis after follow-up (n=16).

RESULTS

In the retrospective analysis, MRI and especially MTO-PET, correlated well to histopathology and clinical diagnosis after follow-up, whereas specificity with CT was low. This was possibly due to the presence of several haematomas/fibrosis which were misdiagnosed as adrenocortical adenomas. In the prospective cohort, sensitivity and specificity with CT were 0.71 and 1.0, respectively, and further characterisation by MRI increased these values to 0.86 and 1.0, whereas maximum sensitivity and specificity were reached when MTO-PET was added.

CONCLUSION

The diagnosis of an adrenocortical adenoma may be established by CT in most patients and by MRI in an additional number. For the few remaining patients needing further characterisation, MTO-PET is advantageous as an additional imaging modality.

Leiomyoma of the adrenal gland presenting as a non-functioning adrenal incidentaloma: case report and review of the literature

A 31-year-old woman was incidentally found to have a large right adrenal mass by computed tomography imaging and underwent a workup that included endocrinological evaluation and positron emission tomography imaging. Laboratory results revealed the mass to be non-functioning. Imaging studies revealed a 9-cm heterogeneous mass that was not FDG avid. Because of concern for adrenal cortical carcinoma, the patient underwent a successful right adrenalectomy. Pathology examination demonstrated an 11-cm circumscribed mass consisting of uniform spindle cells without nuclear pleomorphism, necrosis, or mitotic activity. The diagnosis of leiomyoma was supported by a panel of immunohistochemical stains. Adrenal leiomyomas have been reported in the literature, although most are small and not preoperatively suspicious for malignancy. This case illustrates that benign tumors such as leiomyomas, when large and heterogeneous on imaging, can clinically mimic adrenal cortical carcinomas and should be included in the differential diagnosis of adrenal incidentalomas.