ACR Appropriateness Criteria® Adrenal Mass Evaluation: 2021 Update

Endocrinology application of molecular imaging: current role of PET/CT

BACKGROUND

In recent years, nuclear medicine imaging methods have proven to be of paramount importance in a wide variety of diseases, particularly in oncology, where they are crucial for assessing the extent of disease when conventional methods fall short. Moreover, nuclear imaging modalities are able to better characterize lesions using target agents related to specific pathways (e.g. glucose metabolism, cellular proliferation, amino acid transport, lipid metabolism, specific receptor ligands). The clinical presentation of endocrine diseases encompasses a broad spectrum of sign and symptoms. Moreover, endocrine tumors show varying degrees of aggressiveness from well differentiated and indolent to highly aggressive cancers, respectively.

RATIONALE

With the application of new medicinal radio-compounds and increasingly advanced tomographic imaging technology, the utility of Positron Emission Tomography/Computed Tomography (PET/CT) in the field of endocrine diseases is expanding.

AIM

This review aims to analyze and summarize the primary indications of PET/CT, providing a practical approach for clinicians. A comprehensive literature search on PubMed was conducted to provide an updated overview of the available evidence regarding the use of PET/CT in endocrinology. Within this review, we will discuss the applications of PET/CT, compare different radiopharmaceuticals and highlight the uptake mechanism, excluding neuroendocrine carcinomas from discussion.

CONCLUSIONS

PET/CT is a valuable tool in diagnosing and managing endocrine disorders due to its capacity to furnish both functional and anatomical information, facilitate early lesion detection, guide treatment decisions, and monitor treatment response. Its non-invasive nature and precision make it an integral component of modern endocrine healthcare. This review aims to provide physicians with a clear perspective on the role of PET/CT imaging, discussing its emerging opportunities and appropriateness of use in endocrinological diseases.

Dual Energy-Derived Metrics for Differentiating Adrenal Adenomas From Nonadenomas on Single-Phase Contrast-Enhanced CT

BACKGROUND. Adrenal masses are often indeterminate on single-phase postcontrast CT. Dual-energy CT (DECT) with three-material decomposition algorithms may aid characterization. OBJECTIVE. The purpose of this study was to compare the diagnostic performance of metrics derived from portal venous phase DECT, including virtual noncontrast (VNC) attenuation, fat fraction, iodine density, and relative enhancement ratio, for characterizing adrenal masses. METHODS. This retrospective study included 128 patients (82 women, 46 men; mean age, 64.6 ± 12.7 [SD] years) who between January 2016 and December 2019 underwent portal venous phase abdominopelvic DECT that showed a total of 139 adrenal lesions with an available reference standard based on all imaging, clinical, and pathologic records (87 adenomas, 52 nonadenomas [48 metastases, two adrenal cortical carcinomas, one ganglioneuroma, one hematoma]). Two radiologists placed ROIs to determine the following characteristics of the masses: VNC attenuation, fat fraction, iodine density normalized to portal vein, and for masses with VNC greater than 10 HU, relative enhancement ratio (ratio of portal venous phase attenuation to VNC attenuation). Readers' mean measurements were used for ROC analyses, and clinically optimal thresholds were derived as thresholds yielding the highest sensitivity at 100% specificity. RESULTS. Adenomas and nonadenomas were significantly different (all p < .001) in VNC attenuation (mean ± SD, 18.5 ± 12.9 vs 34.1 ± 8.9 HU), fat fraction (mean ± SD, 24.3% ± 8.2% vs 14.2% ± 5.6%), normalized iodine density (mean ± SD, 0.34 ± 0.15 vs 0.17 ± 0.17), and relative enhancement ratio (mean ± SD, 186% ± 96% vs 58% ± 59%). AUCs for all metrics ranged from 0.81 through 0.91. The metric with highest sensitivity for adenoma at the clinically optimal threshold (i.e., 100% specificity) was fat fraction (threshold, ≥ 23.8%; sensitivity, 59% [95% CI, 48-69%]) followed by VNC attenuation (≤ 15.2 HU; sensitivity, 39% [95% CI, 29-50%]), relative enhancement ratio (≥ 214%; sensitivity, 37% [95% CI, 25-50%]), and normalized iodine density (≥ 0.90; sensitivity, 1% (95% CI, 0-60%]). VNC attenuation at the traditional true noncontrast attenuation threshold of 10 HU or lower had sensitivity of 28% (95% CI, 19-38%) and 100% specificity. Presence of fat fraction 23.8% or greater or relative enhancement ratio 214% or greater yielded sensitivity of 68% (95% CI, 57-77%) with 100% specificity. CONCLUSION. For adrenal lesions evaluated with single-phase DECT, fat fraction had higher sensitivity than VNC attenuation at both the clinically optimal threshold and the traditional threshold of 10 HU or lower. CLINICAL IMPACT. By helping to definitively diagnose adenomas, DECT-derived metrics can help avoid downstream imaging for incidental adrenal lesions.

Inter-method agreement between wash-in and wash-out computed tomography for characterizing hyperattenuating adrenal lesions as adenomas or non-adenomas

OBJECTIVES

To investigate inter-method agreement between wash-out and wash-in computed tomography (CT) to determine whether hyperattenuating adrenal lesions are characterized as adenomas or non-adenomas.

METHODS

We evaluated 243 patients who underwent wash-out CT for a solid enhancing hyperattenuating (i.e., > 10 Hounsfield unit [HU]) adrenal mass of ≥ 1 to < 4 cm. Wash-out (absolute percentage wash-out [APW]; relative percentage wash-out [RPW]) and wash-in values (enhancement ratio [ER]; relative enhancement ratio [RER]) were analyzed by two independent readers. Diagnostic criteria of wash-out CT for adenoma were APW ≥ 60% or RPW ≥ 40% (conventional method). Three different criteria for wash-in CT were set: ER ≥ 3.0; RER ≥ 200%; and RER ≥ 210%. Concordance rate and inter-method agreement between wash-out and wash-in CT were investigated using Gwet's AC1.

RESULTS

For all lesions, concordance rates between wash-out and wash-in CT were > 83%. AC1 between conventional method and ER ≥ 3.0 or between conventional method and RER ≥ 200% were identically 0.843 for reader 1 and 0.776 for reader 2. AC1 between conventional method and RER ≥ 210% were 0.780 for reader 1 and 0.737 for reader 2. For lesions of > 10 to ≤ 30 HU, concordance rates between wash-out and wash-in CT were > 89%. AC1 between conventional method and ER ≥ 3.0 or between conventional method and RER ≥ 200% were identically 0.914 for reader 1 and 0.866 for reader 2. AC1 between conventional method and RER ≥ 210% were 0.888 for reader 1 and 0.874 for reader 2.

CONCLUSION

In approximately 90% of patients with a hyperattenuating adrenal lesion of ≥ 1 to < 4 cm and >10 to ≤ 30 HU, wash-out CT with 15-min contrast-enhanced images may be replaced by wash-in CT.

KEY POINTS

• An enhancement ratio of ≥ 3.0 or a relative enhancement ratio of ≥ 200% appears to be appropriate as the threshold of wash-in computed tomography (CT) comprising unenhanced and 1-min contrast-enhanced CT. • Measurement of enhancement ratio or relative enhancement ratio was reproducible. • We found good agreement between wash-in and wash-out CT for determining whether hyperattenuating adrenal lesions of ≥ 1 to < 4 cm and >10 to ≤ 30 Hounsfield unit would be characterized as adenomas.

Lexicon for adrenal terms at CT and MRI: a consensus of the Society of Abdominal Radiology adrenal neoplasm disease-focused panel

PURPOSE

Substantial variation in imaging terms used to describe the adrenal gland and adrenal findings leads to ambiguity and uncertainty in radiology reports and subsequently their understanding by referring clinicians. The purpose of this study was to develop a standardized lexicon to describe adrenal imaging findings at CT and MRI.

METHODS

Fourteen members of the Society of Abdominal Radiology adrenal neoplasm disease-focused panel (SAR-DFP) including one endocrine surgeon participated to develop an adrenal lexicon using a modified Delphi process to reach consensus. Five radiologists prepared a preliminary list of 35 imaging terms that was sent to the full group as an online survey (19 general imaging terms, 9 specific to CT, and 7 specific to MRI). In the first round, members voted on terms to be included and proposed definitions; subsequent two rounds were used to achieve consensus on definitions (defined as ≥ 80% agreement).

RESULTS

Consensus for inclusion was reached on 33/35 terms with two terms excluded (anterior limb and normal adrenal size measurements). Greater than 80% consensus was reached on the definitions for 15 terms following the first round, with subsequent consensus achieved for the definitions of the remaining 18 terms following two additional rounds. No included term had remaining disagreement.

CONCLUSION

Expert consensus produced a standardized lexicon for reporting adrenal findings at CT and MRI. The use of this consensus lexicon should improve radiology report clarity, standardize clinical and research terminology, and reduce uncertainty for referring providers when adrenal findings are present.

Imaging Recommendations for Diagnosis, Staging, and Management of Adrenal Tumors

Adrenal glands are affected by a wide variety of tumors apart from infective and inflammatory lesions and their noninvasive characterization on imaging is important for the management of these patients. Incidentalomas form the major bulk of adrenal tumors and differentiation of benign adenomas from other malignant lesions, especially in patients with a known malignancy, guide further management. Imaging is an integral part of management along with clinical and biochemical features. The cornerstone of clinical and biochemical evaluation of adrenal tumors is to determine whether the lesion is functional or nonfunctional. Computed tomography (CT) is considered as the workhorse for imaging evaluation of adrenal lesions. CT densitometry and CT contrast washout characteristics are quite reliable in differentiating adenomas from malignant lesions. CT is also the modality of choice for the evaluation of resectability and staging of primary adrenal tumors. Magnetic resonance imaging (MRI) has superior contrast resolution compared to other morphological imaging modalities and is generally used as a problem-solving tool. MRI chemical shift imaging can also be used to reliably detect adrenal adenomas. Ultrasonography (USG) is used as a screening tool that is usually followed by either CT or MRI to better characterize the tumor and it is not routinely used for assessing the resectability, staging, and characterization of adrenal tumors. Another important role of USG is in image-guided sampling of tumors. Fluorodeoxyglucose positron emission tomography-computed tomography and other nuclear medicine modalities are a valuable addition to morphological imaging modalities. Image-guided interventions also play an important role in obtaining tissue samples where diagnostic imaging is not able to characterize adrenal tumors. In the functioning of adrenal tumors, adrenal venous sampling is widely used to accurately lateralize the secreting tumor.

Prevalence of Malignancy in Adrenal Nodules With Heterogeneous Microscopic Fat on Chemical-Shift MRI: A Multiinstitutional Study

BACKGROUND. Homogeneous microscopic fat within adrenal nodules on chemical-shift MRI (CS-MRI) is diagnostic of benign adrenal adenoma, but the clinical relevance of heterogeneous microscopic fat is not well established. OBJECTIVE. This study sought to determine the prevalence of malignancy in adrenal nodules with heterogeneous microscopic fat on dual-echo T1-weighted CS-MRI. METHODS. We performed a retrospective study of adult patients with adrenal nodules detected on MRI performed between August 2007 and November 2020 at seven institutions. Eligible nodules had a short-axis diameter of 10 mm or larger with heterogeneous microscopic fat (defined by an area of signal loss of < 80% on opposed-phase CS-MRI). Two radiologists from each center, blinded to reference standard results, determined the signal loss pattern (diffuse, two distinct parts, speckling pattern, central loss, or peripheral loss) within the nodules. The reference standard used was available for 283 nodules (pathology for 21 nodules, ≥ 1 year of imaging follow-up for 245, and ≥ 5 years of clinical follow-up for 17) in 282 patients (171 women and 111 men; mean age, 60 ± 12 [SD] years); 30% (86/282) patients had prior malignancy. RESULTS. The mean long-axis diameter was 18.7 ± 7.9 mm (range, 10-80 mm). No malignant nodules were found in patients without prior cancer (0/197; 95% CI, 0-1.5%). Four of the 86 patients with prior malignancy (hepatocellular carcinoma [HCC], renal cell carcinoma [RCC], lung cancer, or both colon cancer and RCC) (4.7%; 95% CI, 1.3-11.5%) had metastatic nodules. Detected patterns were diffuse heterogeneous signal loss (40% [114/283]), speckling (28% [80/283]), two distinct parts (18% [51/283]), central loss (9% [26/283]), and peripheral loss (4% [12/283]). Two metastases from HCC and RCC showed diffuse heterogeneous signal loss. Lung cancer metastasis manifested as two distinct parts, and the metastasis in the patient with both colon cancer and RCC showed peripheral signal loss. CONCLUSION. Presence of heterogeneous microscopic fat in adrenal nodules on CS-MRI indicates a high likelihood of benignancy, particularly in patients without prior cancer. This finding is also commonly benign in patients with cancer; however, caution is warranted when primary malignancies may contain fat or if the morphologic pattern of signal loss may indicate a collision tumor. CLINICAL IMPACT. In the absence of prior cancer, adrenal nodules with heterogeneous microscopic fat do not require additional imaging evaluation.

Is the Adrenal Incidentaloma Functionally Active? An Approach-To-The-Patient-Based Review

Adrenal incidentalomas are a common occurrence. Most of them are adrenocortical adenomas that do not cause harm and do not require surgery, but a non-negligible proportion of incidentalomas is represented by functionally active masses, including cortisol-secreting adenomas (12%), pheochromocytomas (3–6%), aldosterone-secreting adenomas (2–3%), as well as malignant nodules, such as adrenocortical carcinomas (2–5%), which can be either functioning or non-functioning. All patients with an adrenal incidentaloma should undergo a few biochemical screening and confirmatory tests to exclude the presence of a functionally active mass. In this approach-to-the-patient-based review, we will summarize current recommendations on biochemical evaluation and management of functionally active adrenal incidentalomas. For this purpose, we will present four case vignettes, whereby we will describe how patients were managed, then we will review and discuss additional considerations tied to the diagnostic approach, and conclude with practical aspects of patient perioperative management. To improve the perioperative management of patients with functional adrenal incidentalomas, multidisciplinary meetings are advocated.

Integration of molecular imaging in the personalized approach of patients with adrenal masses

Adrenal masses are a frequent finding in clinical practice. Many of them are incidentally discovered with a prevalence of 4% in patients undergoing abdominal anatomic imaging and require a differential diagnosis. Biochemical tests, evaluating hormonal production of both adrenal cortex and medulla (in particular, mineralocorticoids, glucocorticoids and catecholamines), have a primary importance in distinguishing functional or non-functional lesions. Conventional imaging techniques, in particular computerized tomography (CT) and magnetic resonance imaging (MRI), are required to differentiate between benign and malignant lesions according to their appearance (size stability, contrast enhanced CT and/or chemical shift on MRI). In selected patients, functional imaging is a non-invasive tool able to explore the metabolic pathways involved thus providing additional diagnostic information. Several single photon emission tomography (SPET) and positron emission tomography (PET) radiopharmaceuticals have been developed and are available, each of them suitable for studying specific pathological conditions. In functional masses causing hypersecreting diseases (mainly adrenal hypercortisolism, primary hyperaldosteronism and pheochromocytoma), functional imaging can lateralize the involvement and guide the therapeutic strategy in both unilateral and bilateral lesions. In non-functioning adrenal masses with inconclusive imaging findings at CT/MR, [¹⁸F]-FDG evaluation of tumor metabolism can be helpful to characterize them by distinguishing between benign nodules and primary malignant adrenal disease (mainly adrenocortical carcinoma), thus modulating the surgical approach. In oncologic patients, [¹⁸F]-FDG uptake can differentiate between benign nodule and adrenal metastasis from extra-adrenal primary malignancies.

Differentiation between heterogeneous adrenal adenoma and non-adenoma adrenal lesion with CT and MRI

PURPOSE

To assess whether heterogeneous adrenal adenomas can be distinguished from heterogeneous non-adenomas with Computed Tomography (CT) and/or Magnetic Resonance Imaging (MRI).

METHOD

From 2009 to 2019, 980 consecutive adrenalectomies were retrospectively identified. Patients without adequate CT/MRI, with homogeneous and/or < 1 cm lesions were excluded. Differences between adenomas and non-adenomas were analyzed using Chi-square, Student t or Fischer tests, and interobserver agreement using weighted kappa test or intraclass correlation coefficient. Independent variables associated with adenomas were searched for using multivariable analysis. Area under the receiver operating characteristic curve (AUC) of the final model and its diagnostic performances were calculated.

RESULTS

Final population comprised 183 patients (106 women, 77 men, mean age 53.2 ± 14.4 years) with 124 non-adenomas and 59 heterogeneous adenomas. Macroscopic or microscopic fat on CT/MRI allowed diagnosis of adenoma with 98% specificity and 63% sensitivity. Interobserver agreement was almost perfect for macroscopic fat (k = 0.82; 95% CI 0.66; 0.94) and substantial for microscopic fat (k = 0.75; 95% CI 0.62; 0.86). A multivariable model including micro- or macroscopic fat [Odds ratio (OR) 81.19; 95% CI 20.17; 572.27], diameter < 5.5 cm (OR 7.32; 95% CI 2.17; 31.28), calcifications (OR 5.68; 95% CI 2.08; 16.18), and hemorrhage (OR 3.10; 95% CI 0.70; 15.35) had an AUC of 0.91 (95% CI 0.86; 0.96), 71% (42/59, 95% CI 58; 82) sensitivity, 93% (115/124; 95% CI 87; 97) specificity, and 86% (157/183; 95% CI 79; 90) accuracy for the diagnosis of adenoma.

CONCLUSION

A multivariable model enables CT/MR diagnosis of heterogeneous adenomas. Presence of microscopic fat, even if partial, in a heterogeneous mass is highly specific of adenoma.

Clinical significance of a 10-mm cutoff size for adrenal lesions: a retrospective study with 547 non-oncologic patients undergoing adrenal computed tomography

PURPOSE

To investigate the proportion of clinically significant adrenal lesions in patients with a subcentimeter adrenal lesion, and the sensitivity of a cutoff size of 10 mm on computed tomography (CT).

METHODS

This retrospective study included consecutive 547 non-oncologic patients who underwent adrenal CT. Clinically significant adrenal lesions were defined as those that were biochemically abnormal (n = 99) or surgically resected according to the clinician's decision (n = 23). Long-axis diameters (LDs) and short-axis diameters (SDs) of the lesions were measured on CT by two independent readers. Likelihood of the focal lesion was analyzed using a five-point scale (1 = very low; 5 = very high). 66 Sensitivities for clinically significant lesions were analyzed according to cutoff size. Proportions of the clinically significant lesions for subcentimeter lesions were analyzed according to the visual score.

RESULTS

Sensitivities for clinically significant lesions for cutoffs of 10, 15, and 20 mm were 93%, 79%, and 63% for LD and 85%, 61%, and 49% for SD for Reader 1 and 89%, 78%, and 65% for LD and 80%, 65%, and 48% for SD for Reader 2, respectively (p < 0.001 for 10 mm versus the other cutoffs). In subcentimeter lesions with visual scores of 1-3, the proportions of clinically significant lesions were 5.4% for LD or SD for Reader 1 and 6.6% for LD and 7.7% for SD for Reader 2, respectively.

CONCLUSION

A lesion LD of ≥ 10 mm was a reasonable cutoff for determining adrenal abnormality. Subcentimeter lesions without visually high suspicion had a low risk of clinical significant lesions in our study cohort. Higher cutoffs significantly decreased sensitivity.