Differentiation of lipid-poor adrenal adenomas from non-adenomas with magnetic resonance imaging: Utility of dynamic, contrast enhancement and single-shot T2-weighted sequences

Optimal and novel imaging of the adrenal glands

PURPOSE OF REVIEW

Adrenal imaging forms an important role in the workup of adrenal masses. The purpose of this review is to briefly review the traditional role of imaging in adrenal diseases and highlight the most recent research and new applications aimed to improve diagnostic accuracy.

RECENT FINDINGS

The current review will focus on new applications of computed tomography (CT), MRI and PET/CT imaging, addressing the implications of artificial intelligence and radiomics in progressing diagnostic accuracy.

SUMMARY

The new applications of adrenal imaging are improving diagnostic accuracy and expanding the role of imaging, particularly with novel PET radiotracers and the use of artificial intelligence.

S, Molina CAF, Elias Jr. J, Muglia VF. Frequency of lipid-poor adrenal adenomas in magnetic resonance imaging examinations of the abdomen

Objective

To estimate the frequency of lipid-poor adenomas (LPAs) in magnetic resonance imaging (MRI) examinations.

Materials and Methods

We retrospectively investigated adrenal lesions on MRI examinations performed in a total of 2,014 patients between January 2016 and December 2017. After exclusions, the sample comprised 69 patients with 74 proven adenomas. Two readers (reader 1 and reader 2) evaluated lesion size, laterality, homogeneity, signal drop on out-of-phase (OP) images, and the signal intensity index (SII). An LPA was defined as a lesion with no signal drop on OP images and an SII < 16.5%. For 68 lesions, computed tomography (CT) scans (obtained within one year of the MRI) were also reviewed.

Results

Of the 69 patients evaluated, 42 (60.8%) were women and 27 (39.2%) were men. The mean age was 59.2 ± 14.1 years. Among the 74 confirmed adrenal adenomas evaluated, the mean lesion size was 18.5 ± 7.7 mm (range, 7.0-56.0 mm) for reader 1 and 21.0 ± 8.3 mm (range, 7.0-55.0 mm) for reader 2 (p = 0.055). On the basis of the signal drop in OP MRI sequences, both readers identified five (6.8%) of the 74 lesions as being LPAs. When determined on the basis of the SII, that frequency was three (4.0%) for reader 1 and four (5.4%) for reader 2. On CT, 21 (30.8%) of the 68 lesions evaluated were classified as LPAs.

Conclusion

The prevalence of LPA was significantly lower on MRI than on CT. That prevalence tends to be even lower when the definition of LPA relies on a quantitative analysis rather than on a qualitative (visual) analysis.

Qualitative Heterogeneous Signal Drop on Chemical Shift (CS) MR Imaging: Correlative Quantitative Analysis between CS Signal Intensity Index and Contrast Washout Parameters Using T1-Weighted Sequences

The aim of this study was to calculate MRI quantitative parameters extracted from chemical-shift (CS) and dynamic contrast-enhanced (DCE) T1-weighted (T1-WS) images of adrenal lesions (AL) with qualitative heterogeneous signal drop on CS T1-WS and compare them to those of AL with homogeneous or no signal drop on CS T1-WS. On 3 T MRI, 65 patients with a total of 72 AL were studied. CS images were qualitatively assessed for grouping AL as showing homogeneous (Group 1, n = 19), heterogeneous (Group 2, n = 23), and no (Group 3, n = 30) signal drop. Histopathology or follow-up data served as reference standard to classify AL. ROIs were drawn both on CS and DCE images to obtain adrenal CS signal intensity index (ASII), absolute (AWO), and relative washout (RWO) values. Quantitative parameters (QP) were compared with ANOVA analysis and post hoc Dunn’s test. The performance of QP to classify AL was assessed with receiver operating characteristic analysis. CS ASII values were significantly different among the three groups (p < 0.001) with median values of 71%, 53%, and 3%, respectively. AWO/RWO values were similar in Groups 1 (adenomas) and 2 (benign AL) but significantly (p < 0.001) lower in Group 3 (20 benign AL and 10 malignant AL). With cut-offs, respectively, of 60% (Group 1 vs. 2), 20% (Group 2 vs. 3), and 37% (Group 1 vs. 3), CS ASII showed areas under the curve of 0.85, 0.96, and 0.93 for the classification of AL, overall higher than AWO/RWO. In conclusion, AL with qualitative heterogeneous signal drop at CS represent benign AL with QP by DCE sequence similar to those of AL with homogeneous signal drop at CS, but different to those of AL with no signal drop at CS; ASII seems to be the only quantitative parameter able to differentiate AL among the three different groups.

ACR Appropriateness Criteria® Adrenal Mass Evaluation: 2021 Update

The appropriate evaluation of adrenal masses is strongly dependent on the clinical circumstances in which it is discovered. Adrenal incidentalomas are masses that are discovered on imaging studies that have been obtained for purposes other than adrenal disease. Although the vast majority of adrenal incidentalomas are benign, further radiological and biochemical evaluation of these lesions is important to arrive at a specific diagnosis. Patients with a history of malignancy or symptoms of excess hormone require different imaging evaluations than patients with incidentalomas. This document reviews imaging approaches to adrenal masses and the various modalities utilized in evaluation of adrenal lesions. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

A Preliminary Study for Distinguish Hormone-Secreting Functional Adrenocortical Adenoma Subtypes Using Multiparametric CT Radiomics-Based Machine Learning Model and Nomogram

Purpose: To explore the application value of multiparametric computed tomography (CT) radiomics in non-invasive differentiation between aldosterone-producing and cortisol-producing functional adrenocortical adenomas. Methods: This retrospective review analyzed 83 patients including 41 patients with aldosterone-producing adenoma and 42 patients with cortisol-producing adenoma. The quantitative radiomics features were extracted from the complete unenhanced, arterial, and venous phase CT images. A comparative study of several frequently used machine learning models (linear discriminant analysis, logistic regression, random forest, and support vector machine) combined with different feature selection methods was implemented in order to determine which was most advantageous for differential diagnosis using radiomics features. Then, the integrated model using the combination of radiomic signature and clinic-radiological features was built, and the associated calibration curve was also presented. The diagnostic performance of these models was estimated and compared using the area under the receiver operating characteristic (ROC) curve (AUC). Result: In the radiomics-based machine learning model, logistic regression model with LASSO (least absolute shrinkage and selection operator) outperformed the other models, which yielded a sensitivity of 0.935, a specificity of 0.823, and an accuracy of 0.887 [AUC = 0.882, 95% confidence interval (CI) = 0.819-0.945]. Moreover, the nomogram representing the integrated model achieved good discrimination performances, which yielded a sensitivity of 0.915, a specificity of 0.928, and an accuracy of 0.922 (AUC = 0.902, 95% CI = 0.822-0.982), and it was better than that of the radiomics model alone. Conclusion: This study found that the combination of multiparametric radiomics signature and clinic-radiological features can non-invasively differentiate the subtypes of hormone-secreting functional adrenocortical adenomas, which may have good potential for facilitating the diagnosis and treatment in clinical practice.

Preresection Radiologic Assessment and Imaging Features of 156 Pathologically Proven Adrenal Adenomas

PURPOSE

The aims of the study were to assess the typical and atypical radiologic features of pathologically proven adrenal adenomas and to determine the relationship between the radiologic and histopathologic classification.

METHODS

We retrospectively studied 156 pathologically proven adrenal adenomas in 154 patients from our institutional databases who have computed tomography (CT) and/or magnetic resonance imaging (MRI) examinations before intervention. We determined the histopathologic diagnosis (typical or atypical) using Weiss scoring and classified the adenomas radiologically into typical, atypical, or indeterminate based on lesion size, precontrast CT attenuation, absolute percentage washout, calcification, and necrosis. The κ statistic was used to assess the agreement between radiologists. The Fisher exact test was used to compare the radiologic and pathological classifications.

RESULTS

In consensus, there were 83 typical, 42 atypical, and 31 indeterminate adrenal lesions. Logistic regression model showed that radiologically atypical adenoma was significantly associated with larger size, lobulated shape, higher unenhanced CT attenuation, heterogeneous appearance, nonfunctioning status, absolute percentage washout of less than 60%, and a signal intensity index of less than 16.5%.Pathologically, 147 adenomas were pathologically typical (Weiss 0), and 9 adenomas were pathologically atypical (Weiss 1-2). Radiologically, there was substantial agreement between both readers, with Cohen κ at 0.71. Approximately 98% of radiologically typical adenomas were pathologically typical. Only 17% of radiologically atypical adenomas were pathologically atypical. All radiologically indeterminate adenomas were pathologically typical. However, some of the radiologically indeterminate and typical adenomas still had an atypical component on pathologic analysis, such as necrosis, nuclear atypia, or oncocytic features.

CONCLUSIONS

Radiologically atypical lesion was significantly associated with larger size and higher unenhanced CT attenuation. Approximately 27% of the cases demonstrated atypical features on imaging. Most radiologically atypical adrenal adenomas are pathologically typical.

Mimics, pitfalls, and misdiagnoses of adrenal masses on CT and MRI

Due to the widespread use of imaging, incidental adrenal masses are commonly encountered. A number of pitfalls can result in misdiagnosis of these lesions, including inappropriate choice of imaging technique, presence of pseudolesions, and overlap of imaging features of different adrenal lesions. This article explores the potential pitfalls in imaging of the adrenal glands, on computed tomography and magnetic resonance imaging, that can lead to misinterpretation. Clues to correct diagnoses are provided to evade potential misinterpretation.

Magnetic resonance imaging of adrenal gland: state of the art

Detection of adrenal lesions, because of the widespread use of imaging and especially high-resolution imaging procedures, is increased. Because of the importance to characterize those findings, magnetic resonance imaging (MRI), in particular chemical shift imaging (CSI), is useful to distinguish whether a lesion is benignant or malignant and to avoid further diagnostic or surgical procedures. It represents the first choice of imaging in patient like children or pregnant women, and a valid complement to other imaging techniques like CT or PET/CT. In this review we analyze the role and characteristic of MRI and the imaging features of most common benignant (adenoma, hyperplasia, pheochromocytoma, hemorrhage, cyst, myelolipoma, teratoma, ganglioneuroma, cystic lymphangioma, hemangioma) and malignant [neuroblastoma, adrenocortical carcinoma (ACC), metastases, lymphoma] adrenal lesions.

Update on Gadolinium-Based Contrast Agent-Enhanced Imaging in the Genitourinary System

OBJECTIVE. The purpose of this article is to review gadolinium-based contrast agent (GBCA)-enhanced MRI applications in the genitourinary system. CONCLUSION. Nephrogenic systemic fibrosis is rare or nonexistent with standard dosing of group II GBCAs. Gadolinium retention, cost, and examination times are emerging considerations affecting GBCA use. GBCA is unnecessary to diagnose adrenal adenomas, simple cysts, and some Bosniak category II cysts; however, it is required to determine solid or septal renal mass enhancement. Biparametric prostate MRI requires high-quality and reproducible DWI; therefore, dynamic contrast-enhanced MRI remains valuable in selected prostate MRI examinations.

The role of dynamic post-contrast T1-w MRI sequence to characterize lipid-rich and lipid-poor adrenal adenomas in comparison to non-adenoma lesions: preliminary results

PURPOSE

The purpose of the article is to compare the features of wash-out (WO) parameters between lipid-rich and lipid-poor adrenal adenomas as well as with a group of non-adenoma adrenal lesions.

METHODS

46 patients (36 F and 10 M, median age 58 years) with unilateral adrenal lesions (35 adenomas, 7 pheochromocytomas, 1 carcinoma, and 3 metastases) were prospectively evaluated; adrenal lesions were divided into adenomas (Group 1) and non-adenomas (Group 2). MR imaging was performed with a 3-Tesla scanner using pre- and post-contrast dedicated sequences. On the basis of the evaluation of qualitative chemical-shift (CS) signal intensity (SI) loss, adrenal adenomas were, respectively, divided in Group 1A (n = 25) as lipid-rich and Group 1B (n = 10) as lipid-poor; non-adenoma adrenal lesions were grouped in Group 2 (n = 11). The following parameters were evaluated: size (mm), CS SI index (%), early (5 min), and delayed (10 min) Relative (R) and Absolute (A) WO values (%).

RESULTS

The comparison of AWO and RWO showed significant (p ≤ 0.05) differences between Group 1A and Groups 1B and 2, both using 5- and 10-min images for calculation; conversely, no differences in these dynamic parameters were found between Group 1B and 2; AWO and RWO values were significantly lower in adrenal lesions of Groups 1B and 2 compared to Group 1A, both using 5- and 10-min images for calculation.

CONCLUSIONS

The quantitative evaluation of WO parameters could not be used to characterize lipid-poor adrenal adenomas for which alternative imaging modalities are required.

Pancreatic neuroendocrine tumor: Correlations between MRI features, tumor biology, and clinical outcome after surgery

PURPOSE

To assess which magnetic resonance imaging (MRI) features are associated with pNETs (pancreatic neuroendocrine tumors) grade based on the WHO classification, as well as identify MRI features related to disease progression after surgery.

MATERIALS AND METHODS

In this Institutional Review Board (IRB)-approved study, 1.5T and 3.0T MRI scans of 80 patients with surgically verified pNETs were assessed. The images were evaluated for tumor location; size; pattern; predominant signal intensity on precontrast T₁ - and T₂ -weighted images, as well as on postcontrast arterial and portal venous phase T₁ -weighted sequences; presence of pancreatic duct dilatation; pancreatic atrophy; restricted diffusion; vascular involvement by the tumor; extrapancreatic tumor spread; and synchronous liver metastases. Tumors were graded based on the WHO classification and patients were followed-up with computed tomography (CT) or MRI after surgical resection. Data were analyzed with Student's t and chi-square tests, logistic regression, and Kaplan-Meier curves.

RESULTS

The MRI features that were associated with aggressive tumors were: size >2.0 cm (odds ratio [OR] = 4.8, P = 0.002), "T₂ nonbright lesions" on T₂ -weighted images (OR = 4.6, P = 0.008), presence of pancreatic ductal dilatation (OR = 4.9, P = 0.024), and restricted diffusion within the lesion (OR = 4.9, P = 0.013). Differences in progression-free survival distribution were found for patients whose pNETs were associated with the following MRI features: size >2.0 cm (χ² (1) = 6.0, P = 0.014), "nonbright lesions" on T₂ -weighted images (χ² (1) = 6.8, P = 0.009), and presence of pancreatic duct dilatation (χ² (1) = 10.9, P = 0.001).

CONCLUSION

MRI features can be used to assess pNETs aggressiveness and identify patients at risk for early disease progression after surgical resection.

LEVEL OF EVIDENCE

3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;47:425-432.

Update on CT and MRI of Adrenal Nodules

OBJECTIVE

The objective of this article is to review the current role of CT and MRI for the characterization of adrenal nodules.

CONCLUSION

Unenhanced CT and chemical-shift MRI have high specificity for lipid-rich adenomas. Dual-energy CT provides comparable to slightly lower sensitivity for the diagnosis of lipid-rich adenomas but may improve characterization of lipid-poor adenomas. Nonadenomas containing intracellular lipid pose an imaging challenge; however, nonadenomas that contain lipid may be potentially diagnosed using other imaging features. Multiphase adrenal washout CT can be used to differentiate lipid-poor adenomas from metastases but is limited for the diagnosis of hypervascular malignancies and pheochromocytoma.

Differentiation between adrenal adenomas and nonadenomas using dynamic contrast-enhanced computed tomography

This study was performed to evaluate the findings including the time density curve (TD curve), the relative percentage of enhancement washout (Washr) and the absolute percentage of enhancement washout (Washa) at dynamic contrast-enhanced computed tomography (DCE-CT) in 70 patients with 79 adrenal masses (including 44 adenomas and 35 nonadenomas) confirmed histopathologically and/or clinically. The results demonstrated that the TD curves of adrenal masses were classified into 5 types, and the type distribution of the TD curves was significantly different between adenomas and nonadenomas. Types A and C were characteristic of adenomas, whereas types B, D and E were features of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma based on the TD curves were 93%, 80% and 87%, respectively. Furthermore, when myelolipomas were excluded, the specificity and accuracy for adenoma were 90% and 92%, respectively. The Washr and the Washa values for the adenomas were higher than those for the nonadenomas. The diagnostic efficiency for adenoma was highest at 7-min delay time at DCE-CT; Washr was more efficient than Washa. Washr ≥34% and Washa ≥43% were both suggestive of adenomas and, on the contrary, suspicious of nonadenomas. The sensitivity, specificity and accuracy for the diagnosis of adenoma were 84%, 77% and 81%, respectively. When myelolipomas were precluded, the diagnostic specificity and accuracy were 87% and 85%, respectively. Therefore, DCE-CT aids in characterization of adrenal tumors, especially for lipid-poor adenomas which can be correctly categorized on the basis of TD curve combined with the percentage of enhancement washout.

Multiple Endocrine Neoplasia Syndromes: A Comprehensive Imaging Review

MEN1, MEN2, and MEN4 comprise a series of familial disorders involving the simultaneous occurrence of tumors in more than one endocrine organ, collectively known as multiple endocrine neoplasia. Patients with this family of disorders develop tumors of the parathyroid gland, pancreas, pituitary gland, adrenal gland, and thyroid gland, along with miscellaneous neuroendocrine tumors of the respiratory and gastrointestinal tracts. Although some patients undergo early prophylactic surgical management, particularly in the setting of familial medullary thyroid carcinoma, many develop tumors later in life. These tumors are often discovered at imaging for screening purposes. Recognition of the imaging features of the known tumors is important for appropriate patient management.