Characterization Of Adrenal Lesions Research Articles

Diagnostic accuracy of 18F-FDG PET/TC for the characterization of adrenal lesions in a heterogeneous population

Searchable abstracts of presentations at key conferences in endocrinology ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Machine learning analysis of adrenal lesions: preliminary study evaluating texture analysis in the differentiation of adrenal lesions

This study aimed to determine the accuracy of texture analysis in differentiating adrenal lesions on unenhanced computed tomography (CT) images. In this single-center retrospective study, 166 adrenal lesions in 140 patients (64 women, 76 men; mean age 56.58 ± 13.65 years) were evaluated between January 2015 and December 2019. The lesions consisted of 54 lipid-rich adrenal adenomas, 37 lipid-poor adrenal adenomas (LPAs), 56 adrenal metastases (ADM), and 19 adrenal pheochromocytomas (APhs). Each adrenal lesion was segmented by manually contouring the borders of the lesion on unenhanced CT images. A texture analysis of the CT images was performed using Local Image Feature Extraction software. First-order and second-order texture parameters were assessed, and 45 features were extracted from each lesion. One-Way analysis of variance with Bonferroni correction and the Mann-Whitney U test was performed to determine the relationships between the texture features and adrenal lesions. Receiver operating characteristic curves were performed for lesion discrimination based on the texture features. Logistic regression analysis was used to generate logistic models, including only the texture parameters with a high-class separation capacity (i.e., P < 0.050). SPSS software was used for all statistical analyses. First-order and second-order texture parameters were identified as significant factors capable of differentiating among the four lesion types (P < 0.050). The logistic models were evaluated to ascertain the relationships between LPA and ADM, LPA and APh, and ADM and APh. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of the first model (LPA vs. ADM) were 85.7%, 70.3%, 81.3%, 76.4%, and 79.5%, respectively. The sensitivity, specificity, PPV, NPV, and accuracy of the second model (LPA vs. APh) were all 100%. The sensitivity, specificity, PPV, NPV, and accuracy of the third model (ADM vs. APh) were 87.5%, 82%, 36.8%, 98.2%, and 82.7%, respectively. Texture features may help in the characterization of adrenal lesions on unenhanced CT images.

Adrenal Lesion Classification on T1-Weighted Abdomen Images with Convolutional Neural Networks

Adrenal lesions are usually discovered incidentally during other health screenings and are usually benign. However, it is vital to take precautions when a malignant adrenal lesion is detected. Especially deep learning models developed in the last ten years give successful results on medical images. In this paper, adrenal lesion characterization on T1-weighted magnetic resonance abdomen images was aimed using convolutional neural network (CNN) which is one of the deep learning methods. Firstly, effects of important model parameters are assessed on performance of CNN, so optimum CNN model is obtained for classification of adrenal lesions. For a fixed number of convolution filters determined in the first stage of the study, CNN model implemented by different kernel sizes were trained. According to the best result obtained, this time the kernel size was kept constant, and experiments were made for different filter numbers. Finally, studies were carried out with CNN structures of different depths and the results were compared. As a result of the studies, when filter is selected as [5 20], the best results in the trainings conducted with a single-block CNN structure are obtained 0.97, 0.90, 0.98, 0.90, 0.90, and 0.94, for accuracy, sensitivity, specificity, precision, F1-score, and AUC score, respectively. The study was compared with the studies in the literature, and it was seen that it was superior to them.

Adrenal Mass Characterization in the Era of Quantitative Imaging: State of the Art.

Simple SummaryNon-invasive characterization of adrenal lesions requires a rigorous approach. Although CT is the cornerstone of adrenal lesion characterization, a multimodality multiparametric imaging approach helps improve confidence in adrenal lesion characterization. Detection and characterization of adrenal lesions have evolved during the past two decades. Although the role of imaging in adrenal lesions associated with hormonal secretion is usually straightforward, characterization of non-functioning adrenal lesions may be challenging to confidently identify those that need to be resected. Although many adrenal lesions can be readily diagnosed when they display typical imaging features, the diagnosis may be challenging for atypical lesions. Computed tomography (CT) remains the cornerstone of adrenal imaging, but other morphological or functional modalities can be used in combination to reach a diagnosis and avoid useless biopsy or surgery. Early- and delayed-phase contrast-enhanced CT images are essential for diagnosing lipid-poor adenoma. Ongoing studies are evaluating the capabilities of dual-energy CT to provide valid virtual non-contrast attenuation and iodine density measurements from contrast-enhanced examinations. Adrenal lesions with attenuation values between 10 and 30 Hounsfield units (HU) on unenhanced CT can be characterized by MRI when iodinated contrast material injection cannot be performed. 18F-FDG PET/CT helps differentiate between atypical benign and malignant adrenal lesions, with the adrenal-to-liver maximum standardized uptake value ratio being the most discriminative variable. Recent studies evaluating the capabilities of radiomics and artificial intelligence have shown encouraging results.

Unenhanced Dual-Layer Spectral-Detector CT for Characterizing Indeterminate Adrenal Lesions.

Background Unenhanced dual-layer spectral-detector CT may facilitate adrenal lesion characterization; however, no studies have evaluated its incremental diagnostic yield for indeterminate lesions (unenhanced attenuation >10 HU) in comparison to that with conventional unenhanced CT. Purpose To determine whether spectral attenuation analysis improves characterization of lipid-poor adrenal adenomas from nonadenomas compared to that with mean attenuation and histogram analysis of conventional CT images. Materials and Methods This retrospective study included patients with indeterminate adrenal lesions who underwent unenhanced dual-layer spectral-detector CT between March 2018 and June 2020. Mean attenuation on conventional 120-kVp images (HUconv), histogram-based percentage negative pixels (proportion of all pixels <0 HU) on conventional 120-kVp images, and mean attenuation on virtual monoenergetic images (VMIs) at 40-140 keV were measured for each lesion. The attenuation difference between virtual monoenergetic 140- and 40-keV images (ΔHU; ie, Hounsfield unit at 140 keV - Hounsfield unit at 40 keV) and ΔHU indexed with HUconv (ΔHU index; ie, ΔHU/HUconv × 100) were calculated. Conventional and virtual monoenergetic imaging parameters were compared between lipid-poor adenomas and nonadenomas by using the Mann-Whitney U test. Receiver operating characteristic analysis was performed to determine the sensitivity for attaining at least 95% specificity in characterizing adenomas from nonadenomas; sensitivity was compared by using the McNemar test. Results A total of 232 patients (mean age ± standard deviation, 67 years ± 11; 145 men) with 129 lipid-poor adenomas and 103 nonadenomas were evaluated. HUconv and mean attenuation on VMIs at 40-140 keV were lower and the percentage negative pixels, ΔHU, and ΔHU index higher in lipid-poor adenomas than in nonadenomas (P < .001 for all). Attenuation differences between adenomas and nonadenomas on VMIs were maximal at 40 keV (23 HU at 40 keV vs 5 HU at 140 keV). The highest sensitivities for differentiating adenomas and nonadenomas were achieved for virtual monoenergetic ΔHU index (77% [99 of 129 adenomas]), attenuation on 40-keV images (71% [91 of 129 adenomas]), and ΔHU (67% [87 of 129 adenomas]) compared to HUconv (35% [45 of 129 adenomas]) and percentage negative pixels (30% [39 of 129 adenomas]) (P < .001 for all; specificity, 95% [98 of 103 nonadenomas]). Conclusion Spectral attenuation analysis enabled differentiation of lipid-poor adenomas from nonadenomas with higher sensitivity than mean attenuation or histogram analysis of conventional CT images. © RSNA, 2021 Online supplemental material is available for this article.

Pitfalls and differential diagnosis on adrenal lesions: current concepts in CT/MR imaging: a narrative review

The purpose of this pictorial essay is to review the imaging findings of adrenal lesions. Adrenal lesions could be divided into functioning or non-functioning masses, primary or metastatic, and benign or malignant. Imaging techniques have undergone significant advances in recent years. The most significant objective of adrenal imaging is represented by the detection and, when possible, characterization of adrenal lesions in order to direct patient management correctly. The detection and management of adrenal lesions is based on cross-sectional imaging obtained with non-contrast CT (tumour density), contrast-enhanced CT including delayed washout (either absolute percentage washout or relative percentage one) and finally with MR chemical shift analysis (loss of signal intensity between in-phase and out-of-phase images including both qualitative and quantitative estimates of signal loss). The small incidental adrenal nodules are benign, in most of cases; some tumors such as lipid-rich adenoma and myelolipoma have characteristic features that can be diagnosed accurately in CT. On contrary, if the presenting contrast-enhanced CT shows an adrenal mass with uncertain or malignant morphologic features, particularly in patients with a known history of malignancy, further evaluations should be considered. The most significative implications for radiologists are represented by how to assess risk of malignancy on imaging and what follow-up to indicate if an adrenal incidentaloma is not surgically removed.

Adrenal Adenomas versus Metastases: Diagnostic Performance of Dual-Energy Spectral CT Virtual Noncontrast Imaging and Iodine Maps.

Background Dual-energy CT allows virtual noncontrast (VNC) attenuation and iodine density measurements from contrast material-enhanced examination, potentially enabling adrenal lesion characterization. However, data regarding diagnostic performance remain limited, and combined diagnostic values have never been investigated. Purpose To determine whether VNC attenuation, iodine density, and combination of the two allow reliable differentiation between adrenal adenomas and metastases. Materials and Methods This retrospective study included patients with adrenal lesions who underwent unenhanced and portal venous phase dual-energy CT between January 2017 and December 2018. Unenhanced, contrast-enhanced, and VNC attenuation, as well as iodine density, were measured for each lesion. Agreement between unenhanced and VNC attenuation was assessed by using Wilcoxon rank-sum test, Pearson correlation coefficient, and Bland-Altman plot. The ratio of iodine density to VNC attenuation was calculated for lesions with positive VNC attenuation. Each parameter was compared between adenomas and metastases; diagnostic performance was evaluated by using the area under the receiver operating characteristic curve (AUC) with sensitivity and specificity. Results A total of 149 patients (mean age, 65 years ± 13 [standard deviation]; 89 men; 98 patients with 104 adenomas; 51 patients with 56 metastases) were evaluated. VNC attenuation showed strong positive correlation with unenhanced attenuation (r = 0.92) but resulted in overestimates of adenoma attenuation (mean bias, +11 HU; P < .001) and was less sensitive (P = .03) in the diagnosis of adenomas compared with unenhanced attenuation (sensitivity of 79% [81 of 102] [95% confidence interval {CI}: 70%, 87%] and specificity of 95% [53 of 56] [95% CI: 85%, 99%] versus sensitivity of 85% [87 of 102] [95% CI: 77%, 92%] and specificity of 96% [54 of 56] [95% CI: 88%, 100%], with thresholds of ≤29 HU and ≤22 HU, respectively). Contrast-enhanced attenuation had no discriminatory ability (AUC, 0.54; 95% CI: 0.45, 0.62). Iodine density yielded moderate performance (sensitivity of 78% [80 of 102] [95% CI: 69%, 86%] and specificity of 71% [40 of 56] [95% CI: 58%, 83%], with a threshold of ≥1.82 mg/mL). The iodine-to-VNC ratio was higher in adenomas than in metastases (mean, 14.5 vs 4.6; P < .001), with sensitivity of 95% (97 of 102; 95% CI: 89%, 98%) and specificity of 95% (53 of 56; 95% CI: 85%, 99%), with a threshold of 6.7 or greater. Conclusion Contrast-enhanced dual-energy CT during the portal venous phase enabled accurate differentiation between adrenal adenomas and metastases by combining virtual noncontrast attenuation and iodine density. Virtual noncontrast imaging alone led to overestimates of adenoma attenuation, and iodine density alone had limited discriminatory utility. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Hindman and Megibow in this issue.

SAT-172 FDG PET/CT in Benign vs. Malignant Adrenocortical Tumors

18F-fluorodeoxyglucose positron emission tomography computed tomography (FDG PET/CT) is frequently used for evaluation of indeterminate adrenal nodules.The objective of this study was to evaluate the diagnostic performance of FDG PET/CT in distinguishing benign adrenocortical adenomas (ACA) from adrenocortical carcinoma (ACC).We identified 139 patients in our institution who completed both FDG PET/CT and adrenal biopsy or adrenalectomy from 2001 to 2019 using the institutional Electronic Medical Record Search Engine (EMERSE). Patients with adrenal pathology revealing non-adrenocortical tumors were excluded. The imaging characteristics of ACAs were compared with ACCs.Sixteen patients with ACAs and 50 patients with ACC were identified; of the latter, 30 were excluded, because FDG PET/CT imaging was completed after adrenalectomy. The average age of the ACC vs. ACA group was 48±14 and 52±17 years, respectively, with a gender composition of 35% and 25% men, respectively. All 20 patients with ACC had FDG avid lesions, defined by imaging report and increased ratio of adrenal tumor maximum standardized uptake value (SUVmax) to hepatic parenchymal average SUV (SUVmean) of greater than 2.5. Among those with ACAs, 11 had positive, 1 had mildly positive, 3 had indeterminate, and 1 had negative FDG PET/CT findings according to the report. Ratio of adrenal SUVmax to hepatic SUVmean was greater in ACC compared to ACA (13.5 versus 1.6, respectively, p = 0.13), but did not reach statistical significance, likely due to the small sample size and unavailability of SUV ratios for all lesions.Our study identified a large number of ACAs that were deemed FDG avid but without adrenal SUVmax to hepatic SUVmean ratio of greater than 2.5. Although the sensitivity, and therefore the negative predictive value, of FDG PET/CT scan is excellent for the diagnosis of ACC, our data does not allow for the calculation of specificity. This is due to the selection bias inherent in our patient population referred for evaluation of unusual adrenal masses, and the fact that ACAs with negative FDG PET/CT often do not undergo surgery or biopsy, and therefore pathology results are not available. Despite this limitation, our findings show that calculation of the ratio of adrenal SUVmax to hepatic SUVmean, rather than lesion SUVmax alone, helps for characterization of adrenal lesions as malignant vs. benign, and that a negative FDG PET/CT is valuable in excluding ACC.

Key Imaging Appearances of Commonly Encountered Pediatric Adrenal Masses

Adrenal masses in children may occur as a result of neoplasm, hemorrhage, infection, or cysts. Ultrasound is the initial imaging modality of choice in suspected adrenal pathology in children. Computed tomography, magnetic resonance imaging, and functional imaging are usually required for confirmation and further characterization of adrenal lesions. This review article highlights the imaging features of common adrenal masses that may involve the adrenal gland in pediatric population.

Characterization of adrenal lesions using MDCT wash-out parameters: diagnostic accuracy of several combinations of intermediate and delayed phases.

To evaluate the diagnostic accuracy of wash-out parameters calculated using multiple intermediate and delayed phases. This prospective study had institutional review board approval and informed consent was obtained from all patients. Between January 2012 and October 2016, 108 consecutive oncologic patients (59 males, 49 females, mean age 52.6years; 129 diagnosed lesions) underwent multiphasic CT protocol including unenhanced (UE), arterial (AE), portal (PE), 5-min (DE-5) and the 15-min (DE-15) delayed phases of adrenal glands. All images were randomly reviewed in consensus by two radiologists experienced in abdominal CT, unaware of clinical or pathologic data. Location, size and density were recorded. Absolute wash-out, percentage wash-out (PWO) and percentage enhancement wash-out ratio were calculated. The thresholds yielding the best accuracy in differentiating adenomas from nonadenomas were retrospectively determined on the basis of ROC curves. The corresponding diagnostic accuracy values were calculated. Paired sample t test was used to assess differences among imaging parameters within subgroups. Student t test was applied to compare lesions between independent subgroups. p values ≤ 0.05 were considered significant. The final diagnosis included 82 adenomas (62 lipid-rich and 20 lipid-poor) and 47 nonadenomas (42 metastases, 3 pheochromocytomas, 2 carcinomas). All the 62 lipid-rich adenomas were correctly diagnosed as benign lesions on the basis of their UE attenuation < 10 HU. The PEAK attenuation was achieved during AE phase for 51/129 lesions (39.5%) and at the time of PE phase in 78/129 lesions (60.5%). The best overall accuracy in diagnosing adenomas (97.6%; 126/129 lesions correctly diagnosed) was obtained using 40% threshold for calculating PWO from PEAK to DE-15 scan. If only an intermediate phase is available, the 15-min delayed scan should be acquired to avoid any drop in diagnostic accuracy. The availability of two intermediate phase may be used to easy CT schedule by obviating the need to acquire a longer delayed phase.

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

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. 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. 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 [SUVmax (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. 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.

Characterization of Adrenal Lesions on Unenhanced MRI Using Texture Analysis: A Machine-Learning Approach.

Adrenal adenomas (AA) are the most common benign adrenal lesions, often characterized based on intralesional fat content as either lipid-rich (LRA) or lipid-poor (LPA). The differentiation of AA, particularly LPA, from nonadenoma adrenal lesions (NAL) may be challenging. Texture analysis (TA) can extract quantitative parameters from MR images. Machine learning is a technique for recognizing patterns that can be applied to medical images by identifying the best combination of TA features to create a predictive model for the diagnosis of interest. To assess the diagnostic efficacy of TA-derived parameters extracted from MR images in characterizing LRA, LPA, and NAL using a machine-learning approach. Retrospective, observational study. Sixty MR examinations, including 20 LRA, 20 LPA, and 20 NAL. Unenhanced T1 -weighted in-phase (IP) and out-of-phase (OP) as well as T2 -weighted (T2 -w) MR images acquired at 3T. Adrenal lesions were manually segmented, placing a spherical volume of interest on IP, OP, and T2 -w images. Different selection methods were trained and tested using the J48 machine-learning classifiers. The feature selection method that obtained the highest diagnostic performance using the J48 classifier was identified; the diagnostic performance was also compared with that of a senior radiologist by means of McNemar's test. A total of 138 TA-derived features were extracted; among these, four features were selected, extracted from the IP (Short_Run_High_Gray_Level_Emphasis), OP (Mean_Intensity and Maximum_3D_Diameter), and T2 -w (Standard_Deviation) images; the J48 classifier obtained a diagnostic accuracy of 80%. The expert radiologist obtained a diagnostic accuracy of 73%. McNemar's test did not show significant differences in terms of diagnostic performance between the J48 classifier and the expert radiologist. Machine learning conducted on MR TA-derived features is a potential tool to characterize adrenal lesions. 4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018.

Chemical Shift MR Imaging of the Adrenal Gland: Principles, Pitfalls, and Applications.

Adrenal lesions are a common imaging finding. The vast majority of adrenal lesions are adenomas, which contain intracytoplasmic (microscopic) fat. It is important to distinguish between adenomas and malignant tumors, and chemical shift magnetic resonance (MR) imaging can be used to accomplish this distinction by depicting the fat in adenomas. Chemical shift imaging is based on the difference in precession frequencies of water and fat molecules, which causes them to be in different relative phases during the acquisition sequence and allows in-phase and opposed-phase images to be obtained. It is important to acquire these images by using the earliest possible echo times, with the opposed-phase echo before the in-phase echo, and by using a single breath hold to preserve diagnostic accuracy. Intracytoplasmic fat is depicted as signal drop on opposed-phase images when compared with in-phase images. Both qualitative and quantitative methods for assessing signal drop are detailed. The appearances of adrenal adenomas and other adrenal tumors on chemical shift MR images are described, and discriminatory ability at chemical shift MR imaging compared with that at adrenal computed tomography (CT) is explained. Other adrenal-related conditions in which chemical shift MR imaging is helpful are also discussed. Chemical shift MR imaging is a robust tool for evaluating adrenal lesions that are indeterminate at nonenhanced CT. However, it is important to know the advantages and disadvantages, including several potential imaging pitfalls. The characterization of adrenal lesions by using chemical shift MR imaging and adrenal CT should always occur in the appropriate clinical setting.

Dual-Energy CT: Applications in Abdominal Imaging

Dual-energy CT (DECT) is a steadily emerging innovative imaging modality. Various applications have been developed and applied to successfully solve diagnostic difficulties that standard CT has in the abdomen. This includes kidney stone differentiation, cholesterol gallstone detection, renal and adrenal lesion characterization, and tumor response monitoring. This article is supposed to give a current update on possible applications of DECT in the abdomen and their evidence.

Adrenal imaging (Part 1): Imaging techniques and primary cortical lesions.

Adrenal glands can be affected by a variety of lesions. Adrenal lesions can either be primary, of adrenal origin, or secondary to other pathologies. Primary adrenal lesions can further be either of cortical or medullary origin. Functioning adrenal lesions can also give clues to the histologic diagnosis and direct workup. Over the years, various imaging techniques have been developed that have increased diagnostic accuracy and helped in better characterization of adrenal lesions non-invasively. In the first part of the two part series, we review adrenal imaging techniques and adrenal cortical tumors such as adenomas, adrenocortical tumors, adrenal hyperplasia and oncocytomas.

Imaging techniques in the characterization of adrenal lesions.

Radiol Bras. 2014 Nov/Dez;47(6):V–VI Currently, with the increasing utilization of sectional imaging methods, most adrenal masses are incidentally found during imaging investigation performed for other indications. Non-functional adenomas constitute the majority of incidentally found adrenal masses. However, the suprarenal gland is also a common site of metastasis and less frequently primary tumors including myelolipoma, pheochromocytoma, and adrenocortical carcinoma. The characterization of an adrenal lesion is critical for an appropriate management of the patient, and is fundamentally based either on the functional or non functional behavior of the lesion, in addition to its benign or malignant nature. Functional adrenal lesions may be symptomatic, with typical clinical and laboratory features, like in many cases of cortical adenomas and pheochromocytomas, which makes their characterization easier. The characterization of non functional adrenal lesions represents a major diagnostic challenge. Extensive lesions may cause symptoms, while smaller lesions are in general incidentally identified or found during staging procedures in cancer patients. In both situations, the characterization of the lesion is strongly based on imaging diagnosis techniques. Fortunately, the advances achieved in the last years allow for a definition of the nature of most adrenal lesions. Computed tomography (CT), magnetic resonance imaging (MRI) and nuclear medicine techniques, including positron emission tomography (PET), may be employed, and all of such techniques are clinically useful in the differentiation of such lesions. Stability is the simplest characteristic to be observed at imaging in order to define the nature of adrenal masses. The absence of growth determined by a simple analysis of previous images represents a consistent characteristic of benignity. The nature of an adrenal lesion is also related to its dimensions; lesions with < 4 cm in diameter tend to be benign, and those above 4 cm in diameter present higher risk for malignancy. CT and MRI techniques can also make the specific diagnosis of adenoma by taking advantage of the abundant amount of intracellular fat that is present in the majority of such lesions. In a pioneering study published in 1991, Lee et al. reported that the radiological attenuation at CT might effectively differentiate adrenal adenomas from non-adenomatous lesions. In a meta analysis, Boland et al. have demonstrated that, with a threshold of 10 Hounsfield units (HU), the test sensitivity for the diagnosis of adenoma would be 71%, and the specificity, 98%. In such a case,

Low yield of chemical shift MRI for characterization of adrenal lesions with high attenuation density on unenhanced CT

To investigate the threshold unenhanced CT density of adrenal nodules at which further evaluation with chemical shift MRI is unlikely to be definitive and therefore not helpful in further characterizing some indeterminate adrenal lesions. Retrospective evaluation of 44 adrenal lesions imaged with unenhanced CT and chemical shift MRI and followed for at least 1 year. Qualitative and quantitative assessment of signal loss on chemical shift MRI was performed. Adenomas were diagnosed if the lesion measured equal or less than 10 HU on unenhanced CT; on MRI a SI index greater than 16.5% or adrenal:spleen chemical shift ratio less than 0.71 was considered diagnostic of adenoma. 31.8% (14/44), 47.7% (21/44), and 20.5% (9/44) of the adrenal lesions had an unenhanced CT attenuation density ≤10, 10-30, and >30 HU. Adrenal lesions with an unenhanced CT density 10-30 and >30 HU had a 76.2% (16/21) and a 33.3% (3/9) chance of being categorized as an adenoma using MRI SI index, respectively. Adrenal lesions with unenhanced attenuation CT density >30 HU had a 66.6% of remaining indeterminate even after evaluation with chemical shift MRI. Chemical shift MRI is reasonable for evaluating adrenal lesions with an unenhanced CT attenuation density less than 30 HU. The likelihood of chemical shift MRI detecting signal loss in lesions CT density greater than 30 HU, however, is low.

Incidental adrenal lesions detected on enhanced abdominal dual-energy CT: Can the diagnostic workup be shortened by the implementation of virtual unenhanced images?

ObjectiveTo determine whether post-processing of the data from portal-phase enhanced dual-energy CT (DECT), with or without the addition of a late enhanced phase acquisition, may enable characterization of adrenal lesions without the need for acquisition of pre-contrast images. Materials and methodsTwenty-two patients with 24 adrenal lesions underwent unenhanced, venous and delayed phase DECT. Of these lesions, 20 were found to be adrenal adenomas, on the basis of histopathology, unenhanced attenuation values between 0 and −10HU, or stability over at least 6 months.For all 24 lesions, true and virtual unenhanced attenuation values were measured based on the data of the portal (VNCp) and the delayed (VNCd) DECT acquisition. The absolute washout values based on the true non-contrast (TNC) and the VNCp and VNCd image series were also measured. The washout was also calculated based on the iodine concentration measured from both contrast-enhanced acquisitions. ResultsMean virtual unenhanced attenuation values of all lesions calculated from the portal phase images was 12.6HU, and was 4.02HU higher than the values based on true unenhanced images (p=0.020). Washout values calculated from virtual unenhanced attenuation based on the VNCp were also significantly different (p=0.0304) while those calculated from VNCd and from iodine concentration correlated with the corresponding values based on the true unenhanced values (p>0.999). ConclusionsOur data indicate that attenuation values of adrenal adenomas based on virtual unenhanced images are significantly higher than those obtained with true unenhanced images. An incidental adrenal lesion with a virtual unenhanced attenuation lower than 10HU can thus be safely characterized as an adenoma.

Combined chemical shift imaging with early dynamic serial gadolinium-enhanced MRI in the characterization of adrenal lesions.

The purpose of this study was to retrospectively evaluate early dynamic serial gadolinium-enhanced and chemical-shift imaging (CSI) MRI to distinguish benign from malignant adrenal tumors. Between July 2007 and December 2011, 205 patients with 239 adrenal lesions (177 adenomas, 54 metastases, 5 pheochromocytomas, and 3 adrenal cortical carcinomas) underwent early dynamic serial gadolinium-enhanced MRI and CSI. CSI was assessed qualitatively and by calculating the adrenal index, and enhancement patterns were evaluated qualitatively and quantitatively. Statistical analyses were performed. Most adenomas exhibited either an arterial blush or homogeneous enhancement, whereas most metastases showed early peripheral or heterogeneous enhancement. Visualization of higher enhancement on arterial and venous phases enabled differentiation of adenomas from metastases in most cases. Moderate to high signal intensity drop on CSI was seen in 95.4% of adenomas and 14.8% of metastases. In lesions with this level of signal intensity drop, 87 of 88 lesions with a capillary blush were adenomas. Early dynamic serial imaging alone was a significant (p < 0.0001) indicator of nonadenoma (area under the curve [AUC], 0.912) with optimal sensitivity of 81% and specificity of 93% for differentiating adenomas from nonadenomas. Combined analysis (CSI and early dynamic serial imaging) was also significant (p < 0.0001 and p=0.0014, respectively) for diagnosing nonadenomas (AUC, 0.983) with optimal sensitivity of 94% and specificity of 98%. Early dynamic serial gadolinium-enhanced MRI aids in characterization of adrenal tumors, especially lesions that are categorized as indeterminate on the basis of CSI.

Focal Adrenal Lesions in Pediatric Patients

Diaphragmatic lesions F ocal adrenal lesions can occur from a variety of underlying congenital and acquired causes in the pediatric population. Although some lesions are discovered incidentally in asymptomatic individuals on imaging studies obtained for other reasons, the majority of pediatric patients with focal adrenal lesions have abdominal pain and a palpable mass. In the neonatal period, the initial imaging modality of choice in the workup of suspected adrenal pathology is ultrasound because of an available acoustic window to visualize suprarenal fossa, easy accessibility, and lack of ionizing radiation. In older children, however, CT or MRI is usually required after initial ultrasound for confirmation and further characterization of adrenal lesions. When generating a differential diagnosis for focal adrenal lesions in the pediatric population, it is important to consider not only congenital, neoplastic, infectious, and traumatic conditions but also the potential mimics of focal adrenal lesions that may present in the suprarenal fossa region (Table 1). The age of the patient, clinical history, and laboratory data can further help narrow the differential diagnosis.