Quantitative CT evaluation of adrenal gland masses: a step forward in the differentiation between adenomas and nonadenomas?

Imaging of Pheochromocytomas and Paragangliomas

Pheochromocytomas/paragangliomas are unique in their highly variable molecular landscape driven by genetic alterations, either germline or somatic. These mutations translate into different clusters with distinct tumor locations, biochemical/metabolomic features, tumor cell characteristics (eg, receptors, transporters), and disease course. Such tumor heterogeneity calls for different imaging strategies in order to provide proper diagnosis and follow-up. This also warrants selection of the most appropriate and locally available imaging modalities tailored to an individual patient based on consideration of many relevant factors including age, (anticipated) tumor location(s), size, and multifocality, underlying genotype, biochemical phenotype, chance of metastases, as well as the patient's personal preference and treatment goals. Anatomical imaging using computed tomography and magnetic resonance imaging and functional imaging using positron emission tomography and single photon emission computed tomography are currently a cornerstone in the evaluation of patients with pheochromocytomas/paragangliomas. In modern nuclear medicine practice, a multitude of radionuclides with relevance to diagnostic work-up and treatment planning (theranostics) is available, including radiolabeled metaiodobenzylguanidine, fluorodeoxyglucose, fluorodihydroxyphenylalanine, and somatostatin analogues. This review amalgamates up-to-date imaging guidelines, expert opinions, and recent discoveries. Based on the rich toolbox for anatomical and functional imaging that is currently available, we aim to define a customized approach in patients with (suspected) pheochromocytomas/paragangliomas from a practical clinical perspective. We provide imaging algorithms for different starting points for initial diagnostic work-up and course of the disease, including adrenal incidentaloma, established biochemical diagnosis, postsurgical follow-up, tumor screening in pathogenic variant carriers, staging and restaging of metastatic disease, theranostics, and response monitoring.

Cystic lesions of the adrenal gland

Cystic lesions of the adrenal glands are relatively uncommon and most of them are clinically silent. Though rarely associated with malignant changes, they may carry clinically detrimental consequences if misdiagnosed. Cystic adrenal lesions exhibit a broad histomorphological spectrum, ranging from pseudocysts, endothelial cysts, epithelial cysts and parasitic cysts. Here we present the case of a young woman with left-sided abdominal pain and contrast-enhanced CT showing a 10.4×7.7×7.8 cm fluid-filled left suprarenal lesion. The patient underwent exploratory laparotomy with cyst excision, and the histopathological examination of the specimen revealed a pseudocyst of the left adrenal gland. Despite being rare, usually benign and asymptomatic, the diagnosis and management of these cystic lesions of the adrenal glands are often unclear. Any functional lesion, potentially malignant lesion or lesion more than 5 cm deserves surgical management, whereas others can be managed conservatively.

Can 3-Phase Computed Tomography Urography Be Used to Characterize Adrenal Nodules? Results in 145 Patients

OBJECTIVE

The aim of the study is to determine whether computed tomography (CT) urography (CTU) can characterize incidental adrenal nodules.

METHODS

This retrospective cohort study was performed at an academic medical center. Patients were identified by free text search of CTU reports that contained the terms "adrenal mass" "adrenal nodule" and "adrenal lesion." Computed tomography urography technique consisted of unenhanced images and postcontrast images obtained at 100 seconds and 15 minutes. The final cohort included 145 patients with 151 adrenal nodules. Nodules were considered lipid-rich adenomas or myelolipomas based on unenhanced imaging characteristics. Absolute and relative washout values were calculated for the remaining nodules, using a cutoff of 60% and 40%, respectively, to diagnose adenomas. Reference standard for lipid-poor adenomas and malignant nodules was histopathology or imaging/clinical follow-up. Mann-Whitney U test was used for comparison of continuous variables, and Fisher exact test was used for categorical variables.

RESULTS

One hundred nodules were lipid-rich adenomas and 3 were myelolipomas. Forty-eight nodules were indeterminate at unenhanced CT, corresponding to 39 lipid-poor adenomas and 9 malignant nodules based on reference standards. Both absolute and relative washout correctly characterized 71% of nodules (34/48), with a sensitivity of 67% and specificity of 89%. Overall, 91% of all adrenal nodules (137/151) were correctly characterized by CTU alone. Lipid-poor adenomas were smaller than malignant nodules (P < 0.01) and were lower in attenuation on unenhanced and delayed images (P < 0.01).

CONCLUSIONS

Adrenal nodules detected at 3-phase CTU can be accurately characterized, potentially eliminating the need for subsequent adrenal protocol CT or magnetic resonance imaging.

Diagnostic value of the relative enhancement ratio of the portal venous phase to unenhanced CT in the identification of lipid-poor adrenal tumors

PURPOSE

Adrenal incidentalomas are common lesions found on abdominal imaging, most of which are lipid-rich adrenal adenomas. Imaging diagnoses differentiating lipid-poor adrenal adenomas (LPA) from non-adenomas (NA) are presently challenging to perform. The aim of the study was to investigate the diagnostic performance of the relative enhancement ratio parameter in identifying LPA from NA.

METHODS

We retrospectively evaluated consecutively presenting patients with lipid-poor adrenal lesions (January 2015 to August 2021). Lesions were divided into LPA and NA (including hyperenhancing and hypoenhancing NA). Kruskal-Wallis and Bonferroni tests were used to determine the differences in feature parameters between these three groups. Receiver operating characteristic curve analysis was performed to determine the sensitivity for diagnosing LPA and NA at 95% specificity; the parameters were compared using the McNemar test.

RESULTS

A total of 253 patients (mean age, 55 ± 12 years; 135 men), 121 with LPA and 132 with NA, were analyzed herein. The sensitivity (achieved at 95% specificity) of the relative enhancement ratio was higher than that of unenhanced attenuation in differentiating LPA from NA (60% vs. 52%, p = 0.064). The relative enhancement ratio yielded a higher sensitivity than unenhanced attenuation (79% vs. 59%, p < 0.001) in differentiating LPA from hypoenhancing NA, and a lower sensitivity (26% vs. 69%, p < 0.001) in differentiating LPA from hyperenhancing NA.

CONCLUSION

The relative enhancement ratio showed better diagnostic performance than unenhanced attenuation in differentiating LPA from hypoenhancing NA, while simultaneously showing poor diagnostic performance in identifying LPA from all NA.

Development and Validation of a Clinical-Image Model for Quantitatively Distinguishing Uncertain Lipid-Poor Adrenal Adenomas From Nonadenomas

Background

There remains a demand for a practical method of identifying lipid-poor adrenal lesions.

Purpose

To explore the predictive value of computed tomography (CT) features combined with demographic characteristics for lipid-poor adrenal adenomas and nonadenomas.

Materials and Methods

We retrospectively recruited patients with lipid-poor adrenal lesions between January 2015 and August 2021 from two independent institutions as follows: Institution 1 for the training set and the internal validation set and Institution 2 for the external validation set. Two radiologists reviewed CT images for the three sets. We performed a least absolute shrinkage and selection operator (LASSO) algorithm to select variables; subsequently, multivariate analysis was used to develop a generalized linear model. The probability threshold of the model was set to 0.5 in the external validation set. We calculated the sensitivity, specificity, accuracy, and area under the receiver operating characteristic curve (AUC) for the model and radiologists. The model was validated and tested in the internal validation and external validation sets; moreover, the accuracy between the model and both radiologists were compared using the McNemar test in the external validation set.

Results

In total, 253 patients (median age, 55 years [interquartile range, 47–64 years]; 135 men) with 121 lipid-poor adrenal adenomas and 132 nonadenomas were included in Institution 1, whereas another 55 patients were included in Institution 2. The multivariable analysis showed that age, male, lesion size, necrosis, unenhanced attenuation, and portal venous phase attenuation were independently associated with adrenal adenomas. The clinical-image model showed AUCs of 0.96 (95% confidence interval [CI]: 0.91, 0.98), 0.93 (95% CI: 0.84, 0.97), and 0.86 (95% CI: 0.74, 0.94) in the training set, internal validation set, and external validation set, respectively. In the external validation set, the model showed a significantly and non-significantly higher accuracy than reader 1 (84% vs. 65%, P = 0.031) and reader 2 (84% vs. 69%, P = 0.057), respectively.

Conclusions

Our clinical-image model displayed good utility in differentiating lipid-poor adrenal adenomas. Further, it showed better diagnostic ability than experienced radiologists in the external validation set.

Relative Enhancement Ratio of Portal Venous Phase to Unenhanced CT in the Diagnosis of Lipid-poor Adrenal Adenomas

Background The development of an accurate, practical, noninvasive, and widely available diagnostic approach to characterize lipid-poor adrenal lesions (greater than 10 HU at unenhanced CT) remains an ongoing demand. Purpose To investigate whether combined assessment of unenhanced and portal venous phase CT allows for the differentiation of lipid-poor adrenal adenomas from nonadenomas. Materials and Methods Patients with lipid-poor adrenal lesions who underwent unenhanced and portal venous phase CT with a single-energy scanner between January 2016 and March 2020 were identified retrospectively. For each lesion, the unenhanced and contrast-enhanced attenuation were measured; the absolute enhancement (contrast-enhanced minus unenhanced attenuation [HU]) and relative enhancement ratio ([absolute enhancement divided by unenhanced attenuation] × 100%) were calculated. The sensitivity achieved at 95% specificity to distinguish adenomas from nonadenomas was determined with receiver operating characteristic curve analysis and compared among parameters with use of the McNemar test. Results A total of 220 patients (mean age ± standard deviation, 66 years ± 12; 134 men) with 131 lipid-poor adenomas and 89 nonadenomas were analyzed. The sensitivity (achieved at 95% specificity) of the relative enhancement ratio (86% [113 of 131 adenomas; 95% CI: 79, 92] at a threshold of >210%) was higher than that of unenhanced attenuation (50% [66 of 131 adenomas; 95% CI: 42, 59] at a threshold of ≤21 HU), contrast-enhanced attenuation (3% [four of 131 adenomas; 95% CI: 1, 8] at a threshold of >120 HU), and absolute enhancement (24% [32 of 131 adenomas; 95% CI: 17, 33] at a threshold of >74 HU; all P < .001). The sensitivities of the relative enhancement ratio were 100% (58 of 58 adenomas; 95% CI: 94, 100), 83% (52 of 63 adenomas; 95% CI: 71, 91), and 30% (three of 10 adenomas; 95% CI: 7, 65) for adenomas measuring unenhanced attenuation of more than 10 HU up to 20 HU, 21-30 HU, and more than 30 HU, respectively. Conclusion A relative enhancement ratio threshold of greater than 210%, measured at unenhanced and portal venous phase CT, accurately differentiated lipid-poor adenomas from nonadenomas, particularly for lesions with unenhanced attenuation of 10-30 HU. © RSNA, 2021 Online supplemental material is available for this article.

Computed tomography (CT) scan identified necrosis, but is it a reliable single parameter for discerning between malignant and benign adrenocortical tumors?

BACKGROUND

Adrenocortical carcinoma is a rare malignant tumor with a poor prognosis. Discernment of adrenocortical carcinoma in an adrenal mass through imaging studies is paramount for early surgical treatment. Recently, necrosis has been proposed as a single morphological parameter for adrenocortical carcinoma diagnosis. The aim of this study was to analyze the measures of diagnostic efficiency of necrosis and the different computed tomography-scan features related to adrenocortical carcinoma diagnosis.

METHODS

We conducted a case-control study of patients surgically treated for an adrenal mass with histopathological report consistent with adrenocortical carcinoma (cases) and adrenocortical adenoma (control patients) between 1987 and 2019. Radiological features on computed tomography scan were collected. Bivariate and multivariate statistical analyses were performed for the different imaging features. The measures of diagnostic efficiency for each feature were calculated. Concordance analysis between image-detected and histopathological-identified necrosis was performed.

RESULTS

Eighteen adrenocortical carcinoma and 41 adrenocortical adenomas were included. Differences between adrenocortical carcinoma and adrenocortical adenoma were found regarding heterogeneity (odds ratio 4.53, 95% confidence interval 2.3-8.9; P < .0001), tumor size ≥4 cm (odds ratio 3.5, 95% confidence interval 2.05-6.14; P < .0001), and attenuation index ≥10 Hounsfield units (odds ratio 1.9, 95% confidence interval 1.3-2.6; P = .001). Necrosis was the most important imaging feature significantly associated with adrenocortical carcinoma (odds ratio 35, 95% confidence interval 5.1-241.6; P < .0001), present in all adrenocortical carcinoma cases. After measures of diagnostic efficiency calculation, necrosis had the highest diagnostic accuracy (98%). Cohen's kappa for concordance between image-detected and histopathological-identified necrosis was 90.4% (P < .0001).

CONCLUSION

Computed tomography scan-detected necrosis is a reliable radiological feature to discern adrenocortical carcinoma from adrenocortical adenomas.

Utility of Intermediate-Delay Washout CT Images for Differentiation of Malignant and Benign Adrenal Lesions: A Multivariate Analysis

OBJECTIVE

The objective of this study was to identify features that impact the diagnostic performance of intermediate-delay washout CT for distinguishing malignant from benign adrenal lesions.

MATERIALS AND METHODS

This retrospective study evaluated 127 pathologically proven adrenal lesions (82 malignant, 45 benign) in 126 patients who had undergone portal venous phase and intermediate-delay washout CT (1-3 minutes after portal venous phase) with or without unenhanced images. Unenhanced images were available for 103 lesions. Quantitatively, lesion CT attenuation on unenhanced (UA) and delayed (DL) images, absolute and relative percentage of enhancement washout (APEW and RPEW, respectively), descriptive CT features (lesion size, margin characteristics, heterogeneity or homogeneity, fat, calcification), patient demographics, and medical history were evaluated for association with lesion status using multiple logistic regression with stepwise model selection. Area under the ROC curve (A_z) was calculated from both univariate and multivariate analyses. The predictive diagnostic performance of multivariate evaluations was ascertained through cross-validation.

RESULTS

A_z for DL, APEW, RPEW, and UA was 0.751, 0.795, 0.829, and 0.839, respectively. Multivariate analyses yielded the following significant CT quantitative features and associated A_z when combined: RPEW and DL (A_z = 0.861) when unenhanced images were not available and APEW and UA (A_z = 0.889) when unenhanced images were available. Patient demographics and presence of a prior malignancy were additional significant factors, increasing A_z to 0.903 and 0.927, respectively. The combined predictive classifier, without and with UA available, yielded 85.7% and 87.3% accuracies with cross-validation, respectively.

CONCLUSION

When appropriately combined with other CT features, washout derived from intermediate-delay CT with or without additional clinical data has potential utility in differentiating malignant from benign adrenal lesions.

Differentiation of Malignant and Benign Adrenal Lesions With Delayed CT: Multivariate Analysis and Predictive Models

OBJECTIVE

The purpose of this study is to identify imaging and patient parameters that affect the diagnostic performance of delayed contrast-enhanced CT for distinguishing malignant from benign adrenal lesions larger than 1 cm in adult patients and to derive predictive models.

MATERIALS AND METHODS

This retrospective study assessed 97 pathologically proven adrenal lesions that had undergone unenhanced, portal venous, and 15-minute delayed CT. Quantitatively, single-parameter evaluations of lesion attenuation (in Hounsfield units) and absolute percentage enhancement washout (APEW) and relative percentage enhancement washout (RPEW) were performed. In addition, descriptive CT features (lesion size, margin definition, heterogeneity vs homogeneity, fat, and calcification) and patients' demographic characteristics and medical history of malignancy were evaluated for association with lesion status using multiple logistic regression with stepwise model selection. Areas under the ROC curve (A_z) were determined for univariate and multivariate analyses. Leave-one-lesion-out cross-validation was applied to ascertain the predictive performance of single-parameter and multivariate evaluations.

RESULTS

The A_z values for unenhanced attenuation, portal venous attenuation, delayed attenuation, APEW, and RPEW were 0.835, 0.534, 0.847, 0.792, and 0.871, respectively. Multivariate analyses revealed that portal venous attenuation, delayed attenuation, and APEW were significant features, with an A_z of 0.923 when combined. The addition of the descriptive CT features increased the A_z to 0.938; patient age and a history of malignancy were additional significant factors, increasing the A_z to 0.956 and 0.972, respectively. The combined predictive classifier yielded 89% accuracy under cross-validation, compared with the best commonly applied single-parameter evaluation (77% for RPEW < 40%).

CONCLUSION

Multivariate imaging evaluation applied to delayed contrast-enhanced CT alone, with or without patient characteristics, improves diagnostic performance for characterizing adrenal lesions beyond those of single-parameter evaluations. Predictive formulas assessing the probabilities of lesion benignity or malignancy are provided.

Collision and composite tumors; radiologic and pathologic correlation

The terms composite and collision tumors have been used interchangeably throughout radiological literature. Both composite and collision tumors involve two morphologically and immunohistochemically distinct neoplasms coexisting within a single organ. However, collision tumors lack the histological cellular intermingling seen in composite tumors. Composite tumors often arise from a common driver mutation that induces a divergent histology from a common neoplastic source while collision tumors may arise from coincidental neoplastic change. The purpose of this review is to provide an overview of abdominal composite and collision tumors by discussing hallmark radiographic and pathological presentations of rare hepatic, renal, and adrenal case studies. A better understanding of the presentation of each lesion is imperative for proper recognition, diagnosis, and management of these unique tumor presentations.

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.

CT sensitivity for adrenal adenoma according to lesion size

PURPOSE

To retrospectively evaluate CT sensitivity for characterizing adrenal adenoma according to lesion size.

MATERIALS AND METHODS

Between January 2004 and November 2012, 140 patients with 140 histologically proven adenomas underwent preoperative adrenal CT protocols consisting of unenhanced CT, early enhanced CT, and delayed enhanced CT. Adenomas were divided into three size groups: small adenoma (n = 60), ≥ 1 to <2 cm; medium adenoma (n = 47), ≥ 2 to <3 cm; and large adenoma (n = 33), ≥ 3 cm. Adenoma was diagnosed when a lesion met one of the following criteria: (a) unenhanced CT attenuation value ≤ 10 HU, (b) absolute percentage washout ≥ 60%, or (c) relative percentage washout ≥ 40%. The standard reference was pathologic examination of an adrenalectomy specimen. Adenoma size, lesion attenuation value, or percentage washout was correlated with the Spearman's rank correlation. CT sensitivities were compared between size groups of adenomas with the Fisher's exact test.

RESULTS

As adenoma size increased, the lesion attenuation value (ρ = 0.324; P = 0.001) increased on unenhanced CT, and the absolute (ρ = -0.186; P = 0.028) or relative (ρ = -0.374; P < 0.001) percentage washout decreased on early and delayed enhanced CT. CT sensitivities were 100% (60/60) for small adenomas, 97.9% (46/47) for medium adenomas, and 66.7% (22/33) for large adenomas (P < 0.001).

CONCLUSIONS

Adrenal CT protocols misdiagnose a substantial number of large adenomas as non-adenomas because CT sensitivity for adenoma markedly decreases, when the lesion size is 3 cm or larger.

Likelihood ratio of computed tomography characteristics for diagnosis of malignancy in adrenal incidentaloma: systematic review and meta-analysis

Purpose

To propose an evidence based diagnostic algorithm using mass characteristics to determine malignancy in patients with adrenal incidentaloma by CTscan.

Methods

A systematic review in Medline, Scopus, relevant reference books and desk searching was performed up to January 2016 with relevant reference checking. The summery estimates of sensitivity, specificity, positive and negative likelihood ratio of different characteristics were calculated in two groups of the articles investigating the cases without previous malignancy and the articles investigating the oncologic cases.

Results

Thirty six articles were included in this study. In the first group with no history of malignancy a positive and negative LR of 3.1 and 0.13 in 4 cm threshold and positive and negative LR of 2.85 and 0 in 10HU density were found. In the second group with history of malignancy positive and negative LR of 2.3 and 0.27 in 3 cm threshold and positive and negative LR of 3.6 and 0.08 in 20HU density were resulted.

Conclusion

The results retrieved in this study considering the limitations show that adrenal incidentaloma with a size less than 4 cm or a mass larger than 4 cm with density less than 10HU in the first group can be managed with imaging follow up. For masses larger than 4 cm with density more than 10HU another diagnostic procedure should be performed. In the second group an adrenal mass larger than 3 cm or less than 3 cm with density more than 20HU should go under operation. But masses smaller than 3 cm with less than 20HU density can be followed by imaging.

Effects of contrast medium injection technique on attenuation values of adrenal glands in healthy dogs during contrast-enhanced computed tomography

OBJECTIVE

To assess the effects of 3 contrast medium injection techniques on attenuation values for canine adrenal glands during contrast-enhanced CT.

ANIMALS

9 healthy Beagles.

PROCEDURES

3 protocols were evaluated in a randomized cross-over design study: 700 mg of iodine/kg at a constant injection rate over 20 seconds (full-dose constant rate), the same dose at a rate following an exponential decay curve over 20 seconds (full-dose decelerated rate), and 350 mg of iodine/kg at a constant injection rate over 10 seconds (half-dose constant rate). Multislice CT images were obtained before and at predetermined time points after the start of contrast medium injection.

RESULTS

Median peak attenuation values were 129, 133, and 87 Hounsfield units with the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injection protocols, respectively. Peak attenuation differed significantly between the full-dose constant rate and half-dose constant rate injection protocols and between the full-dose decelerated rate and half-dose constant rate injection protocols. Median time to peak attenuation did not differ significantly among injection methods and was 30, 23, and 15 seconds for the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injections, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

The dose of contrast medium and the timing of postinjection CT scanning were main determinants of peak attenuation for adrenal glands in healthy dogs; effects of the 3 injection protocols on attenuation were minor. The exponentially decelerated injection method was subjectively complex. A constant injection protocol delivering 700 mg of iodine/kg over 20 seconds, with scans obtained approximately 30 seconds after starting contrast medium injection, provided images with maximum adrenal gland attenuation values.

Adrenal incidentaloma: evaluation and management

Adrenal incidentalomas are adrenal masses discovered incidental to imaging studies performed for reasons unrelated to adrenal pathology. Although most adrenal incidentalomas are non-functioning benign adenomas, their increasing prevalence presents diagnostic and therapeutic challenges. The assessment of adrenal incidentalomas is aimed at deciding whether or not the tumour should be surgically removed. Adrenalectomy is indicated for phaeochromocytoma, other symptomatic hormone-secreting tumours and those with a high risk of malignancy. Biochemical screening for tumour hypersecretion is mandatory in all adrenal incidentalomas, since hormone secreting tumours may be clinically silent. The diagnosis of phaeochromocytoma is of paramount importance because of its life-threatening complications. Non-functioning adrenal incidentalomas need assessment for risk of malignancy, and this is based on the size of the tumour and its imaging characteristics. An observational policy with periodic radiological and biochemical reassessment is pursued in patients with non-functioning incidentalomas with low malignancy risk. The duration and frequency of reassessment remains unclear, as the natural history of adrenal incidentalomas has yet to be clearly defined, and there is a lack of controlled studies comparing surgical intervention with observation. However, the possibility of acquiring autonomous hypersecretion or conversion to malignancy in an incidentaloma diagnosed to be a benign non-functioning lesion is very low, and most patients may be safely discharged after an initial follow-up period of 2 years.

A breast-specific, negligible-dose scatter correction technique for dedicated cone-beam breast CT: a physics-based approach to improve Hounsfield Unit accuracy

The purpose of this research was to develop a method to correct the cupping artifact caused from x-ray scattering and to achieve consistent Hounsfield Unit (HU) values of breast tissues for a dedicated breast CT (bCT) system. The use of a beam passing array (BPA) composed of parallel-holes has been previously proposed for scatter correction in various imaging applications. In this study, we first verified the efficacy and accuracy using BPA to measure the scatter signal on a cone-beam bCT system. A systematic scatter correction approach was then developed by modeling the scatter-to-primary ratio (SPR) in projection images acquired with and without BPA. To quantitatively evaluate the improved accuracy of HU values, different breast tissue-equivalent phantoms were scanned and radially averaged HU profiles through reconstructed planes were evaluated. The dependency of the correction method on object size and number of projections was studied. A simplified application of the proposed method on five clinical patient scans was performed to demonstrate efficacy. For the typical 10-18 cm breast diameters seen in the bCT application, the proposed method can effectively correct for the cupping artifact and reduce the variation of HU values of breast equivalent material from 150 to 40 HU. The measured HU values of 100% glandular tissue, 50/50 glandular/adipose tissue, and 100% adipose tissue were approximately 46, -35, and -94, respectively. It was found that only six BPA projections were necessary to accurately implement this method, and the additional dose requirement is less than 1% of the exam dose. The proposed method can effectively correct for the cupping artifact caused from x-ray scattering and retain consistent HU values of breast tissues.

Distinguishing adrenal adenomas from non-adenomas on dynamic enhanced CT: a comparison of 5 and 10 min delays after intravenous contrast medium injection

AIM

To evaluate the usefulness of several parameters of 5 min compared to 10 min delayed contrast-enhanced CT in distinguishing adenomas from non-adenomas.

MATERIALS AND METHODS

The study population consisted of 94 patients (52 men and 42 women; mean age 62 years) with 103 adrenal lesions (75 adenomas and 28 non-adenomas). In each patient, unenhanced CT was followed by early, 5 and 10 min enhanced CT. Diagnostic parameters included delayed enhanced attenuation at 5 and 10 min, washout attenuation (WO) at 5 and 10 min, absolute percentage washout (APW) at 5 and 10 min, and relative percentage washout (RPW) at 5 and 10 min. The accuracy of each parameter for diagnosing adenomas from non-adenomas was calculated using receiver operating characteristic (ROC) analysis.

RESULTS

Upon comparison between 5 and 10 min delayed contrast-enhanced CT for differentiating total adenomas or lipid-poor adenomas from non-adenomas, there was no significant difference in the area under the binomial ROC curve (Az) values of delayed enhanced attenuation (total adenomas versus non-adenomas, p = 0.164; lipid-poor adenomas versus non-adenomas, p = 0.178), WO (total adenomas versus non-adenomas, p = 0.216; lipid-poor adenomas versus non-adenomas, p = 0.230), APW (total adenomas versus non-adenomas, p = 0.401; lipid-poor adenomas versus non-adenomas, p = 0.870), or RPW (total adenomas versus non-adenomas, p = 0.160; lipid-poor adenomas versus non-adenomas, p = 0.780).

CONCLUSION

Five minute contrast-enhanced CT was as useful as 10 min contrast-enhanced CT for differentiation of adrenal adenomas from non-adenomas.

The washout rate on the delayed CT image as a diagnostic tool for adrenal adenoma verified by pathology: a multicenter study

OBJECTIVES

To establish the undisputed the value of washout rate for adrenal adenoma using delayed enhanced CT, we evaluated diagnostic performance of cut-off value and delayed time of washout rate by final pathologic diagnosis in a multicenter study.

METHODS

We reviewed the pathologic and clinical records of 244 patients underwent adrenalectomies at 5 university hospitals between 2005 and 2009. We calculated the mean Housfield units (HU) of adrenal lesion at non-enhancing CT, and early and delayed enhanced CT using the region of interest. We used ROC curves to determine the specificity and sensitivity of non-enhanced CT scans and the washout rate according to the various cut-off for adrenal adenomas.

RESULTS

We divided the patients into adrenal adenoma group (n = 138) and non-adrenal adenoma group (n = 106) based on final pathologic report. Using the unenhanced images with a threshold of 10 HU, the sensitivity was 45.7 %, and the specificity was 97.1 %. Using the 15-min-washout rate with a threshold of 55 %, the sensitivity was 93.9 %, and the specificity was 95.8 %.

CONCLUSIONS

Regardless of various CT machines and protocols, a washout rate of 15-min-delayed CT was most useful in the diagnosis of adrenal adenomas due to the early inflow and outflow of contrast media in the tissues of adrenal adenomas.

Adrenal imaging: a comprehensive review

The discovery of an incidental adrenal mass (adrenal incidentaloma) continues to rise with the increasing use of cross-sectional imaging. Although most adrenal lesions are benign and asymptomatic, radiologists should guide evaluation of these lesions, whether benign or malignant. This article reviews the various imaging techniques used to evaluate adrenal masses and their relative strengths and weaknesses. It focuses on the most prevalent adrenal pathologies and their typical imaging characteristics, and concludes with a brief discussion of developing techniques, including diffusion-weighted imaging and dual-energy CT.

Incidental adrenal lesions: Accuracy of quadriphasic contrast enhanced computed tomography in distinguishing adenomas from nonadenomas

PURPOSE

To evaluate the accuracy in distinguishing adrenal adenomas from nonadenomas by means of quadriphasic CT exam, including unenhanced (UE), arterial enhanced (AE), portal enhanced (PE) and 5-min delayed enhanced (DE) CT scans.

METHODS

This retrospective study had institutional review board approval; the need for informed consent was waived. From September 2007 to September 2009, 104 adrenal masses were evaluated in 87 patients (49 M, 38 F, mean age 58.4 years) undergoing UE, AE (35-s delay), PE (80-s delay) and DE (5-min delay) CT scans. The mean adrenal attenuation during all imaging phases was measured by two readers. The accuracy values of absolute unenhanced attenuation (UE), absolute wash-out (AWO), relative percentage wash-out (RPWO) and percentage enhancement wash-out (PEW) were assessed by using receiver operator curves (ROC) analysis. The overall accuracy of the quadriphasic protocol and other triphasic protocols were evaluated. A value of p≤0.05 was considered significant.

RESULTS

The accuracy in characterizing adrenal lesions was 86.5% (90/104) for UE attenuation (≤10 HU threshold), 90.1% (82/91) for RPWO (≥30% threshold), 85.7% (78/91) for AWO (≥12 HU threshold) and 83.5% (76/91) for PEW (≥30% threshold), respectively. Quadriphasic CT (accuracy 97.1%, 101/104) performed better than triphasic CT including only AE scan (efficiency 90.0%, 94/104; p=0.011) and triphasic CT including only PE scan (efficiency 96.1%, 100/104; p=0.025).

CONCLUSION

Quadriphasic CT protocol including 5-min DE scan may be used to characterize incidentally detected adrenal masses. RPWO represented the best wash-out parameter for characterizing adrenal lesions.

Incidental and metastatic adrenal masses

In the last decades discoveries of adrenal masses incidentally during the course of diagnostic procedures for unrelated disorders (incidentalomas) have become progressively more frequent. The clinician in this position must answer two main questions: Is the mass benign or malignant?, and To what extent is the adrenal secretion altered? To come to a clinical decision, several diagnostic tools need to be engaged, starting with an accurate and correct radiological evaluation and a hormonal assessment of the adrenal function. When necessary, other diagnostic procedures such as functional imaging and fine-needle biopsy (FNB) can be considered in selected cases. Surgical removal is recommended for clinically relevant hypersecretory masses, as well as for masses suspected to be malignant. Most frequently, adrenal incidentalomas (AIs) are represented by benign cortical adenomas, a subset of which causes a mild hypercortisolism, known as subclinical Cushing's syndrome (SCS). The criteria to define this syndrome, as well as its treatment, are still debated and controversial. AIs that are not surgically removed should be re-examined in time to exclude a supervening increase in size or function. Follow-up criteria have not been established. Laparoscopic surgery is the recommended procedure to remove benign masses. The surgical procedure for adrenal malignancies is still debated.

Evaluation of relative wash-in ratio of adrenal lesions at early biphasic CT

OBJECTIVE

The purpose of this study was to retrospectively evaluate the accuracy of unenhanced attenuation and relative percentage wash-in ratio in early, that is, arterial and portal venous phase, biphasic CT in differentiating adrenal adenomas from metastatic lesions.

MATERIALS AND METHODS

One hundred seven adrenal masses in 86 consecutively registered patients (45 men, 41 women; mean age, 56 years) were evaluated. Diagnosis was achieved with percutaneous biopsy (n = 6), surgery (n = 13), and at least 1 year of imaging follow-up (n = 88). Unenhanced, arterial phase, and portal phase scans were obtained. Diameter and absolute attenuation values in each phase of CT were measured in a region of interest covering one to two thirds of a lesion. Relative percentage wash-in ratio was calculated. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in differentiation of adenomas from metastatic lesions were calculated for unenhanced attenuation and for wash-in ratio. A value of p < 0.05 was considered significant.

RESULTS

The final diagnosis was metastasis in 51 cases and adenoma in 56 cases. A significant difference was found between benign and malignant lesions in regard to diameter (p = 0.001), unenhanced CT attenuation (p = 0.001), and relative percentage wash-in ratio from the arterial to the portal venous scan (p = 0.014). In the differentiation of benign from malignant lesions, the sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of unenhanced CT attenuation (at an 11-HU threshold) were 98%, 86%, 86%, 98%, and 92%, and those of relative percentage wash-in ratio from the arterial to the portal venous phase were 94%, 77%, 79%, 93%, and 85%.

CONCLUSION

Relative percentage wash-in ratio may help in differentiating adenoma from metastasis and in guiding the decision to perform CT directed at the adrenal glands when unenhanced CT is not available.

Adrenal mass imaging with multidetector CT: pathologic conditions, pearls, and pitfalls

The adrenal gland is involved by a range of neoplasms, including primary and metastatic malignant tumors; however, the most common tumor detected is the incidental benign adenoma. Although computed tomographic (CT) findings will not always yield a definitive diagnosis, attention to these findings provides a road map to guide image interpretation. Adenomas typically demonstrate rapid washout, which is defined as an absolute percentage washout (APW) of more than 60% and a relative percentage washout (RPW) of more than 40% on delayed images. Adrenocortical carcinoma typically has an RPW of less than 40%; however, large size and heterogeneity are more reliable indicators of the diagnosis than are washout values. Washout characteristics of pheochromocytoma are variable; in conjunction with high levels of dynamic enhancement, pheochromocytomas may mimic adenoma (ie, APW > 60%, RPW > 40%). Myelolipomas appear as well-defined masses with variable quantities of fat and soft tissue. After contrast material administration, metastases usually demonstrate slower washout on delayed images (APW < 60%, RPW < 40%) than do adenomas, although hypervascular metastases may enhance similarly to pheochromocytoma. Finally, a number of nonadrenal pathologic conditions have been reported to mimic adrenal masses at CT.

Adrenal imaging with multidetector CT: evidence-based protocol optimization and interpretative practice

Computed tomography (CT) is an integral tool in the assessment of adrenal masses. Dedicated adrenal CT is performed for a range of indications, including hormonal abnormalities suggestive of a functional adrenal mass and adrenal cancer staging. It is important to have an understanding of the published data that guide protocol design and image interpretation. Whether an adrenal mass is identified serendipitously or is being imaged for further characterization, there are several CT findings that contribute to the diagnosis, such as lesion size, precontrast attenuation, level of enhancement at 60 seconds and on delayed images, percentage washout on delayed images, histogram analysis, and extent (involvement of the inferior vena cava and bilaterality). In the past decade, a body of pertinent literature has evolved, addressing each of these measures individually.

[Adrenal incidentaloma: management approaches: CT - MRI]

The adrenal gland may be affected by several pathologies, and the detection of an adrenal nodule may occur during the work-up of a biological abnormality, oncologic work-up, or be incidental. Endocrinological and imaging work-up is required in all cases. Cross-sectional imaging has had a great impact on the diagnostic work-up of adrenal nodules. CT, without and with intravenous contrast, is the first line imaging study for evaluation of adrenal nodules. A spontaneous density below 10 HU confirms the benign nature of a nodule. When lesions cannot be characterized, postcontrast CT or MR imaging, including in and out of phase imaging, may allow diagnosis.

Contrast-enhanced sonography of adrenal masses: differentiation of adenomas and nonadenomatous lesions

OBJECTIVE

The aim of this proof-of-principle study was to evaluate contrast-enhanced sonography in the characterization of adrenal masses.

SUBJECTS AND METHODS

Thirty-five consecutively registered patients with newly detected adrenal masses underwent hormonal evaluation and duplex and Doppler sonography followed by contrast-enhanced sonography and CT or MRI. The dynamics of contrast enhancement were analyzed with time-intensity curves. CT and MRI were used as the reference methods for the diagnosis of adenoma and myelolipoma. Metastasis was diagnosed with fine-needle biopsy, and all other adrenal masses were diagnosed at adrenalectomy. Fisher's exact test was used to evaluate the criteria for diagnosis of malignant adrenal masses.

RESULTS

Size greater than 4 cm and hypervascularization were found significantly more often in malignant than in benign lesions (71% vs 21% for size; 57% vs 7% for hypervascularization). At contrast-enhanced sonography, early arterial or arterial contrast enhancement and rapid washout were seen in all patients with primary or secondary malignant lesions of the adrenal gland and in only 22% of patients with benign adrenal masses (p < 0.05). All primary malignant lesions were confirmed at histologic examination. In 32 of 35 patients (91%), findings at CT or MRI were congruent with those at contrast-enhanced sonography in regard to characterization of adenoma versus nonadenomatous lesion (p < 0.001). In two of the 35 cases, however, all imaging methods favored the diagnosis of nonadenomatous lesion, but the histologic result after adrenalectomy was adrenal adenoma. The sensitivity and specificity of contrast-enhanced sonography in the diagnosis of malignant adrenal mass were 100% and 82%.

CONCLUSION

Contrast-enhanced sonography can be used to differentiate adenomas and nonadenomatous lesions with a sensitivity comparable with that of CT and MRI and may be a cost-effective method for preselection of patients with adrenal masses.

Validation of the use of calibration factors between the iodine concentration and the computed tomography number measured outside the objects for estimation of iodine concentration inside the objects: phantom experiment

PURPOSE

The aim of this study was to validate the use of a calibration factor measured outside the object for estimating the iodine concentration inside the object to improve the accuracy of the quantitative contrast-enhanced computed tomography (CT).

MATERIALS AND METHODS

Several known concentrations (0, 6, 9, and 12 mg I/ml) of iodine contrast material (CM) samples were placed inside and outside cylindrical acrylic phantoms of two sizes and were imaged under various combinations of the tube voltages and currents (kV/mAs-80/200, 100/200, 120/200, 140/200) to obtain K factors. The K factors were compared between the phantoms and among the tube voltages. Each CM concentration was estimated from the CT number using the K factor measured outside the phantom.

RESULTS

The K factors varied between the phantoms or among the tube voltages (P < 0.05). Although there were statistically significant variations in K factors among the different regions in a phantom, the mean variation coefficient was 3%-4%. The mean error of the estimated concentration was -5.5%.

CONCLUSION

The CM concentration should be accurately estimated at the region within a patient's body using the K factor measured at the surface of the body regardless of body size and tube voltage.

A rare tumor in the adrenal region: neuron-specific enolase (NSE)-producing leiomyosarcoma in an elderly hypertensive patient

A 73-year-old Japanese woman was referred for examination of right flank pain and progressive hypertension. Abdominal CT incidentally detected a right adrenal mass 8 cm in size. The tumor exhibited isodensity by CT and contained high-intense lesion by T2-weighted MRI. Scintigraphy with (131) I-metaiodobenzylguanidine and (131) I-adosterol showed no abnormal uptake by whole body scan. Positron emission tomography scan with (18) F-2-fluoro-D-deoxyglucose demonstrated an exclusive uptake in the right adrenal mass. Adrenocortical hormone levels and catecholamine secretion were within normal range; however, the level of serum neuron-specific enolase (NSE) was found to be markedly high. After controlling systemic blood pressure with an alpha1-blocker, the right adrenal tumor was surgically removed, along with the right kidney and inferior vena cava which adhered to it. The tumor was pathologically proven to be leiomyosarcoma, which was immunohistochemically positive with alpha-smooth muscle actin and negative with CD57, S-100 and c-kit proteins. Notably, NSE protein was massively expressed in the resected tumor. After surgery blood pressure was controlled with regular medication and serum NSE levels have since normalized. The possibility of leiomyosarcoma should be kept in mind in adrenal incidentalomas with rapid growth and atypical radiological images. Our findings suggest that circulating NSE levels may be clinically useful for early detection of recurrence.

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.

Gastric diverticulum simulating left adrenal incidentaloma in a hypertensive patient

A 46-year-old Japanese male with hypertension was referred for examination of left adrenal tumor incidentally detected by computed tomography (CT) scan. The patient had a 4-month history of hypertension. Abdominal CT demonstrated a low-density mass 2.5 cm in diameter in the left adrenal region that was observed as a high-intense lesion with T2-weighted magnetic resonance imaging. (131) I-adosterol scintigraphy showed normal uptake of bilateral adrenals. The adrenocortical hormone levels were within normal ranges; however, urinary noradrenaline excretion was slightly elevated, likely due to concurrent sleep apnea syndrome. Based on the observation of a very tiny bubble in the ventral portion of the adrenal mass by careful review of CT images examined at a previous hospital, a restudy of abdominal CT with oral contrast was performed. In this restudy abdominal CT we observed positive enhancement of the left adrenal mass, indicating that the adrenal mass was a diverticulum derived from posterior gastric fornix. The present case study reinforces that preoperative differentiation from mimic adrenal tumors is necessary in cases of cystic adrenal mass in the left adrenal region.

Hepatic entropy and uniformity: additional parameters that can potentially increase the effectiveness of contrast enhancement during abdominal CT

AIM

To determine how hepatic entropy and uniformity of computed tomography (CT) images of the liver change after the administration of contrast material and to assess whether these additional parameters are more sensitive to tumour-related changes in the liver than measurements of hepatic attenuation or perfusion.

MATERIALS AND METHODS

Hepatic attenuation, entropy, uniformity, and perfusion were measured using multi-phase CT following resection of colorectal cancer. Based on conventional CT and fluorodeoxyglucose positron emission tomography, 12 patients were classified as having no evidence of malignancy, eight with extra-hepatic tumours only, and eight with metastatic liver disease.

RESULTS

Hepatic attenuation and entropy increased after CM administration whereas uniformity decreased. Unlike hepatic attenuation, entropy and uniformity changed maximally in the arterial phase. No significant differences in hepatic perfusion or attenuation were found between patient groups, whereas arterial-phase entropy was lower (p=0.034) and arterial-phase uniformity was higher (p=0.034) in apparently disease-free areas of liver in patients with hepatic metastases compared with those with no metastases.

CONCLUSION

Temporal changes in hepatic entropy and uniformity differ from those for hepatic attenuation. By reflecting the distribution of hepatic enhancement, these additional parameters are more sensitive to tumour-related changes in the liver than measurements of hepatic attenuation or perfusion.

Dynamic contrast enhanced MRI in the differential diagnosis of adrenal adenomas and malignant adrenal masses

OBJECTIVE

To evaluate the value of dynamic MR imaging in the differential diagnosis of adrenal adenomas and malignant tumors, especially in cases with atypical adenomas.

MATERIALS AND METHODS

Sixty-four masses (48 adenomas, 16 malignant tumors) were included in this prospective study. Signal loss of masses was evaluated using chemical shift MR imaging. Five dynamic series of T1-weighted spoiled gradient echo (FFE) images were obtained, with the acquisition starting simultaneously with i.v. contrast administration (0-100 s) followed by a T1-weighted FFE sequence in the late phase (5th minute). Contrast enhancement patterns in the early (25th second) and late (5th minute) phase images were evaluated. For the quantitative evaluation, signal intensity (SI)-time curves were obtained according to the SIs on the 0th, 25th, 50th 75th and 100th second. Also, the wash-in rate, maximum relative enhancement, time-to-peak, and wash-out of contrast at 100 s of masses in both groups were calculated. The statistical significance was determined by Mann-Whitney U test. To evaluate the diagnostic performance of the quantitative tests, receiver operating characteristic (ROC) analysis was performed.

RESULTS

Chemical shift MR imaging was able to differentiate 44 out of 48 adenomas (91.7%) from non-adenomas. The 4 adenomas (8.3%) which could not be differentiated from non-adenomas by this technique did not exhibit signal loss on out-of-phase images. With a cut-off value of 30, SI indices of adenomas had a sensitivity of 93.8%, specificity of 100% and a positive predictive value of 100%. On visual evaluation of dynamic MR imaging, early phase contrast enhancement patterns were homogeneous in 75% and punctate in 20,83% of the adenomas; while patchy in 56.25% and peripheral in 25% of the malignant tumors. On the late phase images 58.33% of the adenomas showed peripheral ring-shaped enhancement and 10.41% showed heterogeneous enhancement. All of the malignant masses showed heterogeneous enhancement. At the 25th second, the SIs and wash-in rates of the adenomas were significantly higher than those of the malignant masses (p=0.010). Time-to-peak enhancement of the malignant masses was significantly longer than that of the adenomas. With a cut-off value of 52.85 s, the time-to-peak enhancement had 87.5% sensitivity and 80% specificity.

CONCLUSION

Chemical shift MR has a high sensitivity and specificity in the differential diagnosis of adenomas and malignant adrenal masses. However, taking into consideration only the atypical adenomas, chemical shift MRI is of no diagnostic value. Although the diagnostic value of dynamic MRI is lower than chemical shift MRI, in the atypical cases contrast enhancement patterns and time-to-peak and wash-in rates derived from SI-time curve of dynamic MRI give are contributory to the results of chemical shift MRI.

Imaging of adrenal masses

PURPOSE OF REVIEW

This review aims to outline recent developments in adrenal imaging and characterization. Controversies in the management of adrenal incidentalomas will be addressed.

RECENT FINDINGS

Evaluation of density readings on unenhanced computed tomography and on contrast-enhanced delayed series has tremendously improved the characterization of adrenal masses. Attenuation measurements may, however, vary between different scanner types and may also be influenced by patient factors and the scanning technique. Evaluation of the mean percentage washout for adrenal masses on delayed enhanced computed tomography series is independent of such factors and allows the characterization of adrenal lesions with high sensitivity and specificity. In magnetic resonance imaging, dynamic gadolinium-enhanced and chemical-shift techniques have significantly improved the characterization of adrenal masses. Nuclear medicine studies prove to be useful adjuncts. Controversial reports have been published on the role of positron emission tomography/computed tomography in adrenal imaging. Adrenal venous sampling may allow differentiation of aldosteronoma and idiopathic hyperaldosteronism.

SUMMARY

Recent developments in adrenal mass imaging have improved the characterization of adrenal mass lesions. The need for histology sampling of incidentally discovered adrenal masses has been significantly reduced due to the high specificity of these new techniques. Controversies still exist regarding the optimal strategy for hormonal screening of a patient with an incidentally detected adrenal mass.

Quantitative contrast-enhanced computed tomography: is there a need for system calibration?

The purpose of the study was to perform phantom studies to assess the impact of computed tomography (CT) system variability on quantitative measurements of contrast enhancement. A phantom containing tubes of contrast material at dilutions of 120, 1:35, 1:50, 1:100 and 1:200 arranged in air or water was imaged using 11 CT systems at 9 institutions. All systems had undergone routine calibration against air and water in accordance with the manufacturers' recommendations. For a given tube voltage, the relationship between the iodine concentration and CT attenuation value on a single system varied by 17 to 24% over 46-48 weeks. The coefficients of variance for iodine calibration factors across different CT systems were 8.9% in air and 5.1% in water. Calibration of individual CT systems for iodine response is required to allow comparison of quantitative measurements of contrast enhancement across different institutions. Using the iodine calibration factor to express contrast enhancement as iodine concentration would facilitate the universal application of diagnostic enhancement thresholds, especially if the necessary calculations were performed by software installed on the CT console.

Adrenocortical carcinoma: contrast washout characteristics on CT

OBJECTIVE

The purpose of this study was to characterize pathologically proven adrenocortical carcinoma by examination of washout attenuation characteristics on contrast-enhanced CT images.

CONCLUSION

Adrenocortical carcinoma has relative contrast retention on delayed contrast-enhanced CT. All tumors in this series had a relative percentage washout less than 40%, a finding consistent with malignant disease.

Adrenal Lesions: Attenuation Measurement Differences between CT Scanners

PURPOSE

To retrospectively compare unenhanced computed tomographic scans of the same adrenal lesion obtained with two different manufacturers' multidetector scanners to assess whether there are differences in attenuation measurements.

MATERIALS AND METHODS

The study was approved by the local ethical committee, which waived patient consent, and was conducted in compliance with HIPAA. Electronic searching revealed patients with adrenal nodules scanned with both a Siemens 16-detector row scanner and one of eight GE Medical Systems multi-detector row scanners between January 2000 and September 2004 without the use of intravenous contrast material. Lesions were characterized by using histologic findings, fat content, or size stability. Size stability for 6 months was required unless both scans were obtained within 21 days of each other. Two radiologists independently measured lesion attenuation for regression analysis. Lesions considered benign (< or = 10 HU) on one scan and indeterminate (> 10 HU) on the other were separately analyzed, and technical parameters of scanning were compared.

RESULTS

There were 47 patients (27 men, 20 women; age range, 40-86 years; mean age, 64 years) with four metastases, 42 adenomas, and one myelolipoma (long-axis length, 10-85 mm; mean, 24 mm). GE scans were obtained with four-detector row scanners (n = 32), an eight-detector row scanner (n = 2), and 16-detector row scanners (n = 13). Correlation between the two readers was 0.99 for both Siemens and GE scan attenuation measurements. The slope of regression lines for both readers plotting GE attenuation (y-axis) against Siemens attenuation (x-axis) was less than 1, which indicated a slight but statistically significant tendency for GE scans to have lower attenuations than do Siemens scans. For both readers, there were more lesions indeterminate (> 10 HU) on Siemens scans but benign (< or = 10 HU) on GE scans than the reverse (McNemar test, P < .02 for reader 1, not significant for reader 2). Average Siemens and GE scan technical parameters were similar.

CONCLUSION

There are only slight differences in attenuation of adrenal nodules measured on scans obtained with different scanners.

Radiographic evaluation of the incidental adrenal lesion

The detection of incidental adrenal masses has increased substantially with the advent and widespread use of high-resolution cross-sectional imaging techniques such as CT and MRI. The work-up and treatment of these incidentally found adrenal masses continue to be a clinical challenge for radiologists, endocrinologists, and adrenal surgeons. The approach to the evaluation of most of these adrenal masses depends on the radiologic appearance of the lesion, and whether the patient has a known underlying malignancy. The aim of this article is to review imaging features of pathologic abnormalities of the adrenal gland. Recent advances in noninvasive imaging methods that attempt to differentiate benign from malignant lesions also are addressed.

Distinguishing benign from malignant adrenal masses: multi-detector row CT protocol with 10-minute delay

PURPOSE

To retrospectively evaluate the accuracy of precontrast attenuation, relative percentage washout (RPW), and absolute percentage washout (APW) in distinguishing benign from malignant adrenal masses at multi-detector row computed tomography (CT).

MATERIALS AND METHODS

This HIPAA-compliant retrospective study had institutional review board approval; the need for informed consent was waived. One hundred twenty-two adrenal masses were evaluated in 99 patients (51 men, 48 women; age range, 37-86 years) who had undergone CT performed according to the study protocol and who either were given a pathologic diagnosis or underwent follow-up imaging. Unenhanced images were obtained before administration of 120 mL of an intravenous contrast agent with a 75-second scan delay. Delayed images were obtained after 10 minutes. RPW and APW were computed. Receiver operating characteristic (ROC) analysis was performed to compare mean attenuation and both RPW and APW. Analysis was first performed with the exclusion of pheochromocytomas, myelolipomas, and cysts. Precontrast attenuation criteria specific for benignity or malignancy were determined, and ROC analysis of results for the entire nonpheochromocytoma group was then performed.

RESULTS

By using an RPW of 37.5% and excluding cysts and myelolipomas, all malignant lesions were detected with a sensitivity of 100% (17 of 17 lesions) and a specificity of 95% (90 of 95 lesions). Area under the binomial ROC curve (A(z)) values were 0.912, 0.985, and 0.892 for precontrast attenuation, RPW, and APW, respectively. Precontrast attenuation of less than 0 or more than 43 HU indicated benign and malignant entities, respectively. Incorporation of these criteria into the APW analysis yielded a sensitivity of 100% (17 of 17 lesions) and a specificity of 98% (93 of 95 lesions) for a threshold washout value of 52.0%. This attenuation-corrected APW generated the greatest A(z) value (ie, 0.988). Combining all the information available from the protocol yielded a sensitivity of 100% (17 of 17 lesions) and a specificity of 98% (98 of 100 lesions) for differentiating benign from malignant masses.

CONCLUSION

Precontrast attenuation of less than 0 HU supercedes the washout profile in the evaluation of an individual adrenal mass. Noncalcified, nonhemorrhagic adrenal lesions with precontrast attenuation of more than 43 HU should be considered suspicious for malignancy.

Abrupt enlargement of adrenal incidentaloma: a case of isolated adrenal metastasis

A 56-year-old Japanese man was referred for examination of right adrenal tumor (3 cm). He had no apparent preexisting cancer by radiological workup and accordingly, the patient was considered as a nonfunctioning adrenocortical adenoma and scheduled for periodic CT scans every 6 months. However, five months after the initial diagnosis the patient complained of severe right back pain with remarkable enlargement of both adrenals (~20-fold volume). Although the origin of adrenal tumor was uncertain by pathological workup, positron emission tomography (PET) scan with (18)F-2-fluoro-D-deoxyglucose (FDG) eventually revealed a hot spot on left upper lung, which was consistent with a lesion of thickened bulla wall observed by chest CT. The present case is a very rare example of abrupt enlargement of bilateral adrenals due to clinically isolated adrenal metastasis, suggesting the requirement of frequent observation with greatest care regarding morphologic changes of adrenal incidentalomas.