Delayed enhanced CT of lipid-poor adrenal adenomas

OBJECTIVE. Although representing a minority of adrenal adenomas, the lipid-poor variety cannot be accurately identified on unenhanced CT or chemical shift MR imaging. We compared the delayed contrast-enhanced CT features of lipid-poor adenomas with those of lipid-rich adenomas and of adrenal nonadenomas to determine whether there were differences in the washout features between these groups of lesions. SUBJECTS AND METHODS. Eighteen proven lipid-poor adenomas, 56 lipid-rich adenomas, and 40 adrenal nonadenomas underwent CT before, immediately after, and 15 min delay after IV contrast injection. Region-of-interest measurements were made of all adrenal lesions at the three time points. The degree of enhancement, enhancement washout, percentage enhancement washout, and relative percentage enhancement washout were calculated for each adrenal mass. Pooled data were analyzed statistically. Optimal threshold values for diagnosing adrenal adenomas were also determined. RESULTS. The mean CT attenuation of lipid-poor adenomas was significantly higher than that of lipid-rich adenomas at all three phases but not significantly different from that of nonadenomas. The mean percentage enhancement washout on images obtained 15 min after administration of contrast material was similar for lipid-rich and lipid-poor adenomas but was significantly higher than that of nonadenomas. The mean relative percentage enhancement washout was significantly different among all three groups. CONCLUSION. Lipid-poor adenomas cannot be differentiated from adrenal nonadenomas on the basis of a single mean attenuation value. However, lipid-poor adrenal adenomas show enhancement and enhancement washout features nearly identical to lipid-rich adenomas and can be distinguished from nonadenomas on the basis of a percentage washout threshold value of 60% and a relative percentage washout of 40%.     

Radiologie der Nebennieren

An important principle of diagnostic imaging of the adrenal glands is to characterize an adrenal mass as an adenoma using computed tomography (CT) or magnetic resonance imaging (MRI) techniques. Most techniques exploit the fact that typical adrenal adenomas are lipid-rich so that lipid-poor adenomas, however, remain a diagnostic problem. A CT attenuation ≤?10 HU, more than 10% negative pixels as demonstrated by histogram analysis, an absolute washout of more than 60%, a relative washout of more than 40% and a signal drop of more than 20% in opposed-phase images are characteristic for adrenal adenomas. Endocrine dysfunction is diagnosed biochemically and not by means of imaging but are necessary to localize a functioning tumor. An important principle is to combine anatomical with functional imaging studies. Percutaneous biopsy of adrenal glands is only indicated when an adrenal mass is the only potential metastasis of a diagnosed primary tumor.     

Comparison of unenhanced CT and chemical shift MRI in evaluating lipid-rich adrenal adenomas

OBJECTIVE: Our aim was to evaluate adrenal adenomas in patients who underwent both unenhanced CT and chemical shift MRI to determine if adenomas can be characterized with MRI when the findings of CT are indeterminate. MATERIALS AND METHODS: Between January 1999 and June 2003, 40 patients (42 adrenal masses) underwent unenhanced CT and chemical shift MRI and were retrospectively analyzed. Hounsfield units, adrenal-to-spleen chemical shift ratio, and signal-intensity index were obtained for each adrenal mass. Qualitative analysis for loss of signal in each adrenal mass on the opposed-phase images was also performed by two reviewers and compared with the quantitative analyses. A lipid-rich adenoma was diagnosed if the mass measured equal to or less than 10 H, had an adrenal-to-spleen chemical shift ratio of less than 0.71, and had a signal-intensity index of greater than 16.5% or if the mass fulfilled two of the preceding criteria and had follow-up imaging without change. RESULTS: The sensitivities and specificities for diagnosing a lipid-rich adenoma using the qualitative, adrenal-to-spleen chemical shift ratio, signal-intensity index, and unenhanced CT attenuation analyses were 92% (33/36) and 17% (1/6), 100% (36/36) and 100% (6/6), 100% (36/36) and 67% (4/6), and 78% (28/36) and 83% (5/6), respectively. Twenty-eight (67%) lipid-rich adenomas measured equal to or less than 10 H, had an adrenal-to-spleen chemical shift ratio of less than 0.71, and had a signal-intensity index of greater than 16.5%. Eight masses (19%) measured greater than 10 H but had an adrenal-to-spleen chemical shift ratio of less than 0.71 and a signal-intensity index greater than 16.5% and were unchanged at follow-up. CONCLUSION: Eight (62%) of 13 adrenal adenomas measuring greater than 10 H on unenhanced CT were definitively characterized with chemical shift MRI.     

Tumoren der Nebennieren

Clinical/methodical issue

Adrenal masses are very common and are usually detected incidentally. Less frequently, imaging is performed for the localization of the underlying lesion in the case of endocrine disease. The differentiation between adenomas and non-adenomas is fundamental.

Methodical innovations

Adenomas show a low density on unenhanced computed tomography (CT) and a rapid washout of contrast agents. In magnetic resonance imaging (MRI) adenomas are characterized by a low signal in opposed phase imaging as compared to in phase imaging.

Performance

According to the literature a density of less than 10 HU in an adrenal mass has a specificity of 98?% and a sensitivity of 71?% for the presence of an adenoma and MRI is slightly more sensitive. Some adrenal lesions, e.g. cysts or myelolipomas can be diagnosed with high accuracy due to pathognomonic findings.

Achievements

In the majority of cases the synopsis of imaging along with clinical and laboratory findings is necessary for a reliable diagnosis.

Practical recommendations

For the evaluation of an adrenal mass the CT examination should begin with an unenhanced scan, if necessary followed by a washout examination. In the case of MRI in phase and opposed phase imaging are essential components of the examination.     

Adrenal masses: CT characterization with histogram analysis method

PURPOSE: To evaluate a histogram analysis method for differentiating adrenal adenoma from metastasis at computed tomography (CT). MATERIALS AND METHODS: In a retrospective review of 2 years of clinical CT records, 223 adrenal adenomas in 193 patients (115 with contrast material-enhanced CT, 43 with unenhanced and enhanced CT, and 35 with unenhanced CT) and 31 metastases (25 patients with enhanced CT) were found. In 158 patients with adenomas at enhanced CT, diagnosis was based on stable mass size for more than 1 year (n = 135) and characteristic signal intensity decrease at chemical shift magnetic resonance imaging (n = 23). In 35 patients with adenomas at unenhanced CT, mean attenuation was 10 HU or less. Diagnosis of all metastases was based on rapid growth of a mass or new mass in less than 6 months in patients with cancer. Adrenal metastases with extensive necrosis were excluded. Histogram analysis was performed in a circular region of interest (ROI) for mean attenuation, number of pixels, and range of pixel attenuation for all pixels and for the subset of pixels with less than 0 HU ("negative" pixels). Correlation between mean attenuation and percentage negative pixels was calculated. RESULTS: Negative pixels were present in all 74 unenhanced adenomas with mean attenuation of 10 HU or less and in 14 of 16 unenhanced adenomas with mean attenuation above 10 HU. Of 184 enhanced adenomas, only 20 had mean attenuation of 10 HU or less, but 97 contained negative pixels (77 of these 97 masses had mean attenuation above 10 HU). Increase in percentage negative pixels was highly correlated with decrease in mean attenuation of both unenhanced and enhanced adenomas. None of the adrenal metastases had mean attenuation of 10 HU or less or contained negative pixels. CONCLUSION: The histogram method is far more sensitive than the 10-HU threshold method for diagnosis of adrenal adenomas at enhanced CT, with specificity maintained at 100%.     

Low-density pheochromocytoma on CT: a mimicker of adrenal adenoma

OBJECTIVE: Attenuation values on CT of less than 10 H are considered characteristic of adrenal adenomas. Adrenal pheochromocytomas can infrequently contain fat that could result in low attenuation on CT. The purpose of our study was to determine if pheochromocytomas could be confused with adenomas by virtue of their attenuation values on unenhanced CT. MATERIALS AND METHODS: CT attenuation and size of nine adrenal nodules producing pheochromocytoma syndrome were measured on unenhanced CT in nine patients. For five patients who received IV contrast material, washout profiles were also calculated. RESULTS: Two of the nine patients had adrenal lesions with attenuation values of less than 10 H; one had a pheochromocytoma with an attentuation of 9.0 H, and the other had a medullary hyperplasia with an attenuation of 1.8 H. These two nodules showed evidence of microscopic fat at histologic examination. No macroscopic fat was seen on the CT scans. The remaining seven patients had lesions with attenuation values exceeding 10 H (mean value, 25.6 H; range, 1.8-41 H). Mean diameter of the nine tumors (including the hyperplastic nodule) was 3.2 cm (range, 0.8-6.7 cm; SD, +/- 2.3 cm). The two low-attenuation lesions also mimicked adenomas by displaying more than 60% contrast washout on 10-min-delayed contrast-enhanced scans, unlike the other three pheochromocytomas for which we had washout data. CONCLUSION: On CT, pheochromocytomas may have attenuation values less than 10 H and also may display more than 60% washout of contrast agents on delayed scanning. Adrenal pheochromocytomas should be included with adenomas in the differential diagnosis both for masses with low attenuation on unenhanced CT and for lesions exhibiting a high percentage of contrast washout.     

Cross-sectional imaging work-up of adrenal masses

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

Adrenal masses: characterization with combined unenhanced and delayed enhanced CT

PURPOSE: To assess the accuracy of a dedicated adrenal computed tomographic (CT) protocol. MATERIALS AND METHODS: One hundred sixty-six adrenal masses were evaluated with a protocol consisting of unenhanced CT, and, for those with attenuation values greater than 10 HU, contrast material-enhanced and delayed enhanced CT. Attenuation values and enhancement washout calculations were obtained. An adenoma was diagnosed if a mass had an attenuation value of 10 HU or less at unenhanced CT or a percentage enhancement washout value of 60% or higher. RESULTS: The final diagnosis was adenoma in 127 masses and non-adenoma in 39. Masses measuring more than 10 HU on unenhanced CT scans were confirmed at biopsy (n = 28) or were examined for stability or change in size at follow-up CT performed at a minimum interval of 6 months (n = 33). Thirty-six (92%) of 39 non-adenomas and 124 (98%) of 127 adenomas were correctly characterized. The sensitivity and specificity of this protocol were 98% and 92%, respectively. This protocol correctly characterized 160 (96%) of 166 masses. CONCLUSION: With a combination of unenhanced and delayed enhanced CT, nearly all adrenal masses can be correctly categorized as adenomas or non-adenomas.     

Evaluation of adrenal masses with gadolinium enhancement and fat-suppressed MR imaging

A study was undertaken to determine the ability to characterize benign and malignant masses with unenhanced and contrast material-enhanced fast lowangle shot and fat-suppressed spin-echo magnetic resonance (MR) imaging. Thirty patients with adrenal masses detected at computed tomography (CT) underwent MR imaging within 14 days after CT. CT and MR images were interpreted in a prospective, blinded fashion. Sixteen patients had 20 benign adrenal masses, and 14 patients had 18 malignant masses. Quantitative measurements included percentage of contrast enhancement on immediate postcontrast dynamic images and periphery - center signal-to-noise ratio (S/N) on gadolinium-enhanced fat-suppressed images. Qualitative evaluation included determination of the regularity of lesion margins, homogeneity of signal intensity, and local extension. MR imaging depicted all adrenal masses discovered at CT examinations. Lesions ranged in diameter from 1 to 15 (mean, 4.4) cm. No significant difference was observed in percentage of contrast enhancement between benign (90.5% ± 59.0 [standard deviation]) and malignant (110.5% ± 116.4) masses. A difference was observed between periphery - center S/N for benign (?.05 ± 1.5) and malignant (7.7 ± 9.8) masses; overlap between the two, however, occurred. Qualitative evaluation allowed correct characterization of 32 of 38 masses, comparing favorably with CT, which allowed characterization of 30 lesions.     

Diagnosis of adrenal adenoma: value of central spot of high-intensity hyperintense rim sign and homogeneous isointensity to liver on gadolinium-enhanced fat-suppressed spin-echo MR images

Eighty-nine patients with 108 adrenal masses, either adenomas (n = 88) or malignant lesions (n = 20), underwent magnetic resonance imaging (MRI) of the abdomen at 0.5 T for the purpose of determining whether adrenal adenomas could be differentiated from malignant lesions on gadolinium-enhanced fat-suppressed T1-weighted spin-echo (SE) images (Gd-E FS T1WI) and on T2-weighted SE images. The imaging protocol included conventional unenhanced SE T1- and T2-weighted sequences and Gd-E FS T1WI. Three observers independently evaluated signal intensity on unenhanced and enhanced images and also the presence of structures of high signal intensity in the outer margin [hyperintense rim sign (HRS)] or in the center [hyperintense central spot (HCS)] of the adrenal masses. Forty-one (46.5%) of 88 adenomas were homogeneously isointense to liver in unenhanced and enhanced T1-weighted sequences and in T2WI. HCS and HRS were observed in 33/88 (37.5%) and 15/88 (17%) adenomas, respectively, on Gd-E FS T1WI; in contrast, these signs were never revealed in any case of malignant lesions. Sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy in classifying lesions as suggestive of adenoma were 93%, 90%, 98%, 75%, and 93%, respectively. Visual evaluation of details of tumor structures on Gd-E FS T1WI allows good characterization of adrenal masses. HCS, HRS, and homogeneous isointensity to liver are characteristic signs of adrenal adenomas.     

State-of-the-art adrenal imaging.

The adrenal gland is a common site of disease, and detection of adrenal masses has increased with the expanding use of cross-sectional imaging. Radiology is playing a critical role in not only the detection of adrenal abnormalities but in characterizing them as benign or malignant. The purpose of the article is to illustrate and describe the appropriate radiologic work-up for diseases affecting the adrenal gland. The work-up of a suspected hyperfunctioning adrenal mass (pheochromocytoma and aldosteronoma) should start with appropriate biochemical screening tests followed by thin-collimation computed tomography (CT). If results of CT are not diagnostic, magnetic resonance (MR) and nuclear medicine imaging examinations should be performed. CT has become the study of choice to differentiate a benign adenoma from a metastasis in the oncology patient. If the attenuation of the adrenal gland is over 10 HU at nonenhanced CT, contrast material-enhanced CT should be performed and washout calculated. Over 50% washout of contrast material on a 10-minute delayed CT scan is diagnostic of an adenoma. For adrenal lesions that are indeterminate at CT in the oncology patient, chemical shift MR imaging or adrenal biopsy should be performed. Certain features can be used by the radiologist to establish a definitive diagnosis for most adrenal masses (including carcinoma, infections, and hemorrhage) based on imaging findings alone.     

Differentiation of adrenal adenomas from nonadenomas using CT histogram analysis method: A prospective study

Objective

The objective of our study was to prospectively evaluate the effectiveness of computed tomography (CT) histogram analysis method in the differentiation of benign and malignant adrenal masses.

Materials and Methods

Between March 2007 and June 2008, 94 patients (46 males, 48 females, age range: 30-79 years, mean age: 57.7 years) with 113 adrenal masses (mean diameter: 3.03 cm, range: 1.07-8.02 cm) were prospectively evaluated. These included 66 adenomas, 45 metastases and 2 pheochromocytomas. Histogram analysis method was performed using a circular region of interest (ROI) and mean attenuation, total number of pixels, number of negative pixels and subsequent percentage of negative pixels were detected on both unenhanced and delayed contrast-enhanced CT images for each adrenal mass. A mean attenuation threshold of 10 Hounsfield unit (HU) for unenhanced CT and 5% and 10% negative pixel thresholds for both unenhanced and delayed contrast-enhanced CT were calculated by a consensus of at least two reviewers and the correlation between mean attenuation and percentage of negative pixels was determined. Final diagnoses were based on imaging follow-up of minimum 6 months, biopsy, surgery and adrenal washout study.

Results

51 of 66 adenomas (77.3%) showed attenuation values of ≤10 HU and 15 (22.7%) adenomas showed more than 10 HU on unenhanced CT. All of these adenomas contained negative pixels on unenhanced CT. Eight of 66 (12.1%) adenomas showed a mean attenuation value of ≤10 HU on delayed contrast-enhanced scans and 45 adenomas (68.2%) persisted on containing negative pixels. All metastases had an attenuation value of greater than 10 HU on unenhanced CT images. 21 of 45 (46.6%) metastases contained negative pixels on unenhanced images but only seven metastases (15.5%) had negative pixels on delayed contrast-enhanced images. Two pheochromocytomas had negative pixels on both unenhanced and delayed contrast-enhanced CT images. Increase in the percentage of negative pixels yielded high correlation with mean attenuation decreases, both on unenhanced and delayed contrast-enhanced CT. Our sensitivity was 90.9% for the 10% negative pixel percentage threshold compared to 77.2% sensitivity for ≤10 HU mean attenuation threshold for unenhanced CT. Both methods gave a 100% specificity for the diagnosis of adenoma. We also obtained a 37.9% sensitivity for 5% negative pixel threshold and a slightly lower sensitivity of 28.8% for 10% negative pixel threshold compared to the 12.1% sensitivity of ≤10 HU mean attenuation threshold while maintaining 100% specificity for contrast-enhanced CT.

Conclusion

The CT histogram analysis is a simple and easily applicable method which provides higher sensitivity than the commonly used 10 HU threshold mean attenuation method of unenhanced CT and can replace it for the diagnosis of an adenoma. But with contrast-enhanced CT, although 100% specificity is being maintained, the sensitivities obtained are very poor for each method and is therefore likely to limit CT histogram analysis to be used as a clinically useful adjunct in the diagnosis of adenoma.     

Can single-phase dual-energy CT reliably identify adrenal adenomas?

Purpose

To evaluate whether single-phase dual-energy-CT-based attenuation measurements can reliably differentiate lipid-rich adrenal adenomas from malignant adrenal lesions.

Materials and methods

We retrospectively identified 51 patients with adrenal masses who had undergone contrast-enhanced dual-energy-CT (140/100 or 140/80 kVp). Virtual non-contrast and colour-coded iodine images were generated, allowing for measurement of pre- and post-contrast density on a single-phase acquisition. Adrenal adenoma was diagnosed if density on virtual non-contrast images was ≤10 HU. Clinical follow-up, true non-contrast CT, PET/CT, in- and opposed-phase MRI, and histopathology served as the standard of reference.

Results

Based on the standard of reference, 46/57 (80.7 %) adrenal masses were characterised as adenomas or other benign lesions; 9 malignant lesions were detected. Based on a cutoff value of 10 HU, virtual non-contrast images allowed for correct identification of adrenal adenomas in 33 of 46 (71 %), whereas 13/46 (28 %) adrenal adenomas were lipid poor with a density ≥10 HU. Based on the threshold of 10 HU on the virtual non-contrast images, the sensitivity, specificity, and accuracy for detection of benign adrenal lesions was 73 %, 100 %, and 81 % respectively.

Conclusion

Virtual non-contrast images derived from dual-energy-CT allow for accurate characterisation of lipid-rich adrenal adenomas and can help to avoid additional follow-up imaging.

Key Points

? Adrenal adenomas are a common lesion of the adrenal glands. ? Differentiation of benign adrenal adenomas from malignant adrenal lesions is important. ? Dual-energy based virtual non-contrast images help to evaluate patients with adrenal adenomas.     

Quantitative evaluation of norcholesterol scintigraphy, CT attenuation value, and chemical-shift MR imaging for characterizing adrenal adenomas

OBJECTIVE: The objective of our study was to evaluate diagnostic ability and features of quantitative indices of three modalities: uptake rate on norcholesterol scintigraphy, computed tomography (CT) attenuation value, and fat suppression on chemical-shift magnetic resonance imaging (MRI) for characterizing adrenal adenomas. METHODS: Image findings of norcholesterol scintigraphy, CT, and MRI were reviewed for 78 patients with functioning (n = 48) or nonfunctioning (n = 30) adrenal masses. The norcholesterol uptake rate, attenuation value on unenhanced CT, and suppression on in-phase to opposed-phase MRI were measured for adrenal masses. RESULTS: The norcholesterol uptake rate, CT attenuation value, and MR suppression index showed the sensitivity of 60%, 82%, and 100%, respectively, for functioning adenomas of <2.0 cm, and 96%, 79%, and 67%, respectively, for those of >or=2.0 cm. A statistically significant correlation was observed between size and norcholesterol uptake, and between CT attenuation value and MR suppression index. Regarding norcholesterol uptake, the adenoma-to-contralateral gland ratio was significantly higher in cortisol releasing than in aldosterone-releasing adenomas. CONCLUSIONS: The norcholesterol uptake rate was reliable for characterization of adenomas among adrenal masses of >or=2.0 cm. CT attenuation value and MR suppression index were well correlated with each other, and were useful regardless of mass size.     

Characterization of adrenal adenomas and metastases: correlation between unenhanced computed tomography and chemical shift magnetic resonance imaging

PURPOSE: To evaluate the correlation of absolute attenuation values of unenhanced computed tomography (CT) with signal intensity (SI) quantitative analysis on chemical shift (CS) magnetic resonance (MR) imaging in differentiating adrenal adenomas from metastases. MATERIAL AND METHODS: Forty-one adrenal masses (27 adenomas, 14 metastases) were studied with CS MR imaging and unenhanced CT. MR included T1-weighted breathhold gradient-echo in-phase (IP) and opposed-phase (OP) sequences. The SI index (SI-i) [(SIIP-SIOP/SIIP)] x 100% and chemical-shift ratio (CS-r) relative to the spleen [(SIlesion/ SIspleen)OP/(SIlesion/SIspleen)IP] were calculated for each lesion. CT absolute attenuation values were also determined. RESULTS: The mean attenuation value of metastases was significantly greater than that of adenomas (< 0.0001). On MR, the mean SI-i of adenomas was significantly greater than that of metastases (P < 0.0001) and no overlaps were evident. The CS-r of malignant and benign lesions overlapped considerably, and five adenomas (all with indeterminate Hounsfield Unit values at CT) were misclassified as potentially malignant. CT attenuation values were significantly correlated with both MR quantitative analyses. CONCLUSION: Since CS MR imaging and CT both depict the presence of lipids within adrenal lesions, absolute attenuation values are highly correlated with MR quantitative analysis. SI-i is the most reliable tool for differentiating adrenal adenomas from metastases, showing better accuracy than lesion-to-spleen CS-r, in particular for adenomas with indeterminate absolute attenuation values.     

Imaging findings of primary adrenal tumors in pediatric patients

Apart from neuroblastomas, adrenal tumors are rarely seen in children. The most common adrenal tumors are adrenocortical carcinoma and pheochromocytoma. Adrenocortical carcinoma is usually a large heterogeneous, well-marginated mass with solid/cystic areas and calcifications, with poor prognosis. Most of the pheochromocytomas are benign tumors and usually show intense contrast enhancement, the pattern of which may be diffuse, mottled, or peripheral on computed tomography and magnetic resonance imaging. The purpose of this article is to evaluate primary nonneurogenic adrenal tumors.

In children, neoplastic and non-neoplastic lesions might be seen in the adrenal region. Pediatric adrenal lesions may be found incidentally, can be suspected in children that suffer endocrine, metabolic, neurological problems or with an abdominal mass. In fetal life, adrenal glands are much larger than in adults because of the existence of a prominent fetal cortex. Their prominent fetal size is also seen in early neonatal life. Ultrasonography (US) is the initial imaging technique to examine the adrenal glands in newborns. In older children, due to the physiologic atrophy of the fetal adrenal cortex, adrenal limbs are thinner than the adjacent crura of the diaphragm. Consequently, they are much more difficult to specify with US, but can be easily identified on computed tomography (CT) or magnetic resonance imaging (MRI). US is the primary modality for imaging the pediatric abdomen. CT or MRI are used as a problem-solving tool for lesion characterization, to determine the relationship to adjacent tissues, and to differentiate benign from malignant masses after initial US evaluation (1). In older children MRI should be preferred rather than CT examination. In adults, abdominal CT examinations assess tumor washout of contrast material based upon multi-phase CT, which is necessary to characterize adrenocortical masses (especially adenomas). However, pediatric CT examinations should be done in single portal venous phase to comply with “Image Gently” and “as low as reasonably achievable” (ALARA) principles.Primary adrenal tumors are classified according to their origin and function. They might originate from the medulla or cortex, and they are hyperfunctioning or nonfunctioning. Primary medullary tumors encompass a spectrum of sympathetic neuroectodermal tumors, which are neuroblastoma, ganglioneuroblastoma, ganglioneuroma, and pheochromocytoma, all of which stem from the neural crest and may take place anywhere along the sympathetic chain aside from the adrenal gland itself. Neoplasms arising from the adrenal cortex are adrenocortical carcinoma and adenoma.In the literature, few studies have reported imaging findings of pediatric adrenal tumors, including all types of involvement (i.e., benign, malignant, and metastatic) (1–3). The aim of this article is to describe the imaging findings of primary nonneurogenic adrenal tumors.     

Contrast-enhanced ultrasound in evaluation of adrenal lesions with CT/MRI correlation

Most of the adrenal masses are incidentally detected. Multiphasic CT forms the mainstay for diagnosis and characterization of adrenal masses. MRI can further be used if the masses are indeterminate on CT scan. But as these investigations are expensive with risk of radiation exposure, contrast-enhanced ultrasound (CEUS) is currently under evaluation to assess its utility to act as a screening modality to differentiate benign vs malignant adrenal masses This investigative modality is relatively safe and can be used in patients having renal dysfunction or allergy to CT contrast. We, hereby, present a pictorial review of imaging appearance of various adrenal lesions on CEUS with CT and MRI correlation.     

Characterization of indeterminate (lipid-poor) adrenal masses: use of washout characteristics at contrast-enhanced CT

PURPOSE: To determine whether computed tomographic (CT) scans and attenuation measurements on contrast material-enhanced and nonenhanced CT scans could be used to characterize adrenal masses, in particular, to characterize these lesions by using adrenal washout characteristics at contrast-enhanced CT. MATERIALS AND METHODS: Eighty-six patients (49 men, 37 women; age range, 29-86 years; mean age, 72 years) with 101 adrenal lesions depicted at contrast-enhanced CT underwent delayed (mean, 9 minutes) enhanced scanning. Seventy-eight patients also underwent nonenhanced CT. Mean diameter of the benign lesions was 2.1 cm (range, 1.0-4.2 cm); mean diameter of the malignant lesions was 2.3 cm (range, 1.0-4.1 cm). Region-of-interest measurements were obtained at nonenhanced, dynamic enhanced, and delayed enhanced CT and were used to calculate a relative percentage washout as follows: 1 - (Hounsfield unit measurement on delayed image / Hounsfield unit measurement on dynamic image) x 100%. RESULTS: Ninety-nine of 101 lesions were correctly characterized as benign or malignant with a relative percentage washout threshold of 50% on delayed scans; benign lesions demonstrated more than 50% washout; and malignant lesions, less than 50% washout. Two benign lesions demonstrating less than 50% washout were characterized as benign by using conventional CT. CONCLUSION: Calculation of relative percentage washout on dynamic and delayed enhanced CT scans may lead to a highly specific test for adrenal lesion characterization, reduce the need for, and possibly obviate, follow-up imaging or biopsy.     

Adrenal adenomas: characteristic postgadolinium capillary blush on dynamic MR imaging

We sought to evaluate dynamic post-gadolinium contrast enhanced magnetic resonance (MR) imaging characteristics of adrenal adenomas with comparison to those of malignant adrenal tumors. MR images, including in- and out-of-phase spoiled gradient echo (SGE) and dynamic gadolinium enhancement, of 35 adrenal adenomas in 34 patients, and 12 malignant adrenal tumors in 12 patients, were reviewed retrospectively. MR images were assessed for the presence of a capillary blush on immediate postgadolinium SGE images, and for rapid washout of contrast on 45-second postgadolinium SGE images. Thirty-five adrenal adenomas (mean size, 3.1 cm) and 12 malignant adrenal tumors (mean size, 7.4 cm) were assessed. Of 35 adrenal adenomas, 25 (71%) showed a homogeneous capillary blush on immediate postgadolinium images. Thirty-three (94%) adrenal adenomas demonstrated rapid washout on 45-second postgadolinium images (P < 0.001). Of 35 adrenal adenomas, 30 (86%) showed diminished signal intensity (SI) on out-of-phase images. Of 12 malignant adrenal tumors, none showed a homogeneous capillary blush on immediate postgadolinium images. Six (50%) malignant tumors showed negligible enhancement, four (33%) showed irregular patchy enhancement, and two (17%) showed peripheral enhancement (P < 0.001). On 45-second postgadolinium images, 11 (92%) of 12 malignant adrenal tumors showed irregular enhancement. In the majority of adrenal adenomas, an initial homogeneous capillary blush and rapid washout are demonstrated on gadolinium-enhanced dynamic MR imaging. Our preliminary results suggest that this may provide useful complementary information to the appearance of adrenal masses on in- and out-of-phase images.     

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

Objective

To 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 methods

Twenty-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 −10 HU, 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.

Results

Mean virtual unenhanced attenuation values of all lesions calculated from the portal phase images was 12.6 HU, and was 4.02 HU 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).

Conclusions

Our 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 10 HU can thus be safely characterized as an adenoma.