In vivo MR spectroscopic imaging of the adrenal glands: distinction between adenomas and carcinomas larger than 15 mm based on lipid content

ACR Appropriateness Criteria® Adrenal Mass Evaluation: 2021 Update

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

Adrenocortical neoplasms in adulthood and childhood: distinct presentation. Review of the clinical, pathological and imaging characteristics

Adrenocortical tumors (ACT) in adulthood and childhood vary in clinical, histopathological, molecular, prognostic, and imaging aspects. ACT are relatively common in adults, as adenomas are often found incidentally on imaging. ACT are rare in children, though they have a significantly higher prevalence in the south and southeast regions of Brazil. In clinical manifestation, adults with ACT present more frequently with glucocorticoid overproduction (Cushing syndrome), mineralocorticoid syndromes (Conn syndrome), or the excess of androgens in women. Subclinical tumors are frequently diagnosed late, associated with compression symptoms of abdominal mass. In children, the usual presentation is the virilizing syndrome or virilizing association and hypercortisolism. Histopathological grading and ACT classification in malignant and benign lesions are different for adults and children. In adults, the described criteria are the Hough, Weiss, modified Weiss, and Van Slooten. These scores are not valid for children; there are other criteria, such as proposed by Wieneke and colleagues. In molecular terms, there is also a difference related to genetic alterations found in these two populations. This review discusses the imaging findings of ACT, aiming to characterize the present differences between ACT found in adults and children. We listed several differences between magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography-computed (PET-CT) and also performed a literature review, which focuses on studied age groups of published articles in the last 10 years regarding cortical neoplasm and imaging techniques. Published studies on ACT imaging in children are rare. It is important to stress that the majority of publications related to the differentiation of malignant and benign tumors are based almost exclusively on studies in adults. A minority of articles, however, studied adults and children together, which may not be appropriate.

Differential Diagnosis of Adrenal Masses Using Out-of-Phase Flash Imaging

The purpose of this report was to suggest the ability to differentiate adrenal masses by out-of-phase FLASH imaging. The images were obtained with breath-holding at TR/TE 100/12 ms, flip angle 20°. The material included adrenal adenoma (n = 16), nodular hyperplasia (n = 1), pheochromocytoma (n = 5), and adrenal metastatic tumors (n = 7). The signal intensity ratios of the adrenal mass/the diaphragmatic crus, back muscle, and renal cortex were obtained. The mean values of the ratios of adenomas or nodular hyperplasia were significantly different from pheochromocytomas or metastases. Although the number of adrenal masses was fairly small, the ratios of adrenal mass/diaphragmatic crus could distinguish them with no overlapping case. All 17 masses with the ratio of 1.16 or less were adenomas or nodular hyperplasia, whereas all 12 masses with a ratio greater than 1.23 were pheochromocytomas or metastases. This result suggests the ability of out-of-phase FLASH imaging to differentiate adrenal masses.

Application of a protocol for magnetic resonance spectroscopy of adrenal glands: an experiment with over 100 cases

Objective

To evaluate a protocol for two-dimensional (2D) hydrogen proton (1H) magnetic resonance spectroscopy (MRS) (Siemens Medical Systems; Erlangen, Germany) in the detection of adrenal nodules and differentiation between benign and malignant masses (adenomas, pheochromocytomas, carcinomas and metastases).

Materials and Methods

A total of 118 patients (36 men; 82 women) (mean age: 57.3 ± 13.3 years) presenting with 138 adrenal nodules/masses were prospectively assessed. A multivoxel system was utilized with a 2D point-resolved spectroscopy/chemical shift imaging sequence. The following ratios were calculated: choline (Cho)/creatine (Cr), 4.0–4.3/Cr, lipid (Lip)/Cr, Cho/Lip and lactate (Lac)/Cr.

Results

2D-1H-MRS was successful in 123 (89.13%) lesions. Sensitivity and specificity values observed for the ratios and cutoff points were the following: Cho/Cr ≥ 1.2, 100% sensitivity, 98.2% specificity (differences between adenomas/pheochromocytomas and carcinomas/ metastases); 4.0–4.3 ppm/Cr ≥ 1.5, 92.3% sensitivity, 96.9% specificity (differences between carcinomas/pheochromocytomas and adenomas/metastases); Lac/Cr ≤ –7.449, 90.9% sensitivity and 77.8% specificity (differences between pheochromocytomas and carcinomas/adenomas).

Conclusion

Information provided by 2D-1H-MRS were effective and allowed for the differentiation between adrenal masses and nodules in most cases of lesions with > 1.0 cm in diameter.

Adrenal adenoma and metastasis from clear cell renal cell carcinoma: can they be differentiated using standard MR techniques?

BACKGROUND

Chemical-shift magnetic resonance imaging (MRI) has been known to successfully differentiate adenomas from metastases. However, there has been concern that metastasis from extra-adrenal primary malignancies which contain high lipid content such as clear cell renal cell carcinoma (RCC) could mimic adrenal adenomas.

PURPOSE

To evaluate the ability of MR to differentiate adrenal adenoma from metastasis using chemical-shift imaging and MR feature analysis in patients with clear cell RCC.

MATERIAL AND METHODS

This study was institutional review board-approved; informed consent was waived. Eleven patients with 13 metastases and 13 patients with 15 adrenal adenomas in patients with clear cell RCC for evaluation of an adrenal mass underwent MR. Signal intensity on in- and opposed-phases, signal intensity index (SII), size, T2 SI, cystic change, necrosis, and hemorrhage were evaluated. Statistical analyses included Student t-test and Fisher exact test. If available, precontrast CT attenuation of the adrenal adenomas was measured. SII was correlated with attenuation using Pearson correlation coefficient.

RESULTS

Mean size of adenomas was smaller than that of metastases (P < 0.002). Mean SII of adenomas (45.0% ± 24.6) was significantly greater than that of metastases (6.6% ± 4.7; P < 0.001). With a threshold of 16.5% for SII, the sensitivity, specificity, and accuracy for adenomas were 80%, 100%, and 89.2%, respectively. All six lipid-rich adenomas were diagnosed as adrenal adenoma. Three of eight (37.5%) lipid-poor adenomas were misdiagnosed as metastases. While up to 53.8% (7/13) of the metastases demonstrated cystic change, necrosis, or hemorrhage, only one (6.7%) adenoma exhibited cystic change or necrosis (P < 0.05 for all). Precontrast attenuation and SII were significantly correlated: r = -0.810 (P < 0.001).

CONCLUSION

In patients with clear cell RCC who underwent MR for adrenal masses, SII and MR features such as cystic change, necrosis, and hemorrhage were helpful in differentiating adenomas from metastases.

Glutamine/glutamate metabolism studied with magnetic resonance spectroscopic imaging for the characterization of adrenal nodules and masses

PURPOSE

To assess glutamine/glutamate (Glx) and lactate (Lac) metabolism using proton magnetic resonance spectroscopic imaging (1H-MRS) in order to differentiate between adrenal gland nodules and masses (adenomas, pheochromocytomas, carcinomas, and metastases).

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. A total of 130 patients (47 men) with 132 adrenal nodules/masses were prospectively assessed (54 ± 14.8 years). A multivoxel system was used with a two-dimensional point-resolved spectroscopy/chemical-shift imaging sequence. Spectroscopic data were interpreted by visual inspection and peak amplitudes of lipids (Lip), choline (Cho), creatine (Cr), Lac, and Glx. Lac/Cr and Glx/Cr were calculated. Glx/Cr was assessed in relation to lesion size.

RESULTS

Statistically significant differences were observed in Glx/Cr results between adenomas and pheochromocytomas (P < 0.05), however, with a low positive predictive value (PPV). Glx levels were directly proportional to lesion size in carcinomas. A cutoff point of 1.44 was established for the differentiation between carcinomas larger versus smaller than 4 cm, with 75% sensitivity, 100% specificity, 100% PPV, and 80% accuracy. Lac/Cr results showed no differences across lesions. A cutoff point of -6.5 for Lac/Cr was established for carcinoma diagnosis.

CONCLUSION

Glx levels are directly proportional to lesion size in carcinomas. A cutoff point of -6.5 Lac/Cr differentiates carcinomas from noncarcinomas.

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.

Characterization of adrenal lesions with 1.5-T MRI: preliminary observations on comparison of three in-phase and out-of-phase gradient-echo techniques

OBJECTIVE

The purpose of this study was to use previously described quantitative evaluation methods to compare the performance of 3D gradient-recalled echo (GRE) and magnetization-prepared (MP) GRE in-phase and out-of phase sequences with standard 2D GRE technique in the characterization of adrenal lesions.

MATERIALS AND METHODS

The study sample consisted of 44 consecutively registered patients (22 men, 22 women; mean age, 59.1 ± 11.6 years) with 50 adrenal lesions who underwent standard abdominal MRI that included in-phase and out-of-phase 2D GRE (n = 41), 3D GRE (n = 35), MP GRE (n = 36), or a combination of these techniques. The adrenal signal intensity (SI) index and adrenal-to-spleen, adrenal-to-liver, and adrenal-to-muscle SI ratios of each lesion were calculated and compared for the three techniques by independent samples Student t test. The area under the receiver operating characteristic (ROC) curve (AUC) for each evaluation method was determined, and comparisons of independent ROC curves were performed for all sequences.

RESULTS

For all sequences, the mean adrenal SI index and SI ratios of adenomas and nonadenomas differed significantly (p < 0.001). For the 3D GRE and MP GRE techniques, adrenal SI index and modified adrenal-to-spleen ratio, respectively, had the larger AUCs, but the difference was not statistically significant. Different thresholds for the three techniques were recommended for discriminating adenoma from nonadenoma.

CONCLUSION

The results of characterization of adrenal lesions with MP GRE and 3D GRE in-phase and out-of-phase MRI techniques are comparable to those obtained with the reference standard 2D GRE technique. Different thresholds should be selected according to the in-phase and out-of-phase techniques used and for the various evaluation methods.

Characterization of adrenal pheochromocytoma using respiratory-triggered proton MR spectroscopy: initial experience

OBJECTIVE

The aim of our study was to evaluate the feasibility of respiratory-triggered proton single-voxel MR spectroscopy for the diagnosis of adrenal pheochromocytoma and to determine whether certain spectral resonances detected on single-voxel MR spectroscopy are specific for adrenal pheochromocytomas compared with adrenal adenomas.

CONCLUSION

Adrenal pheochromocytomas have a unique MR spectral signature, showing 6.8 ppm resonance that is not seen in adenomas. This unique spectral signature may be attributed to the presence of catecholamines and catecholamine metabolites that are abundant in pheochromocytomas.

Adrenal masses: characterization with in vivo proton MR spectroscopy--initial experience

PURPOSE

To prospectively determine the accuracy of in vivo proton ((1)H) magnetic resonance (MR) spectroscopy in distinguishing adrenal adenomas, pheochromocytomas, adrenocortical carcinomas, and metastases, with histologic or computed tomographic findings and follow-up data as the reference standards.

MATERIALS AND METHODS

This study was approved by the institutional ethics committee, and informed consent was obtained. Sixty consecutive patients (24 male and 36 female patients; mean age, 53 years) harboring adrenal tumors larger than 2 cm in diameter (mean diameter, 4.6 cm +/- 3.4 [standard deviation]) entered the study and were examined with a 1.5-T MR imaging system and point-resolved multivoxel (1)H MR spectroscopy. Thirty-eight patients had adenomas; 10, pheochromocytomas; five, carcinomas; and seven, metastases. Amplitude values for choline, creatine, lipid, and a metabolite peak at precession frequency of 4.0-4.3 ppm were measured. Metabolite ratios (choline-creatine, choline-lipid, lipid-creatine, and 4.0-4.3 ppm/creatine) and cutoff values (obtained by using receiver operating characteristic analyses) were obtained and compared for each type of adrenal mass, which was identified previously on the basis of clinical, hormonal, and pathologic evidence. Results were evaluated with chi(2) and Student t tests. Significance was inferred at P < .05.

RESULTS

Cutoff values of 1.20 for the choline-creatine ratio (92% sensitivity, 96% specificity; P < .01), 0.38 for the choline-lipid ratio (92% sensitivity, 90% specificity; P < .01), and 2.10 for the lipid-creatine ratio (45% sensitivity, 100% specificity) enabled adenomas and pheochromocytomas to be distinguished from carcinomas and metastases. A 4.0-4.3 ppm/creatine ratio greater than 1.50 enabled distinction of pheochromocytomas and carcinomas from adenomas and metastases (87% sensitivity, 98% specificity; P < .01). The best distinction was obtained by comparing choline-creatine and 4.0-4.3 ppm/creatine ratios.

CONCLUSION

(1)H MR spectroscopy can be used to characterize adrenal masses on the basis of spectral findings for benign adenomas, carcinomas, pheochromocytomas, and metastases.

Differentiation of adrenal adenoma and nonadenoma in unenhanced CT: new optimal threshold value and the usefulness of size criteria for differentiation

OBJECTIVE

To determine the optimal threshold for the attenuation values in unenhanced computed tomography (CT) and assess the value of the size criteria for differentiating between an adrenal adenoma and a nonadenoma.

MATERIALS AND METHODS

The unenhanced CT images of 45 patients at our institution, who underwent a surgical resection of an adrenal masses between January 2001 and July 2005, were retrospectively reviewed. Forty-five adrenal masses included 25 cortical adenomas, 12 pheochromocytomas, three lymphomas, and five metastases confirmed by pathology were examined. The CT images were obtained at a slice thickness of 2 mm to 3 mm. The mAs were varied from 100 to 160 and 200 to 280, while the 120 KVp was maintained in all cases. The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy at thresholds of 10 HU, 20 HU, and 25 HU were compared. The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.

RESULTS

The twenty-five adenomas showed significantly lower (p < 0.05) attenuation values (mean+/-SD; 16.3+/-14.9) than the nonadenomas (38.1+/-6.8). Nineteen (90%) of the 20 nonadenomas had attenuation values ranging from 30 to 50 HU. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for diagnosing adenomas were 36%, 100%, 100%, 56%, and 64%, respectively, at a threshold of 10 HU; 60%, 100%, 100%, 67%, and 78%, respectively, at a threshold of 20 HU; and 72%, 95%, 95%, 73%, and 82%, respectively, at a threshold of 25 HU. The adenomas had a significantly (p < 0.05) smaller diameter (2.44+/-1.24 cm) than the nonadenomas (5.09+/-2.37 cm). The size criteria using a diameter of 4-6 cm showed a sensitivity > 90% but a specificity < 70%. Size criteria of 2 or 3 cm had a high specificity of 100% and 80% but a low sensitivity of 20% and 60%.

CONCLUSION

The threshold attenuation values of 20 or 25 HU in the unenhanced CT appear optimal for discriminating an adrenal adenoma from a nonadenoma. The size criteria are of little value in differentiating adrenal masses because of their low specificity or low sensitivity.

ACR Appropriateness Criteria on incidentally discovered adrenal mass

For patients without a history of malignancy, most small (less than 3 cm) incidentally discovered adrenal masses are benign, and extensive and costly workup is usually not justified. For incidentalomas from 3 to 5 cm in size, computed tomography, magnetic resonance imaging, 2-[(18)F]fluoro-2-deoxyglucose positron emission tomography, adrenal biopsy, or surgery can be considered. Lesions larger than 5 cm should be removed because of the higher risk for malignancy. For patients with histories of malignancy, incidentally discovered adrenal masses are more often malignant, and thus even smaller adrenal lesions are suspect. Adrenal biopsy should be reserved for cases in which the results of noninvasive techniques are equivocal.

Adrenal metastases: CT-guided and MR-thermometry-controlled laser-induced interstitial thermotherapy

The aim of the study was to evaluate the feasibility, safety and effectiveness of CT-guided and MR-thermometry-controlled laser-induced interstitial thermotherapy (LITT) in adrenal metastases. Nine patients (seven male, two female; average age 65.0 years; range 58.7-75.0 years) with nine unilateral adrenal metastases (mean diameter 4.3 cm) from primaries comprising colorectal carcinoma (n = 5), renal cell carcinoma (n = 1), oesophageal carcinoma (n = 1), carcinoid (n = 1), and hepatocellular carcinoma (n = 1) underwent CT-guided, MR-thermometry-controlled LITT using a 0.5 T MR unit. LITT was performed with an internally irrigated power laser application system with an Nd:YAG laser. A thermosensitive, fast low-angle shot 2D sequence was used for real-time monitoring. Follow-up studies were performed at 24 h and 3 months and, thereafter, at 6-month intervals (median 14 months). All patients tolerated the procedure well under local anaesthesia. No complications occurred. Average number of laser applicators per tumour: 1.9 (range 1-4); mean applied laser energy 33 kJ (range 15.3-94.6 kJ), mean diameter of the laser-induced coagulation necrosis 4.5 cm (range 2.5-7.5 cm). Complete ablation was achieved in seven lesions, verified by MR imaging; progression was detected in two lesions in the follow-up. The preliminary results suggest that CT-guided, MR-thermometry-controlled LITT is a safe, minimally invasive and promising procedure for treating adrenal metastases.

Value of chemical shift subtraction MRI in characterization of adrenal masses

OBJECTIVE

The purpose of this study was to assess the advantages of the image subtraction technique in chemical shift MRI for the differentiation of adrenal adenomas from nonadenomas.

SUBJECTS AND METHODS

Thirty-five patients with 42 adrenal masses (eight metastases and 34 nonfunctioning adenomas) underwent chemical shift MRI using a double-echo fast low-angle shot sequence. Subsequently, opposed-phase chemical shift MR images were subtracted from in-phase images. The subtraction images were assessed quantitatively and qualitatively. For quantitative assessment, the signal intensity values of the adrenal masses were measured by one investigator with manually defined regions of interest. Qualitative assessment of the subtraction images was performed independently by two investigators, who reported their confidence in diagnosing adenomas versus nonadenomas based on signal intensity of the adrenal masses on subtraction images.

RESULTS

The mean signal intensities were significantly different between adenomas and metastases on subtraction images (213 vs 18; p < 0.0001). There was no overlap in signal intensities between adenomas and metastatic tumors. The accuracy in distinguishing adenomas from metastatic tumors was 100% if the cutoff value of the signal intensity selected was 36-106. Quantitative results corresponding to 100% specificity were also observed, with similar sensitivity. No difference in interpretation between the two investigators occurred.

CONCLUSION

Chemical shift subtraction MRI provides a high confidence level in distinguishing adrenal adenomas from adrenal metastases. The image subtraction technique also facilitates quantitative and qualitative evaluation of adrenal masses in chemical shift MRI.

Hepatic fat fraction: MR imaging for quantitative measurement and display--early experience

The institutional review board approved this HIPAA-compliant study. After all five patients with nonalcoholic fatty liver disease signed a consent, they underwent magnetic resonance (MR) imaging for hepatic fat quantification. The purpose of this study was to develop a fast and accurate method to acquire and display quantitative maps of the percentage of hepatic fat. In-phase and out-of-phase gradient-echo MR imaging was performed with dual flip angles (70 degrees, 20 degrees) to resolve ambiguity of the dominant constituent. T2* corrections were also estimated and applied to generate color-coded maps of the estimated percentage of hepatic fat. MR imaging results were compared with biopsy results in two of five patients, and the technique was validated qualitatively and quantitatively with a water-oil phantom. Results of the phantom study confirmed that the dual-flip angle algorithm can be used to correctly identify the dominant constituent, allowing depiction of 0%-100% of fat content. The estimated liver fat fraction was comparable to quantitative fat measurements at biopsy in both patients (MR imaging, 18.3% +/- 2.8 [standard deviation] and 28.6% +/- 2.4, vs quantitative histopathologic analysis, 11.2% and 28.5%, respectively).

SUPPLEMENTAL MATERIAL

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Magnetic Resonance Imaging of the Adrenal Glands

Differentiation of pathologic alterations of the adrenal glands is still a frequent and challenging problem of daily practice in radiology. Two main groups of patients have to be differentiated: those with clinical symptoms, mainly of endocrinopathies, and those in which a mass of the adrenal gland is detected incidentally. In the first group, magnetic resonance imaging (MRI) plays a minor role, although it allows to detect and often even differentiate the cause of the disease. In the second group, MRI has an excellent performance in differentiating between adenomas and non-adenomatous lesions of the adrenal glands.

MR imaging of the adrenal glands

MR imaging is used commonly for imaging the adrenal glands. Its high-contrast resolution and multiplanar imaging capability enables the detection and characterization of many adrenal masses. The advent of chemical-shift imaging revolutionized the role of MR imaging in characterizing adrenal masses. In this article, the authors discuss the range of MR appearances of common and uncommon adrenal masses, focusing on the nonfunctioning incidentally discovered mass and its characterization methods. MR imaging is continuously improving. The increasing use of higher strength magnets and the introduction of newer coils, sequences, and techniques will help detect and characterize very small adrenal masses, quantify their fat content, and provide exquisite morphologic images of the gland and its vascular supply.

Adrenal carcinoma with a signal loss on chemical shift magnetic resonance imaging

A case of primary adrenal carcinoma that showed a decreased signal in part of the tumor on chemical shift magnetic resonance imaging (CSI) is reported. The patient had clinical symptoms of Cushing syndrome. The tumor was a discrete right adrenal mass about 3.4 cm in largest diameter. It was surgically removed and diagnosed as adrenal carcinoma histopathologically. Two portions where clear cells were prominent were recognized. These areas probably contributed to the signal loss on CSI.

Characterization of adrenal tumors by chemical shift fast low-angle shot MR imaging: comparison of four methods of quantitative evaluation

OBJECTIVE

The aim of our study was to assess quantitative methods of distinguishing adenomas from malignant adrenal lesions using chemical shift fast low-angle shot MR imaging.

MATERIALS AND METHODS

We assessed 102 adrenal tumors in 88 patients (27 hyperfunctioning and 44 nonhyperfunctioning adenomas, 19 metastases, nine pheochromocytomas, and three other adrenal tumors) using chemical shift MR imaging. On the chemical shift imaging, signal intensity index, calculated as [(signal intensity on in-phase imaging - signal intensity on opposed-phase imaging) / (signal intensity on in-phase imaging)] x 100%, was compared with the adrenal-to-spleen ratio, adrenal-to-muscle ratio, and adrenal-to-liver ratio for signal change on opposed-phase fast low-angle shot MR imaging. The tissues in the spleen, paraspinal muscle, and liver were reference tissues.

RESULTS

The signal intensity index had several advantages over the other three parameters calculated. We found no overlap in indexes between adenomas and metastatic tumors. The accuracy in distinguishing adenomas from metastatic tumors was 100% if the cutoff value of the signal intensity index selected was 11.2-16.5%.

CONCLUSION

The signal intensity index is the most reliable evaluation method for differentiating adrenal adenomas from metastatic adrenal tumors.

Normal adrenal gland: in vivo observations, and high-resolution in vitro chemical shift MR imaging-histologic correlation

RATIONALE AND OBJECTIVES

The purpose of this study was to determine whether adrenal cortical lipid affects signal intensity on magnetic resonance (MR) images and to evaluate contrast between cortex and medulla.

MATERIALS AND METHODS

From their clinical database, the authors selected 37 MR imaging studies of patients with adrenal adenomas. Two independent readers compared in-phase and fat-suppressed T1-weighted images, looking for visible lipid-induced signal intensity loss in the adrenal gland. Six adrenal gland specimens obtained after radical nephrectomy were also studied with high-resolution MR imaging, including in-phase, opposed-phase, and fat-suppressed T1-weighted images, and T2-weighted images. Adjacent histologic sections were stained with oil red O for neutral fats and with hematoxylin-eosin, and they were also viewed with polarization light microscopy. The relative amount of lipid was graded as mild, moderate, or intense, and the appearance of the cortex and medulla was compared with that on the MR images.

RESULTS

On the 37 clinical MR studies, there was no visible signal intensity loss within the limbs of the ipsilateral adrenal glands. T2-weighted images of the adrenal specimens showed a thin high-intensity band, corresponding to the appearance of medulla on histologic slices. This could not be seen on any of the T1-weighted images. Region-of-interest measurements were nearly identical for in-phase and opposed-phase images. Histologic analysis showed abundant cortical lipid.

CONCLUSION

Adrenal corticomedullary contrast can be depicted on high-resolution T2-weighted images but not on any T1-weighted images. There is abundant cortical lipid in adrenal specimens, but comparison of in-phase with opposed-phase MR images does not depict it.

Adrenal incidentalomas

The term adrenal incidentaloma refers to an adrenal mass occasionally and unexpectedly discovered by an abdominal imaging procedure performed for reasons a priori unrelated to adrenal dysfunction. The prevalence of adrenal incidentalomas as discovered by computed tomographic scan examination is estimated to be between 1% and 4%. The vast majority of these lesions are of adrenocortical origin, most often adenomas. Identification of steroid or catecholamine-secreting tumors is important but usually solved with appropriate endocrinologic investigations. A difficult problem, however, is to distinguish between benign and malignant primary or secondary tumors. Size less than 4 cm and an unenhanced computed tomographic attenuation under 10 Hounsfield Units (HU) are findings in favor of a benign adrenocortical adenoma, as is a positive NP 59 scintigraphic examination. The pathogenesis of adrenal tumors is not well understood. However, alterations of the cyclic AMP signalling pathway have recently been observed in benign adrenocortical lesions and molecular defects associated with insulin-like growth factor-II overexpression in malignant adrenocortical tumors.

Polymorphic differences from normal in the aldosterone synthase gene (CYP11B2) in patients with primary hyperaldosteronism and adrenal tumour (Conn's syndrome)

OBJECTIVE

The hypertension of Conn's syndrome is due to autonomous aldosterone production by a unilateral adrenocortical adenoma. The source of tumour initiation and the reasons for excess aldosterone production as opposed to cortisol are not known, although variations in the promoter region of the gene coding for aldosterone synthase (CYP11B2) might account for the altered rate of aldosterone secretion.

DESIGN

In a series (n = 27) of well-characterized Conn's syndrome cases, the aldosterone synthase gene (CYP11B2) was screened by single-strand conformational polymorphism (SSCP) for differences from the consensus sequence.

RESULTS

No new mutations were found. The frequencies of two previously described linked polymorphisms, one a change of -344C to T in a putative steroidogenic factor-1 (SF-1) binding site and the other an exchange of intron 2 for that of CYP11B1 (conversion) were measured in tumour and genomic DNA. The frequency of the SF-1 T allele (P < 0.0001) and the conversion allele (P < 0.001) were markedly different between the Conn's syndrome group and the normal controls. However, the frequency did not differ between tumour and genomic DNA in the patient group.

CONCLUSION

While it is unlikely that this difference from normal is related to tumour growth, these genotypes may predispose the tumour to aldosterone production.

Adrenal masses: quantification of fat content with double-echo chemical shift in-phase and opposed-phase FLASH MR images for differentiation of adrenal adenomas

PURPOSE

To quantify fat content in adrenal lesions with double-echo chemical shift magnetic resonance (MR) imaging in a phantom study and to differentiate adrenal adenomas from other adrenal masses by assessing fat content in a clinical study.

MATERIALS AND METHODS

The study consisted of two parts: a phantom study and a clinical study. To explore the effect of the T1 value on in- and opposed-phase MR images of fat-containing tissues, phantom models with various proportions of fat and gadopentetate dimeglumine concentrations were implemented. Signal intensity (SI) indexes ([SI in-phase - SI opposed-phase]/SI in-phase) were calculated with double-echo fast low-angle shot (FLASH) MR imaging. In the clinical study, 23 patients with 28 adrenal masses (16 adrenal adenomas, nine adrenal metastases, and three pheochromocytomas) underwent double-echo FLASH MR imaging, and SI indexes were calculated.

RESULTS

SI index reached a maximum of 0.87 at 53% fat fraction for gadopentetate dimeglumine concentration at 0.5 mmol/L as the simulated T1 of the adrenal mass. The SI indexes of the adrenal adenomas, adrenal metastases, and pheochromocytomas, respectively, were 0.36, -0.15, and -0.07, and estimated fat fraction from the phantom study was 26.5%, 0%, and 0%. All adrenal adenomas contained fat on double-echo FLASH images. There was no overlap in SI index between adenomas and other tumors.

CONCLUSION

Preliminary experience indicates that quantitative measurement of the fat fraction of adrenal masses is possible with the double-echo chemical shift FLASH technique and allows for differentiating adrenal adenomas from other adrenal masses.

Chemical shift: the artifact and clinical tool revisited

The chemical shift phenomenon refers to the signal intensity alterations seen in magnetic resonance (MR) imaging that result from the inherent differences in the resonant frequencies of precessing protons. Chemical shift was first recognized as a misregistration artifact of image data. More recently, however, chemical shift has been recognized as a useful diagnostic tool. By exploiting inherent differences in resonant frequencies of lipid and water, fatty elements within tissue can be confirmed with dedicated chemical shift MR pulse sequences. Alternatively, the recognition of chemical shift on images obtained with standard MR pulse sequences may corroborate the diagnosis of lesions with substantial fatty elements. Chemical shift can aid in the diagnosis of lipid-containing lesions of the brain (lipoma, dermoid, and teratoma) or the body (adrenal adenoma, focal fat within the liver, and angiomyolipoma). In addition, chemical shift can be implemented to accentuate visceral margins (e.g., kidney and liver).

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.

The incidental nonhyperfunctioning adrenal mass: an imaging algorithm for characterization

Nonhyperfunctioning adrenal lesions such as cysts, myelolipomas, adrenal haemorrhage, adenoma and metastases are described. Definitive imaging features that help characterize adrenal cysts, myelolipomas and adrenal haemorrhage are illustrated and the differentiation of benign from malignant adrenal lesions using an algorithmic approach based on lipid sensitive imaging is provided.

Fat suppression techniques in MRI: an update

Due to short relaxation times, fat has a high signal on magnetic resonance images (MRI). This high signal, easily recognized on MRI, may be useful to characterize a lesion. However, small amounts of lipids are more difficult to detect on conventional MRI. In addition, the high signal due to fat may be responsible for artifacts such as ghosting and chemical shift. Lastly, a contrast enhancing tumor may be hidden by the surrounding fat. These problems have prompted development of fat suppression techniques in MRI. Fat may be suppressed on the basis of its difference in resonance frequency with water by means of frequency selective pulses or phase contrast techniques, or on the basis of its short T1 relaxation time by means of inversion recovery sequences. Lastly, hybrid techniques combining several of these fat suppression techniques are also possible. The aim of this paper is to review the basic principles of all these fat suppression techniques and to exemplify their clinical use.

Cleveland Clinic experience with adrenal Cushing's syndrome

PURPOSE

Cushing's syndrome due to adrenal adenoma or adrenocortical carcinoma is rare. To understand better the clinical and biochemical presentation of this disorder, as well as therapy efficacy and patient survival, we conducted a retrospective review.

MATERIALS AND METHODS

Between August 1971 and April 1994, 40 patients presented to our institution with adrenal Cushing's syndrome (27 adenomas and 13 carcinomas). These groups were analyzed with respect to clinical signs and symptoms preoperatively and postoperatively, biochemical analysis, length of postoperative steroid replacement therapy, disease recurrence and patient survival. Followup was obtained by chart review and telephone interviews and averaged 59.6 +/- 66.4 and 47.6 +/- 56.2 months for adenoma and carcinoma patients, respectively.

RESULTS

Women predominated in both groups (26 of 27 adenomas, 11 of 13 carcinomas), and tumors affected the left adrenal gland more frequently (19 of 27 adenomas, 9 of 13 carcinomas). Adenoma patients were younger than carcinoma patients (39.6 +/- 14.4 versus 51.5 +/- 16.6 years, p = 0.026) and presented with smaller tumors (3.3 +/- 1.0 versus 8.6 +/- 4.5 cm., p = 0.001). There was a trend toward increased incidence of glucose intolerance among carcinoma patients but no significant differences in clinical signs or symptoms between adenoma and carcinoma patients could be made. Similarly, while there was no significant difference in biochemical evaluation of adenoma versus carcinoma patients, 24-hour urinary free cortisol and serum lactate dehydrogenase levels tended to be higher among carcinoma patients. In addition 17-ketosteroid and dehydroepiandrosterone sulfate levels were more elevated in carcinoma than in adenoma patients, and several adenoma patients actually had subnormal levels. Among adenoma patients mean length of steroid replacement therapy was 16.8 +/- 9.1 months. However, 7 adenoma patients (25.9%) required greater than 24 months of exogenous steroids, and only 1 of these patients was subsequently weaned off steroid replacement. There were no recurrences among adenoma patients, although there was 1 perioperative death due to hypoglycemia. Ten (76.9%) carcinoma patients had recurrences at a mean followup of 33 months. The 3 and 5-year survival rates were 41.5 and 31.2%, respectively.

CONCLUSIONS

While presenting signs and symptoms and hormonal analysis may suggest benign or malignant disease, only tumor size and patient age are reliable preoperative indicators of adrenal adenoma versus adrenocortical carcinoma among patients with adrenal Cushing's syndrome. Surgery is curative for adenoma patients, but lifelong steroid replacement may be required. Survival remains poor among carcinoma patients.

Fast MR imaging techniques: impact in the abdomen

The increased efficiency of MRI data acquisition has had a substantial impact on clinical MRI of the abdomen. Five particular applications that have thus been affected include breath-hold imaging of liver lesions (including detection, characterization, and biopsy), MR cholangiopan- creatography, practical chemical shift imaging (including liver and adrenal glands), dynamic imaging after contrast media injection, and MR angiography.

Eight echo T2 measurements of adrenal masses: limitations of differential diagnosis by relaxation time determination

PURPOSE

Previous studies have revealed that benign and malignant adrenal masses differ in their T2-related MRI characteristics, but there is sufficient overlap in these characteristics that very accurate differential diagnosis is not possible. This ambiguity might be due to variations inherent in the measurement techniques or to real overlap in the T2 relaxation times of the lesion groups. We attempted to reduce the scatter and overlap of data from adenomas and malignancies by using an eight echo T2 assessment, which we compared with a two echo technique and with reference tissue brightness ratio determinations.

METHOD

Forty-eight adrenal masses in 44 adult patients were assessed; 30 were diagnosed as adenomas and 18 as malignancies by means other than MR. Each lesion was subjected to a single slice eight SE (spin echo) image (TR 2,000, TE 20-160), from which a T2 relaxation time was calculated. T2 relaxation times were also calculated using two echoes (TE 20 and 100), as were lesion/liver, lesion/fat, and lesion/muscle brightness ratios (TE 100). The differential diagnostic efficacies of the techniques were compared by receiver operating characteristic (ROC) analysis.

RESULTS

Although the means of the malignant and benign groups differed, significant overlap was present for each assessment technique. ROC analysis showed that the best differentiation was achieved by the lesion/fat brightness ratio, followed very closely by the eight echo technique. The eight echo technique was significantly better at differentiation than the two echo technique.

CONCLUSION

Although eight echo T2 determination has less variability and permits slightly better differential diagnosis than most other T2-dependent MR techniques, considerable ambiguity persists that may be due to intrinsic overlap in the T2 relaxation characteristics of the lesions rather than to variability in imaging techniques.

Contrast-enhanced dynamic MRI of adrenal masses: classification of characteristic enhancement patterns

OBJECTIVE

This study evaluated the usefulness of dynamic MRI to differentiate various adrenal tumours.

MATERIALS AND METHODS

Sixty-five adrenal tumours (28 adenomas, 22 metastases, seven phaeochromocytomas, five neurogenic tumours and three tuberculous granulomas) were evaluated with gadolinium-enhanced dynamic MRI (13 at 0.5 T, 52 at 1.5 T). In this technique, a series of 12 sequential images (gradient-echo images at 0.5 T and spin-echo images at 1.5 T) were obtained up to 21 min after bolus administration of 0.1 mmol/kg Gd-DTPA.

RESULTS

All 28 adenomas showed peak enhancement in the early phase (< 2 min) and quick washout. Fourteen of 22 metastases showed peak enhancement in the early or middle phase (< 9 min) and slow washout. Six of seven phaeochromocytomas revealed marked peak enhancement in the early phase and little washout. All neurogenic tumours showed gradually increasing enhancement. Granulomas showed little enhancement. As a result, only 14 adrenal masses (27/65, 42%) were correctly classified according to contrast enhancement patterns. However, if we consider each type of enhancement pattern to be specific to adenoma, metastasis, phaeochromocytoma, neurogenic tumour and tuberculous granuloma respectively, 56 of the 65 adrenal masses (86%) could be classified. Seven of the indistinguishable nine tumours were performed at 0.5 T system using gradient-echo sequences.

CONCLUSION

Dynamic MR imaging at 1.5 T is useful in the differentiation of adrenal masses. Imaging at 0.5 T with gradient-echo sequences seems less useful to distinguish adenomas from metastases.

Adrenal tissue characterization with 0.5-T MR imaging: value of T2*-weighted images

The authors investigated the value of magnetic resonance (MR) imaging at 0.5 T for distinguishing adrenal adenomas from adrenal metastases. The series included 23 adrenal adenomas (18 nonhyperfunctioning, five hyperfunctioning) and 23 adrenal metastases from various organs. Adrenal tumor-liver signal intensity ratios on T1-, T2-, and T2*-weighted images were calculated for adrenal tissue characterization. Adrenal adenomas were more precisely distinguished from adrenal metastases on T2*-weighted images (21 of 23, 91%) than on T2-weighted images (15 of 23, 65%). T1-weighted images were not useful for this distinction. In conclusion, T2*-weighted images were better than routine T2-weighted images for distinguishing adrenal adenomas from adrenal metastases. It can be postulated that the total signal intensity of adrenal adenomas, which contain some fat components, decreased on T2*-weighted images because of an out-of-phase effect.

MR of an adrenal pseudocyst

We describe the appearance of an adrenal pseudocyst on MRI and CT. The MR characteristics of the lesion were noteworthy in that the lesion had two components with different imaging characteristics. The larger component was of low signal intensity on both T1- and T2-weighted images and might have been confused with an adrenal adenoma.

Oncologic imaging. Staging and follow-up of renal and adrenal carcinoma

Computed tomography (CT) has emerged from the 1980s to play a dominant role in the pretreatment staging of renal and adrenal carcinomas. For detection, definition (staging), and determination of resectability or recurrence, CT with intravenous contrast enhancement, and more recently, magnetic resonance imaging (MRI) with gadolinium-DTPA, may be the only cross-sectional imaging studies required before institution of appropriate therapy. Carcinoma of the kidney is frequently diagnosed by serendipity or detected on incidental ultrasound or CT examinations. Real-time ultrasound and color flow Doppler offer unique information on tumor vascularity and major venous vascular involvement. Positive predictive values of 96% can be achieved for the diagnosis of renal cell carcinoma using contrast-enhanced CT scanning. For follow-up CT and MRI are the best imaging techniques for evaluation of the retroperitoneum. MRI may distinguish tumor recurrence from fibrosis in selected cases. Because primary neoplasms of the adrenal gland are rare and often exceed 10 cm at the time of initial diagnosis, the functional nature (endocrine) of adrenal carcinoma may be part of the clinical presentation. Because initial stage is critical to survival and extent of surgical therapy, a knowledge of tumor classification is essential to the optimal diagnostic evaluation. Newer imaging tests, CT and MRI, have superseded conventional urography, ultrasound, and radionuclide studies for the diagnosis and staging of adrenal cancer. Early diagnosis and low stage at presentation are critical to survival in patients with adrenal carcinoma. The current concepts for pretreatment imaging evaluation and the role of CT, MRI, and ultrasound are outlined. An oncologic imaging approach based on tumor staging and classification for patients with real or suspected renal cell carcinoma and adrenal carcinoma is essential to optimal patient care.

MRI of the adrenal gland

Current status of magnetic resonance imaging (MRI) of the adrenal gland is reviewed, and basic techniques and sensitivity of MRI for differentiating histologic lesions are also discussed.

Spectroscopic MRI: a tool for the evaluation of systemic lipid storage disease

Spectroscopic MR imaging allows to measure the lipid content of a region inside the human body. This technique has been applied to the case of a woman with a severe multisystemic triglyceride storage disease. Lipid contents of liver, pancreas, kidneys, left ventricle, skeletal muscles (calves, thighs, arms) were measured by using the Dixon spectroscopic imaging sequence. In some heterogeneous muscles, localized proton spectra were recorded. Results agreed with clinical findings (muscle weakness, normal renal and cardiac function, diabetes). These techniques could help to quantify the severity of the disease and to follow up its evolution under therapy.