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

Clinical Guidelines for the Management of Adrenal Incidentaloma

An adrenal incidentaloma is an adrenal mass found in an imaging study performed for other reasons unrelated to adrenal disease and often accompanied by obesity, diabetes, or hypertension. The prevalence and incidence of adrenal incidentaloma increase with age and are also expected to rise due to the rapid development of imaging technology and frequent imaging studies. The Korean Endocrine Society is promoting an appropriate practice guideline to meet the rising incidence of adrenal incidentaloma, in cooperation with the Korean Adrenal Gland and Endocrine Hypertension Study Group. In this paper, we discuss important core issues in managing the patients with adrenal incidentaloma. After evaluating core proposition, we propose the most critical 20 recommendations from the initially organized 47 recommendations by Delphi technique.

Differentiation of malignant from benign pheochromocytomas with diffusion-weighted and dynamic contrast-enhanced magnetic resonance at 3.0 T

OBJECTIVE

To retrospectively evaluate the usefulness of the apparent diffusion coefficients (ADCs) and dynamic contrast-enhanced magnetic resonance (MR) imaging for differentiation of malignant from benign pheochromocytomas at 3.0-T MR.

METHODS

The Institutional Review Board approved this retrospective study, and informed consent was waived. Forty patients with pheochromocytomas underwent diffusion-weighted (DW) MR imaging in addition to T1- and T2-weighted sequences, chemical shift imaging techniques, and dynamic contrast-enhanced MR imaging at 3.0-T MR imaging system. In each patient, precontrast single-shot spin-echo echo-planar DW imaging was performed with b values of 0 and 800 seconds/mm². In each patient, 3-dimensional fat-saturated T1-weighted dynamic contrast-enhanced MR imaging was performed at baseline (precontrast), during the arterial phase, and 1, 2, 3, and 5 minutes after contrast injection. Diagnosis was based on pathologic findings in surgical specimens. Independent samples t test was used to compare ADCs of benign and malignant pheochromocytomas. Receiver operating characteristic curve analysis was used to test the ability of ADCs in differentiating malignant from benign pheochromocytomas. Differences in dynamic contrast-enhanced patterns between malignant and benign pheochromocytomas were analyzed.

RESULTS

Pathologic diagnoses revealed that 29 pheochromocytomas (three from both adrenal glands of the same patient) were benign and 13 were malignant. With b values of 0 and 800 seconds/mm², mean ± SD ADC of malignant pheochromocytomas ([1.175 ± 0.132] × 10⁻³ mm²/s) was larger than that of benign ones ([0.918 ± 0.124] × 10⁻³ mm²/s), and the difference was significant (P < 0.001). Apparent diffusion coefficients obtained with b values of 0 and 800 seconds/mm² were effective for distinguishing malignant from benign pheochromocytomas (area under the receiver operating characteristic curve, 0.906): A threshold value of 1.016 × 10⁻³ mm²/s permitted distinction with high sensitivity (93.3%) and specificity (77.8%). In dynamic contrast-enhanced MR imaging, malignant pheochromocytomas got peak signal intensity earlier (at arterial phase) than benign ones (at 1 minute after contrast injection).

CONCLUSION

In our limited study, ADCs in DW imaging with b values of 0 and 800 seconds/mm and dynamic contrast-enhanced pattern of malignant pheochromocytomas were significantly different from that of benign ones, suggesting that DW imaging and dynamic contrast-enhanced MR imaging may be useful in preoperative characterization and prognosis of pheochromocytomas, especially for those without obvious metastasis and vascular invasion.

Evaluation and management of adrenal incidentaloma

Adrenal incidentaloma is the most common adrenal neoplasm encountered in clinical practice. The timely, accurate, and cost-effective evaluation and management of adrenal lesions found incidentally can be challenging for clinicians. Evaluation begins with biochemical screening and additional imaging. Management strategies vary by patient factors and tumor characteristics. Adrenalectomy is indicated for lesions that are hormonally active, larger than 4-5 cm, symptom-related, and have an imaging appearance that is atypical of a benign lesion.

Magnetic resonance characterization of pheochromocytomas in the abdomen and pelvis: imaging findings in 18 surgically proven cases

PURPOSE

To study the magnetic resonance imaging characteristics of adrenal and extra-adrenal pheochromocytomas in the abdomen and pelvis.

METHODS

We retrospectively reviewed 18 cases of pathologically proven cases of pheochromocytomas in the abdomen and pelvis. These patients have undergone magnetic resonance imaging evaluation before surgery. The study population included 10 men and 7 women (age range, 19-68 years; mean, 38 years). A consensus review of the magnetic resonance images was performed by 2 blinded expert observers. A qualitative evaluation was completed, and the tumors were classified by anatomical location, shape, T2 signal, contrast enhancement, and signal dropout on chemical shift pulse sequences.

RESULTS

On T2-weighted images, most lesions demonstrated mild to moderate increased signal intensity (SI) (n = 12), 5 lesions demonstrated a markedly increased SI, and only 1 lesion demonstrated an isointense SI on T2-weighted images.Five lesions demonstrated marked postcontrast enhancement. Three lesions demonstrated moderate enhancement, and 5 lesions demonstrated mild postcontrast enhancement.The pattern of enhancement was variable: 4 salt and pepper, 4 homogeneous, 3 heterogeneous, and 2 target with central necrosis and hemorrhage. None of the lesions contained significant amount of intracellular lipid, as no lesions demonstrated greater than 16.5% signal dropout on out-of-phase compared with in-phase pulse sequences.

Color-coded duplex endoscopic ultrasound of the adrenals

Imaging of the adrenals by endoscopic ultrasound (EUS) is a valuable technique for detection and localization of adrenal lesions, but endosonomorphological tumor distinction remains difficult. In this single-center study, the amount of blood flow in common adrenal lesions, such as adrenal adenomas, adrenal hyperplasia, and pheochromocytomas, was visualized by color-coded duplex EUS (CD-EUS) and was retrospectively analysed. Therefore, we reviewed our EUS database to evaluate and correlate the perfusion patterns of common adrenal lesions with histologically confirmed diagnosis, possible malignancy, and endosonomorphological features such as echogeneity, echostructure, and tumor size. CD-EUS was performed using an endosonoscope Pentax FG 32 UA with a longitudinal 7.5 MHz sector array and Hitachi EUB 525 ultrasound system. In 38 consecutive patients (male=19; female=19; age: mean 53+/-16 yr SD), perfusion patterns of 46 histologically confirmed adrenal, para- or extra-adrenal lesions of adrenal origin (adenoma: no.=20; nodular hyperplasia: no.=11; pheochromocytoma: no.=15; diameter 26+/-15 mm, range 6-70 mm) were analyzed and classified semiquantitatively as "not" (no.=24), "slightly" (no.=12), "moderately" (no.=4) or "highly" (no.=6) hypervascularized. Compared to adenomas (p=0.003) and nodular hyperplasia (p=0.047), pheochromocytomas showed a significantly higher grade of perfusion. There was no relationship between perfusion patterns and localization of pheochromocytomas (adrenal: 8; paraadrenal: 3; extra-adrenal: 4). Vascularization was not statistically associated with tumor echogeneity, echostructure, malignancy or tumor size. CD-EUS is an additional tool for adrenal endosonographic tumor distinction and seems to improve the endosonographic detection of pheochromocytomas by visualization of hypervascularization. As an overlap of perfusion patterns exists, CD-EUS findings must be interpreted in the context of clinical, laboratory and chemical results.

Paraovarian adrenal rest with MRI features characteristic of an adrenal adenoma

We report MR and sonographic imaging features of an incidentally detected paraovarian adrenal rest in a 44-year-old woman who was being evaluated for menorrhagia. This is the first report of chemical shift imaging identifying the presence of lipid within an adrenal rest as well as rapid washout of contrast. Both of these MR characteristics are typically seen with an adrenal adenoma.

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.

Assessment of parallel acquisition techniques in adrenal magnetic resonance imaging: does increased temporal resolution significantly improve visualization of adrenal lesions?

RATIONALE AND OBJECTIVES

To compare conventional radiofrequency coil reception techniques with parallel coil array acquisition methods in adrenal tissue visualization and to evaluate the dependence of temporal resolution on image quality in adrenal magnetic resonance magnetic resonance (MR) imaging.

MATERIAL AND METHODS

Using a 1.5 T MR imager, conventional and parallel sampled sequences were acquired in 10 healthy volunteers and 10 patients with adrenal lesions. The imaging protocol consisted of: conventional (TR/TE 4,730/125 ms; FA 150 degrees; NA 1; AT 25 s), and two parallel imaging SMASH techniques (TR/TE 4,090/125 ms; FA 150 degrees; NA 1 resulting in an AT of 12 s, as well as NA 2 resulting in an AT of 24 s) with generalized autocalibration T(2)-weighted turbo spin echo sequences with 5 mm slice thickness, 1.6 mm in-plane resolution, and an acceleration factor 2. Severity of breathing motion and aliasing artifact and overall image quality were rated on five-point scales and evaluated with student's t test; a differential receiver operating characteristic (DROC) analysis was performed.

RESULTS

Adrenal gland findings included adenomas, metastases, and hemorrhages. Acceleration of conventional turbo spin echo sequence with one signal average led to an increase in diagnostic power (DROC 0.362) as well as significant improvement in overall image quality (P(Volunteers) =.017; P(Patients) =.042) and reduction of breathing motion artifact in patients (P(Patients) =.012) while improving the temporal resolution. Parallel imaging with two signal averages resulted in further improvement of image quality over conventional imaging (DROC 0.303), (P(Volunteers) =.045; P(Patients) =.022), in the same acquisition time as the conventional method.

CONCLUSION

Parallel acceleration of sequences used for adrenal tissue visualization leads to a significant increase in diagnostic quality by significantly reducing breathing motion artifacts without sacrificing contrast indispensable for adrenal lesion characterization.

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.

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.

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.

Large degenerated adrenal adenomas: radiologic-pathologic correlation

PURPOSE

To correlate the radiologic and pathologic findings and differential diagnosis of large, degenerated adrenal adenomas.

MATERIALS AND METHODS

The authors reviewed the radiologic and pathologic characteristics of 30 large adenomas with cystic regions or areas of heterogeneity that were either intrinsic or demonstrated at contrast material-enhanced computed tomography (CT) or magnetic resonance (MR) imaging. Images of 24 adrenocortical carcinomas were also reviewed to determine whether differentiating characteristics existed.

RESULTS

Most of the adrenocortical adenomas were in asymptomatic women. Ten adenomas contained calcification. Pathologic examination revealed good correlation between heterogeneity and liquefied regions. Histologic examination confirmed regions of adenomatous tissue with areas of hemorrhage, amorphous degenerated material, calcification, and fibrosis. Some tumors contained myelolipomatous foci. Although some clinical and imaging findings differed between the groups, no features could be found that enabled the radiologic differentiation of adenomas from carcinomas.

CONCLUSION

A subgroup of adrenal adenomas are larger, more heterogeneous, and more frequently calcified than those with the usual imaging findings. Central necrosis, hemorrhage, or both are responsible for many of the imaging features. Differentiation of these lesions from other large adrenal masses, including adrenal carcinoma, cannot be made by means of imaging alone; resection is required for the definitive diagnosis.

Incidentally discovered adrenal masses: evaluation with gadolinium enhancement and fat-suppressed MR imaging at 0.5 T

The purpose of the study is to evaluate the ability of Gd-enhancement and fat-suppressed MR imaging operating at midfield strength to characterize incidentally discovered adrenal masses. Sixty patients with 72 adrenal masses incidentally discovered during US or CT exams were studied with a 0.51 MR unit following clinical and laboratory evaluation. After Gd-DTPA intravenous administration a modified three-point Dixon technique was performed in all patients. This technique provided three images sets: conventional T1-weighted SE images, fat-suppressed T1-weighted images and water-suppressed T1-weighted images. Diagnosis was established by means of surgery (11 lesions), fine-needle biopsy (21 lesions) and stability on ultrasonographic follow-up for at least 1 year (range, 12-87 months) from adrenal lesion discovery (40 masses). In most of adenomas (n = 55) an homogeneous enhancement was observed on postcontrast T1WI; however, 15 out of these lesions showed a small focal spot of high intensity in Gd-enhanced fat-suppressed images. On the contrary, malignant conditions (n = 6) and pheochromocytoma (n = 1), all had inhomogeneous signal intensities which were relatively higher after Gadolinium injection as compared with the liver. The fat suppression technique demonstrated areas of bright signal intensity related to high vascularity. The performance of three observers in order to differentiate malignant from benign conditions showed sensitivity, specificity, diagnostic accuracy, positive and negative predictive values of 100, 88.5, 90, 50 and 100% on the basis of gadolinium enhancement only, by utilizing the Dixon technique. In conclusion, although Gd-enhancement and fat-suppressed sequence helped correctly differentiate among the groups of incidentally discovered adrenal masses, the degree of overlap suggests that it is still difficult to characterize individual patients. However, the modified three-point Dixon technique after contrast material administration appears to be a further capability of midfield MRI in the characterization of adrenal tissue.