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

Management of adrenal incidentalomas: European Society of Endocrinology Clinical Practice Guideline in collaboration with the European Network for the Study of Adrenal Tumors

: By definition, an adrenal incidentaloma is an asymptomatic adrenal mass detected on imaging not performed for suspected adrenal disease. In most cases, adrenal incidentalomas are nonfunctioning adrenocortical adenomas, but may also represent conditions requiring therapeutic intervention (e.g. adrenocortical carcinoma, pheochromocytoma, hormone-producing adenoma or metastasis). The purpose of this guideline is to provide clinicians with best possible evidence-based recommendations for clinical management of patients with adrenal incidentalomas based on the GRADE (Grading of Recommendations Assessment, Development and Evaluation) system. We predefined four main clinical questions crucial for the management of adrenal incidentaloma patients, addressing these four with systematic literature searches: (A) How to assess risk of malignancy?; (B) How to define and manage low-level autonomous cortisol secretion, formerly called 'subclinical' Cushing's syndrome?; (C) Who should have surgical treatment and how should it be performed?; (D) What follow-up is indicated if the adrenal incidentaloma is not surgically removed? SELECTED RECOMMENDATIONS: (i) At the time of initial detection of an adrenal mass establishing whether the mass is benign or malignant is an important aim to avoid cumbersome and expensive follow-up imaging in those with benign disease. (ii) To exclude cortisol excess, a 1mg overnight dexamethasone suppression test should be performed (applying a cut-off value of serum cortisol ≤50nmol/L (1.8µg/dL)). (iii) For patients without clinical signs of overt Cushing's syndrome but serum cortisol levels post 1mg dexamethasone >138nmol/L (>5µg/dL), we propose the term 'autonomous cortisol secretion'. (iv) All patients with '(possible) autonomous cortisol' secretion should be screened for hypertension and type 2 diabetes mellitus, to ensure these are appropriately treated. (v) Surgical treatment should be considered in an individualized approach in patients with 'autonomous cortisol secretion' who also have comorbidities that are potentially related to cortisol excess. (vi) In principle, the appropriateness of surgical intervention should be guided by the likelihood of malignancy, the presence and degree of hormone excess, age, general health and patient preference. (vii) Surgery is not usually indicated in patients with an asymptomatic, nonfunctioning unilateral adrenal mass and obvious benign features on imaging studies. We provide guidance on which surgical approach should be considered for adrenal masses with radiological findings suspicious of malignancy. Furthermore, we offer recommendations for the follow-up of patients with adrenal incidentaloma who do not undergo adrenal surgery, for those with bilateral incidentalomas, for patients with extra-adrenal malignancy and adrenal masses and for young and elderly patients with adrenal incidentalomas.

MANAGEMENT OF ENDOCRINE DISEASE: Imaging for the diagnosis of malignancy in incidentally discovered adrenal masses: a systematic review and meta-analysis

OBJECTIVE

Adrenal masses are incidentally discovered in 5% of CT scans. In 2013/2014, 81 million CT examinations were undertaken in the USA and 5 million in the UK. However, uncertainty remains around the optimal imaging approach for diagnosing malignancy. We aimed to review the evidence on the accuracy of imaging tests for differentiating malignant from benign adrenal masses.

DESIGN

A systematic review and meta-analysis was conducted.

METHODS

We searched MEDLINE, EMBASE, Cochrane CENTRAL Register of Controlled Trials, Science Citation Index, Conference Proceedings Citation Index, and ZETOC (January 1990 to August 2015). We included studies evaluating the accuracy of CT, MRI, or (18)F-fluoro-deoxyglucose (FDG)-PET compared with an adequate histological or imaging-based follow-up reference standard.

RESULTS

We identified 37 studies suitable for inclusion, after screening 5469 references and 525 full-text articles. Studies evaluated the accuracy of CT (n=16), MRI (n=15), and FDG-PET (n=9) and were generally small and at high or unclear risk of bias. Only 19 studies were eligible for meta-analysis. Limited data suggest that CT density >10HU has high sensitivity for detection of adrenal malignancy in participants with no prior indication for adrenal imaging, that is, masses with ≤10HU are unlikely to be malignant. All other estimates of test performance are based on too small numbers.

CONCLUSIONS

Despite their widespread use in routine assessment, there is insufficient evidence for the diagnostic value of individual imaging tests in distinguishing benign from malignant adrenal masses. Future research is urgently needed and should include prospective test validation studies for imaging and novel diagnostic approaches alongside detailed health economics analysis.

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.

Magnetic resonance imaging differentiation of adrenal masses at 1.5 T: T2-weighted images, chemical shift imaging, and Gd-DTPA dynamic studies

The purpose of our study was to assess the potential role of spin-echo (SE), chemical shift, and gadolinium-enhanced magnetic resonance imaging (MRI) in the differentiation of adrenal masses. Seventy-two adrenal masses (26 nonhyperfunctioning adenomas, 16 aldosterone-secreting adenomas and 6 other different benign cortical masses, 18 pheochromocytomas, and 6 malignant masses) in 63 patients were evaluated with spin-echo sequences, chemical shift imaging (CSI) and gadolinium diethylenetriamine penta-acetic acid (Gd-DTPA) dynamic studies. Ratios and indices of signal intensity for all examined MRI methods were calculated and examined for significance of difference between different types of adrenal masses. Quantitative magnetic resonance evaluation of adrenal masses showed significant differences (at least alpha < 0.01) between nonhyperfunctioning adenomas vs. pheochromocytomas or vs. malignant lesions or vs. aldosterone-secreting adenomas and between pheochromocytomas vs. malignant lesions. The most specific indicators of adrenal mass character proved to be the CSI ratio based on opposed-phase and in-phase two-dimensional fast low-angle shot (FLASH) images, reflecting lipid content in the lesion, and Gd-DTPA dynamic studies ratios reflecting contrast agent inflow and washout in the lesion: WoMAX/LAST and Dyn1.2-3.2. There was no overlap of CSI ratio between adenomas and pheochromocytomas. The overlap of ranges of CSI ratio between nonhyperfunctioning adenomas and aldosterone-secreting adenomas was only 18.5%. There was no overlap of WoMAX/LAST ratio between adenomas and pheochromocytomas, or adenomas and malignant lesions. The overlap of ranges of Dyn1.2-3.2 ratio between pheochromocytomas and malignant lesions was only 17.6%. MRI enables good visualization and specific characterization of adrenal masses. The optimal MRI protocol for the adrenal region is presented.

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.