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Magnetic resonance imaging of the adrenal gland
1Department of Radiology, Massachusetts General Hospital, Boston 02114, USA.
Abstract:
The authors review their experience with magnetic resonance imaging (MRI) of the adrenal gland and discuss the appearance of adrenal diseases where MRI is clinically useful. A basic description of some of the newer pulse sequences is provided. Fat-suppressed MRI is advantageous because of reduction of cardiac and respiratory motion induced artifacts, accentuation of small differences in tissue contrast, and elimination of chemical shift artifacts. These advantages far outweigh the disadvantages of inhomogeneity of fat suppression and the fewer slices obtained per acquisition. Chemical shift imaging is used to differentiate benign from malignant adrenal diseases based on a gradient echo phase cycling technique. Detailed descriptions of MRI findings in adrenal pheochromocytomas, hemorrhage, cysts, adenomas, myelolipomas, and metastases are provided. Most pheochromocytomas appear markedly hyperintense to the liver on T2-weighted images. However, this appearance is not specific as adrenal metastases and adrenal adenomas may occasionally produce a similar appearance. In addition, pheochromocytomas may occasionally be isointense or hypointense to the liver on T2-weighted images. Differentiation of adrenal metastases from adrenal adenomas with MRI is problematic using signal intensity ratios (33% overlap) or T2 calculations. The future of discriminating between adrenal metastases and adenomas may rest with chemical shift MRI, which uses in- and out-of-phase gradient echo pulse sequences for differentiation. This approach relies on the fact that adrenal adenomas contain fat, while adrenal metastases do not. The reported accuracy of chemical shift imaging in differentiating between adrenal adenomas and adrenal metastases ranges from 96 to 100%. An algorithmic approach to differentiating benign from malignant adrenal diseases is presented that relies on an initial noncontrast CT with CT attenuation values obtained from the adrenal mass. If CT attenuation values are less than zero, the mass is characterized as benign. If the mass remains indeterminate after CT, chemical shift MR is performed. If the mass remains indeterminate after MR, biopsy is required.
Insights
Magnetic resonance imaging (MRI) aids in diagnosing adrenal gland diseases. Chemical shift MRI effectively differentiates benign adrenal adenomas from malignant metastases with high accuracy, improving diagnostic strategies.
Area of Science:
- Radiology
- Medical Imaging
- Oncology
Background:
- Magnetic resonance imaging (MRI) is a valuable tool for evaluating adrenal gland diseases.
- Newer MRI pulse sequences enhance diagnostic capabilities for adrenal pathologies.
- Fat-suppressed MRI offers advantages in reducing motion artifacts and improving tissue contrast.
Purpose of the Study:
- To review the clinical utility of MRI in diagnosing various adrenal gland diseases.
- To describe the MRI appearance of specific adrenal pathologies, including pheochromocytomas, adenomas, and metastases.
- To highlight the role of chemical shift imaging in differentiating benign from malignant adrenal lesions.
Main Methods:
- Review of clinical experience with adrenal MRI.
- Description of fat-suppressed MRI techniques and their benefits.
- Application of chemical shift imaging (gradient echo phase cycling) for lesion characterization.
- Algorithmic approach integrating CT and MRI for differential diagnosis.
Main Results:
- MRI findings for adrenal pheochromocytomas, hemorrhage, cysts, adenomas, myelolipomas, and metastases are detailed.
- T2-weighted imaging shows limitations in differentiating adrenal lesions due to overlapping signal intensities.
- Chemical shift MRI demonstrates high accuracy (96-100%) in distinguishing adrenal adenomas (fat-containing) from metastases (fat-absent).
Conclusions:
- MRI, particularly chemical shift imaging, is crucial for differentiating benign adrenal adenomas from malignant metastases.
- An integrated approach using CT and chemical shift MRI can guide diagnosis and reduce the need for biopsy.
- Accurate characterization of adrenal masses improves patient management and treatment planning.