State-of-the-art MR imaging of the adrenal gland

The authors discuss the appearances of adrenal diseases characterizable with magnetic resonance (MR) imaging (pheochromocytomas, hemorrhage, cysts, adenomas, myelolipomas, and metastases), new imaging techniques, and differentiation of benign from malignant lesions. Most pheochromocytomas appear markedly hyperintense relative to the liver on T2-weighted images. However, this appearance is not specific, since adrenal metastases and adenomas may have similar features. Occasionally, pheochromocytomas may be iso- or hypointense to the liver on T2-weighted images. One of the new techniques for MR imaging of the adrenal gland, fat suppression, reduces cardiac and respiratory motion-induced artifacts, accentuates small differences in tissue contrast, and eliminates chemical shift artifacts. These advantages far outweigh the disadvantages of inhomogeneity of fat suppression and the fewer sections obtained per acquisition. Differentiation of adrenal metastases from adrenal adenomas with MR imaging is problematic with the use of signal intensity ratios (33% overlap) or T2 calculations. The future of discriminating between adrenal metastases and adenomas may rest with chemical shift MR imaging, which uses in-phase and out-of-phase gradient-echo pulse sequences. This approach relies on the fact that adrenal adenomas contain fat whereas metastases do not. The reported accuracy of chemical shift imaging in differentiating adrenal adenomas from metastases is 96%-100%.