STATE-OF-THE-ART MR-IMAGING OF THE ADRENAL-GLAND

The authors discuss the appearances of adrenal diseases characterizabl e with magnetic resonance (MR) imaging (pheochromocytomas, hemorrhage, cysts, adenomas, myelolipomas, and metastases), new imaging technique s, and differentiation of benign from malignant lesions. Most pheochro mocytomas appear markedly hyperintense relative to the liver on T2-wei ghted images. However, this appearance is not specific, since adrenal metastases and adenomas may have similar features. Occasionally, pheoc hromocytomas may be iso- or hypointense to the liver on T2-weighted im ages. One of the new techniques for MR imaging of the adrenal gland, f at suppression, reduces cardiac and respiratory motion-induced artifac ts, accentuates small differences in tissue contrast, and eliminates c hemical shift artifacts. These advantages far outweigh the disadvantag es of inhomogeneity of fat suppression and the fewer sections obtained per acquisition. Differentiation of adrenal metastases from adrenal a denomas with MR imaging is problematic with the use of signal intensit y ratios (33% overlap) or T2 calculations. The future of discriminatin g 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 cont ain fat whereas metastases do not. The reported accuracy of chemical s hift imaging in differentiating adrenal adenomas from metastases is 96 %-100%.