MR-IMAGING OF ADRENAL MASSES - VALUE OF CHEMICAL-SHIFT IMAGING FOR DISTINGUISHING ADENOMAS FROM OTHER TUMORS

OBJECTIVE. CT and conventional MR imaging are helpful in characterizin g adrenal tumors, but a specific diagnosis is not achieved for a subst antial number of lesions. Chemical-shift imaging relies on the differe nt resonance frequencies of protons in water and triglyceride molecule s and therefore may permit a more specific diagnosis of adrenal adenom as, which are known to contain abundant lipid. The purpose of this stu dy was to evaluate the usefulness of chemical-shift MR imaging in the differentiation of adrenal adenomas from other adrenal masses, SUBJECT S AND METHODS. Forty-one adrenal masses (17 nonhyperfunctioning adenom as, two aldosteronomas, six pheochromocytomas, one ganglioneuroma, fiv e adrenal carcinomas, one lymphoma, seven metastases, one case of extr amedullary hematopoiesis, and one leiomyosarcoma) suspected clinically or identified by sonography or CT in 38 patients were prospectively e valuated with MR imaging, Pathologic proof of diagnosis was obtained f or 28 lesions, and stability on imaging follow-up (mean, 19 months) wa s accepted as proof of diagnosis of benign adenoma for 13 lesions. In- phase T1-weighted spin-echo sequences (500/20 [TR/TE]) and opposed-pha se gradient-echo sequences (142/6.3, flip angle = 90 degrees) of the a drenal regions were applied. Quantitative analysis of signal intensity loss in the adrenal lesions relative to reference tissues (liver, mus cle, and spleen) on in-phase and opposed-phase sequences was done to d ifferentiate adenomas from nonadenomas. Region-of-interest signal inte nsity measurements were obtained in a standard fashion by selection of the largest possible representative sample, RESULTS. Using liver as t he reference standard, we found that mean signal intensity ratios were 0.47 (range, 0.23-0.97) for adrenal adenomas and 0.88 (range, 0.65-1. 32) for nonadenomas; signal intensity ratios for two adenomas overlapp ed those of the nonadenomas. Using muscle as the reference standard, w e found that mean signal intensity ratios were 0.44 (range, 0.22-0.66) for adrenal adenomas and 0.85 (range, 0.59-1.39) for nonadenomas; sig nal intensity ratios for two adenomas overlapped those of the nonadeno mas, Using spleen as the reference standard, we found that mean signal intensity ratios were 0.45 (range, 0.27-0.73) for adrenal adenomas an d 0.97 (range, 0.8-1.18) for nonadenomas, with no overlap. The mean si gnal intensity ratios were significantly different between adenomas an d nonadenomas for all three reference tissues (p <.001). CONCLUSION. O ur results show that chemical-shift MR imaging is an important new tec hnique that enables the differentiation of adrenal adenomas from other adrenal masses, reducing the need for biopsy and prolonged imaging fo llow-up in patients with adrenal tumors.