Adrenal masses: Characterization with in vivo proton MR spectroscopy - Initial experience

Purpose: To prospectively determine the accuracy of in vivo proton (H-1) magnetic resonance (MR) spectroscopy in distinguishing adrenal adenomas, pheochromocytomas, adrenocortical carcinomas, and metastases, with histologic or computed tomographic findings and follow-up data as the reference standards. Materials and Methods: This study was approved by the institutional ethics committee, and informed consent was obtained. Sixty consecutive patients (24 male and 36 female patients; mean age, 53 years) harboring adrenal tumors larger than 2 cm in diameter (mean diameter, 4.6 cm +/- 3.4 [standard deviation]) entered the study and were examined with a 1.5-T MR imaging system and point-resolved multivoxel 1H MR spectroscopy. Thirty-eight patients had adenomas; 10, pheochromocytomas; five, carcinomas; and seven, metastases. Amplitude values for choline, creatine, lipid, and a metabolite peak at precession frequency of 4.0-4.3 ppm were measured. Metabolite ratios (choline-creatine, choline-lipid, lipid-creatine, and 4.0-4.3 ppm/creatine) and cutoff values (obtained by using receiver operating characteristic analyses) were obtained and compared for each type of adrenal mass, which was identified previously on the basis of clinical, hormonal, and pathologic evidence. Results were evaluated with X-2 and Student t tests. Significance was inferred at P < .05. Results: Cutoff values of 1.20 for the choline-creatine ratio (92% sensitivity, 96% specificity; P < .01), 0.38 for the choline-lipid ratio (92% sensitivity, 90% specificity; P < .01), and 2.10 for the lipid-creatine ratio (45% sensitivity, 100% specificity) enabled adenomas and pheochromocytomas to be distinguished from carcinomas and metastases. A 4.0-4.3 ppm/creatine ratio greater than 1.50 enabled distinction of pheochromocytomas and carcinomas from adenomas and metastases (87% sensitivity, 98% specificity; P < .01). The best distinction was obtained by comparing choline-creatine and 4.0-4.3 ppm/creatine ratios. Conclusion: 1H MR spectroscopy can be used to characterize adrenal masses on the basis of spectral findings for benign adenomas, carcinomas, pheochromocytomas, and metastases.