In cases where the unenhanced CT measurement was between 10 and 30 HU (ie, indeterminate by CT), applying CSI can be discriminatory. In one study, 89% of adenomas with densities between 10 and 30 HU were correctly characterized by CSI [59]. Another study concluded that up to 60% of lesions misclassified by unenhanced CT attenuation measurements can be correctly characterized as adenomas by MR-CSI [53]. Gabriel et al [60] have demonstrated that even heterogeneous loss of signal is evidence of a benign lesion. Thus, MR-CSI may have better sensitivity and specificity than nonenhanced CT. Diffusion-weighted MRI techniques have been investigated in helping to distinguish benign and malignant masses in various organ systems. Neither Miller et al [61] nor Tsushima et al [62] found that this technique could differentiate adrenal adenomas and nonadenomas. A number of series have studied adrenal lesion amount of contrast enhancement and enhancement pattern on MRI after indeterminate MR-CSI [18-20]. In one series of 46 lipid-poor adrenal lesions, the combination of T2-signal intensity and contrast enhancement could identify adenomas with a sensitivity of 84% to 89%, specificity of 96%, and accuracy of 91% to 94% [20]. Additionally, MRI without and with IV contrast may be considered if there is concern for pheochromocytoma, as the contrast can show the typical bright enhancement of this lesion. Contrast can also confirm lack of enhancement of a cystic lesion. Variant 3: Indeterminate adrenal mass, greater than 2 cm and less than 4 cm on initial imaging. No diagnostic benign imaging features. No history of malignancy. Adrenal specific imaging. For patients with no prior history of malignancy and an incidentally detected adrenal mass without diagnostic benign imaging characteristics >2 cm and <4 cm, dedicated adrenal-specific imaging can be considered at the time of detection to determine if the mass can be diagnosed to be an adenoma [16,37,63].
Adrenal Mass Evaluation. In cases where the unenhanced CT measurement was between 10 and 30 HU (ie, indeterminate by CT), applying CSI can be discriminatory. In one study, 89% of adenomas with densities between 10 and 30 HU were correctly characterized by CSI [59]. Another study concluded that up to 60% of lesions misclassified by unenhanced CT attenuation measurements can be correctly characterized as adenomas by MR-CSI [53]. Gabriel et al [60] have demonstrated that even heterogeneous loss of signal is evidence of a benign lesion. Thus, MR-CSI may have better sensitivity and specificity than nonenhanced CT. Diffusion-weighted MRI techniques have been investigated in helping to distinguish benign and malignant masses in various organ systems. Neither Miller et al [61] nor Tsushima et al [62] found that this technique could differentiate adrenal adenomas and nonadenomas. A number of series have studied adrenal lesion amount of contrast enhancement and enhancement pattern on MRI after indeterminate MR-CSI [18-20]. In one series of 46 lipid-poor adrenal lesions, the combination of T2-signal intensity and contrast enhancement could identify adenomas with a sensitivity of 84% to 89%, specificity of 96%, and accuracy of 91% to 94% [20]. Additionally, MRI without and with IV contrast may be considered if there is concern for pheochromocytoma, as the contrast can show the typical bright enhancement of this lesion. Contrast can also confirm lack of enhancement of a cystic lesion. Variant 3: Indeterminate adrenal mass, greater than 2 cm and less than 4 cm on initial imaging. No diagnostic benign imaging features. No history of malignancy. Adrenal specific imaging. For patients with no prior history of malignancy and an incidentally detected adrenal mass without diagnostic benign imaging characteristics >2 cm and <4 cm, dedicated adrenal-specific imaging can be considered at the time of detection to determine if the mass can be diagnosed to be an adenoma [16,37,63].