MR-CSI (in-phase and opposed-phase gradient-echo scans), which relies on differentiating lesions whether lesions have fat within tumor cells, with malignant lesions having virtually no fat [50]. This has been shown to be correct for 96% to 100% of cases, depending on the study [51,52]. However, these studies were performed in a mixed population of patients with regard to their history of malignancy, so results may not be directly applicable to populations either with or without known malignancy. As in CT washout characterization, there can be false-positives for adenoma when interpreting CSI with particular metastatic lesions, specifically from clear-cell renal cell carcinoma and hepatocellular carcinoma. Because the diagnosis of adenoma relies on the detection of fat within tumor cells and because hepatocellular carcinoma and renal cell carcinoma primary tumors contain fat in their cells, both hepatocellular carcinoma and renal cell carcinoma adrenal metastases can contain fat and, thus, mimic adenomas [58,82,83]. In cases in which the unenhanced CT attenuation 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 Adrenal Mass Evaluation 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.
Adrenal Mass Evaluation. MR-CSI (in-phase and opposed-phase gradient-echo scans), which relies on differentiating lesions whether lesions have fat within tumor cells, with malignant lesions having virtually no fat [50]. This has been shown to be correct for 96% to 100% of cases, depending on the study [51,52]. However, these studies were performed in a mixed population of patients with regard to their history of malignancy, so results may not be directly applicable to populations either with or without known malignancy. As in CT washout characterization, there can be false-positives for adenoma when interpreting CSI with particular metastatic lesions, specifically from clear-cell renal cell carcinoma and hepatocellular carcinoma. Because the diagnosis of adenoma relies on the detection of fat within tumor cells and because hepatocellular carcinoma and renal cell carcinoma primary tumors contain fat in their cells, both hepatocellular carcinoma and renal cell carcinoma adrenal metastases can contain fat and, thus, mimic adenomas [58,82,83]. In cases in which the unenhanced CT attenuation 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 Adrenal Mass Evaluation 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.