For example, simple cystic lesions, or even those with thin septations, can often be characterized on noncontrast T2-weighted imaging based on their homogeneous and very high T2 signal intensity. To differentiate between hemorrhagic or proteinaceous cyst and RCC, a retrospective study shows that homogenous high T1 signal intensity lesions with smooth borders and lesion to renal parenchyma signal intensity ratio of >1.6 predicted the lesion as a benign cyst [53]. Another study of 144 T1-hyperintense lesions demonstrated that diffuse and marked T1-hyperintensity achieved accuracies of 73.6% to 79.9% for the diagnosis of T1- hyperintense cysts [54]. An angular interface with the renal parenchyma on T2-weighted imaging has been shown to be 78% sensitive and 100% specific for differentiating benign exophytic renal masses from malignant masses [55]. Diffusion-weighted imaging, although less accurate than contrast-enhanced MRI, may have some ability to differentiate solid RCC from oncocytomas and characterize the histologic subtypes of RCC [56]. New and specialized MRI sequences have been proposed for the purposes of characterizing the vascularity of renal lesions in patients with renal dysfunction. For example, one small study of 17 renal lesions used arterial spin labeling to detect blood flow in renal masses, which correlated with malignancy [57]. Cystic Renal Masses In a study of 69 cystic renal masses evaluated using the Bosniak classification with CT and MRI, there was CT and MRI agreement in 56 of 69 lesions (81%) and disagreement in 13 of 69 lesions (19%) [29]. CT and MRI were felt to be similar in evaluation of most renal cystic mass lesions. However, MRI may depict additional findings, such as an increase in number of septa, septal or wall thickness, and enhancement. Such findings would result in MRI upgrading cystic lesions and thus might alter patient management [29].
Indeterminate Renal Mass. For example, simple cystic lesions, or even those with thin septations, can often be characterized on noncontrast T2-weighted imaging based on their homogeneous and very high T2 signal intensity. To differentiate between hemorrhagic or proteinaceous cyst and RCC, a retrospective study shows that homogenous high T1 signal intensity lesions with smooth borders and lesion to renal parenchyma signal intensity ratio of >1.6 predicted the lesion as a benign cyst [53]. Another study of 144 T1-hyperintense lesions demonstrated that diffuse and marked T1-hyperintensity achieved accuracies of 73.6% to 79.9% for the diagnosis of T1- hyperintense cysts [54]. An angular interface with the renal parenchyma on T2-weighted imaging has been shown to be 78% sensitive and 100% specific for differentiating benign exophytic renal masses from malignant masses [55]. Diffusion-weighted imaging, although less accurate than contrast-enhanced MRI, may have some ability to differentiate solid RCC from oncocytomas and characterize the histologic subtypes of RCC [56]. New and specialized MRI sequences have been proposed for the purposes of characterizing the vascularity of renal lesions in patients with renal dysfunction. For example, one small study of 17 renal lesions used arterial spin labeling to detect blood flow in renal masses, which correlated with malignancy [57]. Cystic Renal Masses In a study of 69 cystic renal masses evaluated using the Bosniak classification with CT and MRI, there was CT and MRI agreement in 56 of 69 lesions (81%) and disagreement in 13 of 69 lesions (19%) [29]. CT and MRI were felt to be similar in evaluation of most renal cystic mass lesions. However, MRI may depict additional findings, such as an increase in number of septa, septal or wall thickness, and enhancement. Such findings would result in MRI upgrading cystic lesions and thus might alter patient management [29].