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Renal Angiomyolipoma with Minimal Fat: Differentiation from Other Neoplasms at Double-Echo Chemical Shift FLASH MR Imaging¹

¹ From the Departments of Radiology (J.K.K., S.H.K., Y.J.J., K.S.C.) and Urology (H.A., C.S.K., H.P.), Asan Medical Center, University of Ulsan, 388-1 Poongnap-dong, Songpa-gu, Seoul, 138-736, South Korea; and Department of Radiology, Pusan National University Hospital, Pusan, South Korea (J.W.L., S.K.). Received January 25, 2005; revision requested March 29; revision received May 18; final version accepted June 21. Address correspondence to J.K.K. (e-mail: rialto{at}amc.seoul.kr).

View larger version (100K): [in a new window]   Figure 1a: Images in a 60-year-old man with AML with minimal fat. (a) Unenhanced CT scan and (b, c) contrast-enhanced CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrow) in the left kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrow) and spleen (not shown) are 588 au and 687 au, respectively, at in-phase transverse MR imaging (152/5.3) (d) and 290 au and 670 au, respectively, at opposed-phase transverse MR imaging (152/2.7) (e). Signal intensity index is 51%, and tumor-to-spleen ratio is –49%. This tumor was considered an AML with minimal fat at double-echo chemical shift imaging and confirmed as an AML at histopathologic examination.

View larger version (113K): [in a new window]   Figure 1b: Images in a 60-year-old man with AML with minimal fat. (a) Unenhanced CT scan and (b, c) contrast-enhanced CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrow) in the left kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrow) and spleen (not shown) are 588 au and 687 au, respectively, at in-phase transverse MR imaging (152/5.3) (d) and 290 au and 670 au, respectively, at opposed-phase transverse MR imaging (152/2.7) (e). Signal intensity index is 51%, and tumor-to-spleen ratio is –49%. This tumor was considered an AML with minimal fat at double-echo chemical shift imaging and confirmed as an AML at histopathologic examination.

View larger version (101K): [in a new window]   Figure 1c: Images in a 60-year-old man with AML with minimal fat. (a) Unenhanced CT scan and (b, c) contrast-enhanced CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrow) in the left kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrow) and spleen (not shown) are 588 au and 687 au, respectively, at in-phase transverse MR imaging (152/5.3) (d) and 290 au and 670 au, respectively, at opposed-phase transverse MR imaging (152/2.7) (e). Signal intensity index is 51%, and tumor-to-spleen ratio is –49%. This tumor was considered an AML with minimal fat at double-echo chemical shift imaging and confirmed as an AML at histopathologic examination.

View larger version (110K): [in a new window]   Figure 1d: Images in a 60-year-old man with AML with minimal fat. (a) Unenhanced CT scan and (b, c) contrast-enhanced CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrow) in the left kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrow) and spleen (not shown) are 588 au and 687 au, respectively, at in-phase transverse MR imaging (152/5.3) (d) and 290 au and 670 au, respectively, at opposed-phase transverse MR imaging (152/2.7) (e). Signal intensity index is 51%, and tumor-to-spleen ratio is –49%. This tumor was considered an AML with minimal fat at double-echo chemical shift imaging and confirmed as an AML at histopathologic examination.

View larger version (141K): [in a new window]   Figure 1e: Images in a 60-year-old man with AML with minimal fat. (a) Unenhanced CT scan and (b, c) contrast-enhanced CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrow) in the left kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrow) and spleen (not shown) are 588 au and 687 au, respectively, at in-phase transverse MR imaging (152/5.3) (d) and 290 au and 670 au, respectively, at opposed-phase transverse MR imaging (152/2.7) (e). Signal intensity index is 51%, and tumor-to-spleen ratio is –49%. This tumor was considered an AML with minimal fat at double-echo chemical shift imaging and confirmed as an AML at histopathologic examination.

View larger version (117K): [in a new window]   Figure 2a: Images in a 44-year-old man with RCC. (a) Unenhanced CT scans and (b, c) contrast-enhanced transverse CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrows) in the right kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrows) and spleen (not shown) are 310 au and 410 au, respectively, on in-phase transverse MR images (152/5.3) (d) and 305 au and 398 au, respectively, on opposed-phase transverse MR images (152/2.7) (e). The signal intensity index is 2%, and the tumor-to-spleen ratio is 1%. This tumor was considered to be non-AML at double-echo chemical shift imaging and was confirmed as RCC at histopathologic examination.

View larger version (141K): [in a new window]   Figure 2b: Images in a 44-year-old man with RCC. (a) Unenhanced CT scans and (b, c) contrast-enhanced transverse CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrows) in the right kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrows) and spleen (not shown) are 310 au and 410 au, respectively, on in-phase transverse MR images (152/5.3) (d) and 305 au and 398 au, respectively, on opposed-phase transverse MR images (152/2.7) (e). The signal intensity index is 2%, and the tumor-to-spleen ratio is 1%. This tumor was considered to be non-AML at double-echo chemical shift imaging and was confirmed as RCC at histopathologic examination.

View larger version (137K): [in a new window]   Figure 2c: Images in a 44-year-old man with RCC. (a) Unenhanced CT scans and (b, c) contrast-enhanced transverse CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrows) in the right kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrows) and spleen (not shown) are 310 au and 410 au, respectively, on in-phase transverse MR images (152/5.3) (d) and 305 au and 398 au, respectively, on opposed-phase transverse MR images (152/2.7) (e). The signal intensity index is 2%, and the tumor-to-spleen ratio is 1%. This tumor was considered to be non-AML at double-echo chemical shift imaging and was confirmed as RCC at histopathologic examination.

View larger version (98K): [in a new window]   Figure 2d: Images in a 44-year-old man with RCC. (a) Unenhanced CT scans and (b, c) contrast-enhanced transverse CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrows) in the right kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrows) and spleen (not shown) are 310 au and 410 au, respectively, on in-phase transverse MR images (152/5.3) (d) and 305 au and 398 au, respectively, on opposed-phase transverse MR images (152/2.7) (e). The signal intensity index is 2%, and the tumor-to-spleen ratio is 1%. This tumor was considered to be non-AML at double-echo chemical shift imaging and was confirmed as RCC at histopathologic examination.

View larger version (110K): [in a new window]   Figure 2e: Images in a 44-year-old man with RCC. (a) Unenhanced CT scans and (b, c) contrast-enhanced transverse CT scans obtained at corticomedullary (b) and nephrographic and/or excretory (c) phases show a mass (arrows) in the right kidney, without intratumoral fat and with homogeneous enhancement and prolonged enhancement pattern. (d, e) Signal intensities of the tumor (arrows) and spleen (not shown) are 310 au and 410 au, respectively, on in-phase transverse MR images (152/5.3) (d) and 305 au and 398 au, respectively, on opposed-phase transverse MR images (152/2.7) (e). The signal intensity index is 2%, and the tumor-to-spleen ratio is 1%. This tumor was considered to be non-AML at double-echo chemical shift imaging and was confirmed as RCC at histopathologic examination.

View larger version (21K): [in a new window]   Figure 3: ROC curve for the signal intensity index and tumor-to-spleen ratio in differentiation of AMLs with minimal fat from other neoplasms. The area under the ROC curve is 0.975 for the signal intensity index and 0.952 for the tumor-to-spleen ratio. FPF = false-positive fraction, TPF = true-positive fraction.

View larger version (19K): [in a new window]   Figure 4: Scatterplot of the signal intensity index for the AML and non-AML groups. A signal intensity index of 25% was chosen as a cutoff value, and the sensitivity, specificity, and positive and negative predictive values for differentiation of AMLs from other neoplasms were 96%, 93%, 93%, and 96%, respectively.

View larger version (21K): [in a new window]   Figure 5: Scatterplot of the tumor-to-spleen ratio for AML and non-AML groups. When a tumor-to-spleen ratio of –32% was chosen as a cutoff value, the sensitivity, specificity, and positive and negative predictive values for differentiation of AMLs between the two groups were 88%, 97%, 96%, and 90%, respectively.