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Renal Masses: Quantitative Analysis of Enhancement with Signal Intensity Measurements versus Qualitative Analysis of Enhancement with Image Subtraction for Diagnosing Malignancy at MR Imaging¹

¹ From the Department of Radiology, New York University Medical Center, 560 First Ave, Suite HW 202, New York, NY 10016 (E.M.H., G.M.I., G.A.K., W.Y.H., D.C.K., V.S.L.); and Department of Environmental Medicine, Division of Biostatistics, New York University School of Medicine, New York, NY (I.B.L.). Received August 6, 2003; revision requested October 13; revision received October 29; accepted December 15. Address correspondence to G.M.I. (e-mail: gary.israel@med.nyu.edu).

View larger version (119K): [in a new window]   Figure 1. Transverse MR images in 52-year-old woman with bilateral renal masses. A, Unenhanced, and, B, contrast-enhanced fat-suppressed T1-weighted images (3.6/1.4; flip angle, 12°); and, C, subtracted image (obtained by subtracting A from B) show a single mass (long white arrow) in right kidney and two masses (short white arrow and black arrow) in left kidney. The 2.1-cm mass in right kidney has a percentage enhancement of 137%, consistent with an enhancing (malignant) lesion. The subtracted image, C, shows enhancement of thickened and irregular septa within the lesion. At pathologic analysis, this lesion proved to be a renal cell carcinoma. In posterior aspect of left kidney, a 2.5-cm mass (black arrow) shows relative enhancement of 270%, consistent with an enhancing (malignant) lesion. The subtracted image, C, shows enhancement within this lesion. At pathologic analysis, this lesion proved to be a renal cell carcinoma. The third mass (1.9 cm) in the anterior aspect of the left kidney is hyperintense on the unenhanced image, A, and shows –10% relative enhancement, consistent with a nonenhancing (benign) lesion. The subtracted image, C, shows no enhancement within the lesion; this appearance is diagnostic for a benign cyst. At pathologic analysis, this lesion proved to be a hemorrhagic cyst.

View larger version (18K): [in a new window]   Figure 2. Boxplots of percentage relative enhancement of 74 malignant and 19 benign lesions at quantitative analysis. White horizontal bar corresponds to the medians of the distributions, the boxes comprise the middle 50% of the data values, the whiskers extend to the minimum and maximum values, and the horizontal lines outside the whiskers correspond to potential outliers. Inclusion of oncocytomas in the benign lesion category affected the distribution of percentage relative enhancement of benign lesions. Therefore, the median percentage enhancement, instead of the mean, is a more accurate reflection of the center of the distribution of percentage enhancement.

View larger version (102K): [in a new window]   Figure 3. Coronal MR images in 63-year-old man with pathologically proved renal cell carcinoma in left kidney. A, Unenhanced and, B, contrast-enhanced fat-suppressed T1-weighted images (4.2/1.6; flip angle, 20°) show a 2.5-cm exophytic mass (short arrow in B) in left kidney that is hyperintense in signal as compared with renal parenchyma on the unenhanced image. Note small portion of normal kidney (long arrow in B) just inferior to the mass. The percentage enhancement of this mass is –3%, consistent with a nonenhancing (benign) lesion. C, Subtracted image (obtained by subtracting A from B) shows enhancement within the thickened and irregular septa (short arrow) and thickened wall (long arrow) of the mass.

View larger version (139K): [in a new window]   Figure 4. Transverse MR images in 62-year-old man with pathologically proved renal cell carcinoma in right kidney. A, Unenhanced and, B, contrast-enhanced fat suppressed T1-weighted images (3.6/1.4; flip angle, 12°) show a 1.5-cm mass (arrow) in the right kidney that is hyperintense when compared with renal parenchyma on the unenhanced image. The percentage enhancement of this mass is 2%, consistent with a nonenhancing (benign) lesion. C, Subtracted image (obtained by subtracting A from B) shows enhancement within the lesion; this appearance is diagnostic for renal malignancy.