Evaluation of renal masses with contrast-enhanced ultrasound: initial experience

Abstract

Objective: Nearly 25% of solid renal tumors are indolent cancer or benign and can be managed conservatively in selected patients. This prospective study was performed to determine whether preoperative IV microbubble contrast-enhanced ultrasound can be used to differentiate indolent and benign renal tumors from more aggressive clear cell carcinoma.

Subjects and methods: Thirty-four patients with renal tumors underwent preoperative gray-scale, color, power Doppler, and octafluoropropane microbubble IV contrast-enhanced ultrasound. Three blinded radiologists reading in consensus compared rate of contrast wash-in, grade and pattern of enhancement, and contrast washout compared with adjacent parenchyma. Contrast ultrasound findings were compared with surgical histopathologic findings for all patients.

Results: The 34 patients had 23 clear cell carcinomas, three type 1 papillary carcinomas, one chromophobe carcinoma, one clear rare multilocular low-grade malignant tumor, two unclassified lesions, three oncocytomas, and one benign angiomyolipoma. The combination of heterogeneous lesion echotexture and delayed lesion washout had 85% positive predictive value, 43% negative predictive value, 48% sensitivity, and 82% specificity for predicting whether a lesion was conventional clear cell carcinoma or another tumor. Diminished lesion enhancement grade had 75% positive predictive value, 81% negative predictive value, 55% sensitivity, and 91% specificity for non-clear cell histologic features, either benign or low-grade malignant. Combining delayed washout with quantitative lesion peak intensity of at least 20% of kidney peak intensity had 91% positive predictive value, 40% negative predictive value, 63% sensitivity, and 80% specificity in the prediction of clear cell histologic features.

Conclusion: Ultrasound features of gray-scale heterogeneity, lesion washout, grade of contrast enhancement, and quantitative measure of peak intensity may be useful for differentiating clear cell carcinoma and non-clear cell renal tumors.

Fig. 1

47-year-old woman with clear cell carcinoma. Postpeak hyperenhancement (delayed washout) was confirmed both visually and at quantitative analysis. A, Color Doppler image shows heterogeneous 3.8-cm right renal mass with marked flow. B, Split-screen ultrasound images from qualitative analysis (left, gray scale; right, contrast enhanced) obtained 16 seconds after contrast injection show heterogeneous lesion enhancement (arrows) of higher grade than that of adjacent renal parenchyma (asterisks). Early phase heterogeneous enhancement became uniform. C, Split-screen qualitative analysis images 19 seconds after injection show closer to uniform lesion enhancement (arrows) and higher-grade enhancement than of adjacent kidney (asterisk).

Fig. 2

58-year-old woman with metastatic disease consistent with clear cell carcinoma of renal origin. A, Gray-scale ultrasound image shows right renal heterogeneous 5-cm mass (T) projecting within central sinus fat. B, Autotracking contrast quantification mixed-mode image obtained immediately after renal peak shows moderate to marked heterogeneous lesion enhancement (T) compared with adjacent kidney and relative lack of washout. Arrows indicate lesion. C, Time-enhancement curve confirms qualitative visual findings. Tumor (T) data points (white) show higher peak of enhancement with relative lack of washout after renal peak (blue) in corticomedullary phase. ROI = region of interest.

Fig. 3

54-year-old man with 7.0-cm right renal papillary carcinoma. A, Gray-scale image shows minimally heterogeneous 7-cm mass (calipers). B, Color Doppler image shows lesion (T) has confirmed minimal flow. C, Autotracking contrast quantification mixed-mode imaging shows minimal lesion (T) enhancement compared with adjacent renal parenchyma (K). D, Time-enhancement curve confirms qualitative findings. Lesion (T) data points (white) show minimal enhancement compared with renal parenchymal (K) data points (blue).

Fig. 4

60-year-old man with 6.8-cm right renal clear cell carcinoma. A, Power Doppler image shows heterogeneous exophytic solid mass (arrow) with confirmed internal flow. B, Qualitative split-screen gray-scale (left) and contrast-enhanced (right) images obtained 16 seconds after contrast injection shows nodular mixed penetrating and peripheral heterogeneous enhancement (arrows) within tumor (T) that is greater than enhancement of kidney (asterisk). C, Split-mode screen qualitative analysis image obtained 33 seconds after contrast injection, after renal peak, shows lesion (T) has continued higher grade of contrast enhancement (arrows) than adjacent rim of normal renal parenchyma (asterisk), constituting lack of lesion washout.