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

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.