Diagnostic efficacy of contrast-enhanced ultrasonography in solid renal parenchymal lesions with maximum diameters of 5 cm

Objective. The purpose of this study was to evaluate the diagnostic efficacy of contrast-enhanced ultrasonography (CEUS) using a sulfur hexafluoride contrast agent and the cadence contrast pulse sequencing mode in differentiating solid renal parenchymal lesions (SRPLs) with a maximum diameter of 5 cm. Methods. Seventy-one patients with 72 SRPLs with a maximum diameter of 5 cm underwent conventional ultrasonographic and CEUS examinations in our department. The final diagnoses were 44 renal cell carcinomas (RCCs; confirmed by pathologic examination), 24 renal angiomyolipomas (4 by pathologic examination and 20 by computed tomography, magnetic resonance imaging, and follow-up studies), 1 oncocytoma (by pathologic examination), 2 hypertrophied columns of Bertin, and 1 renal abscess (both by computed tomography, magnetic resonance imaging, and follow-up studies). Three observers who were blinded to other results and the final diagnoses reviewed the conventional ultrasonographic and CEUS images. Results. Hyperenhancement in the late phase (30-90 seconds after agent injection) was the most important finding for predicting SRPLs with a maximum diameter of 5 cm to be RCCs. With this criterion, the specificity and sensitivity for diagnosing solid RCCs (<= 55 cm) were 96.4% and 77.3%, respectively. Heterogeneous enhancement was another valuable finding suggestive of RCCs. Most renal angiomyolipomas were homogeneously enhanced with hypoenhancement in the arterial and late phases. Hypertrophied columns of Bertin could be reliably differentiated on CEUS; however, there was an overlap of CEUS appearances between some benign lesions and hypovascular RCCs. Conclusions. Contrast-enhanced ultrasonography could be an effective and necessary examination for differentially diagnosing SRPLs with a maximum diameter of 5 cm.