Do Incidental Hyperechoic Renal Lesions Measuring Up to 1 cm Warrant Further Imaging? Outcomes of 161 Lesions

Abstract

Objective: The purpose of this study was to determine the outcomes of hyperechoic renal lesions measuring 1 cm or less at ultrasound examination.

Materials and methods: This retrospective study included 161 hyperechoic renal lesions measuring 1 cm or less at ultrasound that were evaluated with follow-up ultrasound, CT, or MRI. Follow-up imaging examinations were reviewed to assess for definitive lesion characterization or size stability.

Results: Follow-up included 11 unenhanced CT, 39 contrast-enhanced CT, 52 unenhanced and contrast-enhanced CT, two unenhanced MRI, 50 unenhanced and contrast-enhanced MRI, and 87 ultrasound examinations. At CT or MRI 58.4% of lesions were confirmed to be angiomyolipomas. At CT, one lesion represented a stone, and one a hyperdense cyst. At CT or MRI 11.8% of the lesions had no correlate; 3.1% were not visualized at follow-up ultrasound. An additional 23.6% were stable at 2-year follow-up imaging or beyond. Two lesions were evaluated with only contrast-enhanced CT less than 1 month after ultrasound, and the CT images did not show macroscopic fat or calcification or meet the criteria for a simple cyst. These lesions were considered indeterminate. One lesion in a 65-year-old man was imaged with unenhanced and contrast-enhanced CT 23 months after ultrasound, and the CT showed an increase in size, solid enhancement, and no macroscopic fat. This lesion was presumed to represent renal cell carcinoma. Overall, the one lesion presumed malignant and the two indeterminate lesions constituted 1.9% of the cohort. The other 98.1% of lesions were considered clinically insignificant.

Conclusion: Most hyperechoic renal lesions measuring 1 cm or smaller were clinically insignificant, suggesting that such lesions may not require additional imaging. Patient demographics, symptoms and risk factors for malignancy may help inform the decision to forgo follow-up imaging of such lesions.

Keywords: angiomyolipoma; hyperechoic renal lesion.