Contrast material-enhanced US highly sensitive, specific for indeterminate renal masses

Contrast material-enhanced ultrasonography (US) is a highly sensitive and specific method for characterization of indeterminate renal masses, according to a study published in the April issue of Radiology.

Indeterminate renal masses are a common clinical problem, as there is a broad range of complicated cysts between blatantly benign and malignant lesions. Classification of these masses can be challenging at CT or MRI because of factors like patient size, patient movement, mass size, technique used, image noise, partial-volume averaging and pseudoenhancement, according to the study’s lead author, Richard G. Barr, MD, PhD, of Kent State University in Salem, Ohio, and colleagues.

Contrast-enhanced US has been used to evaluate renal abnormalities, and the method’s agents are comparable to and in some ways more beneficial than those of CT and MRI. Barr and colleagues conducted a long-term follow-up study to determine the utility of contrast-enhanced US in characterizing indeterminate renal masses.

The study included 721 patients who were referred for contrast-enhanced US with 1,018 indeterminate renal masses. The researchers used contrast-enhanced US enhancement patterns to characterize masses as benign or malignant. For the lesions with a definitive diagnosis, 306, or 30 percent, were correlated with contrast-enhanced US findings. One hundred sixty-seven lesions were benign and 139 were malignant. A total of 712 lesions without pathologic diagnoses were followed for a maximum of ten years.

Results revealed that contrast-enhanced US had a sensitivity of 100 percent, specificity of 95 percent, a positive predictive value of 94.7 percent and a negative predictive value of 100 percent. Five false-positive masses were three onocytomas and two Bosniak category three cystic lesions.

One hundred thirty-seven patients had at least 60 months of follow-up. Of this subgroup, 121 had lesions that were classified as benign, two had malignant lesions and 14 had indeterminate lesions at contrast-enhanced US. Two hundred patients had at least 36 months of follow-up, and 181 patients had benign lesions, three had malignant ones and 16 were indeterminate at US. No changes in this group were substantial enough for reclassification.

“The addition of contrast-enhanced US evaluation of indeterminate renal masses can help classify lesions with a high degree of certainty and could decrease the need for follow-up, help convert cases that seemingly require biopsy or surgical removal to necessitating follow-up instead, and demonstrate malignant lesions that might otherwise be followed up,” wrote the authors.

They also suggested that contrast-enhanced US evaluation of renal masses could limit the need for CT and its associated radiation dose or MRI with its costliness. Barr and colleagues also posited the idea that the technology could play an important role in patients with contraindications to CT or MRI contrast materials.