A team led by Dr. Edoardo Raimondi of the University of Ferrara in Italy found that CEUS showed contrast-enhancement wash-in in two-thirds of indeterminate small renal masses on CT or MRI. CEUS facilitates more accurate evaluation of tumor perfusion and vascular enhancement patterns and should be considered in future diagnostic algorithms for managing solid renal masses, according to the researchers.
"It can be a problem-solving tool in the assessment of those indeterminate renal findings," Raimondi said. He presented the study results during a scientific session on Thursday morning.
Renal masses are increasingly detected as incidental findings on ultrasound, CT, and MRI exams, and they are typically evaluated by multidetector contrast-enhanced CT or contrast-enhanced MRI. Small renal masses are less than 3 cm in their largest dimension and are classified as either solid or complex cystic (class 3 or 4 under the Bosniak classification system for renal cystic masses), Raimondi said.
"[It's also important] to remember that almost 50% of small renal masses are [renal cell carcinomas]," he said.
An indeterminate renal mass is a lesion that can't be confidently diagnosed as benign or malignant when it's found, Raimondi said. These lesions can have enhancement on CT between 20 HU and 70 HU, have intermediate signal intensity on MRI, and be isoechoic or hypoechoic on ultrasound.
"So the principal aspect that we have to look at is the enhancement of the lesion," Raimondi said.
Contrast-enhancement wash-in is a typical sign for a malignant solid renal mass, but some benign lesions can also show contrast wash-in, such as oncocytomas. In addition, 17% to 20% of renal tumors are hypovascular on cross-sectional imaging. Furthermore, contrast enhancement of 10 HU to 30 HU -- a level considered to be pseudoenhancement -- can't be confidently suggestive of malignancy, Raimondi said.
Diagnostic value of CEUS
To address this problem, the researchers set out to explore the role and diagnostic value of CEUS for these masses. The study, which was performed from January 2012 to July 2015, included 39 patients (25 men, 14 women; age range, 40-81) who had hypovascular small renal masses with an inconclusive contrast enhancement pattern on CT or MRI. Of these, 32 patients had masses identified on contrast-enhanced CT and seven had masses found on contrast-enhanced MRI.
All 39 patients received CEUS within a week of their CT or MR study. The real-time CEUS pattern of all small renal masses was evaluated to define their diagnostic therapeutic management, Raimondi said.
Of the 39 patients, 13 had no pathological levels of contrast-enhancement, indicating complex cysts. These were classified as Bosniak 2-2F and the patients did not undergo surgery. The other 26, however, had wash-in contrast enhancement. Four of the 26 were deemed to be ineligible for surgery and are currently under follow-up with CEUS or MRI, he said.
Based on the imaging findings and the clinical suspicion for malignancy, the remaining 22 patients received nephron-sparing surgery. Seventeen of the masses were malignant; there were 10 cases of papillary renal cell carcinoma, six cases of clear cell carcinoma, and one chromophobe. The five benign masses consisted of three cases of minimal-fat angiomyolipoma and two cases of oncocytoma.
"CEUS is a useful tool in evaluating real-time enhancement in small renal masses because it's very sensitive for slight tumor blood flow," Raimondi concluded.