A team led by Dr. Sandra Seo Young Kim from Dalhousie University in Halifax found "strong" correlation between ultrasound and cross-sectional imaging of these masses in their study of over 1,400 patients. The findings could help in the development of treatment guidelines for ultrasound for this application.
"Our study demonstrates that ultrasound is an alternative to cross-sectional imaging for monitoring tumor size in patients on active surveillance to minimize patient harm given the strong correlation between the two imaging modalities for small renal masses," Kim and colleagues wrote.
Previous research suggests that 76,000 new cases of renal cancer were diagnosed in 2021, including over 14,000 deaths. The study authors wrote that in recent years, more small renal masses have been found secondary to incidental findings due to increased access and use of abdominal imaging.
Active surveillance has been used as a treatment option for smaller tumors. Previous studies suggest that there is a 1% to 2% chance that masses measuring less than 4 cm in size will spread. This means treatment can be delayed until tumor growth or clinical progression are seen.
Current guidelines, however, don't specify which imaging method should be used for active surveillance. That responsibility is left to physicians and institutions.
The researchers touted ultrasound as a promising method for its cost-efficiency, accessibility, and lack of ionizing radiation compared to cross-sectional imaging with modalities like CT or MRI.
"Given the increased awareness of the risks of ionizing radiation, patients may benefit from active surveillance with a combination of both ultrasound and cross-sectional imaging," they added.
Kim et al wanted to find out the correlation between ultrasound, cross-sectional imaging, and pathological renal mass sizes. They looked at data from 3,046 patients from 14 institutions and separated them into a surgical cohort (1,464 patients) and a small renal mass cohort (1,582 patients).
The surgical cohort saw patients who had an ultrasound scan and cross-sectional imaging within eight weeks of each other and within six months of surgery. The cohort of patients with small renal masses had masses less than or equal to 4 cm.
The researchers found that the correlation coefficients between CT/MRI and pathologic size was 0.93 (p < 0.0001) and 0.90 between ultrasound and pathological (p < 0.0001). The correlation between ultrasound and CT/MRI meanwhile was 0.93 (p < 0.0001). A perfect positive correlation is 1.0.
The team also found that 1,441 (75%) small renal mass measurements were within 0.5 cm and that 149 (7.8%) were greater than 1 cm in difference when comparing ultrasound with CT/MRI.
"Furthermore, there was a higher correlation coefficient between ultrasound and cross-sectional imaging for BMIs less than 30," they added.
For the 25% of patients whose small renal mass measurement differences were more than 0.5 cm, researchers said such miscalculations could impact management. They wrote that repeat axial imaging should be performed prior to intervention in this case if an interval growth or the size of the mass is significant enough.
The team wrote that if there is good baseline agreement between ultrasound and CT/MRI in patients with small renal masses, surveillance with ultrasound can be suggested. However, they added that cross-sectional imaging should be used upon progression and periodic axial imaging to confirm ultrasound findings.
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