Ultrasound can be used for active surveillance of small renal masses, and sonography correlates well with cross-sectional imaging modalities, according to Canadian research published March 6 in Urology.
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.
![Examples of ultrasound findings and techniques. (A) Images in a 39-year-old male patient with a mass in the left thigh. The mass is heterogeneous on the B-mode US image (compared with the patient in D) and showed increased microvascularity (superb microvascular imaging [SMI]) and shear-wave elastography (SWE) values. Undifferentiated pleomorphic sarcoma was diagnosed at biopsy (with pleomorphic rhabdomyosarcoma in surgical specimen). (B) Images in an 18-year-old male patient with a mass in the left leg. The mass is hypoechoic on the B-mode image, with no other findings suggestive of malignancy. The lesion is in contact with the cortex of the tibia, which is slightly irregular. CT revealed a doubtful anteromedial tibial erosion. The microvascular study demonstrated high vascularization, suggestive of malignancy. Periosteal Ewing sarcoma was diagnosed with both histologic and immunohistochemical confirmation. (C) Images in a 69-year-old female patient with a lump growing on the outside of the left leg. Multiple SWE examinations were performed (please note the high values obtained in the measurements, whereas the color map highlights the stiffness relative to adjacent tissues). SMI showed areas of increased vascularization to target for sampling. Undifferentiated spindle cell sarcoma was diagnosed at biopsy, with residual leiomyosarcoma in the surgical specimen after neoadjuvant therapy. (D) Images in a 56-year-old female patient with a mass in the right thigh. The mass is heterogeneous at both B-mode ultrasound (similar to patient A) and MRI (coronal T2-weighted spectral attenuated inversion recovery [SPAIR]; T1-weighted pre-contrast and postcontrast imaging), which even shows uptake after the administration of paramagnetic contrast material, which is traditionally suggestive of malignancy. Low values at SMI and elastography are suggestive of benignity. Spindle cell lipoma was diagnosed at biopsy, with atypical spindle cell lipomatous tumor in the surgical specimen.](https://img.auntminnie.com/mindful/smg/workspaces/default/uploads/2026/08/images-radiol250278fig2.APCFLSvX6p.jpg?auto=format%2Ccompress&dpr=2&fit=crop&h=167&q=70&w=250)
