Follow-up after percutaneous radiofrequency ablation of renal cell carcinoma: contrast-enhanced sonography versus contrast-enhanced CT or MRI

OBJECTIVE. The purpose of this study was to assess, with contrast-enhanced CT or
MRI as the reference imaging technique, the diagnostic performance of low-mechanical-index
contrast-enhanced sonography in detecting local tumor progression after percutaneous
radiofrequency ablation of renal tumors.
Materi als AND METHODS. Twenty-nine patients with 30 renal tumors (18 men,
11 women; mean age, 73 years; range, 53–83 years) underwent percutaneous radiofrequency
ablation at a single center between March 1998 and January 2007. The imaging follow-up
schedule was both contrast-enhanced sonography and CT or MRI 4 months after completion
of treatment and every 4 months for the first year. Thereafter, the follow-up schedule was
contrast-enhanced sonography every 4 months with CT or MRI every 8 months. The chisquare
test with Yates correction was used to evaluate positive and negative predictive values
and accuracy.
RESULTS. One patient was scheduled to undergo surgical resection, and another patient
was lost to follow-up. Twenty-seven patients with 28 renal tumors participated in follow-up.
The concordance between contrast-enhanced sonographic and CT or MRI findings was 100%
for 27 of 28 tumors (96.4%) that had a hypervascular pattern before treatment. In the case of
the tumor that was hypovascular at imaging performed before percutaneous radiofrequency
ablation, local tumor progression was missed at contrast-enhanced sonography. The sensitivity,
specificity, positive predictive value, negative predictive value, and overall accuracy of
contrast-enhanced sonography were 96.6%, 100%, 100%, 95.8%, and 98.1%.
CONCLUSION. Contrast-enhanced sonography is an effective alternative to CT and
MRI in the follow-up of renal tumors managed with percutaneous radiofrequency ablation.