Contrast-enhanced ultrasonography in the follow-up of cryoablation of renal tumours: a feasibility study

Cryotherapy of Renal Lesions: Enhancement on Contrast-Enhanced Sonography on Postoperative Day 1 Does Not Imply Viable Tissue Persistence

OBJECTIVES

To investigate whether persistent enhancement detected on contrast-enhanced sonography at postoperative day 1 (early contrast-enhanced sonography) after cryoablation of renal tumors implies the presence of residual viable tumor tissue, defined as residual enhancing tissue on reference imaging (computed tomography or magnetic resonance imaging) performed 6 months after the procedure.

METHODS

Seventy-four patients with percutaneous cryoablation of renal tumors had early contrast-enhanced sonography from November 2011 to August 2015. Two independent readers evaluated early contrast-enhanced sonographic findings and contrast-enhanced sonographic investigations performed 1 month after cryoablation of lesions that displayed enhancement on early contrast-enhanced sonography. They scored intralesional enhancement in 4 groups: no enhancement, few intralesional vessels, focal enhancing areas, and diffuse enhancement. Inter-reader agreement in evaluating lesion vascularity on early contrast-enhanced sonography was assessed with weighted κ statistics. Computed tomography or magnetic resonance imaging performed 6 months after the treatment was the reference procedure for assessing the absence or presence of residual disease.

RESULTS

Inter-reader agreement in assessing intratumoral vascularization on early contrast-enhanced sonography was very good (κ = 0.90). Enhancement was absent for both readers in 33 of 74 cases; only a few intralesional vessels were visible in 21; whereas diffuse or focal enhancement was present in 13. In the remaining 7 patients, there were differences. Four lesions with focal enhancement on early contrast-enhanced sonography and 1 that was considered avascular had residual tumors on reference imaging. Ablation was successful in the remaining 69 of 74 patients (93%).

CONCLUSIONS

After cryoablation, intratumoral enhancement on early contrast-enhanced sonography does not imply tumor cell viability.

Contrast-enhanced ultrasound (CEUS) of cystic and solid renal lesions: a review

Incidentally detected renal lesions have traditionally undergone imaging characterization by contrast-enhanced computer tomography (CECT) or magnetic resonance imaging. Contrast-enhanced ultrasound (CEUS) of renal lesions is a relatively novel, but increasingly utilized, diagnostic modality. CEUS has advantages over CECT and MRI including unmatched temporal resolution due to continuous real-time imaging, lack of nephrotoxicity, and potential cost savings. CEUS has been most thoroughly evaluated in workup of complex cystic renal lesions, where it has been proposed as a replacement for CECT. Using CEUS to differentiate benign from malignant solid renal lesions has also been studied, but has proven difficult due to overlapping imaging features. Monitoring minimally invasive treatments of renal masses is an emerging application of CEUS. An additional promising area is quantitative analysis of renal masses using CEUS. This review discusses the scientific literature on renal CEUS, with an emphasis on imaging features differentiating various cystic and solid renal lesions.

Contrast-enhanced ultrasound (CEUS): an excellent tool in the follow-up of small renal masses treated with cryoablation

Strict imaging follow-up is mandatory after cryoablation of small renal masses (SRMs). Although it uses ionizing radiation and nephrotoxic iodinated contrast, computed tomography (CT) is still the gold standard test. Contrast-enhanced ultrasound (CEUS) is a novel technique that informs in real time about renal perfusion avoiding radiation and nephrotoxicity. The objective of this study is to compare outcomes between CEUS and CT in the follow-up of SRMs treated with cryoablation, as well as to assess degree of agreement between them. This is a prospective observational study (May 2012 to December 2013) comparing CEUS and CT in 16 patients with SRMs cryoablated. The on-going protocol of the study includes a CT and CEUS 3 months after treatment and then every 6 months during 5 years. Local relapse was defined as the presence of contrast enhancement in the mass. All the CEUS were performed by a single experienced observer (E.S.). Degree of agreement was measured with kappa index. CEUS detected contrast enhancement in three patients (3/16, 18.8%) and CT in two patients (2/16, 12.5%). Degree of agreement between CEUS and CT, according to Landis-Koch classification, was 0.76 (CI 0.33-1.19; p = 0.0165), which is excellent and higher than expected by random. Sensitivity of the test is 93.75% (15/16). Median time of follow-up after cryoablation is 22 months (15.5-36.5). CEUS has an excellent agreement with CT and a high sensitivity in the follow-up of SRMs treated with cryosurgery, demonstrating its usefulness. Due to these encouraging results, it could become a reference test in the near future for monitoring SRMs after ablative treatment.

Contrast-Enhanced Subharmonic and Harmonic Ultrasound of Renal Masses Undergoing Percutaneous Cryoablation

RATIONALE AND OBJECTIVES

The objective of this study was to evaluate and compare contrast-enhanced subharmonic and harmonic ultrasound as tools for characterizing solid renal masses and monitoring their response to cryoablation therapy.

MATERIALS AND METHODS

Sixteen patients undergoing percutaneous ablation of a renal mass provided informed consent to undergo ultrasound examinations the morning before and approximately 4 months after cryoablation. Ultrasound contrast parameters during pretreatment imaging were compared to biopsy results obtained during ablation (n = 13). Posttreatment changes were evaluated by a radiologist and compared to contrast-enhanced magnetic resonance imaging (MRI)/computed tomography (CT) follow-up.

RESULTS

All masses initially showed heterogeneous enhancement with both subharmonic and harmonic ultrasound. Early contrast washout in the mass relative to the cortex was observed in 6 of 9 malignant and 0 of 4 benign lesions in subharmonic mode and 8 of 9 malignant and 1 of 4 benign lesions in harmonic imaging. In cases where the lesion was adequately visualized at follow-up (n = 12), subharmonic and harmonic ultrasound showed accuracies of 83% and 75%, respectively, in predicting treatment outcome. Although harmonic imaging showed less overall error, no significant differences (P > .29) in ablation cavity volumes were observed between MRI/CT and either contrast-imaging mode.

CONCLUSIONS

Subharmonic and harmonic contrast-enhanced ultrasound may be a safe and accurate imaging alternative for characterizing renal masses and evaluating their response to cryoablation therapy. Although subharmonic imaging was more accurate in detecting effective cryoablation, harmonic imaging was superior in quantifying ablation cavity volumes.

Evaluation of renal masses with contrast-enhanced ultrasound

The clinical need for characterising small renal masses (SRMs) is increasing due to their rising incidental detection. This increase is especially seen in younger and older generations and concerns mainly SRMs. Diagnostics is mainly made by contrast-enhanced CT or MRI. However, these imaging methods fail to accurately distinguishing benign from malignant SRMs. Other disadvantages of CT or MRI are high costs, the use of ionizing radiation, nephrotoxicity induced by iodine contrast agents or nephrogenic systemic fibrosis (NSF) induced by gadolinium contrast agents. Contrast-enhanced ultrasound (CEUS) is based on ultrasonography and microbubbles to real-time visualize the renal blood flow without the use of nephrotoxic agents or ionizing radiation. This comprehensive review evaluates the capabilities of CEUS in the diagnostics of benign (angiomyolipomas, cysts, oncocytomas, pseudotumors) and malignant masses (renal cell carcinomas), and focuses on possible future treatment.

Contrast-enhanced ultrasound for the evaluation of the cryolesion after laparoscopic renal cryoablation: an initial report

PURPOSE

Stringent radiological follow-up is essential after renal tumor ablation. Drawbacks of postablation follow-up by contrast-enhanced computed tomography (CECT) are the associated ionizing radiation and nephrotoxic contrast agent. Contrast-enhanced ultrasound (CEUS) has shown potential to demonstrate microvasculature without using either ionizing radiation or toxic contrast agent. We assessed the concordance of enhancement patterns of CEUS and CECT/MRI in cryolesion assessment after laparoscopic renal cryoablation (LCA).

METHODS

From 01/2006 to 01/2009, a CEUS was performed before and after LCA (3 and 12 months) in addition to regular CECT/MRI. Using an enhancement score (0=no enhancement, 1=rim enhancement, 2=diffuse enhancement, 3=localized enhancement, 4=no enhancement defect), the cryolesion was assessed by both modalities, and concordance of enhancement score was assessed.

RESULTS

In total, 45 tumors were included (29 biopsy proven renal cell carcinoma (RCC), mean size 2.66 cm). One cryoablation failed, resulting in a nonenhancing cryolesion apart from the persisting renal tumor. There were no postablation recurrences during the study period. Pre-LCA: Both modalities were available in 26 cases. In 20 out of 26, there was concordance of enhancement score (77%, all cases score 3 or 4). Three months: Both modalities were available in 32 cases. Enhancement score corresponded in 23 out of 32 cases (72%). Seven cases showed enhancement on CECT/MRI ("1" in six cases, "4" in one case) with enhancement score "0"on CEUS. Two cases showed enhancement on CEUS without enhancement on CECT/MRI (specificity 92%, negative predictive value [NPV] 77%). Except one case, all enhancement resolved on subsequent imaging. Twelve months: Both modalities were available in 21 tumors. Enhancement score corresponded in 19 out of 21 cases (91%). Two cases showed enhancement on CEUS without enhancement on CECT/MRI (specificity 90%, NPV 100%).

CONCLUSION

This pilot study shows that CEUS is a safe imaging technique with high concordance of enhancement score between CEUS and CECT/MRI. While cross-sectional imaging seems sensible to demonstrate successful ablation at first follow-up, CEUS might be used to diminish the burden of contrast-enhanced cross-sectional imaging in the long-term follow-up.

Novel ultrasound and DCE-MRI analyses after antiangiogenic treatment with a selective VEGF receptor inhibitor

We report a comparison between tumor perfusion estimates acquired using contrast-enhanced MRI and motion-corrected contrast-enhanced ultrasound before and after treatment with AG-028262, a potent vascular endothelial growth factor receptor tyrosine kinase inhibitor. Antiangiogenic activity was determined by assessing weekly ultrasound and MRI images of rats with bilateral hind flank mammary adenocarcinomas before and after treatment with AG-028262. Images were acquired with a spoiled gradient, 1.5 T magnetic resonance sequence and a destruction-replenishment ultrasound protocol. For ultrasound, a time to 80% contrast replenishment was calculated for each tumor voxel; for MR imaging, a measure of local flow rate was estimated from a linear fit of minimum to maximum intensities. AG-028262 significantly decreased tumor growth and increased the time required to replenish tumor voxels with an ultrasound contrast agent from 2.66 to 4.54 s and to fill with an MR contrast agent from 29.5 to 50.8 s. Measures of flow rate derived from MRI and ultrasound demonstrated a positive linear correlation of r2 = 0.86.

Contrast-enhanced ultrasound using a time-intensity curve for the diagnosis of renal cell carcinoma

OBJECTIVE

• To evaluate the usefulness of contrast-enhanced ultrasound (CEUS) for the diagnosis of renal cell carcinoma by employing a time-intensity curve (TIC).

PATIENTS AND METHODS

• From May 2008 to October 2009, CEUS was performed prior to surgery in 30 patients with renal masses. • In all, 10 of the 30 patients had cystic renal masses. The final diagnoses of all patients were pathologically confirmed. Contrast enhancement as a function of time was measured in two (tumour or solid component of cystic lesions and normal parenchyma) regions of interest (ROI) and TICs were obtained. • The time to the contrast enhancement peak (TTP), intensity change from the baseline to peak (ΔI) and ΔI/TTP of the tumour and the normal parenchyma were measured from the TIC.

RESULTS

• Pathological diagnoses were renal cell carcinoma in 30 patients. • The TTP of the cancer was shorter than that of the normal parenchyma in all cases (6.0 ± 2.0 vs 10.4 ± 3.0 s; P < 0.0001). • The ΔI did not differ between the cancer and normal parenchyma [21.3 ± 5.9 vs 20.9 ± 7.0 decibels (db); P= 0.68]; the ΔI/TTP of the cancer was significantly higher than that of the normal parenchyma (3.9 ± 1.4 vs 2.2 ± 0.94 db/s; P < 0.0001). • TIC patterns of solid cancer and cystic cancer were very similar.

CONCLUSIONS

• An objective and quantitative diagnosis of renal cell carcinoma by CEUS using a second-generation ultrasound contrast agent can be made by employing a TIC. • The TIC patterns of solid and cystic cancers were very similar, despite their morphological and vascular differences. • CEUS using TIC is a promising tool in the diagnosis of cystic renal cancer.

Immediate effect of kidney cryoablation on renal arterial structure in a porcine model studied by imaging cryomicrotome

PURPOSE

Injury to blood microvessels has a crucial role in effective cryoablation for renal masses. We visualized vascular injury induced by a clinically applied cryoablation instrument and established a microvascular diameter threshold for vascular damage.

MATERIALS AND METHODS

In 5 anesthetized pigs 1 kidney each was exposed and 3, 17 gauge cryoneedles were inserted in 1 pole. Tissue was exposed to freezing for 2 x 10 minutes with a 10-minute thaw between freezes. After nephrectomy the arteries were injected with fluorescence dyed casting material and the kidney was frozen to -20C and cut in 40 to 60 micron slices in the imaging cryomicrotome, where fluorescent images of the cutting plane of the bulk were obtained. This resulted in a 3-dimensional image of the arterial tree that was segmented, resulting in unbranched vessel segments. Histograms were constructed with the total segment length per diameter bin plotted as function of diameter.

RESULTS

The ablated zone was sharply demarcated on fluorescent and normal light images. Mean +/- SD diameter at the peak of the histogram from control areas was 152.4 +/- 5.3 micron. Compared to control areas the peak diameter of ablated areas was shifted to a larger diameter by an average of 25.4 +/- 2.6 micron.

CONCLUSIONS

Immediate renal cryoablation injury destroys arteries smaller than 180 micron. Branching structures of larger arteries remain anatomically intact and connected to vascular structures in surrounding tissue.

Motion corrected cadence CPS ultrasound for quantifying response to vasoactive drugs in a rat kidney model

OBJECTIVE

To establish the ability of contrast-enhanced motion corrected cadence pulse sequencing (CPS) to detect changes in renal blood flow induced by vasoactive substances in rats.

METHODS

Ultrasound contrast media was administered as a constant rate infusion into a phantom at a known rate and CPS data acquired. Rats were anesthetized and predrug CPS estimates of replenishment rate were made for the right kidney. Real-time motion correction was applied, and parametric images were generated from the CPS data. Group 1 rats (n = 7) were administered a vasodilator and group 2 rats (n = 3) were administered a vasoconstrictor. The CPS imaging of the kidney was repeated after ample time for drug effects to occur.

RESULTS

Contrast CPS accurately estimated flow velocity in the phantom model. In addition, CPS defined statistically significant differences between pre- and postdrug blood flow in the renal medulla (vasodilator, P < .01; vasoconstrictor, P < .0001) and cortex (vasoconstrictor, P < .0001).

CONCLUSIONS

We conclude that motion-corrected CPS ultrasound provides real-time quantification of renal blood flow alterations and may prove useful for the assessment of blood flow in transplanted kidneys.

Minimally invasive surgery using ablative modalities for the localized renal mass

Due to a number of evolving devices and modalities to treat the small, localized renal mass, the physician and patient have the opportunity to choose an appropriate therapy from several treatment options. Minimally invasive surgery to ablate a localized renal tumor is an alternative strategy to nephron-sparing surgery for the small renal mass. Even though partial nephrectomy has been established as an optimal technique for nephron-sparing surgery, patients who have comorbidities and renal insufficiency would potentially benefit from less invasive treatment. With respect to those concerns, several articles are discussed here regarding thermal ablative therapy for the small renal mass along with oncological outcomes and complications among these modalities compared to conventional procedures. In this review, a comprehensive PubMed search was conducted. For the purposes of reviewing the current status of thermal ablative modalities for the small renal mass, only articles written in English published from 1992 to 2009 were considered. Cryoablation and radiofrequency ablation are the most utilized and potentially promising therapies that are evolving as nephron-sparing minimally invasive surgery for patients with a localized renal tumor. High-intensity focused ultrasound, a relatively new modality to treat the renal mass, needs further study. All modalities require long-term follow up with unified reporting methods in terms of patient selection, pre- and post-treatment evaluation, treatment description, and analysis of outcome.