Expansion of an ablated site and induction of apoptosis after microwave coagulation therapy in rat liver

Single-arm prospective study comparing ablation zone volume between time zero and 24 h after microwave ablation of liver tumors

PURPOSE

Percutaneous thermal ablation is an effective treatment for primary and metastatic liver tumors and is a recommended local therapy for early-stage hepatocellular carcinoma (HCC). Reported evidence shows an increase in the ablation zone volume over the first 24-h post-liver ablation. This report compares ablation zone volumes immediately at the completion (T = 0) of 26 microwave ablations of liver tumors to 24-h post-procedure (T = 24) volumes.

MATERIALS AND METHODS

20 patients, 13 (65%) males, underwent a total of 26 hepatic microwave ablations (MWA) under ultrasound guidance. Contrast-enhanced CT (CECT) or MRI was performed immediately and another CECT 24 h post operatively. Evaluation of the ablation zone and comparison of the two post-operative scans were done using BioTrace software. The expansion of ablation zones on post-op CECTs was matched point by point per direction. The distance between each 2 points was measured and grouped by distance. The incidence of each specific distance was then converted into a percentage, first for each case separately, then for all cases altogether. Data were tested by a matched paired one-sided t test.

RESULTS

The median lesion diameter was 1.5 cm (range 0.5-3.3) with 16 (62%) HCC cases and 9 hepatic metastases (4 neuroendocrine carcinoma, 4 colorectal carcinomas, 1 breast carcinoma, 1 pancreatic cancer). The data show a consistent volume expansion greater than 30% (p = 7.7e-5) 24-h post-ablation, where the median expansion is 57%. Distances between T = 0 and T = 24 equal to 3-7 mm occur in over 35% of the cases.

CONCLUSION

The ablation zone expansion at 24-h post-op was not uniform. The final ablation zone is difficult to predict at the time of the procedure. The awareness of the ablation zone expansion is important when treating near-critical structures, managing the heat sink effect, and preserving liver parenchyma.

Friend or Foe? Locoregional Therapies and Immunotherapies in the Current Hepatocellular Treatment Landscape

Over the last several decades, a number of new treatment options for patients with hepatocellular carcinoma (HCC) have been developed. While treatment decisions for some patients remain clear cut, a large numbers of patients have multiple treatment options, and it can be hard for multidisciplinary teams to come to unanimous decisions on which treatment strategy or sequence of treatments is best. This article reviews the available data with regard to two treatment strategies, immunotherapies and locoregional therapies, with a focus on the potential of locoregional therapies to be combined with checkpoint inhibitors to improve outcomes in patients with locally advanced HCC. In this review, the available data on the immunomodulatory effects of locoregional therapies is discussed along with available clinical data on outcomes when the two strategies are combined.

Crosstalk between microwave ablation and ferroptosis: The next hot topic?

Microwave ablation has been one form of thermal ablation in treatments for many tumors, which can locally control unresectable tumors. Ferroptosis is iron-dependent cell death caused by the cumulative reactive oxygen species and lipid peroxidation products. Recently, increasing evidence has shown that ferroptosis might play a vital role in MWA-induced tumor suppression. In this article, we briefly illustrate the concept of ferroptosis, the related signal pathways and inducers, the basic principle of microwave ablation in killing tumors, and the key molecules released after microwave ablation. Then, we describe the cross-talking molecules between microwave ablation and ferroptosis, and discussed the potential mechanism of microwave ablation-induced ferroptosis. This review explores the therapeutic target of ferroptosis in enhancing the systemic antitumor effect after microwave ablation, providing theoretical support in combinational microwave ablation with pro-ferroptosis therapy.

Residual vital ratio: predicting regrowth after radiofrequency ablation for benign thyroid nodules

PURPOSE

To determine a novel quantitative index, residual vital ratio(RVR) by contrast-enhanced ultrasound(CEUS) with conventional Ultrasound(US), to early predict nodule regrowth after radiofrequency ablation (RFA)for benign thyroid nodules.

METHODS

This retrospective study evaluated 186 patients with 206 benign thyroid nodules underwent RFA. Patients were followed at 1, 3, 6, 12 months and every 12 months thereafter by conventional US, CEUS and clinical evaluation. RVR was defined as the initial ratio of residual vital volume to the total volume calculated by CEUS and conventional US at the first follow-up period after RFA. The relationship between RVR and regrowth was investigated.

RESULTS

The mean volume of thyroid nodules was 10.09 ± 12.90 ml (range 0.40-71.39 ml), which decreased significantly to 2.33 ± 4.65 ml (range 0-36.75 ml) (p < .001) after a mean follow-up time of 22.50 ± 13.29 months (range 6-68 months) with a mean VRR as 85.26 ± 15.02% (range 32.23-100%). The overall incidence of regrowth was 12.62% (26/206) and the mean timing of regrowth was 20.77 ± 12.03 months (range 6-48 months). Multivariate logistic regression revealed that RVR (OR = 1.050, 95%CI 1.025-1.075), initial volume(OR = 1.033, 95%CI 1.000-1.066), location close to critical structures (OR = 5.967, 95%CI 1.898-18.760) and vascularity (OR = 2.216, 95%CI 1.185-4.143) were independent factors associated with regrowth. According to receiver-operating characteristic curve, the area under curve for RVR to regrowth was 0.819 (95% CI 0.740-0.897, p < .001) with the optimal cutoff value of 44.5% (sensitivity 80.8%, specificity 74.7%).

CONCLUSION

RVR was not only an independent factor but also an early quantitative predictor for regrowth. If RVR was larger than 44.5%, the nodule tended to regrowth in the follow-up.

Histological Correlation for Radiofrequency and Microwave Ablation in the Local Control of Hepatocellular Carcinoma (HCC) before Liver Transplantation: A Comprehensive Review

Simple Summary

Liver cancer is a growing problem around the world. Drugs for liver cancer have limited effect, there are not enough donors for liver transplants and many patients are not candidates for surgery to remove the tumor. In many of these cases, hyperthermia can destroy the tumor in situ with minimally invasive methods such as radiofrequency or microwave ablation. In this paper we review the literature evaluating success rates for complete ablation as judged by actual examination of treated tumors that were removed when patients received a liver transplant. While notable successes can be achieved with ablation, the published studies indicate both that complete treatment is not as common as thought and that imaging methods such as computed tomography and magnetic resonance scans do not completely identify residual cancer. There is therefore an important opportunity for improvement in the treatment of this disease.

Abstract

Radiofrequency ablation (RFA) and microwave ablation (MWA) are the most widely studied and applied ablation techniques for treating primary and secondary liver tumors. These techniques are considered curative for small hepatic tumors, with post-ablation outcomes most commonly assessed by an imaging follow up. However, there is increasing evidence of a discrepancy between radiological and pathological findings when ablated lesions are evaluated following liver resection or liver transplantation. A comprehensive review of the available literature reporting the complete pathological response (cPR) following RFA and MWA was performed to estimate the success rate and identify the factors associated with treatment failure. Following RFA, cPR is reported in 26–96% of tumors compared to 57–95% with MWA. Larger tumor size and vessels larger than 3 mm adjacent to the treated tumor are the most important factors identified by previous studies associated with viable residual tumors after RFA. Correlating post-ablation radiological studies with pathological findings shows that computed tomography (CT) and magnetic resonance imaging (MRI) have low sensitivity but high specificity for detecting residual viable or recurrent hepatocellular carcinoma (HCC) tumors. There are promising recent reports combining multiprobe ablation techniques with three-dimensional treatment planning software and stereotactic-aiming instrumentation to achieve more than 90% cPR in both small and large HCC tumors. In conclusion, the reported success for achieving cPR in HCC following RFA and MWA is highly variable in different studies and decreases with increasing lesion size and unfavorable tumor characteristics. Very few studies have reported a high rate of cPR. As these studies are single-center and retrospective, they need to be further validated and reproduced in other clinical settings.

Uridine/UMP metabolism and their function on the gut in segregated early weaned piglets

Uridine monophosphate (UMP) is a major nucleotide analogue in mammalian milk and uridine (UR) is its gastro-intestinal metabolite in vivo. This study aims to investigate the functional effects of UMP and UR on the gut in vitro and in vivo. Twenty-one piglets were randomly allotted into three groups, the control group, UMP group and UR group, and orally administered UMP or UR for 10 days. Results showed that UMP and UR supplements improved the ADG of piglets, and decreased the diarrhea rate. UR increased the jejunum villus length/crypt depth ratio, Claudin-3 and E-cadherin expression, and the pyrimidine nucleotide metabolic enzymes including CMPK1, RRM2, UPRT, CTPS1 and CTPS2 in the duodenal mucosa. Both the UMP and UR decreased the expression of CAD and RRM2 at the jejunal mucosa. Moreover, UMP and UR increased the apoptosis ratio of intestinal epithelial cells in in vivo and in vitro experiments. Taken together, oral administration of UR and UMP could improve the small intestinal morphology, promote epithelial cell apoptosis and renewal of intestinal villus tips, and benefit intestinal development and health thus improving the growth performance and reducing the risk of diarrhea in early-weaned piglets.

Evaluation of liver lesions by use of shear wave elastography and computed tomography perfusion imaging after radiofrequency ablation in clinically normal dogs

OBJECTIVE To evaluate acute changes of the liver by use of shear wave elastography (SWE) and CT perfusion after radiofrequency ablation (RFA). ANIMALS 7 healthy Beagles. PROCEDURES RFA was performed on the liver (day 0). Stiffness of the ablation lesion, transitional zone, and normal parenchyma were evaluated by use of SWE, and blood flow, blood volume, and arterial liver perfusion of those regions were evaluated by use of CT perfusion on days 0 and 4. All RFA lesions were histologically examined on day 4. RESULTS Examination of the SWE color-coded map distinctly revealed stiffness of the liver tissue, which increased from the normal parenchyma to the transitional zone and then to the ablation zone. For CT perfusion, blood flow, blood volume, and arterial liver perfusion decreased from the transitional zone to the normal parenchyma and then to the ablation zone. Tissue stiffness and CT perfusion variables did not differ significantly between days 0 and 4. Histologic examination revealed central diffuse necrosis and peripheral hyperemia with infiltration of lymphoid cells and macrophages. CONCLUSIONS AND CLINICAL RELEVANCE Coagulation necrosis induced a loss of blood perfusion and caused tissue hardening (stiffness) in the ablation zone. Hyperemic and inflammatory changes of the transitional zone resulted in increased blood perfusion. Acute changes in stiffness and perfusion of liver tissue after RFA could be determined by use of SWE and CT perfusion. These results can be used to predict the clinical efficacy of RFA and to support further studies, including those involving hepatic neoplasia.

Understanding the nuances of microwave ablation for more accurate post-treatment assessment

Microwave ablation (MWA) is a relatively new thermal modality for minimally invasive procedures compared with radiofrequency ablation. Although MWA and radiofrequency ablation are thermal modalities, their underlying physics and principles greatly differ. Consequently, it is imperative that clinicians be aware of how these differences impact realized ablation volumes to consistently ensure technical success and better patient outcomes. This paper will review the nuances specific to MWA technology (i.e., tissue properties, perfusion/heat sink effect, ablation assessment, imaging accuracy and tissue contraction) that are often overlooked based on familiarity with conventional thermal modalities to guide more accurate assessment of post-treatment MWA volumes.

Study on the effect of chemoembolization combined with microwave ablation for the treatment of hepatocellular carcinoma in rats

PURPOSE

We aimed to evaluate the combining effects of transarterial chemoembolization (TACE) and open local thermal microwave ablation in a hepatocellular carcinoma animal model.

METHODS

Tumor cubes were implanted into the liver of 30 male inbred ACI rats. Groups of 10 animals were treated at 13 days (TACE or microwave ablation) and 16 days (microwave ablation) postimplantation with combined therapy of TACE (0.1 mg mitomycin C; 0.1 mg iodized oil; 5.0 mg degradable starch microspheres) and microwave ablation (2450 Mhz; 45 s; 35 W) (study group A), TACE alone (control group B), or microwave ablation alone (control group C). At day 12 and day 25 tumor size was measured via magnetic resonance imaging and the relative growth ratio was calculated. Hepatic specimens were immunohistochemically examined for the expression of vascular endothelial growth factor (VEGF).

RESULTS

Mean growth rates were 1.34±0.19 in group A, 3.19±0.13 in group B, and 4.18±0.19 in group C. Compared with control groups B and C, tumor growth rate in group A was significantly inhibited (P < 0.01). The VEGF-antibody reaction in peritumoral tissue (staining intensity at portal triad, percent antibody reaction and staining intensity at central vein) was significantly lower in group A compared with group B (P < 0.01). No significant difference between group A and group C could be observed.

CONCLUSION

This investigation shows improved results of TACE followed by microwave ablation as treatment of hepatocellular carcinoma in a rat model, compared with single therapy regimen regarding the inhibition of growth rate and reduction of VEGF-level in peritumoral tissue.

Chronological changes of radiofrequency ablation zone in rabbit liver: an in vivo correlation between gross pathology and histopathology

OBJECTIVE

To examine the gross pathology and histopathology of ablation zones created from radiofrequency (RF) ablation and to correlate their chronological changes.

METHODS

A total of 48 in vivo ablation zones (16 rabbit livers) were obtained immediately after and also 30 min, 1 h and 2 h after RF ablation and were subjected to haematoxylin and eosin (H&E) staining, nicotinamide adenine dinucleotide (NADH) diaphorase staining, terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. Chronological changes in gross pathology and histopathology were evaluated and correlated with each other.

RESULTS

Peripheral red zones on gross pathology correlated with peripheral zones on H&E staining, lightly stained peripheral zones on NADH staining and peripheral positive zones on TUNEL staining. Central white zones on gross pathology correlated with combined central and border zones on H&E staining, central negative zones on NADH staining and combined central-positive and middle-negative zones on TUNEL staining. Boundary visibility between central white and peripheral red zones on gross pathology was significantly higher at 1 and 2 h than immediately after RF ablation. As time increased after RF ablation, visibility of the border zone on H&E staining and the grade of positively stained hepatocytes in the peripheral zone on TUNEL staining increased.

CONCLUSION

Chronological changes in gross pathology of RF ablation zones correlated well with histopathology. The boundary between the central white and peripheral red zones tended to become clear at 1 h after RF ablation. Advances in knowledge: (1) RF ablation zones show chronological changes on gross pathology and histopathology. (2) Gross pathology and histopathology correlate well with each other.

Thermal and mechanical high-intensity focused ultrasound: perspectives on tumor ablation, immune effects and combination strategies

Tumor ablation technologies, such as radiofrequency-, cryo- or high-intensity focused ultrasound (HIFU) ablation will destroy tumor tissue in a minimally invasive manner. Ablation generates large volumes of tumor debris in situ, releasing multiple bio-molecules like tumor antigens and damage-associated molecular patterns. To initiate an adaptive antitumor immune response, antigen-presenting cells need to take up tumor antigens and, following activation, present them to immune effector cells. The impact of the type of tumor ablation on the precise nature, availability and suitability of the tumor debris for immune response induction, however, is poorly understood. In this review, we focus on immune effects after HIFU-mediated ablation and compare these to findings using other ablation technologies. HIFU can be used both for thermal and mechanical destruction of tissue, inducing coagulative necrosis or subcellular fragmentation, respectively. Preclinical and clinical results of HIFU tumor ablation show increased infiltration and activation of CD4⁺ and CD8⁺ T cells. As previously observed for other types of tumor ablation technologies, however, this ablation-induced enhanced infiltration alone appears insufficient to generate consistent protective antitumor immunity. Therapies combining ablation with immune stimulation are therefore expected to be key to boost HIFU-induced immune effects and to achieve systemic, long-lasting, antitumor immunity.

Quantitative evaluation of striated muscle injury by multiscale blob features method

PURPOSE

This study aimed to use the multiscale blob feature (MBF) method to quantitatively evaluate porcine striated muscle injuries.

METHODS

A porcine striated muscle injury model was induced by microwave ablation and anhydrous acetic acid injection, respectively. Then, both 2D sonographic and histological features of the lesions were recorded and compared. Later, MBF was used to quantitatively evaluate the porcine striated muscle injuries by extracting the texture features from the 2D ultrasonogram via measuring eight textural parameters (Mean, SDev, NOB, [Formula: see text], [Formula: see text], HOD, DOD, and POD).

RESULTS

Microwave ablation produced oval or round-like lesions, which had a pale gray color, with an echo attenuation detected at lesion center due to carbonization; anhydrous acetic acid injection produced long, stripped lesions, which had a slate-gray color, with a gas-like intense echo at lesion center. There were significant differences in Mean, [Formula: see text] and POD between the muscle samples treated by microwave ablation and the control samples, as well as significant differences in NOB, [Formula: see text] and POD between the muscle samples treated by anhydrous acetic acid injection and the control. There were significant differences in Mean, [Formula: see text], NOB, and [Formula: see text] between the muscle samples treated by microwave ablation and those treated by anhydrous acetic acid injection.

CONCLUSION

Quantitative evaluation of striated muscle injuries using the MBF method was able to differentiate the muscle injuries caused by microwave ablation and anhydrous acetic acid injection, suggesting that this method may be a potential and reliable tool for quantitative evaluation of muscle injuries.

Thermal Ablative Therapies and Immune Checkpoint Modulation: Can Locoregional Approaches Effect a Systemic Response?

Percutaneous image-guided ablation is an increasingly common treatment for a multitude of solid organ malignancies. While historically these techniques have been restricted to the management of small, unresectable tumors, there is an expanding appreciation for the systemic effects these locoregional interventions can cause. In this review, we summarize the mechanisms of action for the most common thermal ablation modalities and highlight the key advances in knowledge regarding the interactions between thermal ablation and the immune system.

Thermal tissue change induced by a microwave surgical instrument in a rat hepatectomy model

BACKGROUND

Microwaves exhibit great potential in tissue heating, which causes effective coagulation. Using this energy, we have developed the microwave coagulation surgical instrument (MWCX) for clinical application. Here, we characterized the impact of MWCX on tissues including heating property, tissue change, and spread of thermal injury.

METHODS

Hepatectomy was performed with MWCX using a rat model. The resections were completed using various energy levels and powers. Tissue temperature during radiation was recorded. Tissue change and lateral thermal injury (LTI) was assessed immediately, 7 days, 3 months, and 6 months after resection.

RESULTS

All cutting and hemostasis procedures were successfully accomplished. Major histologic findings consisted of deformation or destruction of hepatocytes, tissue edema, and peripheral hemorrhage. At various energy levels, 200 to 1000 J, the tissue was heated up to approximately 80°C to 140°C causing 2.7- to 6.5-mm LTI on the 7th day. LTI was then decreased gradually in the following term. At certain energy levels, the application of neither 20 W nor 40 W induced significant difference in both heating and LTI.

CONCLUSIONS

MWCX achieved effective tissue coagulation with relevant tissue injury, and it should be a good candidate for clinical application.

Microwave ablation treatment of liver cancer with a 2,450-MHz cooled-shaft antenna: pilot study on safety and efficacy

To evaluate efficacy of microwave ablation in a primary clinical study, sixty patients (44 men, 16 women; mean age 53 years) with 96, 1-8 cm (mean 3.20 ± 0.17 cm) liver cancers were treated with 2,450-MHz internally cooled-shaft antenna. Complete ablation (CA) and local tumor progression (LTP) rates as well as complications were determined. CA rates in small (<3.0 cm), intermediate (3.1-5.0 cm) and large (5.1-8.0 cm) liver cancers were 96.4% (54/56), 92.3% (24/26) and 78.6% (11/14), respectively. During a mean follow-up period of 17.17 ∓ 6.52 months, LTP occurred in five (5.21%) treated cases. There was no significant difference in the CA and LTP rates between the HCC and liver metastasis patient subgroups (P<0.05). Microwave ablation provides a reliable, efficient, and safe technique to perform hepatic tumor ablation.

Microwave ablation of the liver: a description of lesion evolution over time and an investigation of the heat sink effect

AIM

Microwave ablation has been successfully used to treat unresectable liver tumours for many years. However, despite its widespread use, there seems to be a relative paucity of experimental data regarding lesion evolution and the effects of any surrounding vasculature on ablation morphology. The aim of this study was to investigate the principal pathological changes in the liver following microwave ablation, in particular the heat sink effect. In addition we carefully reviewed the available literature to provide an overview of all relevant pathological studies.

METHODS

Microwave ablation was carried out on male rats at various distances from the hilum. Histological (H&E) and immunocytochemical (caspase 3) analyses of the lesion were performed at various time points; 0, 4, 24, 48  hours, 2 weeks and 1 month. A literature review was carried out using Medline, Embase and the Cochrane database to identify all relevant histological studies.

RESULTS

The lesion underwent complete coagulative necrosis and was extremely regular at the ablation edge with no evidence of any influence from surrounding blood vessels at all time points. H&E and caspase 3 results were consistent and microwave caused little collateral damage outside the intended ablation zone.

CONCLUSION

This study suggests that microwave ablation is extremely concise and is minimally affected by the heat sink effect. Comparative investigations with other treatment modalities are required.

Development of a highly efficient implanted thermal ablation device: in vivo experiment in rat liver

OBJECTIVES

To evaluate an implanted thermal ablation device that can be heated with high efficiency using a resonant circuit as the implant.

METHODS

16 rats were used. The implants, adjusted at a resonance frequency of 4 MHz, were fixed on the surface of the liver of rats under laparotomy. In 14 of 16 rats, an alternating magnetic field (AMF) was applied for 6 min with an output of 300 W from outside the body using a ferrite core applicator. The implant temperature during AMF exposure was measured. The 14 rats were divided into 5 groups, depending on time from AMF application until they were sacrificed (1 h, 1 day, 3 days, 7 days and 1 month after application). Two rats not exposed to AMF were used as controls. Livers were removed and evaluated; the cross-sectional area and width of the ablated region were measured.

RESULTS

During AMF exposure, the implant temperature rose to 127.8±39.3 °C (mean±standard deviation). The cross-sectional area of the ablated region was largest after 1 day and tended to decrease with time. The widths of the ablated region were 4.87±0.22 mm, 4.15±0.36 mm, 3.67±0.58 mm and 3.24±0.16 mm in the 1 day, 3 day, 7 day and 1 month groups, respectively. No significant differences (p<0.05) were seen in either cross-sectional area or width of the ablated region.

CONCLUSION

Sufficient heat for ablation was obtained in vivo using a newly developed implanted thermal ablation device. This device may be a new option for thermal ablation therapy.

Microwave ablation treatment of liver cancer with 2,450-MHz cooled-shaft antenna: an experimental and clinical study

PURPOSE

To evaluate effects of microwave ablation with a 2,450-MHz internally cooled-shaft antenna in animal experiments and in a clinical study.

METHODS

Microwave ablation was performed using a cooled-shaft antenna in eight in vivo (36 ablations) porcine livers. The coagulation diameters achieved in different microwave ablation parameter groups were compared. Sixty patients (44 men, 16 women; mean age 53 years) with 96, 1-8 cm (mean 3.20 +/- 0.17 cm) liver cancers were treated with the same microwave ablation technique. Complete ablation (CA), local tumor progression (LTP) rates and complications were determined.

RESULTS

In vivo livers, short axis diameter correlated with the coagulation duration in a sigmoidal curve fashion (60-W group R(2) = 0.76, 80-W group R(2) = 0.87), with a relative plateau achieved within 10 min for power settings of 60 or 80 W. Within 10 min in the 60 and 80-W groups, respectively, 89 and 85.76% of maximum short axis diameter were achieved. CA rates in small (3.0 cm), intermediate (3.1-5.0 cm) and large (5.1-8.0 cm) liver cancers were 96.43% (54/56), 92.31% (24/26) and 78.57% (11/14), respectively. During a mean follow-up period of 17.17 +/- 6.52 months, LTP occurred in five (5.21%) treated cancers. There was no significant difference in the CA and LTP rate between the HCC and liver metastasis patient subgroups (P > 0.05).

CONCLUSIONS

The short axis diameter enlargement has a relative plateau within 10 min by fixing power output to 60 or 80 W, using the 2,450-MHz internally cooled-shaft antenna in vivo porcine livers. Effective local tumor control was achieved during one microwave ablation session.

Thermal ablation for unresectable liver tumours, time to move forward?

Even with the advent of laparoscopic techniques for liver tumours, classic resections still represent a major undertaking for numerous liver lesions. The avoidance of surgery using ablative techniques has been the aim for over 20 years. Large volumes can now be rapidly treated with low morbidity with the many technical developments and modifications of the delivery probes. Despite these advances recurrences rates remain high with all of the presently available techniques. The biological and pathophysiological basis underlying may help explain their limitations and are important in understanding where they may be appropriately applied and ways in which they may be improved in the future.

Hepatic microwave ablation: a review of the histological changes following thermal damage

Microwave (MW) ablation therapy is a local treatment by which tumours are destroyed by coagulation from the passage of MWs into cells. The aim of this review is to examine histological results obtained from preclinical and clinical studies. A literature search was undertaken for all studies focusing on MW therapy and in which lesions were excised for a complete histopathological examination after treatment. Two main zones were described after ablative therapy (central and transitional). Both corresponded to specific microscopic characteristics and evolved over time in a precise manner. No viable cells even up to 6 cm in diameter were demonstrated in 93% of lesions after treatment. Microwave therapy is a reliable technique under a variety of clinical situations. Future investigations are needed to compare MW with other ablative techniques to identify factors that influence the effectiveness of the various techniques and to determine specific indications.

Novel tumor-ablation device for liver tumors utilizing heat energy generated under an alternating magnetic field

BACKGROUND AND AIMS

We have developed a novel tumor-ablation device for liver tumors utilizing heat energy induced by magnesium ferrite (MgFe(2)O(4)) particles under an alternating magnetic field (AMF) produced by electric currents. This novel device can repeatedly heat liver tumors at lower temperature than usual heating devices, such as radiofrequency ablation therapy, with slight infliction of pain. This study assesses its heating effect on rat liver tumors as local therapy.

METHOD

The small needle was manufactured from MgFe(2)O(4) particles by sintering at 1100 degrees C. After a MgFe(2)O(4) needle was inserted into liver tumors comprising of dRLh-84 cells, the tumors were heated for 30 min under an AMF. We examined cellular activity by using nicotinamide adenine dinucleotide (NADH) diaphorase staining and terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) staining, and evaluated the effect of suppressing tumor growth by sequentially comparing the tumor diameter with that of the control group.

RESULTS

The mean temperature of the heated tumors was 60.2 +/- 1.8 degrees C. The tumor cells were constricted, and chromatin of nuclei had shrunk immediately after heating. The heat-injury area that contained the tumors was negative for NADH diaphorase activity. After 3 days, the tumor cells in the heat-injury area became positive for TUNEL staining, which detects cell death. At 7 days, the mean tumor diameters were significantly smaller in the heating group than in the control group (6.15 +/- 0.47 mm vs 16.89 +/- 2.69 mm; P < 0.05).

CONCLUSION

This device, utilizing heat energy induced by ferromagnetic metal under an AMF, appears useful as local thermotherapy for human liver cancer.

Analysis of apoptosis and cell proliferation after high intensity-focused ultrasound ablation combined with microbubbles in rabbit livers

OBJECTIVE

To analyze apoptosis and expression of proliferating cell nuclear antigen (PCNA) sequentially in the rabbit liver tissue after high-intensity focused ultrasound (HIFU) ablation combined with microbubbles.

METHODS

Fifty rabbits were divided into two groups randomly. Rabbits in group I received injections with ultrasound contrast agent Sonovue, before HIFU ablation, on their livers and those in group II were ablated by a single HIFU exposure without microbubbles. Rabbits were killed on days 0, 1, 3, 7 and 14 after HIFU ablation. The livers were excised for light microscopic examination with hematoxylin and eosin staining, immunohistochemical staining for PCNA expression and terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick end labeling (TUNEL) staining for apoptosis.

RESULTS

A fibra tissue band composed of fibrocytes and capillary vessels, which was detected by light microscope in the rim of the targeted area after 3 days in group I, was wider than that in group II. The apoptosis index (the number of apoptotic events divided by the total cell number in the same field) and PCNA-positive index (the number of PCNA-positive cells divided by the total cell number in the same field) in group I on days 0, 1, 3, 7 and14 after HIFU ablation were higher than those in group II.

CONCLUSION

Microbubbles can improve the apoptosis and cell proliferation in zones surrounding coagulated necrosis areas after HIFU ablation, which may be explored to benefit enhanced HIFU treatment.

Study of sequential histopathologic changes, apoptosis, and cell proliferation in rabbit livers after high-intensity focused ultrasound ablation

OBJECTIVE

The purpose of this study was to investigate the sequential changes of rabbit liver tissue after high-intensity focused ultrasound (HIFU) ablation in histopathologic characteristics, apoptosis, and expression of proliferating cell nuclear antigen (PCNA).

METHODS

Thirty-five rabbits were anesthetized and received HIFU ablation on livers after laparotomy. Rabbits were killed at 0, 1, 24, 72, 144, 216, and 336 hours after HIFU ablation. The livers were cut off and examined under a light microscope with hematoxylin-eosin staining and under a transmission electron microscope. Proliferating cell nuclear antigen expression was detected by immunohistochemical staining, and apoptosis was observed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling (TUNEL).

RESULTS

After HIFU ablation, fibra bands were detected under the light microscope in the rim of targeted areas after 72 hours, and the band became wide sequentially. Cells labeled by TUNEL and PCNA-positive cells were detected to different extents in surrounding tissues but not in targeted areas at 0, 1, 24, 72, 144, 216, and 336 hours after HIFU ablation. The apoptosis index detected by TUNEL reached a peak value at 72 hours after ablation, and the highest PCNA-positive index was found at 144 hours after ablation. Apoptotic bodies and oncotic mitochondria in surrounding areas were observed under the electron microscope.

CONCLUSIONS

After HIFU ablation, coagulated necrotic tissues became organized and fibra encapsuled gradually. Apoptosis and cell proliferation were detected in surrounding areas, which provided some implications for controlling HIFU treatment, although thermometry was not done to correlate the HIFU region with the cellular damage region, limiting correlation of the results.

Experimental study on microwave tissue coagulation of canine pancreas

AIM: To evaluate the feasibility and safety of microwave tissue coagulation to pancreas through the observation of physiological state and pathological changes after the coagulation of canine pancreas.

METHODS: Microwave tissue coagulation of fifteen healthy mongrel dogs' pancreas was performed hrough laparotomy. The power and time were set on 50 Watt and three minutes respectively. The 5 coagulated points were selected at an interval of 1 cm. The blood amylase and other parameters were examined regularly after the operation. The dogs were killed at the instant time (n = 5), the 1^st d (n = 5) and 1^st wk (n = 5) after the operation. Hematoxylin and eosin (HE) staining together with nicotinamide adenine dinucleotide (NADH) and TUNEL staining was used to observe the pathological changes.

RESULTS: The level of blood amylase increased immediately after the operation and the maximal value occurred within 48-72 h. Furthermore, it returned to normal level 1 wk later if no complications occurred. The segmental microwave lesions included hyperintense zone of coagulative necrosis and peripheral hypointense zone. Apoptosis was observed at the peripheral zone 1 d after the operation. The fibrosis and tissue absorption occurred finally 1 wk after the operation.

CONCLUSION: Microwave tissue coagulation is safe and feasible, and it may be used in the treatment of pancreatic cancer at the late stage.

Patterns of heat shock protein (HSP70) expression and Kupffer cell activity following thermal ablation of liver and colorectal liver metastases

The time course and extent of thermal ablative injury differs in liver compared to tumour tissue. This may be influenced by differences in the expression of heat shock proteins (HSP) and the response of Kupffer cells to thermal injury. This study determines the expression and response of HSP70 and Kupffer cells to thermal ablative injury in a Murine model of colorectal liver metastases. Thermal ablation by laser (Nd-YAG wavelength 1064 nm) was induced in liver and colorectal cancer liver metastases in CBA strain mice. Laser energy was applied at 2 W for 50 s and produced incomplete tumour ablation. Established tissue injury was assessed in separate groups of animals at time points ranging from 12 h to 21 days following therapy. HSP70 and Kupffer cell expression at the margins of coagulated tissue was determined by immunohistochemical staining for HSP70 and F4/80 antigens, respectively. HSP70 was faintly expressed in the cytoplasm of all tumour cells, with distinct clusters exhibiting intense cytoplasmic and nuclear HSP70 staining (130+/-19 cells mm-2). Comparatively, HSP70 expression was uncommon in untreated control liver specimens (2+/-2 cells mm-2, p<0.001). Thermal ablation increased expression of HSP70 at coagulated tissue margins. The peak response in tumours occurred at 2 days post-ablation and was significantly greater than the peak response in liver, occurring at 12 h (809+/-80 cells mm-2 vs. 454+/-52 cells mm-2, p<0.001). HSP70 expression remained significantly elevated for 7 days following therapy in tumour tissue, compared to 3 days in liver. Kupffer cell numbers in untreated control tumours were significantly lower than in untreated control livers (285+/-23 cells mm-2 vs. 451+/-30 cells mm-2, p<0.001). Following thermal ablation, there was an initial decrease in Kupffer cell numbers at the margin of coagulation with subsequent persistent increases thereafter. In liver tissue, the peak Kupffer cell response occurred at 5 days post-therapy and was significantly greater than the peak response in tumour tissue 3 days post-thermal ablation (1074+/-34 cells mm-2 vs. 860+/-53 cells mm-2, p=0.007). Thermal ablation produces a greater and more prolonged HSP70 response in colorectal liver metastases than in liver tissue. It also induces persistent increases in Kupffer cell activity in liver and tumour tissue.

Radiofrequency versus microwave ablation in a hepatic porcine model

PURPOSE

To compare microwave (MW) and radiofrequency (RF) ablation in a hepatic porcine model.

MATERIALS AND METHODS

Institutional animal research committee approval was obtained. Nineteen pigs were divided into groups based on time of sacrifice (group A, immediate; group B, 2 days; group C, 28 days; group D, 28 days). Groups A, B, and C each underwent a combination of RF and MW ablation. Group D underwent either four MW or four RF ablations. Ablation was performed with a prototype MW device (915 Mhz, 40 W, 10 minutes) and a commercial RF system (150 W, 10 minutes, 3-cm deployment). Computed tomography (CT) was performed in groups B and C at 2 days and in group C at 28 days. Group D underwent serial laboratory testing. Specimens were serially sectioned, and short-axis diameter and length of each were measured. The percentage deflection caused by local blood vessels (heat-sink effect) was also measured in group A. Likelihood ratio tests and unpaired t tests were used for statistical analyses as appropriate.

RESULTS

MW ablation zones were longer at days 0, 2, and 28 (P < .05), but short-axis diameter was not different from that with RF ablation at any time point (P > .05). Local blood vessels caused 3.5% +/- 5.3 (standard deviation) deflection at MW ablation compared with 26.2% +/- 27.9 at RF ablation (P < .05). MW and RF ablation zones were indistinguishable at CT or pathologic evaluation. Laboratory test results were similar between RF ablation-only animals and MW ablation-only animals, with the exception of a slightly higher alkaline phosphatase levels at day 2 in RF ablation-only animals (P < .02).

CONCLUSION

MW and RF ablation zones are similar in pathologic appearance and imaging characteristics. Increased length with MW ablation is likely caused by the length of the radiating segment of the antenna. MW ablation may be less affected by the heat-sink effect that is thought to contribute to local recurrence after RF ablation.

Mechanisms of Focal Heat Destruction of Liver Tumors

BACKGROUND

Focal heat destruction has emerged as an effective treatment strategy in selected patients with malignant liver tumors. Radiofrequency ablation, interstitial laser thermotherapy, and microwave treatment are currently the most widely applied thermal ablative techniques. A major limitation of these therapies is incomplete tumor destruction and overall high recurrences. An understanding of the mechanisms of tissue injury induced by focal hyperthermia is essential to ensure more complete tumor destruction. Here, the currently available scientific literature concerning the underlying mechanisms involved in the destruction of liver tumors by focal hyperthermia is reviewed.

METHODS

Medline was searched from 1960 to 2004 for literature regarding the use of focal hyperthermia for the treatment of liver tumors. All relevant literature was searched for further references.

RESULTS

Experimental evidence suggests that focal hyperthermic injury occurs in two distinct phases. The first phase results in direct heat injury that is determined by the total thermal energy applied, tumor biology, and the tumor microenvironment. Tumors are more susceptible to heat injury than normal cells as the result of specific biological features, reduced heat dissipating ability, and lower interstitial pH. The second phase of hyperthermic injury is indirect tissue damage that produces a progression of tissue injury after the cessation of the initial heat stimulus. This progressive injury may involve a balance of several factors, including apoptosis, microvascular damage, ischemia-reperfusion injury, Kupffer cell activation, altered cytokine expression, and alterations in the immune response. Blood flow modulation and administration of thermosensitizing agents are two methods currently used to increase the extent of direct thermal injury. The processes involved in the progression of thermal injury and therapies that may potentially modulate them remain poorly understood.

CONCLUSION

Focal hyperthermia for the treatment of liver tumors involves complex mechanisms. Evidence suggests that focal hyperthermia produces both direct and indirect tissue injury by differing underlying processes. Methods to enhance the effects of treatment to achieve complete tumor destruction should focus on manipulating these processes.

Disruption of erythrocytes distinguishes fixed cells/tissues from viable cells/tissues following microwave coagulation therapy

Microwave coagulation therapy (MCT) has recently been applied to treat hepatic tumors. However, the histological changes in the liver following MCT have not been fully elucidated. A type of cell death known as microwave fixation has been reported in areas adjacent to the microwave irradiator electrodes, and these areas are without acid phosphatase (AcP) activity. Diagnosis of microwave-fixed tissue by hematoxylin and eosin (HE) staining is very difficult because morphology is well maintained for months. In an effort to clarify the histological changes and the mechanisms of microwave fixation, we performed HE staining, enzyme histochemistry for AcP, and electron microscopy in both rat and human liver samples after MCT. Although the microwave-fixed tissues maintained their structure on HE staining, membranes of microwave-fixed cells were seriously damaged and there were no apparent organelle structures in these cells on electron microscopy. Erythrocytes were also damaged in these tissues on both light and electron microscopy. The cause of microwave fixation is thought to be injury of the membrane, which is similar to coagulative necrosis. In conclusion, microwave fixation can be considered a type of coagulative necrosis without enzyme digestion. Disruption of erythrocytes on HE staining is an interesting and important diagnostic clue in distinguishing nonviable fixed tissues from viable tissues following MCT.

Study of apoptosis and heat shock protein (HSP) expression in hepatocytes following radiofrequency ablation (RFA)

BACKGROUND

Radiofrequency ablation (RFA) of the liver produces necrosis of the hepatocytes. Histological examination shows a sharp demarcation between ablated and normal liver tissue. This experiment was carried out to study the cellular injury produced by RFA in area surrounding the ablated tissue and effect of reperfusion on this zone.

MATERIAL AND METHODS

Five pigs underwent RFA of liver parenchyma. Four pigs were sacrificed 30 min after RFA and one pig was sacrificed 5 days later. Ablated lesions including surrounding liver parenchyma was examined for apoptosis and HSP 70 expression.

RESULTS

There was a zone of transition surrounding the necrotic ablated area that showed apoptosis as well as increased HSP 70 expression. This was more prevalent in the pig that was sacrificed 5 days later.

CONCLUSION

RFA produces sub lethal injury in the zone of transition causing apoptosis and increase in HSP 70 expression. Increased HSP expression enhances immunogenicity of these cells that can have therapeutic implications for the treatment of liver.

Progressive microvascular injury in liver and colorectal liver metastases following laser induced focal hyperthermia therapy

BACKGROUND AND OBJECTIVES

Focal hyperthermia by laser or radiofrequency is currently the preferred method for local ablation of liver tumors. The underlying mechanism of action of focal hyperthermia, in particular the relationship between the microvascular and tissue effect is uncertain and was investigated in a murine model.

STUDY DESIGN/MATERIALS AND METHODS

Focal hyperthermia produced by a Neodymium-Yttrium-Aluminium-Garnet laser (wavelength 1,064 nm) was applied to the normal liver and colorectal cancer liver metastases in inbred male CBA strain mice at 2 W for 50 seconds (100 J). Tissue injury was assessed at 0, 24, 48, 72, 120, and 168 hours following therapy by measurements of necrosis in tissue sections stained for nicotinamide adenine dinucleotide (NADH) diaphorase activity. Characteristics of microvascular injury were assessed at the various time points by scanning electron microscopy (SEM) of vascular resin casts, Laser Doppler flowmetry, and confocal in vivo microscopy.

RESULTS

Focal hyperthermia produced progressive tissue and vascular injury. There was an initial reduction in blood flow and increased vascular permeability in the microcirculation of both tumor and liver tissue immediately following heat application as assessed by laser Doppler flowmetry and confocal in vivo microscopy, respectively. SEM of vascular casts showed heterogeneous regions of microvascular injury immediately following heat application. The extent of initial vascular disruption or occlusion on SEM of vascular resin casts (mean+/-SE) was significantly less than the tissue necrosis in liver (1.9+/-0.1 mm vs. 3.0 mm+/-0.2 mm P<0.001), but was equivalent to the tissue injury in tumor tissue (3.5 mm+/-0.2 mm vs. 3.6 mm+/-0.1 mm P = 0.907). This was followed by a progressive increase in both microvascular and tissue injury in liver and tumor that peaked by 72 hours following treatment. The peak microvascular injury and tissue damage in liver (6.6 mm+/-0.2 and 6.3 mm+/-0.2 mm, respectively) was significantly greater than the extent of microvascular and tissue damage in tumors (4.8 mm+/-0.2 mm and 4.5 mm+/-0.2 mm, respectively) (P<0.001). The progression of microvascular injury in liver and tumor at times preceded the tissue injury.

CONCLUSION

Focal hyperthermia produces both progressive microvascular and tissue damage in liver and colorectal liver metastases. An increase in tissue injury following focal hyperthermia may be a direct result of progressive microvascular damage. Tumor vessels appear more susceptible to direct focal hyperthermia destruction than liver sinusoids. The liver sinusoids are however more susceptible to progressive damage or occlusion following the initial laser thermal stimulus.

Microwave cell death: Immunohistochemical and enzyme histochemical evaluation

In Japan, microwave coagulation therapy (MCT) has been used for the management of primary and metastatic liver cancer. Needle biopsy examination from the lesion has frequently shown the presence of nucleated cancer cells in histopathological examinations, prompting the conclusion that cancer cells are not completely eliminated by microwave therapy, whereas computed tomography and ultrasonography examinations show tumor regression. To determine whether microwave-treated tissue contains functionally viable cells, an examination of the Na+-K+-ATPase protein and its activity using immunohistochemical and enzyme histochemical methods were carried out in microwave-treated rat liver. Four concentric, morphologically identifiable zones around the microwave probe needle appeared 2 days after treatment. Zone A, which was between the innermost spongy zone and the outer necrotic zone, contained only slight morphological alterations in the hepatocytes, which had slightly hyperchromatic nuclei and mildly eosinophilic cytoplasm. The hepatocytes in zone A were found to be positive for the Na+-K+-ATPase antigenicity but negative for enzyme activity, indicating that zone A was undergoing cell death, although morphologically this was not discernible. This type of cell death caused by microwave treatment is morphologically different from previously known types of cell death, either oncosis or apoptosis.

Thermal ablative therapy for malignant liver tumors: a critical appraisal

The management of primary and secondary malignant liver tumors poses a great challenge to clinicians. Although surgical resection is the gold-standard treatment, most patients have unresectable malignant liver tumors. Over the past decade, various modalities of loco-regional therapy have gained much interest. Among them, thermal ablative therapy, including cryotherapy, microwave coagulation, interstitial laser therapy, and radiofrequency ablation (RFA), have been proven to be safe and effective. Despite the effective tumor eradication achieved within cryotherapy, the underlying freeze/thaw mechanism has resulted in serious complications that include bleeding from liver cracking and the 'cryoshock' phenomenon. Thermal ablation using microwave and laser therapy for malignant liver tumors is curative and is associated with minimal complications. However, this treatment modality is effective only for tumors <3 cm diameter. Radiofrequency ablation seems to be the most promising form of thermal ablative therapy in terms of a lower complication rate and a larger volume of ablation. However, its use is restricted by the difficulty encountered when using imaging studies to monitor the areas of ablation during and after the procedure. Moreover, the techniques of RFA need to be refined in order to achieve the same oncological radicality of malignant liver tumors as achieved by surgical resection. As each of the loco-regional therapies has its own advantages and limitations, a multidisciplinary approach using a combination of therapies will be the future trend for the management of malignant liver tumors.

Histologic Evaluation and Treatment Outcome after Sequential Radiofrequency Ablation and Hepatic Resection for Primary and Metastatic Tumors

Operative manipulation during hepatic resection (HR) causes tumor cell shedding which is a factor in disease recurrence. Radiofrequency ablation (RFA) causes coagulative necrosis and was used to destroy the tumor before HR. We evaluated tumor necrosis and recurrence of hepatic malignancies treated by sequential RFA/HR. A retrospective review of patients treated with sequential RFA/HR from April 1999 to January 2002 was performed. A Radionics 500-kW RF generator was used to ablate lesions via H2O-cooled electrodes under ultrasound guidance. Segmental HR was performed after RFA. Resected specimens were reviewed with hematoxylin and eosin staining and for apoptosis. Patient follow-up ranged from 10 to 33 months with evaluation of salient clinical, radiologic, and laboratory parameters. Seven patients (four male and three female) ages 62.1 ± 10.3 years had sequential RFA/HR. Four patients had hepatocellular carcinoma (HCC) and three had colorectal metastases (CRm). The tumors were unifocal right-lobe lesions measuring 4.1 ± 0.9 cm with a resection margin of 0.4 to 2.5 cm. Extensive necrosis was noted but intact nests of tumor cells occurred in all specimens with minimal apoptosis. Three of seven patients (two HCC and one CRm) developed pulmonary metastases at 3 to 20 months with one HCC patient developing concurrent liver metastases. Two deaths occurred in the HCC group. Sequential RFA/HR may minimize local recurrence; however, the high incidence of pulmonary metastases raises concern of transvenous migration. The histologic findings demonstrate foci of intact tumor cells after RFA. Controlled study of additional patients with long-term follow-up is necessary to better understand these findings.

Microwave coagulation therapy accelerates growth of cancer in rat liver

BACKGROUND/AIMS

Although microwave coagulation therapy (MCT) has been performed for liver cancer, there has been no report examining the influence of this therapy on the growth of possible remnant cancer.

METHODS

A solid cube of AH-130 cells (ascites hepatoma cell line) was implanted into the left lateral lobe of the rat liver. Five days later, MCT was applied to the middle liver lobe of these rats. Tumor growth and cytokine levels in plasma and the liver were compared between rats that underwent MCT and rats that did not.

RESULTS

The mean tumor weight in the MCT group (222.6+/-51.5 mg, mean+/-SD) was significantly greater than that in the control group (126.7+/-19.7 mg, P<0.01) at postoperative day (POD) 5. Immunohistochemistry for anti-proliferating cell nuclear antigen showed the labeling index in the MCT group (90.4%) to be higher than that in the control group (76.7%, P<0.01). Liver basic fibroblast growth factor and transforming growth factor-beta 1 levels in the MCT group on POD 3 were significantly higher than levels in the control group.

CONCLUSIONS

The present study suggests the clinically important finding that MCT accelerates the growth of small residual tumors in the liver.