Thermal protection with 5% dextrose solution blanket during radiofrequency ablation

American Association of Clinical Endocrinology Disease State Clinical Review: The Clinical Utility of Minimally Invasive Interventional Procedures in the Management of Benign and Malignant Thyroid Lesions

OBJECTIVE

The objective of this disease state clinical review is to provide clinicians with a summary of the nonsurgical, minimally invasive approaches to managing thyroid nodules/malignancy, including their indications, efficacy, side effects, and outcomes.

METHODS

A literature search was conducted using PubMed and appropriate key words. Relevant publications on minimally invasive thyroid techniques were used to create this clinical review.

RESULTS

Minimally invasive thyroid techniques are effective and safe when performed by experienced centers. To date, percutaneous ethanol injection therapy is recommended for recurrent benign thyroid cysts. Both ultrasound-guided laser and radiofrequency ablation can be safely used for symptomatic solid nodules, both toxic and nontoxic. Microwave ablation and high-intensity focused ultrasound are newer approaches that need further clinical evaluation. Despite limited data, encouraging results suggest that minimally invasive techniques can also be used in small-size primary and locally recurrent thyroid cancer.

CONCLUSION

Surgery and radioiodine treatment remain the conventional and established treatments for nodular goiters. However, the new image-guided minimally invasive approaches appear safe and effective alternatives when used appropriately and by trained professionals to treat symptomatic or enlarging thyroid masses.

Minimally invasive treatment of pediatric head and neck dermoids: percutaneous drainage and radiofrequency coblation

BACKGROUND

Dermoids are common benign head and neck cysts in children containing a variety of different skin elements. Current standard treatment is surgical removal that sometimes requires extensive dissection to ensure complete resection and often leaves unwanted facial scarring. A minimally invasive treatment alternative should offer a similar rate of success with a decrease in operative complexity, recovery time and postoperative scarring.

OBJECTIVE

To assess the outcomes of our minimally invasive percutaneous treatment of head and neck dermoids, we reviewed our 9-year interventional radiology (IR) department experience.

MATERIALS AND METHODS

The medical records, imaging and procedural details were reviewed from a cohort of pediatric patients with dermoids treated in our IR department from January 2009 through February 2018. Patients in the study underwent ultrasound (US)-guided cyst puncture, 3% Sotradecol (sodium tetradecyl sulfate [STS]) emulsification of the thick cyst contents allowing complete drainage, and radiofrequency coblation of the cyst wall.

RESULTS

In this retrospective study, we report on 22 dermoids in 21 patients. The average patient age was 3 years. Twenty-one of the 22 dermoids were successfully treated for an overall success rate of 95%. Four intraosseous dermoids were successfully treated using computed tomography (CT) guidance instead of, or in addition to, US. Average follow-up time was 22 months.

CONCLUSION

The combination of percutaneous cyst drainage using STS as an emulsifying agent followed by radiofrequency coblation is a safe, effective, minimally invasive treatment for pediatric patients with head and neck dermoids.

Immediate Clinical Success After Percutaneous Ablation of Extra-adrenal Paraganglioma

Paragangliomas (PGLs) are catecholamine-secreting neoplasms of chromaffin cells and represent a rare but curable cause of secondary hypertension. Surgery is the treatment of choice for symptomatic PGLs. A small (7 mm) extra-adrenal PGL was diagnosed in the right retroperitoneal space in a 19-year-old patient affected by symptomatic hypertension unresponsive to medical treatment. Indication to percutaneous radiofrequency ablation (RFA) was given by a multidisciplinary team on the basis of the size of the nodule, the surgical risks, the young age of the patient, and his wish to reduce as much as possible the post-interventional rehabilitation. To our knowledge, the use of percutaneous RFA in the treatment of retroperitoneal extra-adrenal primary paragangliomas has never been described. We describe its feasibility and the patient's clinical outcome.

Effect of a poloxamer 407-based thermosensitive gel on minimization of thermal injury to diaphragm during microwave ablation of the liver

AIM

To assess the insulating effect of a poloxamer 407 (P407)-based gel during microwave ablation of liver adjacent to the diaphragm.

METHODS

We prepared serial dilutions of P407, and 22.5% (w/w) concentration was identified as suitable for ablation procedures. Subsequently, microwave ablations were performed on the livers of 24 rabbits (gel, saline, control groups, n = 8 in each). The P407 solution and 0.9% normal saline were injected into the potential space between the diaphragm and liver in experimental groups. No barriers were applied to the controls. After microwave ablations, the frequency, size and degree of thermal injury were compared histologically among the three groups. Subsequently, another 8 rabbits were injected with the P407 solution and microwave ablation was performed. The levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN) and creatinine (Cr) in serum were tested at 1 d before microwave ablation and 3 and 7 d after operation.

RESULTS

In vivo ablation thermal injury to the adjacent diaphragm was evaluated in the control, saline and 22.5% P407 gel groups (P = 0.001-0.040). However, there was no significant difference in the volume of ablation zone among the three groups (P > 0.05). Moreover, there were no statistical differences among the preoperative and postoperative gel groups according to the levels of

ALT, AST, BUN and Cr in serum (all P > 0.05).

CONCLUSION

Twenty-two point five percent P407 gel could be a more effective choice during microwave ablation of hepatic tumors adjacent to the diaphragm. Further studies for clinical translation are warranted.

Protective and Heat Retention Effects of Thermo-sensitive Basement Membrane Extract (Matrigel) in Hepatic Radiofrequency Ablation in an Experimental Animal Study

PURPOSE

To evaluate the protective effect of using thermo-sensitive basement membrane extract (Matrigel) for hydrodissection to minimize thermal injury to nearby structures and to evaluate its heat sink effect on the ablation zone in radiofrequency ablation (RFA) of the liver.

MATERIALS AND METHODS

First, the viscosity profile and heat sink effect of Matrigel were assessed during RFA in vitro and ex vivo. Fresh pig liver tissue was used, and the temperature changes in Matrigel and in 5% dextrose in water (D5W) during RFA were recorded. Then, the size of the ablation zone in the peripheral liver after RFA was measured. Second, in an in vivo study, 45 Sprague-Dawley rats were divided into three groups of 15 rats each (Matrigel, D5W and control). In the experimental groups, artificial ascites with 10 ml of Matrigel or D5W were injected using ultrasound guidance prior to RFA. The frequency of thermal injury to the nearby organs was compared among the three groups, with assessments of several locations: near the diaphragm, the abdominal wall and the gastrointestinal (GI) tract. Finally, the biological degradation of Matrigel by ultrasound was evaluated over 60 days.

RESULTS

First, Matrigel produced a greater heat retention (less heat sink) effect than D5W during ex vivo ablation (63 ± 9 vs. 26 ± 6 °C at 1 min on the surface of the liver, P < 0.001). Hepatic ablation zone volume did not differ between the two groups. Second, thermal injury to the nearby structures was found in 14 of 15 cases (93.3%) in the control group, 8 of 15 cases (53.3%) in the D5W group, and 1 of 15 cases (6.7%) in the Matrigel group. Significant differences in the thermal injury rates for nearby structures were detected among the three groups (P < 0.001). The most significant difference in the thermal injury rate was found in locations near the GI tract (P = 0.003). Finally, Matrigel that was injected in vivo was gradually degraded during the following 60 days.

CONCLUSIONS

Using thermo-sensitive Matrigel as a hydrodissection material might help reduce the frequency of collateral thermal injury to nearby structures, especially in locations close to the GI tract, compared to conventional D5W. Additionally, Matrigel did not increase the heat sink effect on the ablation zone during ablation and was degraded over time in vivo.

A clinical study of thermal monitoring techniques of ultrasound-guided microwave ablation for hepatocellular carcinoma in high-risk locations

To confirm the safety and effectiveness of the minimally invasive thermal monitor technique on percutaneous ultrasound-guided microwave ablation (MWA) for hepatocellular carcinoma (HCC) in high-risk locations, a total of 189 patients with 226 HCC nodules in high-risk locations were treated with MWA. The real-time temperature of the tissue between the lesion margin and the vital structures was monitored by inserting a 21G thermal monitoring needle. The major indexes of technical success, technique effectiveness, local tumour progression and complications were observed during the follow-up period. Technical success was acquired in all patients. Technique effectiveness was achieved with one session in 119 lesions based on contrast-enhanced ultrasound (CEUS) 3-5 days after treatment. An additional 95 lesions achieved technique effectiveness at the second session. Within the follow-up period of 6-58 months (median 38 months), the 1-, 2-, 3-, and 4-year local tumour progression rate was 11.1%, 18.1%, 19.1%, and 19.9%, respectively. There were no major complications in all the patients except for the common side effects. These results indicate that the thermal monitor technique can be applied to prevent major complications in vulnerable structures and allow percutaneous MWA to achieve satisfactory technique effectiveness in the treatment of HCC in high-risk locations.

Factors related to recurrence of the benign non-functioning thyroid nodules after percutaneous microwave ablation

PURPOSE

To determine the factors affecting the recurrence of the solitary benign thyroid nodules (BTN) after microwave ablation (MWA).

MATERIALS AND METHODS

Between January 2013 and January 2015, a total of 110 patients with at least one solid thyroid nodule (solid component ≥ 80%) were enrolled. MWA was performed under continuous ultrasound (US) guidance. Before and during the follow-up, the thyroid nodule volume, thyroid function and cosmetic complaints were evaluated. Recurrence is defined by the new blood flow in the total ablation area or/and > 50% increase in nodule volume.

RESULTS

Almost all thyroid nodules were significantly decreased in size after MWA. After 12 months, the average volume of thyroid nodules was decreased from 12.6 ± 15.1 to 3.2 ± 5.7 ml. Of the total 110 patients, 16 cases had recurrence 12 months after MWA, and these patients had a larger initial volume than that of the non-recurrence patients (11.6 ± 14.9 vs. 23.9 ± 12.5, p < 0.01). The recurrence group also demonstrated more irregular blood vessels (1.8 8 ± 1.1 vs. 2.8 5 ± 1.3, p < 0.05), and a lower energy (1575.5 ± 674.3 J/ml vs. 1172.3 ± 454.2 J/ml, p < 0.01). In addition, 81.2% (13/16) of the patients in the recurrence group were adjacent to the vital structures, which is significantly higher than that of the non-recurrence group 28.7% (27/94) (p < 0.01).

CONCLUSIONS

The US-guided MWA results in a satisfactory long-term outcome of the patients with a benign solitary thyroid nodule. We identified three risk factors for recurrence: initial volume, vascularity and the energy per 1 ml reduction in nodular volume.

Design and validation of a thermoreversible material for percutaneous tissue hydrodissection

Interventional oncology procedures such as thermal ablation are becoming routine for many cancers. Hydrodissection-separating tissues with fluids-protects tissues near the treatment zone to improve ablation's safety and facilitate more aggressive treatments. However, currently used fluids such as normal saline and 5% dextrose in water (D5W) migrate in the peritoneum, reducing their protective efficacy. As a hydrodissection alternative, we investigated a thermoreversible poloxamer 407 (P407) solution. Such a material can be injected as a liquid which then forms a semi-solid gel at body temperature without syneresis. The desired gelation temperature of 32°C was achieved with 15.4 wt/wt % P407. Viscosity analysis revealed the lowest viscosity and ideal injection point was at 14°C. Solution viscosity increased during gelation, to a peak of 65 kPa*s at 40°C. The electrical impedance of P407 was significantly greater than isotonic saline, but lower than D5W, indicating its potential for electrical protection. The P407 gel was similar to other hydrodissection fluids at ultrasound and CT imaging. Ex vivo liver ablations showed that P407 protects neighboring tissues, but may require a thicker barrier for comparable protection to D5W. Overall, we found that the P407 solution is a feasible alternative to traditional hydrodissection fluids and warrants additional study.

Evaluation of a thermoprotective gel for hydrodissection during percutaneous microwave ablation: in vivo results

PURPOSE

To evaluate whether thermoreversible poloxamer 407 15.4 % in water (P407) can protect non-target tissues adjacent to microwave (MW) ablation zones in a porcine model.

MATERIALS AND METHODS

MW ablation antennas were placed percutaneously into peripheral liver, spleen, or kidney (target tissues) under US and CT guidance in five swine such that the expected ablation zones would extend into adjacent diaphragm, body wall, or bowel (non-target tissues). For experimental ablations, P407 (a hydrogel that transitions from liquid at room temperature to semi-solid at body temperature) was injected into the potential space between target and non-target tissues, and the presence of a gel barrier was verified on CT. No barrier was used for controls. MW ablation was performed at 65 W for 5 min. Thermal damage to target and non-target tissues was evaluated at dissection.

RESULTS

Antennas were placed 7 ± 3 mm from the organ surface for both control and gel-protected ablations (p = 0.95). The volume of gel deployed was 49 ± 27 mL, resulting in a barrier thickness of 0.8 ± 0.5 cm. Ablations extended into non-target tissues in 12/14 control ablations (mean surface area = 3.8 cm(2)) but only 4/14 gel-protected ablations (mean surface area = 0.2 cm(2); p = 0.0005). The gel barrier remained stable at the injection site throughout power delivery.

CONCLUSION

When used as a hydrodissection material, P407 protected non-targeted tissues and was successfully maintained at the injection site for the duration of power application. Continued investigations to aid clinical translation appear warranted.

Approaches to the difficult drainage and biopsy

Percutaneous abscess drainage and percutaneous biopsy are effective and widely used techniques in the diagnosis and treatment of patients with abdominal or pelvic abscesses and lesions. Some abscesses and lesions can initially appear unsuitable for percutaneous access for a variety of reasons. This article reviews the circumstances in which collections or lesions may appear undrainable or inaccessible to percutaneous biopsy, and it describes techniques for overcoming these circumstances.

Temporary organ displacement coupled with image-guided, intensity-modulated radiotherapy for paraspinal tumors

Background

To investigate the feasibility and dosimetric improvements of a novel technique to temporarily displace critical structures in the pelvis and abdomen from tumor during high-dose radiotherapy.

Methods

Between 2010 and 2012, 11 patients received high-dose image-guided intensity-modulated radiotherapy with temporary organ displacement (TOD) at our institution. In all cases, imaging revealed tumor abutting critical structures. An all-purpose drainage catheter was introduced between the gross tumor volume (GTV) and critical organs at risk (OAR) and infused with normal saline (NS) containing 5-10% iohexol. Radiation planning was performed with the displaced OARs and positional reproducibility was confirmed with cone-beam CT (CBCT). Patients were treated within 36 hours of catheter placement. Radiation plans were re-optimized using pre-TOD OARs to the same prescription and dosimetrically compared with post-TOD plans. A two-tailed permutation test was performed on each dosimetric measure.

Results

The bowel/rectum was displaced in six patients and kidney in four patients. One patient was excluded due to poor visualization of the OAR; thus 10 patients were analyzed. A mean of 229 ml (range, 80–1000) of NS 5-10% iohexol infusion resulted in OAR mean displacement of 17.5 mm (range, 7–32). The median dose prescribed was 2400 cGy in one fraction (range, 2100–3000 in 3 fractions). The mean GTV D_min and PTV D_min pre- and post-bowel TOD IG-IMRT dosimetry significantly increased from 1473 cGy to 2086 cGy (p=0.015) and 714 cGy to 1214 cGy (p=0.021), respectively. TOD increased mean PTV D95 by 27.14% of prescription (p=0.014) while the PTV D05 decreased by 9.2% (p=0.011). TOD of the bowel resulted in a 39% decrease in mean bowel D_max (p=0.008) confirmed by CBCT. TOD of the kidney significantly decreased mean kidney dose and D_max by 25% (0.022).

Conclusions

TOD was well tolerated, reproducible, and facilitated dose escalation to previously radioresistant tumors abutting critical structures while minimizing dose to OARs.

Percutaneous interstitial brachytherapy for adrenal metastasis: technical report

We developed and evaluated the feasibility of a brachytherapy technique as a safe and effective treatment for adrenal metastasis. Adapting a paravertebral insertion technique in radiofrequency ablation of adrenal tumors, we developed an interstitial brachytherapy for adrenal metastasis achievable on an outpatient basis. Under local anesthesia and under X-ray CT guidance, brachytherapy applicator needles were percutaneously inserted into the target. A treatment plan was created to eradicate the tumor while preserving normal organs including the spinal cord and kidney. We applied this interstitial brachytherapy technique to two patients: one who developed adrenal metastasis as the third recurrence of uterine cervical cancer after reirradiation, and one who developed metachronous multiple metastases from malignant melanoma. The whole procedure was completed in 2.5 hours. There were no procedure-related or radiation-related early/late complications. FDG PET-CT images at two and three months after treatment showed absence of FDG uptake, and no recurrence of the adrenal tumor was observed for over seven months until expiration, and for six months until the present, respectively. This interventional interstitial brachytherapy procedure may be useful as a safe and eradicative treatment for adrenal metastasis.

Hemorrhagic cardiac tamponade: rare complication of radiofrequency ablation of hepatocellular carcinoma

Local treatment for hepatocellular carcinoma (HCC) has been widely used in clinical practice due to its minimal invasiveness and high rate of cure. Percutaneous radiofrequency ablation (RFA) is widely used because its treatment effectiveness. However, some serious complications can arise from percutaneous RFA. We present here a rare case of hemorrhagic cardiac tamponade secondary to an anterior cardiac vein (right marginal vein) injury during RFA for treatment of HCC.

US findings after irreversible electroporation ablation: radiologic-pathologic correlation

PURPOSE

To characterize ultrasonographic (US) findings after irreversible electroporation (IRE) to determine the utility of these findings in the accurate assessment of ablation margins.

MATERIALS AND METHODS

The institutional animal care and use committee approved the study. IRE ablation (n = 58) was performed in vivo in 16 pig livers by using two 18-gauge electroporation electrodes with 2-cm tip exposure, 1.5- or 2.0-cm interelectrode spacing, and an electroporation generator. Energy deposition was applied at 2250-3000 V (pulse length, 50-100 μsec; pulse repetition, 50-100). Ablations were performed under US guidance. Images were obtained during ablation and at defined intervals from 1 minute to 2 hours after the procedure. Zones of ablation were determined at gross and histopathologic examination of samples obtained from animals sacrificed 2-3 hours after IRE. Dimensions of the histologic necrosis zone and US findings were compared and subjected to statistical analysis, including a Student t test and multiple linear regression.

RESULTS

Within 20-50 pulse repetitions of IRE energy, the ablation zone appeared as a hypoechoic area with well-demarcated margins. During the next 8-15 minutes, this zone decreased in size from 3.4 cm ± 0.5 to 2.5 cm ± 0.4 and became progressively more isoechoic. Subsequently, a peripheral hyperechoic rim measuring 2-7 mm (mean, 4 mm ± 1) surrounding the isoechoic zone developed 25-90 minutes (mean, 41 minutes ± 19) after IRE. The final length of the treatment zone, including the rim, increased to 3.3 cm ± 0.6. The final dimensions of the outer margin of this rim provided greatest accuracy (1.7 mm ± 0.2) and tightest correlation (r(2) = 0.89) with gross pathologic findings. Histologic examination demonstrated widened sinusoidal spaces that progressively filled with spatially distributed hemorrhagic infiltrate on a bed of hepatocytes with pyknotic nuclei throughout the treatment zone.

CONCLUSION

US findings in the acute period after IRE are dynamic and evolve. The ablation zone can be best predicted by measuring the external hyperechoic rim that forms 90-120 minutes after ablation. This rim is possibly attributable to evolving hemorrhagic infiltration via widened sinusoids.

Ablative therapies for renal tumors

Owing to an increased use of diagnostic imaging for evaluating patients with other abdominal conditions, incidentally discovered kidney masses now account for a majority of renal tumors. Renal ablative therapy is assuming a more important role in patients with borderline renal impairment. Renal ablation uses heat or cold to bring about cell death. Radiofrequency ablation and cryoablation are two such procedures, and 5-year results are now emerging from both modalities. Renal biopsy at the time of ablation is extremely important in order to establish tissue diagnosis. Real-time temperature monitoring at the time of radiofrequency ablation is very useful to ensure adequacy of ablation.

Bowel displacement and protection techniques during percutaneous renal tumor thermal ablation

Although bowel injury is a rare complication of renal radiofrequency ablation, the potential consequences can be devastating. Therefore, it is prudent to perform bowel displacement/protection procedures when feasible. The main bowel displacement techniques include hydrodissection, gas-insufflation, balloon interposition, and electrode torquing. In this article, these techniques are discussed and the steps involved in performing these procedures are enumerated.

Percutaneous CT-guided radiofrequency ablation of renal cell carcinoma: efficacy of organ displacement by injection of 5% dextrose in water into the retroperitoneum

OBJECTIVE

The objective of this study was to evaluate the effectiveness of CT-guided injection of 5% dextrose in water solution (D5W) into the retroperitoneum to displace organs adjacent to renal cell carcinoma.

MATERIALS AND METHODS

An interventional radiology database was searched to identify the cases of patients who underwent CT-guided percutaneous radiofrequency ablation of biopsy-proven renal cell carcinoma in which D5W was injected into the retroperitoneal space to displace structures away from the targeted renal tumor. The number of organs displaced and the distance between the renal tumor and adjacent organs before and after displacement with D5W were assessed.

RESULTS

The cases of 135 patients with 139 biopsy-proven renal cell carcinomas who underwent 154 percutaneous CT-guided radiofrequency ablation procedures were found in the search. Thirty-one patients with 33 renal cell carcinomas underwent 36 ablation procedures after injection of D5W into the retroperitoneal space. Fifty-five organs were displaced away from renal cell carcinoma with this technique. The average distance between adjacent structures and renal cell carcinomas before displacement was 0.36 cm (range, 0.1-1.0 cm). The average distance between structures and adjacent renal cell carcinomas after displacement was 1.94 cm (range, 1.1-4.3 cm) (p < 0.0001). The average volume of D5W used to achieve organ displacement was 273.5 mL. No complications were associated with this technique.

CONCLUSION

CT-guided injection of D5W into the retroperitoneum is an effective method for displacing vital structures away from renal cell carcinoma.

Bowel displacement for CT-guided tumor radiofrequency ablation: techniques and anatomic considerations

PURPOSE

To describe safety and efficacy of bowel displacement techniques and determine lesion characteristics that are likely to necessitate bowel displacement.

PATIENTS AND METHODS

A retrospective review of patients who underwent CT-guided renal tumor radiofrequency ablation (RFA) (January 2006-August 2008) was conducted. Techniques included hydrodissection, additional manual torquing of the RFA probe, and additional angioplasty balloon interposition. The goal was to displace bowel from the probe by at least 10 to 20 mm. Air-filled balloon interposition was intended as a thermal barrier. Pre- and postbowel displacement distances were measured by CT. Saline volumes were recorded. Multivariate stepwise regression analysis was used to determine the influence of laterality, renal location, and morphology of renal lesions on their proximity to the colon and use of bowel displacement techniques.

RESULTS

RFA was performed on 57 consecutive patients. Eleven (19%) patients had bowel displacement attempts. Median pre-RFA lesion edge to colon distance for nondisplaced vs displaced was 43 mm (range 10-100 mm) vs 6 mm (range 0-16 mm), respectively (P < 0.05). Two variables were significant for bowel displacement (F-ratio = 4.681, P = 0.006): Tumor position within the kidney in the craniocaudal plane (P = 0.014) and anterior-posterior plane (P = 0.007). Lower pole and posterior lesions tended to be closer to the colon and more likely to necessitate bowel displacement. Orientation in the medial-lateral plane (P = 0.77) and exophytic nature of the lesion (P = 0.83) were not significant features. Hydrostatic bowel displacement was always the first-line technique and was completely and partly successful in 8 (73%) and 1 (9%) attempts, respectively. Partial success was augmented by probe torquing (distance increased from 1 mm to 16 mm and then to 23 mm with torquing). Mean saline injection: 105 mL (range 55-440 mL). There were two complete failures (18%) in which bowel was displaced only by 0 to 2 mm despite injection of 280 to 440 mL. Balloon interposition was attempted in these two cases. Five minor complications occurred in the nondisplaced cohort. No complications occurred in the bowel displacement cohort.

CONCLUSION

Lower pole, posterior renal lesions are more likely to necessitate bowel displacement. Bowel displacement techniques are effective and safe in displacing bowel.

Needlescopic ablation of small adrenal masses

Needlescopic adrenal ablative therapy is an attractive therapeutic option for the management of small adrenal masses. The spectrum of neoplasms that can be ablated includes isolated solid organ metastases (lung, kidney, liver), nonisolated but symptomatic (painful) adrenal metastasis, and small, nonmetastatic, hormonally active adrenal tumors. Moreover, needlescopic ablation offers an effective minimally morbid intervention for patients who are poor surgical candidates either due to advanced age and/or significant comorbid conditions. Ablative techniques described to date include radiofrequency ablation (RFA), cryoablation, and chemical ablation. Most procedures can be performed under percutaneous radiographic guidance on an outpatient basis. By and large, the bulk of clinical experience with adrenal ablation pertains to RFA. Successful ablation is usually dependent upon lesion size, with tumors 5 cm or smaller demonstrating the highest successful ablation rates. The most frequently described adverse sequelae of adrenal ablation are local tumor recurrences. However, many of these local recurrences can be managed by repeat ablation, with patients demonstrating durable oncologic outcomes.

Thermal protection during percutaneous thermal ablation procedures: interest of carbon dioxide dissection and temperature monitoring

Percutaneous image-guided thermal ablation of tumor is widely used, and thermal injury to collateral structures is a known complication of this technique. To avoid thermal damage to surrounding structures, several protection techniques have been reported. We report the use of a simple and effective protective technique combining carbon dioxide dissection and thermocouple: CO(2) displaces the nontarget structures, and its low thermal conductivity provides excellent insulation; insertion of a thermocouple in contact with vulnerable structures achieves continuous thermal monitoring. We performed percutaneous thermal ablation of 37 tumors in 35 patients (4 laser, 10 radiofrequency, and 23 cryoablations) with protection of adjacent vulnerable structures by using CO(2) dissection combined with continuous thermal monitoring with thermocouple. Tumor locations were various (19 intra-abdominal tumors including 4 livers and 9 kidneys, 18 musculoskeletal tumors including 11 spinal tumors). CO(2) volume ranged from 10 ml (epidural space) to 1500 ml (abdominal). Repeated insufflations were performed if necessary, depending on the information given by the thermocouple and imaging control. Dissection with optimal thermal protection was achieved in all cases except two patients where adherences (one postoperative, one arachnoiditis) blocked proper gaseous distribution. No complication referred to this technique was noted. This safe, cost-effective, and simple method increases the safety and the success rate of percutaneous thermal ablation procedures. It also offers the potential to increase the number of tumors that can be treated via a percutaneous approach.

Perineural air injection as a means of prevention of thermal injury of the sciatic nerve during radio frequency ablation: a preliminary experimental study in rabbits

OBJECTIVE

The purpose of this study was to determine whether perineural air injection before radio frequency (RF) ablation of thigh muscles can minimize thermal injury to the sciatic nerve.

METHODS

Eighteen percutaneous RF ablation procedures were performed in the thighs of 9 rabbits (control, n = 9, right thigh; experimental, n = 9, left thigh) with an internally cooled electrode (1-cm active tip). In the control group, the tip of the electrode was located in posterior muscles 5 mm away from the sciatic nerve before ablation. In the experimental group, sonographically guided air injection into the perineural space was performed just before ablation. Animals were killed 7 days after ablation, and the presence or absence of pathologic changes of the sciatic nerves (axonal necrosis, myelin digestion, endoneurial fibrosis, perineurial fibrosis, and dystrophic calcification) in both groups were compared under an optical microscope.

RESULTS

Perineural air injection was achieved successfully with a single puncture in all rabbits in the experimental group. All of the pathologic findings were observed much more frequently in the control group, and the differences in the frequencies of axonal necrosis and myelin digestion of the sciatic nerve between the groups were clinically significant (P < .05).

CONCLUSIONS

Perineural air injection may be useful for reducing the frequency of thermal injury during RF ablation of lesions adjacent to nerves.

Percutaneous renal cryoablation: current status

Over the last 13 years, renal cryoablation has emerged as a promising technique for the treatment of solid renal tumors. The improvement in imaging modalities such as ultrasound, computed tomography and MRI, as well as the introduction of thinner probes, has led to the spread of the minimally invasive percutaneous approach. We review the historical background of percutaneous renal cryoablation (PRC), present its basic principles, mention the contemporary clinical data and outcomes of this technique and suggest future directions for its wider application in renal tumors. Early results have demonstrated that it may offer an alternative for the treatment of small renal masses with the advantages of minimal complications, spared renal function, decreased overall costs and equivalent oncologic efficacy. Long-term results are required in order to apply this minimally invasive technique to a broader spectrum of patients.

Using an electrode as a lever to increase the distance between renal cell carcinoma and bowel during CT-guided radiofrequency ablation

The technique of using an electrode as a lever to increase the distance between renal cell carcinoma (RCC) and bowel during CT-guided radiofrequency ablation (RFA) is described. CT-guided percutaneous RFA was performed in two patients with two RCCs, which were in close proximity to the adjacent bowel. A sterile drape was placed on the electrode handle following appropriate electrode placement within the tumor in order to displace the kidney upward and to widen the distance to >5 mm between RCC and bowel (RCC-to-bowel distance). In patient 1, the RCC-to-bowel distance increased from 3 mm to 6 mm; in patient 2, from less than 2 mm to 6 mm. Follow-up CT performed 1 month after RFA demonstrated not only complete ablation of the two RCCs but also no thermal injury to the bowel adjacent to the tumors. In conclusion, an electrode might be used as a lever to increase RCC-to-bowel distance during CT-guided RFA by placing a sterile drape on it.

Multiple-Electrode Radiofrequency Ablation of Hepatic Malignancies: Initial Clinical Experience

OBJECTIVE

The objective of our study was to retrospectively analyze our initial clinical experience with percutaneous multiple-electrode radiofrequency ablation and evaluate its safety and efficacy for treating hepatic malignancies.

MATERIALS AND METHODS

Thirty-eight malignant hepatic tumors (mean diameter, 2.7 cm; range, 0.7-10.0 cm) in 23 patients (12 men and 11 women; mean age, 65 years; range, 40-84 years) were treated in 26 radiofrequency ablation sessions with an impedance-based multiple-electrode system. One, two, or three (mean, 2.4) 17-gauge electrodes were placed, and tumors were ablated using a combination of CT and sonography for guidance and monitoring. Electrodes were placed in close proximity (mean spacing: two electrodes, 1.0 cm; three electrodes, 1.4 cm) to treat large tumors or were used independently to treat several tumors simultaneously. Contrast-enhanced CT scans were obtained immediately after ablation to determine technical success and evaluate for complications. Follow-up CT scans at 1, 3, 6, 9, and 12 months (mean, 4 months) after ablation were obtained to assess for tumor progression and new metastases.

RESULTS

Local control was achieved in 37 of 38 tumors, 34 of which were treated in one session. Ablations created with closely spaced electrodes had a mean diameter of 4.9 cm. The total ablation time was reduced by approximately 54% compared with an equivalent number of ablations performed with a single-electrode system (1,014 vs 2,196 minutes). Three complications occurred: one death from a presumed postprocedure pulmonary embolus, one pneumothorax, and one asymptomatic perihepatic hemorrhage.

CONCLUSION

Multiple-electrode radiofrequency ablation appears to be a safe and effective means of achieving local control in large or multiple hepatic malignancies at short-term follow-up.