Cryolesion Size Research Articles

An in vitro analysis of the size and shape of cryolesions for facet joint denervation

ObjectivesLumbar facet joint syndrome (LFJS) is the cause of lower back pain in 15–54% of the patients. Clinical studies of cryotherapy for LFJS have reported promising outcomes. However, few studies have focused on the technical aspects of cryoneurolysis for LFJS.The aim of the study was to determine the size and shape of cryolesions in vitro and to determine how they are affected by the duration of freezing, size of the cryoprobe and distance and angulation to an osseous boundary layer. Materials and methodsTwo different cryolesion generators were used. Cryolesions were generated in tempered physiologic NaCl solution in the vicinity of an osseous surface. The size of the cryoprobes, duration of freezing, distance to the bone surface and angulation of the probe were studied. Cryolesions were recorded with a video camera during their emergence. Images at distinct time points were analysed using digital image processing software. ResultsThe probe size, the system in use and the duration of the freezing cycle were the main determinants for the size of the cryolesion. The vicinity of the osseous boundary resulted in a modest increase in the size of the cryolesion. Angulation of the cryoprobe towards the osseous boundary is of minor importance for the size of the contact area to the nerve. ConclusionFor cryoneurolysis of LFJS, duration of freezing, temperature and probe size are the main determinants of lesion size and thus the probability of success of the procedure. A tangential approach of the probe is not essential.

Arterial Clamping Increases Central Renal Cryoablation Efficacy: An Animal Study.

The minimally invasive treatment of small renal masses with cryoablation has become increasingly widespread during the past 15 years. Studies with long-term follow-up are beginning to emerge, showing good oncological control, however, tumors with a central and endophytic location seem to possess an increased risk of treatment failure. Such tumors are likely to be subjected to a high volume of blood giving thermal protection to the cancerous cells. Arterial clamping during freezing might reduce this effect but at the same time subject the kidney to ischemia. The aim of this study was to evaluate the effect of renal artery clamping during cryoablation in a porcine survival model. Ten Danish Landrace pigs (approximately 40 kg) underwent bilateral laparoscopic cryoablation with clamping of the right renal artery during freezing. The cryoablation consisted of a standard double-freeze cycle of 10-minute freeze followed by 8 minutes of thaw. Arterial clamping subjected the right kidney to 2 cycles of ischemia (10 minutes) with perfusion in between. After surgery, the animals were housed for 14 days prior to computed tomography perfusions scans, radioisotope renography, and bilateral nephrectomy. No perioperative or postoperative complications were experienced. Mean differential renal function was 44% (95% confidence interval: 42-46) in the clamped right kidney group and 56% (95% confidence interval: 54-58) in the nonclamped left kidney group, P < .05. The ±5% technical inaccuracy is not accounted for in the results. Mean maximum temperature between freeze cycles was 5.13°C (95% confidence interval: -0.1 to 10.3) in the clamped right kidney group and 22.7°C (95% confidence interval: -16.6 to 28.8) in the nonclamped left kidney group, P < .05. Mean cryolesion volume, estimated on computed tomography perfusion, was 12.4 mL (95% confidence interval: 10.35-14.4) in the clamped right kidney group and 6.85 mL (95% confidence interval: 5.57-8.14) in the nonclamped left kidney group, P < .05. Pathological examination shows a higher degree of vital cells in the intermediate zone of the cryolesions in the nonclamped left kidneys when compared with the clamped right kidneys. Arterial clamping increases cryolesion size by approximately 80%, and pathologic examinations suggest a decreased risk of vital cells in the intermediate zone. The clamped kidneys showed no sign of injury from the limited ischemic insult. This study was limited by being a nontumor model.

Computed Tomography Contrast Enhancement Following Renal Cryoablation--Does it Represent Treatment Failure?

For minimal invasive treatment of small renal masses, cryoablation has gained popularity. Treatment success is defined as the absence of contrast enhancement on postoperative imaging of the cryoablated lesion, but contrast enhancement does not necessarily equal treatment failure. This present study investigates the proportion of spontaneous resolutions after initial contrast enhancement in relation to cryoablation. Data were collected from a prospectively maintained clinical database containing all patients treated with primary laparoscopic and percutaneous cryoablation between August 2005 and December 2013. All images were evaluated with regard to preoperative aspects and dimensions used for an anatomical classification (PADUA) score, cryolesion size, contrast enhancement pattern, and tissue density. A total of 107 patients with a biopsy-verified malignant tumor were included in the study. On postoperative imaging, 33 (31%) patients presented with contrast enhancement. Spontaneous resolution was observed in 15 (45%) patients after a mean follow-up time of 14 months. Patients with cryolesions that resolved spontaneously were found to have a less anatomical complex tumor compared to patients with treatment failure (PADUA 7.8 vs 9.5, p < 0.01). A total of seven patients with a PADUA score ≥10 and contrast-enhancing cryolesions were found to have treatment failure. No association was found among body mass index, histology, treatment modality, enhancement pattern, number of applied cryoprobes, and resolution. Postoperative contrast enhancement is commonly observed after cryoablation and a large portion of these lesions often resolves spontaneously, thus not representing treatment failure. In patients with a high preoperative PADUA score and postoperative contrast enhancement of the cryolesion, treatment failure or recurrent disease should be suspected.

Reporting Standards for Percutaneous Thermal Ablation of Renal Cell Carcinoma

WITH the increasing incidence of renal cell carcinoma (RCC) in the United States and the increasing proportion of patients with tumors detected at an early stage (1–5), nephron-sparing approaches are becoming more popular. These alternatives to radical nephrectomy include partial nephrectomy, wedge resection, and, more recently, in situ thermal ablation. Five-year survival rates after partial nephrectomy are equivalent to those after radical nephrectomy (6–8), supporting the rationale of in situ tumor destruction to further reduce morbidity and invasiveness. In situ thermal destruction of RCC uses techniques that destroy tumor tissue through heating (eg, radiofrequency [RF] ablation, microwave ablation, laser interstitial therapy, high-intensity focused ultrasound [US]) or freezing (eg, cryotherapy). Each of these techniques relies on controlled energy delivery to minimize collateral damage to normal renal parenchyma and other surrounding structures. In the United States, RF ablation and cryoablation are currently the most widely used techniques for in situ RCC destruction. Thermal ablation of RCC may be performed percutaneously, laparoscopically, or through open surgery. Our current understanding of the role of percutaneous thermal ablation in the management of primary RCC is limited by a paucity of prospective studies (9,10). Given the relative newness of this technology, most series to date report short-term or midterm outcomes, with no reports extending to 5 years of survival outcomes. No randomized trials have been performed to date comparing thermal ablation against a gold standard (ie, partial nephrectomy) or against other thermal ablation techniques. The optimal size range of RCC amenable to thermal ablation has not been clearly defined and is closely related to anatomic factors that influence the ability to deposit sufficient thermal dose to coagulate tissue, including proximity to major vessels and the urinary collecting system, which can act as a heat sink. The kidney has approximately four times the blood flow of the liver, so convective heat loss during thermal ablation is potentially significant (11). The role of percutaneous thermal ablation compared with laparoscopic or open thermal ablation also remains a topic of controversy. The combination of thermal ablation with other imageguided therapies (eg, transcatheter embolization) and adjuvant therapies such as chemotherapy and antiangiogenic agents for larger RCCs in patients who are poor operative candidates is another potential use of this technique. Although most recent reports of percutaneous RCC ablation have involved RF ablation, other ablation technologies are now available with percutaneous applicators (eg, cryoablation, microwave, laser interstitial therapy), and reporting standards should be uniform for all forms of energy-based ablation. This document provides recommended reporting standards for physicians performing percutaneous thermal ablation of primary RCC and will serve as a template in the design of clinical trials to further evaluate this technology. From the Section of Vascular and Interventional Radiology, Department of Radiology (T.W.I.C.), New York University School of Medicine, New York, New York; Department of Radiology (S.F.M.), University of Western Ontario, Peterborough Regional Health Center, Peterborough, Ontario, Canada; Department of Radiology, Gastrointestinal/Genitourinary Division (D.A.G.), Massachusetts General Hospital; Department of Radiology (S.N.G.), Beth Israel Deaconess Medical Center, Boston; Department of Radiology (C.J.G.), Lahey Clinic Medical Center, Burlington; Department of Radiology (D.A.P.), University of Massachusetts Memorial Health Care, Worcester, Massachusetts; Department of Radiology (T.B.K.), University of California San Diego Medical Center, San Diego, California; Department of Radiology (D.S.), The Reading Hospital and Medical Center, Reading, Pennsylvania; and Department of Radiology (J.F.C.), University of Colorado Health Sciences Center, Denver, Colorado. Received June 19, 2006; revision requested June 19; final revision received June 29; and accepted July 3. Address correspondence to T.W.I.C., c/o Tricia McClenny, Society of Interventional Radiology, 3975 Fair Ridge Dr, Suite 400 North, Fairfax, VA 22033; E-mail: mcclenny@sirweb.org

Follow-up of renal masses after cryosurgery using computed tomography; enhancement patterns and cryolesion size

To describe the characteristics of cryolesions as seen on computed tomography (CT), for size and enhancement patterns, and to assess correlations between these imaging findings and histopathological diagnosis, as in renal cryosurgery the tumour is ablated in situ and the follow-up is mainly based on imaging. Forty-seven patients with a suspicious renal mass of <or=4 cm had a laparoscopic cryoablation; biopsies were taken during surgery and after cryosurgery the follow-up was by CT at 3, 6, 9, 12, 18, 24, 30 and 36 months. One radiologist reviewed the CT images, measured the diameter of the cryolesions, and described enhancement patterns. In 26 patients there were follow-up CT data for >or=6 months; the mean (range) tumour size was 2.4 (1.3-3.8) cm and the mean follow-up was 17.2 (6-36) months. One cryolesion showed residual tumour on the first scan after treatment. Of the other 25 cryolesions, 20% showed rim enhancement after treatment, including one also showing focal enhancement. This enhancement had disappeared within 6 months. All cryolesions showed non-enhancing infiltration of the perirenal fatty tissue. The mean diameter of the cryolesions decreased by 38% in 12 months. These results were independent of histopathological diagnosis. Using CT, there is rim enhancement in 20% of cryolesions in the first 6 months after renal cryoablation, with a mean reduction in the diameter of the cryolesions of 38% in the first year. These findings are independent of the histopathological diagnosis.

1243: Follow-Up of Renal Masses after Cryosurgery Using Computerized Tomography; Enhancement Patterns and Cryolesion Size

1243: Follow-Up of Renal Masses after Cryosurgery Using Computerized Tomography; Enhancement Patterns and Cryolesion Size

A design method for mixed gas Joule–Thomson refrigeration cryosurgical probes

A cryosurgical probe is a medical instrument that is designed to kill cancerous tissue by exposure to cryogenic temperatures. The most important figure of merit for a cryosurgical probe of fixed size is the dimension of the cryolesion that can be generated within a specified time during a surgical procedure. The optimization of the cryoprobe, through variation of the geometry, operating conditions, or working fluid composition, should be aimed directly at this clinical goal rather than at maximizing the refrigeration capacity, COP, or minimizing the tip temperature. This unique optimization criterion has created the need for a design method that considers both the probe design and the heat transfer details external to the probe (e.g. the blood perfusion and metabolic heat rate in the patient). This paper outlines a design method that will allow manufacturers of cryosurgical probes to identify an optimum combination of refrigerant mixture, cryoprobe geometry, and other cycle operating conditions. Specifically, a numerical model of the development of a cryolesion has been developed and verified; this model relates the size of the cryolesion, refrigeration required, and tip temperature. A detailed model of the cryoprobe refrigeration cycle relates the refrigeration to the tip temperature that can be achieved. The integration of these models allows the designer to select the optimal cryoprobe based on cryolesion size. This paper focuses on optimizing the mixed gas composition; however, the design technique is generic and can be used to select other system parameters.

Renal cryoablation: Outcome at 3 years: Gill IS, Remer EM, Hasan WA, Strzempkowski B, Spaliviero M, Steinberg AP, Kaouk JH, Desai MM, Novick AC, Section of Laparoscopic and Minimally Invasive Surgery, Glickman Urological Institute and Department of Radiology, Cleveland Clinic Foundation, Cleveland, OH

We report intermediate term oncological followup data on 56 patients undergoing laparoscopic renal cryoablation, of whom each completed a 3-year followup. Since September 1997, 56 patients undergoing laparoscopic renal cryoablation have completed a followup of 3 years each. The postoperative followup protocol comprised serial magnetic resonance imaging (MRI) at 1 day, months 1, 3, 6, 12, 18 and 24, and yearly thereafter for 5 years. Computerized tomography guided needle biopsy of the cryolesion was performed 6 months postoperatively and repeated if MRI findings were abnormal. Followup data were obtained prospectively. For a mean renal tumor size of 2.3 cm mean intraoperative size of the created cryolesion was 3.6 cm. Sequential mean cryolesion size on MRI on postoperative 1 day, and at 3 and 6 months, and 1, 2 and 3 years was 3.7, 2.8, 2.3, 1.7, 1.2 and 0.9 cm, representing a 26%, 39%, 56%, 69% and 75% percent reduction in cryolesion size at 3 and 6 months, and 1, 2 and 3 years, respectively. At 3 years 17 cryolesions (38%) had completely disappeared on MRI. Postoperative needle biopsy identified locally persistent/recurrent renal tumor in 2 patients. In the 51 patients undergoing cryotherapy for a unilateral, sporadic renal tumor 3-year cancer specific survival was 98%. There was no open conversion, kidney loss, urinary fistula, dialysis requirement, or perirenal or port site recurrence in any patients. Three-year outcomes following renal cryoablation are encouraging. Longer term (5-year) data are necessary to determine the proper place of renal cryotherapy among minimally invasive, nephron sparing options.

Magnetic Resonance Imaging Findings and Histopathological Observations After Percutaneous Renal Cryoablation in the Rabbit Model

We investigated sequential changes in MRI and relevant histopathological findings after PRC. A total of 15 rabbits were examined with MRI and sacrificed immediately (3), and 7 (4), 45 (4) and 90 (4) days after PRC. MRI studies were reviewed for the signal intensity of cryolesions and correlated with pathological findings. MRI and pathological measurements of cryolesion sizes were compared using the paired t test. CCN was produced in central areas of cryolesions and associated with hemorrhage, hemolysis, fibrous granulation and fibrosis that was orderly through days 1 to 90. Signal intensity was slightly hyperintense on T1-weighted spin-echo images immediately after PRC, and hyperintense on T1 and T2-weighted fast spin-echo images at 7 days. On T2-weighted fast spin-echo images there was a hypointense zone in peripheral areas between the central area and renal parenchyma at the prior 2 stages, which was consistent with PCN histologically. It was enhanced at 7 days. At 45 and 90 days the signal intensity of cryolesions was isointense or hypointense on the 2 sequences. Parenchymal injury adjacent to cryolesions was histologically recognized and visible as a hyperintense zone in 2 lesions at 45 days. This zone was enhanced in 2 lesions at 45 and 90 days. No statistical significance was apparent between the 2 measurements of cryolesions and CCN sizes (p <0.05). The MRI appearance of cryolesions reflects orderly histopathological findings. MRI distinguishes CCN from PCN, reveals injury to the renal parenchyma outside of cryolesions and accurately estimates the size of cryolesions and CCN.

RENAL CRYOABLATION: OUTCOME AT 3 YEARS

We report intermediate term oncological followup data on 56 patients undergoing laparoscopic renal cryoablation, of whom each completed a 3-year followup. Since September 1997, 56 patients undergoing laparoscopic renal cryoablation have completed a followup of 3 years each. The postoperative followup protocol comprised serial magnetic resonance imaging (MRI) at 1 day, months 1, 3, 6, 12, 18 and 24, and yearly thereafter for 5 years. Computerized tomography guided needle biopsy of the cryolesion was performed 6 months postoperatively and repeated if MRI findings were abnormal. Followup data were obtained prospectively. For a mean renal tumor size of 2.3 cm mean intraoperative size of the created cryolesion was 3.6 cm. Sequential mean cryolesion size on MRI on postoperative 1 day, and at 3 and 6 months, and 1, 2 and 3 years was 3.7, 2.8, 2.3, 1.7, 1.2 and 0.9 cm, representing a 26%, 39%, 56%, 69% and 75% percent reduction in cryolesion size at 3 and 6 months, and 1, 2 and 3 years, respectively. At 3 years 17 cryolesions (38%) had completely disappeared on MRI. Postoperative needle biopsy identified locally persistent/recurrent renal tumor in 2 patients. In the 51 patients undergoing cryotherapy for a unilateral, sporadic renal tumor 3-year cancer specific survival was 98%. There was no open conversion, kidney loss, urinary fistula, dialysis requirement, or perirenal or port site recurrence in any patients. Three-year outcomes following renal cryoablation are encouraging. Longer term (5-year) data are necessary to determine the proper place of renal cryotherapy among minimally invasive, nephron sparing options.

THE EFFECTS OF INTENTIONAL CRYOABLATION AND RADIO FREQUENCY ABLATION OF RENAL TISSUE INVOLVING THE COLLECTING SYSTEM IN A PORCINE MODEL

Ablative techniques for the treatment of urological malignancy are gaining acceptance and they are likely to become more widely used in clinical practice. Indications and limitations of the technologies are still evolving. In a porcine model we evaluated the safety and efficacy of cryotherapy and radio frequency ablation (RFA) of cortical and deep renal tissue. In 11 swine argon gas based cryoablation or RFA of renal tissue adjacent to the collecting system was performed using a laparoscopic or percutaneous approach. Lesions created in renal units 30 days or 2 hours prior to harvest were termed chronic or acute. Using single or multiple 17 gauge cryoneedles or 3.0 mm cryoprobes and 2 freeze-thaw cycles (10-minute freeze and 5-minute thaw) 13 acute and 10 chronic cryolesions were made. Using a single 16 gauge umbrella-shaped RFA probe and 2 heating cycles to maximum impedance 13 acute and 4 chronic RFA lesions were made. Gross and microscopic tissue analysis was performed to assess lesion size and renal parenchymal, collecting system and arterial effects. Acute cryolesion size estimation by laparoscopic or transcutaneous ultrasound (US) was compared with pathological lesion size. Acute cryolesions on hematoxylin and eosin staining demonstrated uniform coagulative necrosis of renal parenchyma and chronic cryolesions demonstrated uniform necrosis with fibrous scar formation. Interlobar artery (adjacent to renal pyramid) preservation occurred in 7 of 13 acute and 5 of 9 chronic cryolesions. Urothelial architecture was preserved in 8 of 13 acute and 7 of 9 chronic cryolesions. Acute and chronic RFA lesions demonstrated indeterminate necrosis on hematoxylin and eosin staining, although triphenyl tetrazolium chloride staining of gross specimens confirmed necrosis most definitively in renal cortex. Interlobar artery preservation occurred in 6 of 13 acute and 3 of 4 chronic RFA lesions. Urothelial architecture was preserved in 1 of 13 acute and 2 of 4 chronic RFA lesions. Acute cryolesion dimensions measured by laparoscopic US equaled or underestimated lesion size measured grossly in all 6 cases. Lesion dimensions measured by transcutaneous US equaled or underestimated true lesion size in 3 of 6 cases. In 3 of 6 lesions transcutaneous US overestimated true lesion size by 20%, 76% and 260%, respectively. Renal cortical tissue can be effectively destroyed by cryoablation or RFA. However, treatment of deep parenchymal lesions with either modality may result in incomplete ablation. Cryosurgery but not RFA spares the collecting system in an acute setting. However, healing or regrowth of the urothelium may occur with time after RFA. Laparoscopic US is more accurate for cryolesion monitoring than transcutaneous US.

Effect of Intentional Cryo-Injury to the Renal Collecting System.

We determined the short-term and long-term sequelae of intentional cryoablation of the renal pelvicaliceal system and evaluated whether continuous irrigation of the renal pelvicaliceal system with warm saline protects it against cryo-injury. In 12 swine open bilateral renal cryoablation using an argon gas based system was performed to create a cryolesion in the lower pole that was intentionally extended into the collecting system. A single cryoprobe was used to create a 3 cm ice ball in group 1 (6 animals) and 2, 3 mm cryoprobes were used to create a 4.5 cm ice ball in group 2 (6). In all 12 right kidneys pelvicaliceal warming (range 38C to 42C) was performed using continuous retrograde saline irrigation through an indwelling 5Fr ureteral catheter. In all 12 left kidneys cryoablation was performed without pelvicaliceal warming. Real-time confirmation of caliceal involvement by the cryolesion was obtained by retrograde ureteropyelogram. Immediately after cryo-injury 6 left and 6 right kidneys were harvested for histology and the animals with a solitary kidney were followed for 1 to 3 months. Nadir cryoprobe tip temperature was -136C with a mean cryolesion time of 10.5 minutes. Cryolesion size was comparable in the right vs left kidneys in groups 1 and 2 (2.9 vs 3.0 and 4.7 vs 4.6 cm, respectively). Similarly cryoablation time was comparable between the right and left kidneys in groups 1 and 2 (11.3 vs 10.8 and 11.9 vs 12.2 minutes, respectively). Two animals died of aspiration pneumonia (1) and wound dehiscence (1). In all 10 surviving animals no instance of urinary extravasation was noted. At 1-month followup regrowth of normal urothelium occurred with some scarring of the lamina propria or underlying smooth muscle. Adjacent renal parenchyma was replaced by fibrous scar. At 3 months the cryo-injured collecting system was completely healed with a fibrous scar. There were no appreciable histological differences between the kidneys with or without warm pelvicaliceal irrigation. Our data suggest that absent physical puncture injury of the collecting system with the cryoprobe tip the cryodamaged renal collecting system heals by secondary intention in a watertight manner. These data have clinical relevance for facilitating cryoablation of a small, localized, central renal tumor in proximity to the pelvicaliceal system.

Laparoscopic renal cryoablation in 32 patients

Objectives. Laparoscopic renal cryoablation is a developmental minimally invasive nephron-sparing treatment alternative for highly select patients with small renal tumors. We present our evolving experience with this procedure. Methods. Thirty-two patients (34 tumors) with a mean tumor size of 2.3 cm on preoperative computed tomography underwent laparoscopic renal cryoablation. As dictated by the tumor location, cryoablation was performed by either the retroperitoneal (n = 22) or the transperitoneal (n = 10) laparoscopic approach using real-time ultrasound monitoring. A double freeze-thaw cycle was routinely performed. Results. The mean surgical time was 2.9 hours, cryoablation time 15.1 minutes, and blood loss 66.8 mL. For a mean intraoperative ultrasonographic tumor size of 2 cm, the mean cryolesion size was 3.2 cm. The hospital stay was less than 23 hours in 22 (69%) of 32 patients. Sequential magnetic resonance imaging scans demonstrated a gradual contraction in the mean diameter of the cryolesions. Of the 20 patients who underwent a 1-year follow-up magnetic resonance imaging scan, the cryoablated tumor was no longer visible in 5. Of note, 23 patients have now undergone a 3 to 6-month follow-up computed tomography-directed biopsy of the cryoablated tumor site; the biopsy was negative for cancer in all 23 patients. No evidence of local or port-site recurrence was found during a mean follow-up of 16.2 months. Conclusions. Critical long-term data regarding laparoscopic renal cryoablation, a developmental technique, are awaited. However, our initial experience is cautiously optimistic. Despite its significant potential for false-negative results, it is encouraging that the follow-up computed tomography-directed needle biopsies at 3 to 6 months were negative for cancer in 23 of 23 patients.

MR imaging of the kidneys after laparoscopic cryoablation.

We describe the MR imaging findings of patients who underwent laparoscopic renal lesion cryoablation. Twenty-one patients (men, 11; women, 10; age range, 36-84 years; average age, 65.5 years; SD, 11.9) with 23 small renal masses (< or =4 cm) underwent laparoscopic renal lesion cryoablation. Twenty patients (22 masses) underwent follow-up MR imaging on the first day after surgery, 12 (13 masses) at 1 month, 16 (18 masses) at 3 months, 14 (15 masses) at 6 months, and 12 (12 masses) at 12 months. Three radiologists retrospectively reviewed MR images for the signal intensity, characteristics, and size of cryolesions. CT-guided needle biopsy was performed 6 months after cryoablation (18 patients) and no evidence of malignancy was discovered. Including all lesions at all times on T1-weighted images, cryolesion signal intensity was isointense to renal parenchyma (47/76, 61.8%) or isointense with hyper- or hypointense foci (7/76, 9.2%). On T2-weighted images, almost all lesions (72/76, 94.7%) were isointense or hypointense, and there was a hypointense rim between the cryolesion and renal parenchyma in 38.2% of lesions (29/76). A thin peripheral rim of enhancement was noted in 19.7% (14/74) of lesions. Cryolesions decreased in size an average of 61.5% (SD, 22.82; n = 12) at 1 month, 78.7% (SD, 13.5; n = 17) at 3 months, 83.5% (SD, 24.3; n = 15) at 6 months, and 94.2% (SD, 8.1; n = 11) at 1 year after cryoablation (one patient was not scanned 1 day after cryoablation and was not included in our calculations). After renal cryoablation, MR imaging revealed common signal characteristics such as low-signal-intensity rims on T2-weighted images, enhancement patterns such as thin peripheral rims, and interval size changes.

Thermal Characteristics of a Hepatic Cryolesion Formedin Vitroby a 3-mm Implantable Cryoprobe

The objective of the investigation was to characterize the hepatic cryolesion formed with an implantable needle (3 × 100 mm) cryoprobe. This was used to produce cryolesions in isolated porcine liver tissue equilibrated to 37°C in a water bath. The shape, size, and temperature zones within the cryolesion and the effect of single versus repeated freeze–thaw cycles on cryolesion size were studied. The final shape of the cryolesion at 15–20 min freezing was cylindrical and its distal hemispherical end extended 8 mm beyond the tip of the cryoprobe. The rate of increase in maximum diameter was logarithmic and decreased from 4.7 mm/min during the first 5 min to 0.4 mm/min during the fourth 5-min period of freezing. By contrast, the rate of increase in volume was linear and ranged from 9.6 to 7.9 ml/min during the corresponding periods. The volume of the hepatic cryolesion after 20 min of continuous freezing was significantly greater than that of the cryolesion formed with 20 min of cumulative freezing interrupted by a 5-min spontaneous thaw. The ultimate temperatures reached and the cooling rates varied in different zones within the cryolesion depending on distances away from and alongside the cryoprobe. Diameter measurements taken in isolation do not reflect the actual growth rate of the cryolesion. Volume measurements define more accurately the amount of tissue frozen and leftin situ.Prolonged freezing beyond 20 min did not increase the diameter of the cryolesion. A single continuous freeze produces a larger cryolesion than two freeze–thaw cycles of the same freezing duration.

Hepatic cryosurgery precision: evaluation of ultrasonography, thermometry, and impedancemetry in a pig model.

One of the main problems of the use of liver cryosurgery is to be sure that a defined hepatic volume has been completely destroyed. We undertook an experimental pig study to determine histopathological evolution of cryolesions, to evaluate the value of intraoperative sonography, thermometry, and impedancemetry to monitor necrosis and to evaluate clinical and biological repercussions of hepatic cryosurgery. Forty-eight cryolesions were obtained by freezing each liver lobe of 12 experimental pigs during a 5-min contact with a flat cryoprobe cooled with liquid nitrogen. Cryolesions and the surrounding liver were monitored during cryosurgery by six thermocouple electrodes, five impedance electrodes, and intraoperative sonography. Animals were sacrificed immediately, 6 hr and between day 1 and day 32 after the procedure. Cryolesions were excised, and a full size pathological study was carried out. No morbidity or mortality was observed. At the end of the freezing time, cryolesions were hemispheric in shape, and their radius measured by sonography was 17.7 +/- 1.2 mm (mean +/- SD). Microscopic study showed sequential tissue alterations with edema, ischemic necrosis, tissue slough, and granulation. Cryolesions were sharply delineated from the normal liver tissue. The radius of necrosis at days 2 and 3 was 17 +/- 0.3 mm (mean +/- SD). It showed good correlation with the cryolesion size measured by intraoperative sonography. The temperature threshold to obtain complete normal liver necrosis was -15 degrees C. We found impedancemetry too difficult to use and not precise enough to monitor cryonecrosis. We conclude that intraoperative sonography and thermometry are useful means to monitor the extent of cryonecrosis during liver cryosurgery.

Hepatic cryosurgery precision evaluation of ultrasonography, thermometry, and impedancemetry in a pig model

One of the main problems of the use of liver cryosurgery is to be sure that a defined hepatic volume has been completely destroyed. We undertook an experimental pig study to determine histopathological evolution of cryolesions, to evaluate the value of intraoperative sonography, thermometry, and impedancemetry to monitor necrosis and to evaluate clinical and biological repercussions of hepatic cryosurgery. Forty-eight cryolesions were obtained by freezing each liver lobe of 12 experimental pigs during a 5-min contact with a flat cryoprobe cooled with liquid nitrogen. Cryolesions and the surrounding liver were monitored during cryosurgery by six thermocouple electrodes, five impedance electrodes, and intraoperative sonography. Animals were sacrificed immediately, 6 hr and between day 1 and day 32 after the procedure. Cryolesions were excised, and a full size pathological study was carried out. No morbidity or mortality was observed. At the end of the freezing time, cryolesions were hemispheric in shape, and their radius measured by sonography was 17.7 ± 1.2 mm (mean ± SD). Microscopic study showed sequential tissue alterations with edema, ischemic necrosis, tissue slough, and granulation. Cryolesions were sharply delineated from the normal liver tissue. The radius of necrosis at days 2 and 3 was 17 ± 0.3 mm (mean ± SD). It showed good correlation with the cryolesion size measured by intraoperative sonography. The temperature threshold to obtain complete normal liver necrosis was −15°C. We found impedancemetry too difficult to use and not precise enough to monitor cryonecrosis. We conclude that intraoperative sonography and thermometry are useful means to monitor the extent of cryonecrosis during liver cryosurgery. © 1996 Wiley-Liss, Inc.

Cardiac Cryolesions: Factors Affecting Their Size and a Means of Monitoring Their Formation

Twenty-seven endocardial cryolesions were created in mongrel dogs and analyzed to determine the effects on cryolesion size of both the initial myocardial temperature (37°C versus 12°C) and the pressure within the nitrous oxide delivery line (tank pressure of more than 700 pounds per square inch [psi] versus tank pressure of less than 700 psi). In addition, local myocardial temperatures were monitored to determine their utility in the intraoperative determination of the extent of cryothermic cell death. Cryolesion volume was significantly affected by both the initial myocardial temperature ( p > 0.001) and the line pressure ( p = 0.014). In a 37°C myocardium, the mean lesion volume ranged from 0.501 ± 0.183 cc at line pressures lower than 700 psi to 0.839 ± 0.258 cc at line pressures greater than 700 psi. In a 12°C myocardium, the mean volume was 1.151 ± 0.436 cc at line pressures lower than 700 psi and 1.361 ± 0.288 cc at line pressures higher than 700 psi. A myocardial temperature of 0°C occurs at the edge of the area of cell death. When analyzing the range from −5° to +5°C, the probability of a point at or lower than 0°C falling inside the cryolesion is 84.2%. Monitoring intra-myocardial temperature will predict the border of a cryolesion.

The Effect of Local Anesthesia and Epinephrine on the Size of Cryolesions in the Experimental Animal

Using the pig as an experimental animal, cryolesions were made 20 minutes after injecting the freeze sites with either saline, 1% Lidocaine, or 1% lidocaine with Epinephrine 1:100,000. The size of the cryolesion was measured 1 week later by injecting the animal with a vital dye and measuring the nonstained areas with a compensating planimeter. Saline and lidocaine had no consistent effect on the size of the necrotic tissue produced by freezing, but epinephrine significantly augmented (47 percent) the killing effectiveness of cryosurgery. If local anesthesia is to be used for cryosurgery, it should contain a vasoconstricting agent.

The Effect of Local Anesthesia and Epinephrine on the Size of Cryolesions in the Experimental Animal

The Effect of Local Anesthesia and Epinephrine on the Size of Cryolesions in the Experimental Animal