EDUCATION EXHIBITS 887 Percutaneous Cryoabla- tion of ......888 July-August 2010 radiographics.rsna.org Introduction Renal cancer represents 3%–4% of all malignan-cies, with approximately

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887EDUCATION EXHIBITS

Brian C. Allen, MD • Erick M. Remer, MD

Percutaneous cryoablation of renal tumors requires a number of important steps for success and relies heavily on imaging for treat-ment planning, intraprocedural guidance and monitoring, detec-tion of untreated tumor, and surveillance for disease progression. Imaging-guided percutaneous cryoablation has several advantages over laparoscopic cryoablation. In particular, computed tomography (CT) and magnetic resonance (MR) imaging allow global evaluation of the ablation zone and an accurate depiction of the treatment mar-gin. Ultrasonography allows real-time guidance of probe placement but cannot help depict ice ball formation as accurately as CT or MR imaging. Multiphasic CT or MR imaging should be performed at structured intervals following ablation. Treated tumors are expected to decrease in size over time, and lesion growth and internal or nodu-lar enhancement are suspicious for tumor recurrence or progres-sion. Complications include probe site pain, hematoma, incomplete ablation, and recurrent tumor. Current limitations of percutaneous cryoablation include the inability to control hemorrhage without in-traarterial access and a lack of long-term follow-up data. Nevertheless, percutaneous cryoablation is an effective choice for minimally invasive nephron-sparing treatment of renal tumors.©RSNA, 2010 • radiographics.rsna.org

Percutaneous Cryoabla-tion of Renal Tumors: Patient Selection, Tech-nique, and Postproce-dural Imaging1

Abbreviations: RCC = renal cell carcinoma, RF = radiofrequency

RadioGraphics 2010; 30:887–902 • Published online 10.1148/rg.304095134 • Content Codes: 1From the Imaging Institute, Cleveland Clinic, 9500 Euclid Ave, Cleveland, OH 44195. Recipient of a Cum Laude award for an education exhibit at the 2008 RSNA Annual Meeting. Received June 25, 2009; revision requested October 7 and received November 10; accepted November 19. For this CME activity, the authors, editors, and reviewers have no relevant relationships to disclose. Address correspondence to E.M.R. (e-mail: [email protected]).

See the commentary by Sandler and Ahrar following this article.

©RSNA, 2010

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leARnInG OBJeCTIVeSAfter reading this article and taking the test, the reader

will be able to:

List the advan- ■

tages of cryoablation over radiofrequency ablation in the treatment of renal tumors.

Discuss the ex- ■

pected postcryoab-lation imaging findings.

Describe the post- ■

procedural imaging features of incom-plete cryoablation and disease progres-sion.

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TEACHING POINTS

888 July-August 2010 radiographics.rsna.org

IntroductionRenal cancer represents 3%–4% of all malignan-cies, with approximately 54,000 new cases having been projected for 2008 (1). The increasing use of cross-sectional imaging has led to a growing number of incidentally discovered renal tumors, and any solid renal lesion discovered at ultra-sonography (US) or enhancing lesion discovered at computed tomography (CT) or magnetic resonance (MR) imaging has a high likelihood of being malignant (2–4). Radical nephrectomy re-mains the standard of reference against which all other forms of surgical treatment must be mea-sured (5). Recently, “nephron-sparing” therapies have become more common, and 5-year survival rates for patients who undergo partial nephrec-tomy are similar to those for radical nephrectomy patients (6). Minimally invasive therapies are per-formed with the aim of preserving renal function and decreasing pain, morbidity, length of hospital stay, and procedure time. Initially, these therapies were performed laparoscopically, but now some patients are candidates for percutaneous tumor ablation. The primary ablation techniques are cryoablation and radiofrequency (RF) ablation, which afford minimally invasive treatment while maximizing nephron preservation. Technical improvements have led to an increasing use of percutaneous ablation for small renal tumors.

In this article, we discuss and illustrate percu-taneous cryoablation in terms of patient selec-tion and treatment planning, technical aspects (including guidance with US, CT, and MR imag-ing), results, postablation imaging findings, and complications.

Patient Selection and Treatment Planning

Radical nephrectomy is the standard of refer-ence for treatment of renal cell carcinoma (RCC), and the outcomes of other therapies should be compared with those of nephrectomy. Because partial nephrectomy has demonstrated outcomes similar to those of total nephrectomy, there is a growing trend toward the use of other nephron-sparing therapies.

Cryoablation has been performed using open, laparoscopic, and percutaneous approaches. Per-cutaneous treatment of RCC is ideal for patients in whom partial or complete nephrectomy is un-desirable or contraindicated (7, 8). Such patients include those who are likely to develop numerous tumors over the course of a lifetime (eg, patients with von Hippel–Lindau syndrome, elderly pa-

tients, and patients with medical comorbidities or renal failure). Cryoablation has also been used in patients with a solitary kidney or renal remnants to maximize the nephron-sparing effort with preservation of renal function, since creatinine levels have been shown to increase only mini-mally following the procedure (9). In general, at our institution, patients who can tolerate a partial nephrectomy are treated by the urologic sur-geons. If a patient is thought to be a poor surgical candidate or has undergone prior ipsilateral renal surgery, cryoablation is offered. These general guidelines have been relaxed somewhat as longer-term outcomes of cryoablation have started to become available (10).

The ideal renal tumor for the percutaneous approach is small (<3 cm), partially exophytic, and posteriorly located in a patient who cannot tolerate a partial nephrectomy. Because long-term results of renal tumor ablation are not yet available, many authors believe that, to prevent tumor growth, the main indications for cryoab-lation should include comorbid medical condi-tions, prior renal surgery, or a solitary kidney (11). Relative contraindications for percutaneous cryoablation include younger patient age, larger tumors, hilar and centrally located tumors, and cystic neoplasms (12). To avoid the risk of adja-cent organ injury, posterior tumors are preferred for treatment, whereas central lesions have been associated with a higher rate of treatment failure (13). Larger (>4-cm) tumors may be treated with good short-term results, but hemorrhagic compli-cations are more common (11,14).

To be considered for cryoablation, a patient should have recently undergone multiphasic CT or MR imaging. This allows confirmation of a renal mass, detection of lymphadenopathy and metastatic disease, and assessment for renal vein tumor extension, and provides an overview of the vascular anatomy. The aim is to ablate the exact volume of tissue that would need to be resected at partial nephrectomy.

Percutaneous therapies rely on radiologic and percutaneous biopsy findings for diagnosis. Inves-tigation has suggested that a substantial percent-age (up to 37%) of patients referred for percuta-neous therapy actually have benign renal masses (15). This is related to the fact that some lesions, including benign cystic lesions, angiomyolipomas with minimal fat, and oncocytomas may be difficult to differentiate from RCC. Some authors further suggest that a biopsy-proved diagnosis should be made before ablation. Others stress that there is a significant degree of inaccuracy when a benign diagnosis is made from frozen specimens, and a

RG • Volume 30 Number 4 Allen and Remer 889

fair number of needle biopsies yield indetermi-nate results (16,17). Consequently, some authors recommend that lesions be ablated despite nega-tive biopsy results (16,17). Although the need for biopsy-proved diagnosis prior to ablation is controversial, most authors agree that, at a mini-mum, biopsy should be performed at the time of ablation to gather information for guiding further treatment. If a benign diagnosis is made, oncologic surveillance is not necessary. In general, at our institution, percutaneous biopsy is performed im-mediately prior to ablation, which in turn is then performed before biopsy results are available.

Technical Aspects of CryoablationThe primary thermal ablation techniques used for renal tumors are RF ablation and cryoablation. RF

ablation causes coagulative necrosis by the appli-cation of an alternating current through an elec-trode, which generates frictional heat. The amount of heat generated depends on distance from the electrode, intensity of the RF current, and dura-tion of application of the RF current (18).

Cryoablation makes use of rapid cooling to cause cell death. Two sequential and synergistic mechanisms lead to cell death. Intra- and ex-tracellular ice crystals are directly cytotoxic and lead to cell dehydration and rupture. When the frozen tissue is thawed, there is microvascular occlusion with cell hypoxia, resulting in indirect ischemic injury (19).

During cryoablation, a cryoprobe—most often a straight metallic shaft—is inserted into the target tissue. A liquid gas, most commonly argon, is used to rapidly cool the cryoprobe. An ice ball forms along the cryoprobe shaft and enlarges over time (Fig 1). Cell death is time- and tem-perature dependent, with the critical threshold for cell death being between −19.4°C and −40°C (20). The cryoprobe itself reaches −190°C. The ice ball must extend at least 3 mm beyond the tumor margin to achieve a tissue temperature of −20°C at the margin, and the goal should be an ice ball margin of at least 5 mm to avoid residual or untreated tumor (21).

Studies have shown that an initial freeze fol-lowed by thawing and additional freezing (double freeze-thaw cycle) results in a larger amount of liquefaction necrosis and improves treatment efficacy, and this approach is routinely used clini-cally (22). The first freeze lasts 8–15 minutes, and the second freeze lasts 5–20 minutes (11). Temperature monitoring and imaging are used to determine when freezing is adequate. Following the procedure, cryoprobes are actively warmed with helium gas and are removed when they reach body temperature.

Tissue freezing becomes less effective as the distance from the cryoprobe increases. The use of multiple probes affords shorter tissue-probe distances throughout the mass. Cryoprobes are available in various sizes (1.4–8 mm) and yield different-sized and -shaped ice balls. The simul-taneous use of multiple cryoprobes can shape the ice so that it encompasses an entire tumor (Fig 2). Probes should be positioned 1 cm from the tumor margin and 1–2 cm from each other (23). The use of multiple probes creates a syner-gistic effect that results in the formation of even more ice (24,25).

Figure 2. Axial unenhanced CT scan shows multiple cryoprobes, which may be used simultaneously to treat large or multiple lesions.

Figure 1. Photograph obtained during cryoablation shows a laparoscopic cryoprobe and an ice ball.


As mentioned earlier, cryoablation has been performed with open, laparoscopic, and percu-taneous approaches. Proponents of the laparo-scopic approach suggest that it allows the opera-tor to move vital structures and to place larger cryoprobes, and also allows surgical hemostasis. During percutaneous ablation, better intrapro-cedural monitoring can be achieved with CT or MR imaging than with US, which has limited capability to monitor deeper structures due to the acoustic shadowing produced by the ice ball in the constrained laparoscopic environment. With percutaneous treatment, CT allows easy, rapid, accurate depiction of the ablation zone due to the decreased attenuation of frozen tissue. Percu-taneous treatment is less invasive and does not require manipulation of intraabdominal contents. Other benefits include a more rapid recovery and fewer complications.

Cryoablation versus RF AblationCryoablation allows treatment of central lesions near the ureter and collecting system, since there is less risk of ureteral stricture than with RF abla-tion (26,27). Cryoablation is less painful than RF ablation, and intraprocedural determination of treatment adequacy is easier, since multiple cryo-probes can be placed and used simultaneously (28,29). Unfortunately, cryoablation involves an increased risk of hemorrhagic complications, since blood vessels are not cauterized as they are with RF ablation.

A meta-analysis of 47 studies (1375 treated lesions) that compared cryoablation with RF ablation found that repeat ablation was required more frequently with RF ablation (8.5% of cases versus 1.3% for cryoablation), and that local tumor progression occurred more frequently with RF ablation (12.9% versus 5.2%) (30). Metastatic disease was also more common in the RF ablation group (2.5% of cases versus 1%) (30). One series comparing cryoablation with RF ablation found less tumor persistence or recurrence with cryoab-lation (11.1% of cases versus 1.8%) (31).

Results of AblationShort- and intermediate-term results with abla-tion of renal masses have been favorable. The short-term (follow-up = 11 months) rate of tu-mor recurrence following laparoscopic cryoabla-tion is low (0%–5% of cases), with technical suc-cess and efficacy being achieved in up to 100% of cases for tumors less than 7 cm in size (11,32).

An intermediate-term (follow-up ≥3 years) study of 56 patients who had undergone laparoscopic cryoablation showed an overall survival rate of 89%, a cancer-specific survival rate of 98%, and a cryoablation-specific survival rate of 100% (10). Only 3.6% of patients had biopsy-proved persis-tent or recurrent tumor (10). Long-term results with laparoscopic cryoablation were also favor-able. Patients who were followed up for at least 5 years had an 83% overall survival rate, a 95% cancer-specific survival rate, and a 78% disease-free survival rate (33). Similar results were found by comparing laparoscopic partial nephrectomy with laparoscopic cryoablation (34).

A meta-analysis comparing percutaneous abla-tion with open and laparoscopic surgical ablation demonstrated a primary effectiveness rate of 87% for the former, compared with 94% (P < .05) for the latter. The secondary effectiveness rates (ie, success rates after two treatments) were 92% and 95%, respectively; the difference between these two percentages was not statistically significant. Thus, more than one session may be required to successfully treat masses percutaneously. On the other hand, in a study by Hui et al (35), major complications occurred in 3% of cases of percu-taneous treatment and in 7% of open procedures (P < .05).

Comparison of the results of short-term laparoscopy (60 patients) and percutaneous cryoablation (30 patients) at one hospital showed similar rates of recurrent or unablated tumor (10% of cases versus 6.7%; P = 0.68) (36). This study also showed fewer major complications but more minor complications after percutane-ous cryoablation (36). The disease-free survival rate was 100% for both groups at 14.5 months. Furthermore, percutaneous therapy resulted in hospital charges that were 40% lower, as well as a shorter hospital stay (1.1 versus 2.4 days) (36).

At our institution, similar results have been achieved in 244 laparoscopy patients and 63 percutaneous cryoablation patients. Patients with a solitary kidney or prior renal surgery are much more likely to be treated percutaneously (30% of cases) than laparoscopically (12%). Complication rates for the two approaches are similar, and the rates of recurrence do not differ significantly.

Percutaneous CryoablationPercutaneous cryoablation consists of several steps, including planning the ablation, targeting the lesion to be treated, guiding placement of the probe, monitoring the ablation, and determining the treatment end point (37).


A preprocedural contrast material–enhanced examination is helpful for planning and carry-ing out tumor ablation. The patient is placed in a position that affords easy access to the tumor. To improve access, patients may be positioned prone and obliquely. At times, vital organs impede ac-cess to the mass. Success has been reported in displacing these structures with water, carbon di-oxide, or balloons (Fig 3) (38,39). Bowel may be protected with positional or mechanical displace-ment. One group suggests that a pneumothorax be intentionally created in the treatment of upper pole lesions to obviate multiple passes across the

pleura (Fig 3d) (40). The genitofemoral nerve descends laterally along the psoas muscle, and injury may result in postprocedural pain (41,42). Those who are performing ablations should be aware of this anatomy to protect against injury.

Intrarenal structures are also subject to dam-age from cryoablation; however, blood vessels are relatively resistant due to flowing blood. The collecting system is also relatively resistant to freezing, but animal studies suggest that if it is damaged, it heals in a watertight manner without stricture (26,27).

Figure 3. Techniques for improving the outcome of ablation. (a) CT-guided hydrodissection. Unenhanced CT scan shows how sterile water (arrow) may be instilled to displace intraabdominal organs, such as bowel (arrowhead), away from the intended ablation zone. (b) Unenhanced CT scan shows a balloon catheter displac-ing the liver (arrow). (c) CT scan obtained after the intravenous administration of contrast material shows how such contrast material may be used to better depict isoattenuating renal masses (arrowhead). (d) CT scan shows an intentionally created pneumothorax (arrow), which may be beneficial in treating upper pole lesions by obviating multiple passes across the pleura. Dashes indicate a 1-cm mass at the upper pole of the kidney.


With respect to patient sedation and monitor-ing, different approaches are used. Some groups advocate general anesthesia to control respiration and maximize patient tolerance. Other investiga-tors (ourselves included) use conscious seda-tion to negate the risk associated with the use of anesthetics, in keeping with our philosophy that percutaneous cryoablation should be a minimally invasive outpatient procedure.

US GuidanceUS is universally available, making it an attractive choice for guiding percutaneous therapy. How-ever, larger patients may have limited acoustic penetrance, making small tumors difficult to visu-alize. Also, probes have limited echogenicity and are best seen during initial placement.

During the freezing process, the leading edge of the ice ball is an echogenic surface with strong posterior shadowing (Fig 4). As a result, multiple views are required to ensure adequate margins. The leading margin of the ice ball may be ob-scured by posterior shadowing if the US probe is not positioned on the side opposite the tumor from the cryoprobe (43,44). At some centers, cryoprobes are placed under US guidance, and the procedure is monitored with CT (36). US may be better suited to the laparoscopic environment, since the transducer can be placed on the side of the kidney opposite the tumor (43). We believe that US is suboptimal (compared with CT or MR imaging) for monitoring percutaneous cryoabla-tion due to the shadowing produced by the ice ball, which prevents the operator from visualizing which portion of the tumor has been treated.

CT GuidanceCryoprobe guidance with CT is best achieved with CT fluoroscopy. Because the kidney often moves significantly during respiration, a coopera-tive patient, or one who is under general anesthe-sia, facilitates a smooth procedure. CT provides a global view of the entire cryolesion, and there is no need to rely on the acoustic window as with US. One challenge is the isoattenuating renal tumor, which may require intravenous contrast material for visualization (Fig 3c).

During the procedure, the ice ball has low at-tenuation and sharply defined borders (Fig 5). CT also allows determination of cell death, which is 3 mm inside the edge of the ice ball. One drawback to CT guidance or monitoring is the use of ion-

izing radiation, resulting in exposure to both the operator and the patient. At our institution, cryo-probes are placed under CT fluoroscopic guid-ance, and the procedure is monitored with CT.

MR Imaging GuidanceMR imaging allows the operator to image in any plane. A global view of the ablation site is provided, and it is possible to visualize lesions that cannot be visualized with US or CT. The ice ball is markedly hypointense relative to the renal parenchyma, and imaging may be performed in near real time (Fig 6) (45). Disadvantages include the relatively limited availability of in-terventional MR imaging units. In addition, MR imaging–compatible cryoprobes are required. MR imaging guidance is more expensive, and there is a general lack of familiarity with such guidance among interventionalists. However, lack of ionizing radiation is a significant advantage of MR imaging guidance over CT guidance.

Low-field-strength open MR imaging is typi-cally used, with T1- and T2-weighted images allowing sufficient contrast between the ice ball, tumor, and kidney. The procedure typically lasts 3–4 hours and requires repeated breath holds of up to 60 seconds. General anesthesia may be required (46).

Postablation ImagingPostablation imaging is generally performed at increasing follow-up intervals if no suspicious findings are seen. At our institution, patients are imaged 1, 3, 6, 12, 18, and 24 months after ablation and at 12-month intervals thereafter

Figure 4. US image shows an ice ball (cursors) with an echogenic surface (ar-row) and strong posterior shadowing.


Figure 6. MR imaging–guided cryoablation. Fat-sup-pressed T1-weighted MR im-age shows a well-marginated, hypointense ice ball (arrow). Note the tracking of the ice ball along the probe shaft.

Figure 5. CT-guided percutaneous cryoablation. (a) Axial CT scan obtained with the patient in the left lateral decubitus position shows a posterior, partially exophytic mass. (b) CT scan shows the mass, the cryoprobe (long arrow), and early ice ball formation (arrowhead). Short arrows indicate a small perinephric hematoma. (c) CT scan obtained later in the procedure again shows the hematoma (arrows). The enlarging ice ball has uniformly low attenuation and is well marginated. Cryoablation is ideal for treatment of this lesion, which measures less than 3 cm, is partially exophytic, and is located posteriorly. Note that the ablation margin extends 0.5–1.0 cm beyond the mass.


of cases show some persistent enhancement in the ablation zone without residual tumor in the first few months after ablation (Fig 8) (49,50). The presence of peripheral enhancement during this time is relatively common, and biopsy should not be performed, since this enhancement will likely disappear and, besides, may be difficult to target. Infiltration in the fat surrounding the ablation zone may enhance in the acute period as well (49). Any nodular or central enhancement, or any increase in the size of the ablation zone, should raise concern for incomplete treatment or disease recurrence.

normal MR Imaging FindingsAs with CT, the ablation zone at MR imaging is larger than the pretreated tumor. The ablation zone has a variable appearance with T1- and T2-weighted sequences, but cryolesions are typically T1 isointense or heterogeneously isointense rela-tive to the renal parenchyma and heterogeneously T2 hypointense (47). Following the administra-tion of gadolinium-based contrast material, there is clear delineation of the ablation zone border (Fig 9).

Figure 7. Normal early postprocedural CT ap-pearance of the cryoablation zone. (a) Prepro-cedural unenhanced CT scan shows a posterior, partially exophytic renal mass. (b) Unenhanced CT scan obtained 1 day after the procedure shows a low-attenuation ablation site, a small perinephric hematoma (arrow), and mild stranding. (c) On a contrast-enhanced CT scan obtained at the same time as b, the ablation zone (arrowhead) has low attenuation, is well demarcated, does not enhance, and is larger than the renal mass seen on the pre-procedural image (cf a).

to assess for disease recurrence or progression. Multiphasic CT or MR imaging both with and without contrast material may also be performed. We prefer MR imaging due to its superior contrast resolution (47). Initial imaging may be performed on the first day after the procedure, especially if no contrast material is given during the procedure. This imaging is used to assess for completeness of the procedure and for complica-tions such as hematoma.

Postablation Findings

normal CT FindingsThe use of intravenous contrast material is essen-tial in the postprocedural period, and the resulting images should be compared with the preabla-tion images. Immediately following ablation, the treatment zone appears larger than the original tumor, since a margin of normal parenchyma has intentionally been ablated. The ablation zone has low attenuation, does not typically enhance, and should decrease in size over time (Fig 7) (48). The amount of stranding surrounding the ablation zone should also decrease over time. Although ab-lated tumors do not typically enhance, 15%–20%


Figure 9. Normal postprocedural MR imaging appearance of the cryoablation zone. (a) Preprocedural contrast-enhanced CT scan shows a nearly isoattenuating mass located posteriorly (arrow). (b, c) Unen-hanced (b) and gadolinium-enhanced (c) fat-suppressed T1-weighted MR images obtained 1 day after ablation show heterogeneous high signal intensity within the ablation zone (arrowhead in b), a finding that makes the detection of enhancement difficult. (d) Postcontrast subtraction T1-weighted MR image helps confirm the lack of residual enhancement within the ablation zone.

Figure 8. Persistent enhancement following cryoablation. (a) Contrast-enhanced CT scan shows a peripherally enhancing lesion in the posterior kidney (arrow). (b) Contrast-enhanced CT scan obtained 1 day after cryoablation shows the lesion with persistent peripheral enhancement (arrowhead), even though the ablation zone fully encompasses the lesion. The enhancement re-solved within 6 months of ablation.


The ablation zone should decrease in size over time, a finding that is consistent with ablation site involution (Fig 10). One study showed an average decrease in the size of the ablation zone of 26% at 3 months, 56% at 1 year, and 75% at 2 years, with complete resolution at 3 years in 38% of cases (10).

Lack of enhancement is a reliable indicator of successful cryoablation (51). Residual viable tumor is typically T2 hyperintense and enhances. Image subtraction is often helpful for detecting subtle enhancement. Thin, smooth peripheral enhancement is relatively common and likely represents reactive change and interstitial hemor-rhage. In approximately 35% of cases, ablation zones demonstrate early peripheral enhancement 1 day after ablation (47). Some authors advocate waiting 6 months after technically successful renal cryoablation before performing contrast-enhanced MR imaging (52).

Figure 11. Residual tumor following cryoablation. (a) Preprocedural contrast-enhanced CT scan shows a peripheral renal tumor (arrow). (b) Follow-up subtraction T1-weighted MR image shows a peripheral area of enhancement (arrowhead), a finding that is consistent with incomplete ablation.

Figure 10. Interval decrease in the size of the cryoablation defect. (a) Contrast-enhanced T1-weighted MR image obtained 6 months after ablation shows a cryoablation zone without en-hancement (arrow). (b) On a contrast-enhanced T1-weighted MR image obtained 1 year after ablation, the ablation zone (arrow) has decreased in size. (c) On a contrast-enhanced T1-weighted MR image obtained 2 years after ablation, the ablation zone (arrow) has completely involuted, resulting in a cortical scar.


As with CT, postprocedural images should be compared with the preablation images. Residual unablated tumor is seen as enhancing tissue of variable shape within the boundaries of the mass at preablation imaging (Fig 11). Recur-rence is most common at the periphery of the cryoablation site and is characterized by new nodular enhancement or internal enhancement at follow-up imaging (Fig 12). If the size of the ablation zone increases or remains unchanged, recurrence may be suspected and biopsy should be performed (10).

Complications of AblationIn a multicenter study of 271 patients treated with laparoscopic or percutaneous ablation, Johnson et al (53) found 30 complications, five of which (1.8% of the study population) were major. These major complications included sig-nificant hemorrhage (Fig 13), ileus, ureteropelvic junction obstruction (for RF ablation), conver-sion to open nephrectomy, and urine leak (for RF ablation). Minor complications included urinary tract infection, pneumonia, minor hemorrhage, an elevated creatinine level, and wound infection. Pain and paresthesias at the surgical site were the most common complications (n = 14) (53).

Figure 12. Tumor recurrence (disease progression). (a) Preprocedural contrast-enhanced CT scan shows an enhancing RCC (arrow). (b) Gadolinium-enhanced T1-weighted MR image obtained 6 months after ablation shows cortical loss in the ablation zone, with no enhancement to suggest tumor recurrence. (c) MR image obtained 2 years after ablation (image is slightly cephalad to b) shows an enhancing nodule at the periphery of the ablation zone (arrowhead).

Figure 13. Postablation hemor-rhage. Coronal multiplanar reformat-ted image from contrast-enhanced CT data obtained 1 day after ablation shows a high-attenuation hematoma in the ablation zone (arrowhead) and left psoas muscle (arrow).


A urine leak in cryoablation is rare, since inten-tional “cryoinjury” heals in a watertight manner (26). Postablation hemorrhage commonly mani-fests with flank pain, whereas pseudoaneurysm manifests with gross hematuria with or without flank pain (Fig 14) (54). Bowel obstruction and ureteropelvic junction strictures have been reported with RF ablation. Probe track seeding following cryoablation is extremely rare (Fig 15).

ConclusionsPercutaneous cryoablation is an effective choice for minimally invasive nephron-sparing treatment of renal tumors. Intraprocedural monitoring affords visualization of the forming ice ball and helps detect proximity to surrounding structures. Percutaneous treatment is less invasive than other nephron-sparing surgeries, is associated with fewer severe complications, and can be per-formed on an outpatient basis with conscious se-

dation. In addition, it is 2.2–2.7 times less costly than open or laparoscopic surgery (55). Current limitations include the inability to control hemor-rhage without intraarterial access and a lack of long-term follow-up data.

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Figure 14. Pseudoaneurysm in a 74-year-old man who developed intermittent gross he-maturia 5 months after undergoing renal RF ablation. (a) Postcontrast T1-weighted MR image shows curvilinear intense enhancement in the ablation zone (arrow). (b) Conven-tional angiogram shows successful coil embolization of a pseudoaneurysm (arrowhead).

Figure 15. Probe track seeding in an 84-year-old man in whom percutaneous cryoablation of a 3.5-cm lower pole RCC was apparently successful. The ablation was performed with four cryoprobes. Follow-up gadolinium-enhanced T1-weighted MR image obtained 7 months after ablation shows an enhancing perinephric nodule (short arrow) near the ab-lation zone (long arrow). The nodule proved to be a high-grade anaplastic tumor.


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This article meets the criteria for 1.0 AMA PRA Category 1 CreditTM. See pp 1149–1156.

Teaching Points July-August Issue 2010

Percutaneous Cryoablation of Renal Tumors: Patient Selection, Technique, and Postprocedural ImagingBrian C. Allen, MD • Erick M. Remer, MD

RadioGraphics 2010; 30:887–902 • Published online 10.1148/rg.304095134 • Content Codes:

Page 888The ideal renal tumor for the percutaneous approach is small (<3 cm), partially exophytic, and posteri-orly located in a patient who cannot tolerate a partial nephrectomy.

Page 889Cryoablation makes use of rapid cooling to cause cell death. Two sequential and synergistic mecha-nisms lead to cell death. Intra- and extracellular ice crystals are directly cytotoxic and lead to cell dehydration and rupture. When the frozen tissue is thawed, there is microvascular occlusion with cell hypoxia, resulting in indirect ischemic injury (19).

Page 896The ablation zone should decrease in size over time, a finding that is consistent with ablation site involu-tion (Fig 10).

Page 896Lack of enhancement is a reliable indicator of successful cryoablation (51). Residual viable tumor is typi-cally T2 hyperintense and enhances. Image subtraction is often helpful for detecting subtle enhancement.

Page 897As with CT, postprocedural images should be compared with the preablation images. Residual unab-lated tumor is seen as enhancing tissue of variable shape within the boundaries of the mass at preab-lation imaging (Fig 11). Recurrence is most common at the periphery of the cryoablation site and is characterized by new nodular enhancement or internal enhancement at follow-up imaging (Fig 12). If the size of the ablation zone increases or remains unchanged, recurrence may be suspected and biopsy should be performed (10).

Figure 12. Tumor recurrence (disease progression). (a) Preprocedural contrast-enhanced CT scan shows an enhancing RCC (arrow). (b) Gadolinium-enhanced T1-weighted MR image obtained 6 months after ablation shows cortical loss in the ablation zone, with no enhancement to suggest tumor recurrence. (c) MR image obtained 2 years after ablation (image is slightly cephalad to b) shows an enhancing nodule at the periphery of the ablation zone (arrowhead).

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EDUCATION EXHIBITS 887 Percutaneous Cryoabla- tion of ......888 July-August 2010 radiographics.rsna.org Introduction Renal cancer represents 3%–4% of all malignan-cies, with approximately