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Minimally Invasive Treatment of Malignant Hepatic Tumors: At the Threshold of a Major Breakthrough¹

¹ From the Departments of Radiology, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Dr, San Antonio, TX 78284-7800 (G.D.D., O.I.K., H.R.); University of Pennsylvania, Philadelphia (M.C.S); Beth Israel Deaconess Medical Center, Boston, Mass (R.A.K.); Ospedale Civile, Vimercate, Milan, Italy (T.L.); University College London, Middlesex Hospital, London, England (W.R.L., A.R.G.); Kumamoto University, Kumamoto, Japan (Y.Y); Erciyes University, Kayseri, Turkey (O.I.K); and Hanyang University, Seoul, South Korea (H.R). Recipient of a Summa Cum Laude award and an Excellence in Design award at the 1998 RSNA scientific assembly. Received May 17, 1999; revisions requested July 22 and received August 24; accepted August 25. Address reprint requests to G.D.D.

	Abstract

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Six existing minimally invasive techniques for the treatment of primary and secondary malignant hepatic tumors—radio-frequency ablation, microwave ablation, laser ablation, cryoablation, ethanol ablation, and chemoembolization—are reviewed and debated by noted authorities from six institutions from around the world. All of the authors currently believe that surgery remains the treatment of choice for patients with resectable hepatic tumors. However, the clinical results of each of the minimally invasive techniques presented have exceeded those obtained with conventional chemotherapy or radiation therapy. Thus, for nonsurgical patients, these techniques are becoming standard independent or adjuvant therapies. In addition, with continued improvement in technology and increasing clinical experience, one or more of these minimally invasive techniques may soon challenge surgical resection as the treatment of choice for patients with limited hepatic tumor.

Index Terms: Alcohol ablation • Cryotherapy • Interventional procedures, technology • Lasers, interstitial therapy • Liver neoplasms, chemotherapeutic infusion, 761.1266 • Liver neoplasms, therapy, 761.1266 • Radiofrequency (RF) ablation

	Introduction

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Primary and secondary malignant hepatic tumors are some of the most common tumors worldwide. Unfortunately, chemotherapy and radiation therapy are ineffective treatment methods. Surgical resection is considered the only potentially curative option; however, few patients are surgical candidates (1–3). Recent results from multiple investigations indicate that several minimally invasive treatment techniques are very effective for treating primary and secondary malignant hepatic tumors and that they may replace surgical resection in the near future (4,5).

In this article, international experts present their experience with six promising minimally invasive treatment techniques: radio-frequency ablation, microwave ablation, laser ablation, cryoablation, ethanol ablation, and chemoembolization (Fig 1). Aspects of each technique including mechanism of action, equipment, patient selection, treatment technique, and recent patient outcome are presented. The benefits and limitations of each technique are discussed.

View larger version (131K): [in this window] [in a new window] [Download PPT slide]   Figure 1.   Computer-generated image depicts the essential elements of US-guided percutaneous ablation of liver tumors as well as representative pre- and postablation CT scans.

	Radio-frequency Ablation: Perspectives from Gerald D. Dodd III, Okkes I. Karahan, and Hyunchul Rhim

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Mechanism
Alternating electric current operated in the range of radiofrequency can produce a focal thermal injury in living tissue. Shielded needle electrodes are used to concentrate the energy in selected tissue. The tip of the electrode conducts the current, which causes local ionic agitation and subsequent frictional heat (Fig 2) (13). Temperatures in excess of 50°C produce coagulative necrosis. A 2–5-cm spherical thermal injury can be produced with each ablation.

View larger version (177K): [in this window] [in a new window] [Download PPT slide]   Figure 2a.   Mechanism of radio-frequency ablation. (a) Schematic depicts a four-prong needle electrode in which an alternating electric current at 460 KHz has caused ionic agitation around the electrode tip. (b) Schematic illustrates the ionic agitation, which causes frictional heat immediately around the needle. (c) Schematic shows how the heat caused by the agitation expands by conduction into the surrounding tissues to form a roughly spherical thermal injury.

View larger version (166K): [in this window] [in a new window] [Download PPT slide]   Figure 2b.   Mechanism of radio-frequency ablation. (a) Schematic depicts a four-prong needle electrode in which an alternating electric current at 460 KHz has caused ionic agitation around the electrode tip. (b) Schematic illustrates the ionic agitation, which causes frictional heat immediately around the needle. (c) Schematic shows how the heat caused by the agitation expands by conduction into the surrounding tissues to form a roughly spherical thermal injury.

View larger version (144K): [in this window] [in a new window] [Download PPT slide]   Figure 2c.   Mechanism of radio-frequency ablation. (a) Schematic depicts a four-prong needle electrode in which an alternating electric current at 460 KHz has caused ionic agitation around the electrode tip. (b) Schematic illustrates the ionic agitation, which causes frictional heat immediately around the needle. (c) Schematic shows how the heat caused by the agitation expands by conduction into the surrounding tissues to form a roughly spherical thermal injury.

View larger version (165K): [in this window] [in a new window] [Download PPT slide]   Figure 3a.   Photographs show radio-frequency ablation needle electrodes in use today, including a 15-gauge needle electrode with four retractable prongs (Rita Medical Systems) (a), a 14-gauge needle electrode with 10 retractable prongs (Radiotherapeutics) (b), and a 17-gauge internally cooled-tip needle in a three-needle cluster (Radionics) (c).

View larger version (179K): [in this window] [in a new window] [Download PPT slide]   Figure 3b.   Photographs show radio-frequency ablation needle electrodes in use today, including a 15-gauge needle electrode with four retractable prongs (Rita Medical Systems) (a), a 14-gauge needle electrode with 10 retractable prongs (Radiotherapeutics) (b), and a 17-gauge internally cooled-tip needle in a three-needle cluster (Radionics) (c).

View larger version (188K): [in this window] [in a new window] [Download PPT slide]   Figure 3c.   Photographs show radio-frequency ablation needle electrodes in use today, including a 15-gauge needle electrode with four retractable prongs (Rita Medical Systems) (a), a 14-gauge needle electrode with 10 retractable prongs (Radiotherapeutics) (b), and a 17-gauge internally cooled-tip needle in a three-needle cluster (Radionics) (c).

Patient Selection and Technique
Most investigators are limiting treatment with radio-frequency ablation to patients with four or fewer, 5-cm or smaller, primary or secondary malignant hepatic tumors and no extrahepatic tumor. Ideal tumors are smaller than 3 cm in diameter, completely surrounded by hepatic parenchyma, 1 cm or more deep to the liver capsule, and 2 cm or more away from large hepatic or portal veins. Subcapsular liver tumors can be ablated, but their treatment is usually associated with greater procedural and postprocedural pain. Tumors adjacent to large blood vessels are more difficult to ablate completely because the blood flow in the vessels cools the adjacent tumor, thus limiting the extent of the ablation. Ablation of tumors adjacent to the larger portal triads causes increased pain and poses the risk of damage to the associated bile ducts. Contraindications to treatment include sepsis, severe debilitation, or uncorrectable coagulopathies.

Any of the radio-frequency devices can be used percutaneously or intraoperatively. Percutaneous ablation can be performed on an outpatient basis with use of conscious sedation alone. Ultrasonography (US) is the primary modality for guiding the procedure, although both computed tomography (CT) and magnetic resonance (MR) imaging can be used.

The goal of radio-frequency thermal ablation is to kill the target tumor as well as a 5–10-mm circumferential cuff of adjacent normal hepatic parenchyma. Each ablation requires exact placement of the electrode tip in the tumor. A single ablation takes 8–20 minutes, raises local tissue temperatures to 100 C, and produces an approximate 2–5-cm spherical thermal injury. The size of each ablation is delineated sonographically by echogenic microbubbles that are produced during the ablation.

Ablation strategies must vary with the size of each lesion. On the basis of a 3-cm thermal injury, tumors less than 2 cm in diameter can be treated with one or two ablations, tumors 2–3 cm require at least six overlapping ablations, and tumors greater than 3 cm require at least 12 overlapping ablations (Fig 4). The length of a single procedure depends on the number of ablations performed.

View larger version (134K): [in this window] [in a new window] [Download PPT slide]   Figure 4a.   Radio-frequency ablation treatment strategies. On the basis of a 3-cm-diameter spherical thermal injury created by a single ablation, the following three ablation strategies can be used to treat most tumors. (a) Schematic illustrates how tumors less than 2 cm can easily be treated with one ablation. The active elements of the ablation needle are centered across the tumor. (b) Schematic shows how tumors 2-3 cm in diameter are treated by six overlapping ablations. Four ablations are performed in the x-y plane, and two are performed along the z axis. All ablations are positioned to touch the center of the tumor. If placed correctly, the ablations create an inner spherical injury that measures 3.7 cm in diameter. (c) Schematic depicts systematically overlapped "thermal cylinders," which are a more effective way to ablate large tumors, rather than creating random overlapping ablations (such as seen in b). Each cylinder is created by overlapping individual ablations along a single needle tract from the deepest to the most superficial portions of a tumor. Each ablation and thermal cylinder is overlapped by 50%.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 4b.   Radio-frequency ablation treatment strategies. On the basis of a 3-cm-diameter spherical thermal injury created by a single ablation, the following three ablation strategies can be used to treat most tumors. (a) Schematic illustrates how tumors less than 2 cm can easily be treated with one ablation. The active elements of the ablation needle are centered across the tumor. (b) Schematic shows how tumors 2-3 cm in diameter are treated by six overlapping ablations. Four ablations are performed in the x-y plane, and two are performed along the z axis. All ablations are positioned to touch the center of the tumor. If placed correctly, the ablations create an inner spherical injury that measures 3.7 cm in diameter. (c) Schematic depicts systematically overlapped "thermal cylinders," which are a more effective way to ablate large tumors, rather than creating random overlapping ablations (such as seen in b). Each cylinder is created by overlapping individual ablations along a single needle tract from the deepest to the most superficial portions of a tumor. Each ablation and thermal cylinder is overlapped by 50%.

View larger version (113K): [in this window] [in a new window] [Download PPT slide]   Figure 4c.   Radio-frequency ablation treatment strategies. On the basis of a 3-cm-diameter spherical thermal injury created by a single ablation, the following three ablation strategies can be used to treat most tumors. (a) Schematic illustrates how tumors less than 2 cm can easily be treated with one ablation. The active elements of the ablation needle are centered across the tumor. (b) Schematic shows how tumors 2-3 cm in diameter are treated by six overlapping ablations. Four ablations are performed in the x-y plane, and two are performed along the z axis. All ablations are positioned to touch the center of the tumor. If placed correctly, the ablations create an inner spherical injury that measures 3.7 cm in diameter. (c) Schematic depicts systematically overlapped "thermal cylinders," which are a more effective way to ablate large tumors, rather than creating random overlapping ablations (such as seen in b). Each cylinder is created by overlapping individual ablations along a single needle tract from the deepest to the most superficial portions of a tumor. Each ablation and thermal cylinder is overlapped by 50%.

At our own institution, we have treated 86 patients with hepatic tumors. There is sufficient follow-up (mean, 9 months) to allow a preliminary evaluation of our results in 46 patients, 25 with hepatocellular carcinoma and 21 with metastases. These 46 patients had 76 tumor nodules ranging from 0.7 to 4.9 cm in diameter (mean, 2.8 cm). A total of 462 ablations were performed in 95 sessions. Follow-up CT scans showed complete ablation in 27 of 38 (71%) hepatocellular carcinoma nodules and 17 of 38 (45%) metastases (Fig 5). The lower complete ablation rate in our patients with hepatic metastases may have been caused by a higher frequency of regional microscopic tumor invasion into the adjacent hepatic parenchyma than is seen in patients with hepatocellular carcinoma nodules. Overall, there have been few complications in our series; two patients had intrahepatic arterial hemorrhages, a small area of one patient's diaphragm was inadvertently ablated when a subdiaphragmatic tumor was treated, and two patients developed tumor seeding along the needle tract.

View larger version (145K): [in this window] [in a new window] [Download PPT slide]   Figure 5a.   CT evaluation of radio-frequency thermal ablation. (a) CT scan obtained before ablation shows a hypervascular hepatocellular carcinoma (arrow). (b) CT scan obtained after ablation shows that the tumor has become avascular. Note the prominent peritumoral hyperemia around the treated tumor (arrowheads) that is caused by the ablation process.

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 5b.   CT evaluation of radio-frequency thermal ablation. (a) CT scan obtained before ablation shows a hypervascular hepatocellular carcinoma (arrow). (b) CT scan obtained after ablation shows that the tumor has become avascular. Note the prominent peritumoral hyperemia around the treated tumor (arrowheads) that is caused by the ablation process.

	Microwave Ablation: Perspective from Yasuyuki Yamashita

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

Mechanism
In microwave coagulation therapy or ablation, molecular dipoles are vibrated and rotated, resulting in thermal coagulation of the target tissue. The basic mechanism of heat generation in living tissue consists of rotation of water molecules (Fig 6). The rotation follows the alternating electric field component of the ultra-high-speed (2,450-MHz) microwaves (15). Microwaves emitted from the distal segment of a percutaneous probe cause the thermal coagulation of the adjacent tissues.

View larger version (182K): [in this window] [in a new window] [Download PPT slide]   Figure 6.   Microwave ablation physics. Drawing shows how microwaves heat biologic tissue by causing rotation of water molecules.

View larger version (127K): [in this window] [in a new window] [Download PPT slide]   Figure 7.   Photograph shows microwave ablation equipment, including a 150-W, 2,450-MHz microwave generator (Microtaze; Heiwa, Osaka, Japan) (left) and needle electrodes (right).

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 8.   Microwave ablation of swine liver. Photograph of the cut surface of the liver shows an elliptical ablation (yellow arrowheads) around the distal shaft (arrow) of the monopolar electrode. Note the tip of the electrode (asterisk).

View larger version (110K): [in this window] [in a new window] [Download PPT slide]   Figure 9a.   CT evaluation of microwave ablation performed in a 68-year-old man with hepatocellular carcinoma who had previously been treated with arterial chemoembolization with iodized oil. (a) Enhanced CT scan obtained before embolization shows a hypervascular tumor nodule (arrowheads). (b) Unenhanced CT scan obtained 7 days after embolization shows incomplete accumulation of iodized oil in the tumor (arrow). (c) Sonogram obtained before microwave ablation (left) shows a 35-mm hypoechoic nodule in the anterior segment of the right hepatic lobe (arrows). Sonogram obtained immediately after treatment (two emissions) (right) shows a markedly echogenic region of coagulation (arrow) that has replaced the tumor. (d) Enhanced CT scan obtained 4 days after microwave ablation shows ablated tissue as unenhanced areas within and around the tumor (arrows). (e) Dynamic CT scan obtained 9 months after treatment shows that the lesion (arrow) has decreased in size, without evidence of new tumor growth.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 9b.   CT evaluation of microwave ablation performed in a 68-year-old man with hepatocellular carcinoma who had previously been treated with arterial chemoembolization with iodized oil. (a) Enhanced CT scan obtained before embolization shows a hypervascular tumor nodule (arrowheads). (b) Unenhanced CT scan obtained 7 days after embolization shows incomplete accumulation of iodized oil in the tumor (arrow). (c) Sonogram obtained before microwave ablation (left) shows a 35-mm hypoechoic nodule in the anterior segment of the right hepatic lobe (arrows). Sonogram obtained immediately after treatment (two emissions) (right) shows a markedly echogenic region of coagulation (arrow) that has replaced the tumor. (d) Enhanced CT scan obtained 4 days after microwave ablation shows ablated tissue as unenhanced areas within and around the tumor (arrows). (e) Dynamic CT scan obtained 9 months after treatment shows that the lesion (arrow) has decreased in size, without evidence of new tumor growth.

View larger version (160K): [in this window] [in a new window] [Download PPT slide]   Figure 9c.   CT evaluation of microwave ablation performed in a 68-year-old man with hepatocellular carcinoma who had previously been treated with arterial chemoembolization with iodized oil. (a) Enhanced CT scan obtained before embolization shows a hypervascular tumor nodule (arrowheads). (b) Unenhanced CT scan obtained 7 days after embolization shows incomplete accumulation of iodized oil in the tumor (arrow). (c) Sonogram obtained before microwave ablation (left) shows a 35-mm hypoechoic nodule in the anterior segment of the right hepatic lobe (arrows). Sonogram obtained immediately after treatment (two emissions) (right) shows a markedly echogenic region of coagulation (arrow) that has replaced the tumor. (d) Enhanced CT scan obtained 4 days after microwave ablation shows ablated tissue as unenhanced areas within and around the tumor (arrows). (e) Dynamic CT scan obtained 9 months after treatment shows that the lesion (arrow) has decreased in size, without evidence of new tumor growth.

View larger version (109K): [in this window] [in a new window] [Download PPT slide]   Figure 9d.   CT evaluation of microwave ablation performed in a 68-year-old man with hepatocellular carcinoma who had previously been treated with arterial chemoembolization with iodized oil. (a) Enhanced CT scan obtained before embolization shows a hypervascular tumor nodule (arrowheads). (b) Unenhanced CT scan obtained 7 days after embolization shows incomplete accumulation of iodized oil in the tumor (arrow). (c) Sonogram obtained before microwave ablation (left) shows a 35-mm hypoechoic nodule in the anterior segment of the right hepatic lobe (arrows). Sonogram obtained immediately after treatment (two emissions) (right) shows a markedly echogenic region of coagulation (arrow) that has replaced the tumor. (d) Enhanced CT scan obtained 4 days after microwave ablation shows ablated tissue as unenhanced areas within and around the tumor (arrows). (e) Dynamic CT scan obtained 9 months after treatment shows that the lesion (arrow) has decreased in size, without evidence of new tumor growth.

View larger version (112K): [in this window] [in a new window] [Download PPT slide]   Figure 9e.   CT evaluation of microwave ablation performed in a 68-year-old man with hepatocellular carcinoma who had previously been treated with arterial chemoembolization with iodized oil. (a) Enhanced CT scan obtained before embolization shows a hypervascular tumor nodule (arrowheads). (b) Unenhanced CT scan obtained 7 days after embolization shows incomplete accumulation of iodized oil in the tumor (arrow). (c) Sonogram obtained before microwave ablation (left) shows a 35-mm hypoechoic nodule in the anterior segment of the right hepatic lobe (arrows). Sonogram obtained immediately after treatment (two emissions) (right) shows a markedly echogenic region of coagulation (arrow) that has replaced the tumor. (d) Enhanced CT scan obtained 4 days after microwave ablation shows ablated tissue as unenhanced areas within and around the tumor (arrows). (e) Dynamic CT scan obtained 9 months after treatment shows that the lesion (arrow) has decreased in size, without evidence of new tumor growth.

	Laser Ablation: Perspectives from William R. Lees and Alison R. Gillams

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
The first interstitial thermal ablation of a tumor performed with laser therapy was reported by Bown in 1983 (20). Since then, experimental studies have shown that a reproducible thermal injury can be produced with neodymium yttrium aluminum garnet (Nd YAG) lasers (21). Nd YAG lasers have been used to treat tumors of the esophagus, stomach, colon, and pulmonary bronchus (22–25). The first use of lasers to treat patients with hepatomas and hepatic metastases was reported by Hashimoto et al (26) and Steger et al (27), respectively.

Mechanism
From a single, bare 400-mm laser fiber, light at optical or near-infrared wavelengths will scatter within tissue and be converted into heat. Light energy of 2.0–2.5 W will produce a spherical volume of coagulative necrosis 2 cm in diameter. Use of higher power results in charring and vaporization around the fiber tip.

Two methods have been developed for producing larger volumes of necrosis. The first consists of firing multiple bare fibers arrayed at 2-cm spacing throughout a target lesion (27). The second uses cooled-tip diffuser fibers that can deposit up to 30 W over a large surface area, thus diminishing local overheating (28).

Equipment
Portable solid-state lasers are now available with power outputs up to 30 W (Fig 10). This energy can be delivered through fibers over 10 m in length with the great advantage of being fully compatible with MR imaging. A portable laser costs $20,000–$50,000, and a set of fibers costs approximately $2,000 but can be used to treat up to 50 patients per set.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figure 10.   Photograph shows a typical solid-state laser generator.

The procedure is always guided with US combined with either CT or MR imaging (Fig 11). Sonography is quick and easy if visualization is adequate, but use of CT or MR imaging can add three-dimensional precision at the expense of lengthening the procedure. The major advantages of MR imaging are enhanced lesion visualization due to use of long-acting liver-specific contrast agents, true multiplanar imaging capabilities coupled with three-dimensional navigation, and visualization of temperature change and coagulation (Fig 12) (29).

View larger version (94K): [in this window] [in a new window] [Download PPT slide]   Figure 11a.   MR imaging-guided laser ablation. (a) Photograph shows a patient positioned in an MR imaging unit (0.2-T Viva [Siemens Medical Systems, Iselin, NJ]) with the radiologist performing the procedure. (b) Sagittal MR image obtained after administration of ferumoxide contrast material shows the high-signal-intensity tumor (arrow) into which two needles (arrowheads) have been inserted.

View larger version (155K): [in this window] [in a new window] [Download PPT slide]   Figure 11b.   MR imaging-guided laser ablation. (a) Photograph shows a patient positioned in an MR imaging unit (0.2-T Viva [Siemens Medical Systems, Iselin, NJ]) with the radiologist performing the procedure. (b) Sagittal MR image obtained after administration of ferumoxide contrast material shows the high-signal-intensity tumor (arrow) into which two needles (arrowheads) have been inserted.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 12a.   Laser ablation of colorectal metastases. (a) MR image shows needles (arrows) positioned in a high-signal-intensity tumor (arrowheads) prior to treatment. (b) MR image shows low signal intensity (arrow) within the lesion caused by laser coagulation of the tumor.

View larger version (118K): [in this window] [in a new window] [Download PPT slide]   Figure 12b.   Laser ablation of colorectal metastases. (a) MR image shows needles (arrows) positioned in a high-signal-intensity tumor (arrowheads) prior to treatment. (b) MR image shows low signal intensity (arrow) within the lesion caused by laser coagulation of the tumor.

Treatment effectiveness is assessed with CT performed 18–24 hours after ablation and before discharge (Fig 13). Pain is common, and vigorous pain control is vital after the procedure. Nonsteroidal anti-inflammatory analgesics are very helpful in controlling the pain associated with the intense inflammatory response.

View larger version (142K): [in this window] [in a new window] [Download PPT slide]   Figure 13a.   Imaging evaluation of laser ablation of hepatocellular carcinoma. (a) Arterial-phase CT scan obtained before ablation shows a hypervascular hepatocellular carcinoma (arrow) in the right hepatic lobe. (b) Axial T2-weighted MR image obtained immediately after laser ablation shows the low-signal-intensity tumor with a high-signal-intensity rim (arrows) caused by acute peritumoral hyperemia. (c) Portal-phase CT scan obtained 24 hours after ablation shows the avascular tumor (arrow), indicating 98% ablation.

View larger version (117K): [in this window] [in a new window] [Download PPT slide]   Figure 13b.   Imaging evaluation of laser ablation of hepatocellular carcinoma. (a) Arterial-phase CT scan obtained before ablation shows a hypervascular hepatocellular carcinoma (arrow) in the right hepatic lobe. (b) Axial T2-weighted MR image obtained immediately after laser ablation shows the low-signal-intensity tumor with a high-signal-intensity rim (arrows) caused by acute peritumoral hyperemia. (c) Portal-phase CT scan obtained 24 hours after ablation shows the avascular tumor (arrow), indicating 98% ablation.

View larger version (138K): [in this window] [in a new window] [Download PPT slide]   Figure 13c.   Imaging evaluation of laser ablation of hepatocellular carcinoma. (a) Arterial-phase CT scan obtained before ablation shows a hypervascular hepatocellular carcinoma (arrow) in the right hepatic lobe. (b) Axial T2-weighted MR image obtained immediately after laser ablation shows the low-signal-intensity tumor with a high-signal-intensity rim (arrows) caused by acute peritumoral hyperemia. (c) Portal-phase CT scan obtained 24 hours after ablation shows the avascular tumor (arrow), indicating 98% ablation.

In patients with colorectal metastases, survival is governed by technical success in ablating the tumor and a 5-10-mm margin of normal liver around the tumor and by the biologic behavior of the tumor. The parameters that correlate with good outcome are the same as those for surgery: fewer than five tumors, tumors smaller than 5 cm, slow growth rate, and no extrahepatic tumor (28–33). In our own data, there is a significant difference between pre-1995 and post-1995 results because of technical improvements. Major advances in laser ablation in the past 12 months will not be reflected in outcome data for several years. Although survival rate depends on the biologic behavior of a tumor, patients with carefully selected non-colorectal metastases (eg, from breast cancer and sarcoma) show similar survival characteristics.

	Cryoablation: Perspective from Robert A. Kane

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Cryoablation is the oldest of the local thermal ablation techniques. Cooper first suggested its use for treating liver tumors in 1963 (34). Since then, there have been multiple clinical reports detailing its use for the treatment of primary and secondary malignant hepatic tumors (35–39).

Mechanism
Cryoablation is a method of in situ tumor ablation in which subfreezing temperatures are delivered through penetrating or surface cryoprobes in which a cryogen is circulated. Thermally conductive material allows cooling at the probe tip while the shaft and delivery hoses are insulated (Fig 14). Irreversible tissue destruction occurs at temperatures below -20°C to -30°C. Cell death is caused by direct freezing, denaturation of cellular proteins, cell membrane rupture, cell dehydration, and ischemic hypoxia. Cryolesions as large as 6–8 cm in diameter can be created safely.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 14.   Photograph shows a 3-cm-long, oval ice ball developing around the conductive tip of a 5-mm cryoprobe. Note that the propagation of ice is maximal perpendicular to the probe, with very little forward propagation. This necessitates that the probe tip must reach the deep edge of the lesion for optimal treatment.

View larger version (126K): [in this window] [in a new window] [Download PPT slide]   Figure 15.   Photograph shows 5-mm and 10-mm penetrating cryoprobes, as well as a surface disc-type cryoprobe.

At present, cryoablation is primarily an open surgical technique with fewer than 10% of patients treated laparoscopically (Fig 16). US is the most predominantly used method of guiding the procedure. Depending on tumor size, one or two probes are placed centrally within the lesion with the tips of the probes touching the deep edge of the tumor. The cryogenic material (-196°C) is circulated through the probes. The ice ball is visualized as an echogenic, expanding, hemispherical rim (Fig 17). Freezing is continued until the cryolesion extends through the tumor and into the adjacent normal tissue, with the goal of achieving a 5–10-mm ablation margin. This first freeze takes 5–15 minutes and is followed by a spontaneous thaw and a second freeze to reach and slightly exceed the original cryoablation margin. After the second freeze, the cryoprobe is heated and removed, and the tract is packed for hemostasis.

View larger version (103K): [in this window] [in a new window] [Download PPT slide]   Figure 16.   Intraoperative photograph of cryoablation of a large liver tumor shows two penetrating cryoprobes (open arrows) as well as a surface disc probe (solid straight arrow) on the opposing surface. A small intraoperative US transducer (arrowhead) and a flexible rubber "fish" (curved arrow) used to protect vital structures adjacent to the frozen liver are also seen.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 17a.   US guidance of hepatic cryoablation. (a) Sonogram shows an echogenic 5-mm cryoprobe (arrow) placed centrally within a relatively isoechoic colon metastasis (arrowheads). (b) Sonogram obtained at the partial freeze stage (ie, at 3 minutes) demonstrates that the ice ball (arrow) has extended to the lateral margin of the tumor, but the anterior margin (arrowheads) is still visible. (c) Sonogram obtained at the complete freeze stage (ie, at 8 minutes) shows the ice ball (arrow), which now completely encompasses and extends beyond the anterior margin of the tumor, indicating a successful ablation.

View larger version (147K): [in this window] [in a new window] [Download PPT slide]   Figure 17b.   US guidance of hepatic cryoablation. (a) Sonogram shows an echogenic 5-mm cryoprobe (arrow) placed centrally within a relatively isoechoic colon metastasis (arrowheads). (b) Sonogram obtained at the partial freeze stage (ie, at 3 minutes) demonstrates that the ice ball (arrow) has extended to the lateral margin of the tumor, but the anterior margin (arrowheads) is still visible. (c) Sonogram obtained at the complete freeze stage (ie, at 8 minutes) shows the ice ball (arrow), which now completely encompasses and extends beyond the anterior margin of the tumor, indicating a successful ablation.

View larger version (155K): [in this window] [in a new window] [Download PPT slide]   Figure 17c.   US guidance of hepatic cryoablation. (a) Sonogram shows an echogenic 5-mm cryoprobe (arrow) placed centrally within a relatively isoechoic colon metastasis (arrowheads). (b) Sonogram obtained at the partial freeze stage (ie, at 3 minutes) demonstrates that the ice ball (arrow) has extended to the lateral margin of the tumor, but the anterior margin (arrowheads) is still visible. (c) Sonogram obtained at the complete freeze stage (ie, at 8 minutes) shows the ice ball (arrow), which now completely encompasses and extends beyond the anterior margin of the tumor, indicating a successful ablation.

View larger version (119K): [in this window] [in a new window] [Download PPT slide]   Figure 18a.   CT evaluation of hepatic cryoablation. (a) Pretreatment CT scan shows a colorectal metastasis (arrow) in the dome of the liver that measures 3.5 cm. (b) CT scan obtained 4 days after cryoablation shows a low-attenuation cryolesion (arrow) measuring 5 x 6 cm completely encompassing the tumor site. Small gas bubbles are also seen, a finding indicative of necrosis. (c) Follow-up CT scan obtained 8 months after cryoablation shows the residual cryolesion (arrow) markedly decreased in size as a result of healing and fibrosis.

View larger version (146K): [in this window] [in a new window] [Download PPT slide]   Figure 18b.   CT evaluation of hepatic cryoablation. (a) Pretreatment CT scan shows a colorectal metastasis (arrow) in the dome of the liver that measures 3.5 cm. (b) CT scan obtained 4 days after cryoablation shows a low-attenuation cryolesion (arrow) measuring 5 x 6 cm completely encompassing the tumor site. Small gas bubbles are also seen, a finding indicative of necrosis. (c) Follow-up CT scan obtained 8 months after cryoablation shows the residual cryolesion (arrow) markedly decreased in size as a result of healing and fibrosis.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 18c.   CT evaluation of hepatic cryoablation. (a) Pretreatment CT scan shows a colorectal metastasis (arrow) in the dome of the liver that measures 3.5 cm. (b) CT scan obtained 4 days after cryoablation shows a low-attenuation cryolesion (arrow) measuring 5 x 6 cm completely encompassing the tumor site. Small gas bubbles are also seen, a finding indicative of necrosis. (c) Follow-up CT scan obtained 8 months after cryoablation shows the residual cryolesion (arrow) markedly decreased in size as a result of healing and fibrosis.

At our institution, there have been no deaths in 107 consecutive cryoablations. Others, however, have reported deaths, which occurred more often in patients in whom very large volumes of tumor were cryoablated and for whom death was related to renal failure, disseminated intravascular coagulation, and sepsis. Minor complications of fever, leukocytosis, and transient elevated values from liver function tests occurred in the majority of patients. Major complications developed in fewer than 20% of patients in our series, and most of these were related to bleeding. No tumor seeding has been reported. Local failure (ie, tumor recurrence at the cryoablation site) occurred in 13% (35).

	Ethanol Ablation: Perspective from Tito Livraghi

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Worldwide, ethanol injection therapy or ablation is probably the most accepted minimally invasive method of treating primary malignant hepatic tumors. Its acceptance is based on the ease of treatment, minimal and inexpensive therapeutic equipment required, and good clinical results.

Mechanism
Within neoplastic cells, ethanol causes dehydration of the cytoplasm and subsequent coagulation necrosis, followed by fibrous reaction. Within neoplastic vessels, ethanol induces necrosis of endothelial cells and platelet aggregation, thus causing thrombosis and tissue ischemia.

The size and shape of the induced necrosis is not always reproducible. It varies with histologic characteristics, degree of vascularization, presence of capsule or septa, and tissue consistency. Hepatocellular carcinoma is the most responsive tumor. The largest tumor treated effectively with ethanol ablation was an 8.2-cm hepatocellular carcinoma that was ablated in less than 1 hour with a one-shot technique (40).

Equipment
The materials consist of sterile ethanol 95%, a syringe, connecting tubing, and a multihole 21-gauge needle with a conical tip (PEIT needle, Hakko, Tokyo, Japan) (Fig 19). The cost of the needle, syringe, tubing, and ethanol is $45.

View larger version (91K): [in this window] [in a new window] [Download PPT slide]   Figure 19.   Photograph shows ethanol ablation equipment, which consists of a syringe, sterile 95% ethanol, and a 20-cm-long, 21-gauge needle with a closed conical tip and three terminal holes (Hakko).

According to the size and number of the lesions, ethanol ablation is performed either as an outpatient multisession technique or as an inpatient one-shot technique under general anesthesia. In most instances, hepatocellular carcinomas smaller than 5 cm are treated on an outpatient basis, and larger tumors are treated with the one-shot inpatient technique. For both, ethanol is injected percutaneously under sonographic guidance. For an outpatient procedure, 1–8 mL of ethanol is injected per session, two times per week for a total of four to 12 sessions (Fig 20). In an inpatient one-shot procedure, 62 mL of ethanol is delivered in 13 injections over a mean time of 30 minutes, and the patient has a mean hospital length of stay of 3.8 days. CT is performed to evaluate the success of treatments (Fig 21) (40,41).

View larger version (141K): [in this window] [in a new window] [Download PPT slide]   Figure 20a.   US guidance of ethanol ablation. (a) Pretreatment sonogram shows a 3.2-cm hepatocellular carcinoma with the tip of the treatment needle (arrow) visible in the tumor. (b) Sonogram obtained after injection of ethanol shows diffuse increase in echogenicity of the tumor (arrow).

View larger version (135K): [in this window] [in a new window] [Download PPT slide]   Figure 20b.   US guidance of ethanol ablation. (a) Pretreatment sonogram shows a 3.2-cm hepatocellular carcinoma with the tip of the treatment needle (arrow) visible in the tumor. (b) Sonogram obtained after injection of ethanol shows diffuse increase in echogenicity of the tumor (arrow).

View larger version (122K): [in this window] [in a new window] [Download PPT slide]   Figure 21a.   CT evaluation of ethanol ablation of hepatocellular carcinoma. (a) CT scan obtained before ablation shows an encapsulated 7-cm hepatocellular carcinoma (arrow). (b) CT scan obtained 3 years after ethanol ablation shows that the tumor (arrow) has decreased markedly in size and shows no contrast enhancement. The tumor was treated by a single-session injection of 60 mL of ethanol.

View larger version (125K): [in this window] [in a new window] [Download PPT slide]   Figure 21b.   CT evaluation of ethanol ablation of hepatocellular carcinoma. (a) CT scan obtained before ablation shows an encapsulated 7-cm hepatocellular carcinoma (arrow). (b) CT scan obtained 3 years after ethanol ablation shows that the tumor (arrow) has decreased markedly in size and shows no contrast enhancement. The tumor was treated by a single-session injection of 60 mL of ethanol.

	Chemoembolization: Perspective from Michael C. Soulen

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
There have been more reports on chemoembolization of hepatic tumors than there have been for all five previously discussed minimally invasive treatment techniques combined (45–50). Although good response rates have been seen, the search for just the right combination of existing or new chemotherapeutic agents continues.

Mechanism
Normal liver tissue receives 75% of its blood supply from the portal vein and 25% from the hepatic artery. Hepatic malignancies receive 95% of their blood supply from the hepatic artery (Fig 22). Embolization of the hepatic artery selectively induces ischemic necrosis in tumors, while the normal liver tissue survives off the portal blood supply.

View larger version (111K): [in this window] [in a new window] [Download PPT slide]   Figure 22.   Drawing shows the blood supply to the liver and hepatic tumor. The tumor derives 95% of its blood supply from the hepatic artery. Normal liver parenchyma receives only 25% of its blood supply from the artery and the remaining 75% from the portal vein.

Equipment
Chemoembolization is easily accomplished with off-the-shelf catheters and guide wires. A 4–5-F hydrophilic Cobra catheter and a hydrophilic wire suffice for about half of the procedures. Use of a microcatheter through a guiding 4–5-F diagnostic catheter is necessary for small or tortuous arteries. Embolization is performed with a mixture of chemotherapeutic drugs, iodized poppy seed oil, and particles (of either polyvinyl alcohol or gelatin sponge) (Figs 23, 24). The cost for catheters, guide wires, chemotherapeutic agents, and embolic agents is approximately $1,000.

View larger version (97K): [in this window] [in a new window] [Download PPT slide]   Figures 23.   Photograph shows embolic agents used for hepatic chemoembolization, including gelatin sponge powder (Gelfoam; Upjohn, Kalamazoo, Mich), polyvinyl alcohol particles (Interventional Therapeutics, San Francisco, Calif; Biodyne, El Cajon, Calif), and iodized poppy seed oil (Ethiodol; Savage Laboratories, Melville, NY).

View larger version (99K): [in this window] [in a new window] [Download PPT slide]   Figure 24.   Photograph shows chemotherapeutic drugs used for hepatic chemoembolization, including cisplatin (Platinol), doxorubicin (Rubex), and mitomycin-C (Mutamycin) (all from Bristol-Myers Squibb Oncology, Princeton, NJ).

Patients must abstain from solid food overnight but continue a vigorous fluid intake. On the morning of the procedure, hydration and premedication with antibiotics, antiemetics, and sedatives are intravenously administered. Diagnostic visceral angiography is performed to map hepatic arterial anatomy and to assess portal blood flow. The right or left hepatic artery is catheterized and chemoembolized to near-stasis (Fig 25). Intraarterial lidocaine and conscious sedation are used for pain control. Patients are discharged when their postembolization syndrome (fever and pain) has subsided, at an average of 1.5 days.

View larger version (180K): [in this window] [in a new window] [Download PPT slide]   Figure 25a.   Chemoembolization of hepatic tumor. (a) Right hepatic arteriogram, obtained after a microcatheter has been advanced into the right hepatic artery through a 5.5-F diagnostic catheter parked in the celiac artery, demonstrates a hypervascular tumor in the posterior segment. (b) CT scan obtained before chemoembolization shows a low-attenuation hepatoma (arrow) occupying most of the posterior segment of the right hepatic lobe. (c) Postchemoembolization CT scan demonstrates a 65% reduction in tumor volume (arrow) with dense, persistent uptake and retention of the iodized oil. Oil retention correlates positively with tumor necrosis and helps predict longer survival.

View larger version (121K): [in this window] [in a new window] [Download PPT slide]   Figure 25b.   Chemoembolization of hepatic tumor. (a) Right hepatic arteriogram, obtained after a microcatheter has been advanced into the right hepatic artery through a 5.5-F diagnostic catheter parked in the celiac artery, demonstrates a hypervascular tumor in the posterior segment. (b) CT scan obtained before chemoembolization shows a low-attenuation hepatoma (arrow) occupying most of the posterior segment of the right hepatic lobe. (c) Postchemoembolization CT scan demonstrates a 65% reduction in tumor volume (arrow) with dense, persistent uptake and retention of the iodized oil. Oil retention correlates positively with tumor necrosis and helps predict longer survival.

View larger version (106K): [in this window] [in a new window] [Download PPT slide]   Figure 25c.   Chemoembolization of hepatic tumor. (a) Right hepatic arteriogram, obtained after a microcatheter has been advanced into the right hepatic artery through a 5.5-F diagnostic catheter parked in the celiac artery, demonstrates a hypervascular tumor in the posterior segment. (b) CT scan obtained before chemoembolization shows a low-attenuation hepatoma (arrow) occupying most of the posterior segment of the right hepatic lobe. (c) Postchemoembolization CT scan demonstrates a 65% reduction in tumor volume (arrow) with dense, persistent uptake and retention of the iodized oil. Oil retention correlates positively with tumor necrosis and helps predict longer survival.

Patient Outcome
Response rates for primary and most metastatic tumors are 60%–80%, with an average duration of 1 year. Recurrent tumors in the liver can be treated again. A meta-analysis of survival among patients with hepatoma indicated that the survival rates of patients who underwent chemoembolization were 70% at 1 year, 40% at 3 years, and 10% at 5 years (45). The range of reported survival rates at each interval is substantial, because these rates are strongly influenced by various prognostic factors, including tumor burden, tumor stage, underlying cirrhosis, and uptake and retention of the chemoembolic mixture (45–50).

No controlled trials exist that adequately evaluate the survival benefit of chemoembolization for patients with hepatoma. There are limited data on chemoembolization of liver metastases. For metastatic colon cancer, the 1-year survival rate is consistently reported at about 70% among patients with good performance status (45). At our institution, the survival rate drops to 55% at 2 years and 23% at 3 years. Median survival is 24 months, which is double that reported for patients undergoing systemic chemotherapy. However, substantial institutional biases may be present. There are no phase III trials for chemoembolization of metastatic colon cancer. Limited series have reported good results with chemoembolization of metastases from neuroendocrine tumors, ocular melanoma, and some sarcomas. Serious complications, most commonly liver abscess or necrosis, occur after 5% of procedures. The 30-day mortality rate is 1%–3%, with some of the deaths being disease related (45–50).

	Benefits and Limitations of Current Treatments

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
Radio-frequency Ablation: Perspective from Gerald D. Dodd III
The main advantage of radio-frequency ablation is the ability to create a well-controlled focal thermal injury with minimal morbidity and no mortality to date. Unlike ethanol ablation, radio-frequency ablation appears effective for treating both hepatocellular carcinoma and hepatic metastases. Furthermore, it requires fewer sessions to treat the same tumor than does ethanol ablation. Radio-frequency ablation is much less toxic than chemoembolization and better controlled. The size of the thermal injury created by a single radio-frequency ablation is larger than that created by a single laser ablation; hence, there is less chance of missing tumor. Cryoablation requires laparoscopy or laparotomy, and its complication rate is greater than that for radio-frequency ablation. The main limitation of radio-frequency ablation is the difficulty in heating normal liver; thus, the marginal tumor recurrence rate is greater than desired.

Microwave Ablation: Perspective from Yasuyuki Yamashita
The main advantage of microwave ablation is the ability to create complete coagulative necrosis by heat regardless of the presence of fibrous tissue or a septum. Therefore, this therapy is effective for fibrous tumors and metastatic tumors that are usually resistant to ethanol ablation or chemoembolization. The mechanism, indications, and advantages and disadvantages of microwave ablation are similar to those of radio-frequency ablation. In comparison with radio-frequency ablation, however, the time required for microwave ablation is very short (<60 seconds) and the shape of the necrosis is usually elliptical. Therefore, microwave ablation is less invasive but requires more sessions to treat larger tumors.

Laser Ablation: Perspectives from William R. Lees and Alison R. Gillams
Although radio-frequency ablation techniques can deliver more energy into tissue than laser ablation techniques, there is little practical difference between radio-frequency ablation and the latest cooled-tip diffuser fiber laser ablation technology. The laser technique has the advantage of being fully compatible with MR imaging, whereas radio-frequency ablation is not. Both techniques are now so powerful that control of energy deposition is a major issue; only MR imaging offers the potential for accurate real-time monitoring of the extent of the ablation.

Cryoablation: Perspective from Robert A. Kane
None of these six methods of minimally invasive treatment of hepatic tumors are directly comparable, since the patient populations, extent of disease, and other factors are quite different. In addition, there have been no prospective comparative studies. Cryoablation appears to be the most optimal approach for treating larger volume tumors (>3 cm), and long-term follow-up data show some actual survival benefit. The technique offers precise real-time US assessment of the ablation process with 85%–90% successful local control, which is superior to other ablative techniques. The major limitation for cryoablation is that it requires a laparotomy or at least laparoscopy with general anesthesia and a 3–5-day hospital stay. Consequently, it is substantially more expensive than percutaneous techniques.

Ethanol Ablation: Perspective from Tito Livraghi
Ethanol ablation is easy, inexpensive, safe, and repeatable. In small and medium-sized hepatocellular carcinomas, long-term results of ethanol ablation and surgery are comparable. In large encapsulated hepatocellular carcinomas, ethanol ablation can achieve a complete necrosis up to about 8 cm in diameter. In multiple hepatocellular carcinomas, ethanol ablation is less toxic than chemoembolization and better controlled. However, in a prospective study of small hepatocellular carcinomas, the rate of complete ablation was 10% higher with radio-frequency ablation than with ethanol ablation and was achieved in shorter treatment times (42). Ethanol ablation is less effective than thermal ablation techniques such as radio-frequency ablation for the treatment of liver metastases.

Chemoembolization: Perspective from Michael C. Soulen
The high rate of intrahepatic relapse after surgical resection of liver tumors testifies to the frequency of radiologically occult tumors. All local ablative techniques fail to treat the entire organ at risk. Most hepatic tumors in unscreened populations are too bulky to be treated with percutaneous ablation. Some smaller tumors are not accessible to percutaneous ablation by virtue of their location. Regional therapies such as hepatic artery infusion or chemoembolization treat the entire liver and can be performed irrespective of the size and location of tumors. However, regional therapy is not as effective as localized high-energy devices in killing individual tumors. The combination of regional and local therapy can be used when lesions are too large or numerous to be treated by ablation alone.

	Conclusions

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 
The adoption of any new technique for the treatment of primary or secondary malignant hepatic tumors depends on the patient population, the therapeutic goal, and the efficacy of the technique. Patients with extensive intrahepatic tumor or concomitant extrahepatic tumor are not likely to derive any benefit from these therapies. Patients with limited intrahepatic tumor fit into two general categories: those with surgically resectable tumors and those who are not surgical candidates because of unsuitable tumor location, tumor number, or general clinical condition.

In patients who are not surgical candidates, the adoption of a new therapeutic technique requires that its results are equal to or better than those provided by systemic chemotherapy. The response (visual decrease in tumor size on CT scans) to systemic chemotherapy has been reported to be around 15%–20% (4). Improving these results is not difficult; all of the minimally invasive (nonoperative) techniques produce a better local response. The choice of which technique to use in these patients depends on the extent of the tumor. Chemoembolization appears to offer the best hope of controlling tumors greater than 5 cm in diameter or more than four tumors in number, whereas each of the thermal ablative techniques appears to produce better results in smaller tumors.

The treatment of patients with surgically resectable hepatic tumors by alternative minimally invasive techniques is much more challenging. These patients can be cured potentially if all visible tumor is resected or destroyed. The replacement of hepatic resection requires that the new technique yield similar success in tumor eradication with less morbidity and mortality. The success rate of resecting a known tumor and obtaining a tumor-free resection margin is approximately 90%. To date, none of the new minimally invasive techniques has yielded comparable results. Of the six methods described herein, cryoablation has the best results, with a 15% local tumor recurrence rate. Unfortunately, cryoablation shares many of the drawbacks of hepatic resection. Chemoembolization does not offer the chance of cure and thus should not be used in this patient population. Ethanol ablation is effective for treating small hepatocellular carcinoma and although it kills less than 90% of all treated tumors, the fact that it can be repeated over and over in a patient population at high risk for recurrent tumor makes it a viable alternative therapy for hepatocellular carcinoma. The three thermal ablative techniques, radio-frequency, microwave, and laser ablation, are in their evolutionary infancy. Each is an excellent technique for debulking tumors; however, all yield complete tumor ablation rates of less than 90%. This failure is due to a cooling effect created by the copious portal venous blood flow in the normal liver parenchyma surrounding the tumors. This problem appears less significant in the treatment of hepatocellular carcinoma occurring in the cirrhotic liver than it is in the treatment of hepatic metastases. Recent refinements in the technology of both radio-frequency and laser ablation may overcome this problem. The smaller lesion produced by microwave ablation makes it less useful than either radio-frequency or laser ablation. If the complete ablation rate of any of the percutaneous thermal ablative techniques can be increased to 90%, the added advantages of minimal morbidity and the ability to repeat the procedure as necessary will make them the preferred treatment technique.

Radio-frequency ablation, microwave ablation, laser ablation, cryoablation, ethanol ablation, and chemoembolization are very promising, minimally invasive techniques for treating primary and secondary malignant hepatic tumors. We predict that one or a combination of these techniques will replace most hepatic resections in the near future. The percutaneous application of these techniques will markedly increase the role of the interventional radiologist in oncologic therapy.

	References

Top Abstract Introduction Radio-frequency Ablation:... Microwave Ablation: Perspective... Laser Ablation: Perspectives... Cryoablation: Perspective from... Ethanol Ablation: Perspective... Chemoembolization: Perspective... Benefits and Limitations of... Conclusions References

 

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