Routines of US-guided percutaneous RFA

Indications

• Single tumor ≤5cm; multiple tumors≤3, ≤3cm
• Child-Pugh class A or B
• Platelet >50,000/mm3 Prothrombin time>50%
• No portal venous thrombosis or extrahepatic metastasis

Routine protocol

1.   Planning US in outpatient
2. Routine lab exam (CBC, Liver function, coagulation, tumor marker)
3. Admission one day before RFA
4. Overnight fasting (> 6 hours)
5. Getting informed consent
6. IV conscious sedation (pethidine/fentanyl HCl), drip infusion
7. Real time vital sign monitoring §US-guided percutaneous RFA with free hand technique
8. IV atropine sulfate (PRN)
9. Immediate follow-up 3 phase-CT
10. Discharge one day after RFA

Fig.: Scenery of US-guided percutaneous RFA of the liver

Planning

Scoring for predicted technical difficulty: POSCH system

We developed a new scoring system for feasibility assessment in planning US. A feasibility score was calculated by summation of the points in each category (score range 5-20). Patients are assessed using this system at planning US on the outpatient basis to know a feasibility of percutaneous RFA. If any 4 in any category was determined, the patient was considered unfeasible for percutaneous RFA.

Fig.: POSCH scoring system

Fig.: A. Arterial phase of MR shows a 3.6 cm- mass in segment V, abutting the GB (white arrow) and portal vein (black arrow). B. The scoring in each category is as shown. The feasibility score is 10.

Considering usual shape of RFA zone

 Internally-cooled electrode (Valleylab) tends to make ovoid ablation zone of which axis is parallel to shaft and multi-tined expandable electrode (Boston Scientific, Angiodynamics) produces ovoid ablation zone perpendicular to shaft. We should consider the shapes of the index tumor and usual ablation zone in planning to conform their shapes to each other.

Fig.: Internally-cooled electrode (single type) usually produces ovoid lesion along the axis of the electrode. On the other hand, multi-tined electrode produces ovoid lesion perpendicular to the electrode axis

Ablating indistinct tumor

US-guided RFA for treating isoechogenic tumor or very small HCC which is indiscernible with background cirrhotic nodules is often encountered. If CT-guidance is not available, followings are helpful.

- Making use of US contrast agent

Fig.: A. Local tumor progression (HCC) of RFA was diagnosed at CT (arrow). B. It couldn’t be delineated in grayscale US. C. Sonovue-enhanced US demonstrates small recurrent HCC well (arrow). D. RFA using 2cm single Cool-tip electrode is being performed. E. Immediate CT shows technical success of RFA.

- Making use of adjacent normal anatomical structures (hepatic vessel)

Fig.: A. Grayscale US shows suspicious hypoechoic index tumor (arrow). B. Serial images of CT revealed the index tumor (HCC) (arrow) is very close to S3 segmental portal vein (arrowheads). C. Color Doppler US demonstrates subtle hypoechoic mass (arrow) at the end of S3 portal vein (arrowheads). D. RFA electrode (arrow) is inserted. E. CT shows technical success.

- Making use of RVS (real-time virtual sonography)

Fig.: While the index tumor is not clearly delineated on grayscale US, it is very evident on virtual US image which was reconstructed from contrast-enhanced CT images. This method help operator be convinced of poorly-delineated tumor. Left side approach was adopted for this procedure

Targeting

Transverse scan during tumor puncture

Exact centering of RF electrode can not be overemphasized. Though shaft of RF electrode and target are demonstrated on US simultaneously, it doesn’t guarantee both objects are aligned exactly in a same plane. Therefore, we should rotate US transducer 90° and perform transverse scan before/after puncturing tumor to assure location of electrode is appropriate.

Fig.: A. Rotation of US transducer. B. Gd-enhanced MR shows small HCC in segment V (arrow). C, D. Longitudinal and transverse scan after tumor puncture. Arrowheads indicates electrode shaft. E. Immediate CT shows technical success of RFA.

Respiration control

Sometimes, different degrees of respiration change the configuration of ovoid tumor or displace dangerous structure from the electrode path, which makes the RFA procedure easier and the results more desirable.

Fig.: A. Long axis of index tumor is near vertical (cross marks) in expiration. B. Inspiration makes long axis of the tumor oblique (cross marks). C. Electrode is inserted to tumor along its long axis, which conforms the shape of RFA zone to the configuration of the index tumor.

Traversing normal parenchyma for subcapsular tumor

This technique is important to prevent tumor seeding caused by direct tumor puncture. However, it is not always feasible due to relationship between the degree of tumor bulging and the angle of RF electrode path. In this case, we should diminish the number of tumor puncture as low as possible.

Fig.: A, B. Gd-enhanced MR and US shows HCC at subcapsular area of the liver. C. RF electrode (arrowheads) is inserted into the tumor (dotted line) after traversing normal hepatic parenchyma. Yellow line represents the liver capsule.

Detouring electrode path

Frequently, we meet the cases in which important anatomical structure such as large vessel is located in the expected RF electrode path. This detouring technique is useful in avoiding large vessels as well as conforming electrode to ovoid tumor. It is easier to do in patient with non-cirrhotic liver because of its less rigidity.

Fig.: A. Index tumor (cross marks) is located in deep area of segment VII of the liver on US. Note a large hepatic vein at the presumed path of RF electrode (yellow dotted arrow). B. RF electrode is inserted to the index tumor after detouring hepatic vein (compressed hepatic vein)(arrow) is seen near electrode shaft (arrowheads). C. After tract ablation, detouring path of RF electrode is demonstrated by echogenic line (thin arrows). D-F. Serial coronal MPR images of immediate CT shows similar detouring course of RF electrode (thin arrows).

Using non-dominant hand

Sometimes, it is very helpful to use non-dominant hand during targeting as long as the operator is familiar with it. Utilizing the other side of US transducer is mandatory for safe and complete ablation in some special situations.

Fig.

Fig.: A, B. CT and Doppler US shows that the index tumor (HCC) (arrows) is located behind the large portal vein which blocks RF electrode if right-handed approach is adopted. C. RF electrode (arrowheads) is being inserted using left-handed approach. D. Immediate CT shows technical success of RFA.

Fig.: A. Echogenic index tumor (cross marks) is located at the dome of segment II of the liver. It abuts the diaphragm and the cardiac base. Right-handed approach is impossible because the stomach (asterisk) is in the way of presumed RF electrode path despite respiration. Risk of direct cardiac puncture is also high. B. Presumed RF electrode path by left-handed approach (arrow). C. RFA is being performed. D. Immediate CT (sagittal MPR) shows technical success without any complication. Linear low density line (arrowheads) represents ablated electrode tract.

Keeping safety distance from the risky organs

Collateral thermal damage is a major problem of RFA. It is desirable to keep adjacent organs away 5 mm from the tip and 10 mm from the shaft in case of Cool-tip electrode. Based on our experiences, this interval guaranteed both safe and complete ablation.

Fig.: A. Index tumor (arrow) abuts the colon. B. RF electrode (arrowheads) is inserted to upper area of tumor (dotted line) and its shaft is 13mm away from the colon. C. Immediate CT shows technical success without colon injury.

Fig.: A. Index tumor (arrow) is very close to the diaphragm. RF electrode (arrowheads) is inserted into the tumor and its tip is 7mm (cross marks) away from the diaphragm. B. Immediate CT shows technical success without collateral thermal injury of the diaphragm.

For multiple overlapping ablation

Although overlapping technique is commonly used for large tumor, it is not technically easy because of impairment of US visibility by shadowing.

- From deep to superficial; Establishing enough distance between electrode locations

Fig.: A. Index tumor (arrow, white dotted line) measures 3.3 cm which seems to need 2 times of overlapping ablation. B,C. Deep portion of the tumor is treated by the 1st ablation. RF electrode (arrowheads) is located near deep-left margin of the tumor. Small superficial-right portion of the tumor (arrow) still can be seen. D,E. 2nd ablation was targeted to small visible tumor portion along the superior border of the 1st ablation (yellow dotted line).

- In-advance placement of all electrodes before starting ablation

Fig.: Simultaneous multiple electrodes insertion

Fig.: A. Index tumor measures 4.0 cm in segment VII of the liver. B. Both cluster (arrow) and single (arrowhead) electrodes were inserted into the tumor along a long axis of the tumor. C. Superficially-inserted cluster electrode is operating. D. Deeply-inserted single electrode is operating. E. Technical success was noted by inserting both cluster (arrow) and single (arrowhead) electrode in advance.

Monitoring & Contolling

Artificial ascites/Artificial pleural effusion

These are often essential in case of the tumor at the hepatic dome in which, otherwise, percutaneous RFA is unfeasible. Artificial ascites are superior to artificial pleural effusion in that artificial ascites can both improve US visibility and prevent collateral thermal damage.

Fig.: Artificial ascites making

Fig.: Stepwise scheme for artificial ascites infusion

Fig.: A, B. Index tumor (HCC) (arrow) is seen at the right hepatic dome on CT, but US can not delineate it due to shadowing by lung base. C. Sheath (small arrows) is placed between the visceral and parietal peritoneum. D. Artificial ascites (5DW) (asterisk) is instilled through the sheath. E. Index tumor begins to be seen on US. F, G. RFA is being performed. H. Immediate CT shows technical success. See artificial ascites (asterisk)

Local anesthetics infiltration to perihepatic space

In case of subcapsular RFA, we infiltrate local anesthetics at the perihepatic space, more specifically beneath the parietal peritoneum of abdominal wall using long-shafted needle. it decreases pain dramatically if sufficient amount of local anesthetics is injected at the appropriate area. It is important to cover whole peritoneum contacting RFA zone after considering respiratory motion and the expected RFA zone.

Fig.: A. Index tumor (asterisk) is seen at the anteroinferior corner of segment IV of the liver and it abuts peritoneum. B. Lidocaine is infiltrated using long shaft spinal needle under US guidance. C. Hypoechoic band (small arrows) is newly formed by injected local anesthetics in the abdominal wall beneath the parietal peritoneum. D. RFA is being performed. VAS of this patient is 3.

Managing vasovagal reflex

This is an important issue for successful RFA performed under conscious sedation. Pain-induced vasovagal reflex usually lowers heart rate and blood pressure with or without symptoms of nausea/vomiting. In severe cases, it can cause syncope and even cardiac arrest. When patient shows severe cardiodepression (heart rate decrease > 30% of baseline or heart rate <40 bpm), we conduct following protocol in order.

• Lowering RF power output
• Head-down tilting (because pathogenesis of this reflex involves blood flow to brain)
• Atropine sulfate: IV bolus injection

In our recent study, location of the ablation zone abutting central portal vein (up to 2nd order branch), old age, and female sex are revealed to be significant risk factors for severe cardiovascular depression during the RFA of the liver under conscious sedation by multivariate analysis.

In case of subcostal approach

We prefer intercostal to subcostal approach due to 1) displacement of RF electrode by respiration, 2) degradation of tumor visibility by patient’s gradual poor cooperation. However, index tumor infrequently can be seen only in subcostal scan. We have several tips for this situation. 

• Electrode should be as perpendicular as possible to the respiratory excursion
• Use multi-tined electrode rather than internally-cooled one.
• Remember graduations on the shaft at the skin level, and adjust it when moved. (Don’t use metallic clamps to indicate the calculated depth of insertion)

Fig.: Skin burn (arrowheads) caused by clamping-induced denudation of insulation on RF electrode (arrow). This patient did not complain of any skin pain due to local anesthesia. It was healed after conservative management. (Actually, it happened during CT-guided RFA. Mosquito clamps was used to indicate the calculated depth of electrode insertion from the skin to the index tumor)

Lever technique in decubitus position

Lever technique means pushing down of electrode shaft outside the body. When performed in left lateral decubitus position, it elevates electrode tip, and subsequently the liver, which increases the distance between ablation zone and the colon. It looks advantageous in reducing risk of collateral thermal injury of the colon in cases of RFA for the tumor in right inferior segment.

Fig.: A. Hepatic metastasis (arrow) of colon cancer in segment VI abuts hepatic flexure of the colon. B. RF electrode is inserted into the index tumor (dotted line). Distance between the hepatic capsule and RF electrode measures 12mm. C, D. Lever technique in lateral decubitus position is performed. E. US figures shows difference in location of RFA zone and electrode shaft by using lever technique. F. CT shows no complication of the colonic loop.

Fig.: Changes according to use or no use of lever technique

Bending technique

We often should treat both small and large tumors in a single session RFA (i.e. 3.2 and 1.1cm). If we are to use Cool-tip electrode, it is ideal to use both cluster and single electrode, but the patient has to pay too much. In this situation, bend technique is very helpful. After treating larger tumor with cluster electrode routinely, just bend two (possibly one) shafts out and use only one (possible two) shaft. Remember removing two grounding pads for 2nd step.

Fig.: A. There are two index tumors (HCC) (arrows) in segment VII of the liver. The larger one measured 3.2cm on US. B, C. The larger HCC is ablated using cluster Cooltip electrode in a routine manner. D. After finishing first RFA, two of three electrode shaft is being bent by operator. E. After bending, remaining one straight electrode is inserted to the smaller HCC (1.1cm). F. Second RFA is performed after removing two grounding pads from the patient. G, H. Immediate CT shows technical success. Note the difference in the size of RFA zone by each type of electrode (arrows).

Post-RFA Management

Tract ablation

Slow withdrawal of RF electrode using low-level power output (about 40-60W) ablates electrode path. Speed of electrode withdrawal and power output should be coordinated to keep electrode temperature 60-70°C. Linear echogenic change of electrode path indicates appropriateness. It is very important in preventing hemorrhage and tumor seeding after RFA. Patients usually feel pain when electrode tip passes peritoneum.

Fig.: Usual findings of ablated tract after RFA. A. It is shown as echogenic line from RFA zone to the hepatic capsule on US (arrowheads). B. On hepatic arterial phase of immediate CT, ablated tract is shown as low density line with or without reactive hyperemia (arrowheads). C. Color Doppler US should not show any color signal.

Doppler US after removal of RF electrode

This is important step for early detection of post-RFA bleeding. When color signal is noted along electrode path on color Dopper US, spectral Dopper should be done to exclude artifact possibly caused by echogenic line of ablated tract. When arterial or portal venous waveform is demonstrated, we observe it for 10 min with color Doppler US. Based on our experiences, most patients (>95%) show gradual decrement and cessation of bleeding within 10 min. If not, it should be considered to perform CT/angiography, and then, embolization.

Fig.: Pulsed Doppler US immediately after removal of RF electrode shows arterial bleeding along the tract ablation site. Observation using color Doppler US shows gradual decrease of color signal. Bleeding was ceased after 5 minutes. This patient did not experienced any complication.

RF-cauterization under Dopper US-guidance

We have some experiences of this technique. After withdrawal of RF electrode, bleeding with arterial waveform had been continued over 10-minute observation. We re-inserted RF electrode parallel to color line (“tandem technique”) and did second RFA at the origin of color signal beside the original ablation zone. In all cases, acute bleeding was controlled.

Fig.: A. Doppler US after tract ablation shows intense color signal with arterial waveform. This bleeding continued over 10 minutes. B. RF electrode (arrowheads) is inserted under color Doppler US guidance. C. RF-cauterization is performed (40W, 10 sec). D. Color Doppler after RF-cauterization shows cessation of bleeding. E. Immediate CT shows small perihepatic hematoma (small arrows). This patients showed stable vital sign after the procedure.

3-D analysis of ablative margin

 “Side-by-side” comparison of pre- and post-RFA CT has limitations in evaluating ablative margins, especially in vertical or oblique direction. We devised new method using CT image fusion and radial MPR technique. It enabled us to evaluate ablative margins virtually in whole directions objectively and quantitatively. Reviewing our cases, 3mm or greater ablative margin turned out to be required to prevent local tumor progression of HCC over 2cm.   

Fig.: A. Pre-RFA CT B. Post-RFA CT C. Fusion of pre- & post-RFA CT. After fusion, radial MPR was performed with its center of rotation at the center of tumor. Inner window shows radial MPR image made 11-0  5-6 o’clock direction. On MPR image, we can see insufficient ablative margin at 4 o’clock direction (arrow) D. Post-TACE non-enhanced CT after 13 months demonstrates Lipiodol nodule (arrow) at the area concordant with insufficient ablative margin.