Joseph R. Durham, M.D., F.A.C.S., R.P.V.I., José M. Velasco, M.D., Vikram D. Krishnamurthy, M.D., Tina J. Hieken, M.D.
1 Which of the following most accurately represents the average speed at which ultrasound waves move through the human body?
A 350 m/s
B 2000 m/s
C 500 cm/s
D 1540 m/s
E 800 m/s
Ref.: 1
Comment
Sound moves through biologic tissue at a speed that is dependent on tissue density. Sound moves more slowly through less dense matter, such as air (330 m/s), and more quickly through high-density material, such as bone (4050 m/s). The average speed of sound through human tissue is 1540 m/s. Specific examples of propagation speeds through tissue are 1459 m/s for fat, 1520 m/s for brain, 1550 m/s for liver, 1560 m/s for kidneys, and 1580 m/s for muscle. Because most soft tissues have similar density and therefore sound passes through them at a similar speed, ultrasound machines are designed on the assumption that the speed of sound through soft tissues is 1540 m/s.
Answer
D
2 Concerning acoustic impedance, which of the following statements is true?
A It can be amplified by increasing the gain on the ultrasound equipment.
B It is influenced by the density of the tissue and the velocity of the sound wave.
C It permits the operator to distinguish between two structures even if their densities are the same.
D It is calculated by multiplying the amplitude of the waves by the density of the tissue.
E The greater the difference in impedance between two tissues, the less energy is reflected to the transducer.
Ref.: 1
Comment
Diagnostic ultrasonography is centered on the analysis of sound waves that have been reflected back to the ultrasound transducer. Impedance is the acoustic resistance to sound traveling in a medium. Acoustic impedance is dependent on the speed of sound in the tissue and the density of the tissue and can be calculated as acoustic impedance = density × velocity. Sound wave properties are not the only parameters that shape ultrasound physics. The medium (tissue) carrying the sound is a major contributor to events. The compressibility of a material determines, in part, the way that sound is carried along within that material. Because sound forms compressions and rarefactions, the ability of the tissue to be compressed and stretched determines just how well sound can be propagated through the tissue. Hard tissues (e.g., bone) are difficult to compress and thus impede the formation of compressions and rarefactions when they carry sound waves. As a result, hard materials have high acoustic impedance when compared with softer tissues (e.g., muscle), which have low acoustic impedance. Therefore, the ease with which sound is transmitted through a substance is termed impedance. The interface between two adjacent tissues serves as a major source for reflecting sound waves back to the transducer. When two adjacent tissues have different impedance values, the sound wave reflects back to the transducer. The greater the difference in impedance between the two tissues, the less energy is transferred to the next tissue and more energy is reflected back. Fortunately, differences in impedance between most soft tissues are small. These small differences are enough to cause a reflection of the sound waves to provide the information for generating an image; at the same time, the differences are small enough to allow enough amplitude for passage of some sound waves past the tissue interface into deeper tissues. These small differences in impedance are sufficient to make ultrasound a workable diagnostic modality. Increasing the gain on the machine does not affect any of these parameters.
Answer
B
3 Which of the following statements regarding transducers is false?
A Higher-frequency transducers have poor penetration and good resolution
B The higher the frequency, the shorter the wavelength.
C Longer wave lengths result in deeper penetration.
D Axial resolution is independent of frequency.
E The piezoelectric effect is defined as the “conversion of electrical to mechanical energy.”
Ref.: 1
Comment
Ultrasound transducers contain crystals. When a sound wave mechanically deforms one of the crystals, voltage is produced. The corollary is also true: when a crystal has voltage applied to it, it deforms and a sound wave is generated. This is described as the piezoelectric effect and has practical applications to the field of ultrasonography. The crystals used in ultrasound machines initially act as speakers that send out and receive sound waves. The returning sound that is reflected back causes the crystals to vibrate and generate voltage.
High-frequency transducers provide high-resolution images at the expense of tissue penetration. In ultrasonography, three types of resolution exist: axial resolution, lateral resolution, and temporal resolution. Axial resolution is the ability to distinguish one object from another object below it. It is dependent on frequency. By definition, a higher frequency means a shorter wavelength. Because the depth of penetration is dependent on the wavelength, a higher frequency results in less tissue penetration. Lateral resolution is the ability to differentiate between two objects that are next to each other. It is independent of frequency and is dependent on the width of the beam. Temporal resolution is the perception of real-time movement and is dependent on the frame rate.
Answer
D
4 Which of the following descriptors regarding echogenicity is not true?
A Hyperechoic tissues are brighter than the surrounding tissue.
B Hypoechoic tissues are less dark than the surrounding tissue.
C Isoechoic tissues are similar in appearance to surrounding tissue.
D Anechoic tissues appear as black sonographic images.
E Simple cysts are hyperechoic.
Ref.: 1
Comment
Echogenicity refers to the appearance of a specific tissue or structure on the ultrasound image relative to its ability to reflect the ultrasound wave. A region in a sonographic picture in which echoes are brighter than those in nearby structures is referred to as hyperechoic. In contrast, hypoechoic areas appear darker than surrounding areas. Isoechoic areas appear similar to surrounding structures, and anechoic areas appear dark or black, without echoes, on a sonographic image. Simple cysts appear as anechoic images with posterior enhancement.
Answer
E
5 Which of the following artifacts is often associated with visualization of the diaphragm?
A Reverberation
B Posterior enhancement
C Mirror image
D Comet tail
E Black boundary
Ref.: 1
Comments
See Question 8.
Answer
C
6 Which of the following artifacts is often associated with visualization of a simple cyst?
A Reverberation
B Posterior enhancement
C Mirror image
D Comet tail
E Black boundary
Ref.: 1
Comments
See Question 8.
Answer
B
7 Which of the following artifacts is often associated with visualization of a bullet?
A Reverberation
B Posterior enhancement
C Mirror image
D Comet tail
E Black boundary
Ref.: 1
Comments
See Question 8.
Answer
D
8 Which of the following artifacts is often associated with visualization of bone?
A Reverberation
B Posterior enhancement
C Mirror image
D Comet tail
E Black boundary
Ref.: 1
Comments
Although the utility of ultrasound is unquestionable, certain problems do exist with it. Artifacts are errors in ultrasound images that occur because the machine design is based on assumptions that are not always true. Reverberation takes place when sound waves are trapped between two areas and the waves are forced to bounce back and forth. Some of this trapped energy eventually returns to the transducer. However, the temporal delay leads to an artifact in the image. A reverberation artifact often resembles a ladder, with hyperechoic areas representing the rungs. Reverberation artifact usually occurs with strong specular reflectors such as bone. Ultrasound images of fluid-filled structures, such as cysts, sometimes display an artifact known as posterior enhancement. This artifact occurs because the ultrasound machine makes the assumption that sound waves are uniformly attenuated by tissue. Fluids are efficient at transmitting sound waves. As the sound travels through a cyst and reaches the tissue below it, the attenuation changes. The ultrasound machine interprets this change incorrectly, and posterior enhancement is the result. Posterior enhancement appears as a hyperechoic (bright) area below the fluid-filled structure. When sound waves are reflected by a curved surface, such as the diaphragm or bladder, instead of by a flat surface, a mirror-image artifact may appear. When the transducer sound waves strike a piece of metal, the metal can act as a bell and continue “ringing” for a longer time than the actual contact between the ultrasound wave and the metal object. As this additional sound energy returns to the transducer, it is incorrectly interpreted as having come from a deeper location. The result is a hyperechoic line extending from the metallic object that resembles a comet tail. The black boundary artifact is an artificially created black line located at fat-water interfaces such as muscle-fat interfaces. It results in a sharp delineation of the muscle-fat boundary that is sometimes visually appealing but not an anatomic structure. This is an artifact seen on magnetic resonance imaging (MRI), not on ultrasound.
Answer
A
9 Which of the following is not a sonographic characteristic of an inflamed gallbladder?
A Gallbladder distention
B Pericholecystic fluid
C Wall thickness of 2 mm
D Sonographic Murphy sign
E Gallstones
Ref.: 1
Comments
The sonographic diagnosis of cholelithiasis is generally indicated by the presence of a mobile, hyperechoic, intraluminal object with posterior shadowing. If these three criteria are not met, the diagnosis is less certain. Gallbladder distention, pericholecystic fluid, a sonographic Murphy sign, and gallstones can all be seen on a sonogram in the presence of cholecystitis. Gallbladder wall thickness is considered abnormal if it is greater than 3 mm.
Answer
C
10 Which of the following are not characteristic of the sonographic appearance of a malignant thyroid nodule?
A Hypoechoic in comparison with surrounding tissue
B Peripheral calcifications
C Irregular margins
D Absence of cystic areas
E Heterogeneity
Ref.: 1
Comments
Ultrasound has proved useful in the evaluation of thyroid carcinoma. Thyroid cancers are often seen as heterogeneous hypoechoic lesions with irregular borders. When microcalcifications are present (psammoma bodies), they are located in the interior of the lesion, not at the periphery. Cystic thyroid masses are usually benign.
Answer
B
11 Which of the following statements regarding focused abdominal sonography for trauma (FAST) is true?
A It can reliably evaluate the retroperitoneum.
B It can quickly detect the presence of pericardial fluid or a pleural effusion.
C It is useful in detecting a cardiac contusion.
D It is considered a replacement for computed tomography (CT).
E It can reliably detect diaphragmatic injuries.
Ref.: 1
Comments
Focused abdominal sonography for trauma has become a vital component in the initial evaluation of trauma patients. Currently, the primary focus of the FAST examination is to detect fluid presumed to be blood, but as time progresses, more advanced applications will undoubtedly arise. The examination is completed quickly during a primary survey (of an unstable patient) or a secondary survey (of a stable patient) and focuses on detecting fluid in the pericardial space and dependent portions of the abdomen. The examination is divided into three parts: cardiac, abdominal, and thoracic. The cardiac examination consists of a sagittal view in the subxiphoid region. The abdominal examination focuses on longitudinal views of the left and right upper quadrants and a transverse view of the pelvis. The thoracic portion is an upward scan from the upper abdominal quadrants and can detect pleural effusions or pneumothorax. Despite the usefulness of the FAST examination, it does have limitations. The FAST examination can quickly evaluate for the presence of both pericardial fluid and pleural effusion. However, it does not evaluate the retroperitoneum and does not detect a cardiac contusion. CT still has many practical applications in trauma patients and has not been fully replaced by the FAST examination. Transabdominal ultrasound has several advantages over CT, including cost, portability, safety, and speed of the examination. However, ultrasound examinations are operator dependent. The quality of the images, or lack thereof, depends on the technical expertise of the person operating the ultrasound machine.
Answer
B
12 Regarding vascular arterial ultrasound imaging, which of the following statements is true?
A In Doppler ultrasound of blood flow, the reflected wave returning to the transducer has the same frequency as the transmitted wave.
B For Doppler ultrasound, the transducer should be held at a 90-degree angle to the body.
C Arterial stenosis leads to decreased flow velocity.
D Carotid artery duplex ultrasound scanning allows assessment of arterial plaque morphology, as well as estimation of the degree of carotid artery stenosis caused by the plaque.
E In dialysis access patients, duplex ultrasonography does not generally assess arterial inflow for arteriovenous (AV) fistulas or grafts accurately.
Ref.: 1
Comments
Doppler ultrasound relies on the fact that the sound wave that has been reflected back to the transducer from a moving object has a different frequency than does the transmitted wave. The change in frequency is known as the Doppler shift, named after the Austrian physicist Christian Doppler who described it in 1842. If the transducer is held at a 90-degree angle while performing Doppler ultrasonography, regardless of the actual velocity in a blood vessel, the ultrasound machine will read zero velocity. This is because the theoretical velocity is calculated by the equation V = Δf c/2f cos θ (where V is velocity, c is the speed of sound in soft tissue, Δf is the change in frequency of reflected versus transmitted sound waves, f is the frequency of transmitted sound, and cos θ is the angle between the ultrasound wave and the direction of motion of the target). Because the cosine of 90 degrees is zero, the theoretical velocity would be zero if the transducer is held at a 90-degree angle to the target. The ideal angle of insonation is 60 degrees. Analysis of the Doppler shift is used to determine the speed and direction of blood flow. Unless the arterial stenosis is so severe that blood flow is slowed almost to zero, the velocity increases in arterial stenosis. As its name implies, duplex ultrasonography uses two diagnostic modalities: (1) high-resolution gray-scale B-mode imaging (anatomic information) and (2) Doppler spectral analysis of blood flow patterns (physiologic information). B-mode imaging allows visualization of plaque location, composition, and morphology. Soft plaques and plaques with an irregular intimal surface (ulceration) may be relatively unstable and pose more risk for cerebral thromboembolic events and stroke than might dense fibrous plaques with a smooth intimal lining. Doppler spectral measurement of flow velocities allows accurate assessment of the degree of carotid artery stenosis. As with other ultrasound diagnostic modalities, the accuracy and reliability of vascular ultrasound imaging are dependent on the skill and experience of the operator. Ultrasound imaging is very useful in patients requiring hemodialysis access. Vein mapping can be performed preoperatively to determine the best vessels to support an AV fistula and postoperatively to assess fistula maturation. It can also be used to assess the arterial inflow for a fistula or graft. Ultrasound of new AV grafts may be limited by air entrained in the wall of the prosthetic graft.
Answer
D
13 Which of the following statements best describes the use of breast ultrasound imaging?
A It should be used instead of breast biopsy.
B It can be used to distinguish between cystic and solid masses.
C It is considered an initial screening test to evaluate the entire breast.
D It can be used to define microcalcifications.
E It should not be used in lieu of stereotactically guided biopsies even if the lesion is detected ultrasonographically.
Ref.: 1
Comments
As the technology of breast ultrasonography has continued to improve, the uses for which it is being applied have increased. Although breast ultrasound can aid in the performance of breast biopsy and other interventional modalities, ultrasound images cannot replace the information that biopsy provides. Breast ultrasound is used in the work-up of a palpable breast mass to aid in the differentiation of a cystic from a solid mass. A simple cyst in the breast appears anechoic in comparison to the surrounding breast tissue. Breast ultrasound is performed early in the work-up of breast lesions but is not generally used as a screening tool. It is difficult to adequately characterize (and often to even visualize) microcalcifications with breast ultrasound. If suspicious calcifications are seen on mammography, stereotactic biopsy should be performed for a thorough evaluation. Ultrasound-guided biopsy should be used preferentially whenever the lesion has been defined sonographically.
Answer
B
14 Regarding intraoperative ultrasound, which of the following statements is true?
A It is very accurate in determining vessel encasement by tumor.
B It necessitates the presence of a board-certified radiologist in the operating room.
C It generally doubles the operative time.
D It is less sensitive than CT in locating small pancreatic tumors.
E Open intraoperative ultrasound is confounded by more artifacts than laparoscopic ultrasound is.
Ref.: 1
Comments
Intraoperative ultrasound imaging has become an important part of the evaluation of many conditions. It may be performed both by open means and laparoscopically. In addition to being a valuable tool for determining vascular encasement by tumor, intraoperative ultrasound has also proved useful for delineating small pancreatic tumors not well seen on CT. For intraoperative ultrasound, a board-certified radiologist does not have to be present. However, the surgeon performing this test should have sufficient training and experience to be technically proficient in ultrasound imaging. Laparoscopy is being used in a growing number of situations, as is laparoscopic ultrasound imaging. Laparoscopic ultrasound has been used to help assess the extent of tumor invasion and to guide treatment. It can also detect small, intraparenchymal tumors in organs such as the pancreas or liver. In experienced hands, laparoscopic ultrasound can provide much of the same diagnostic information as intraoperative cholangiography and conventional intraoperative ultrasound. Newer probes with biopsy-guiding devices have made the application of laparoscopic ultrasound much more user friendly.
Answer
A
15 Endoscopic ultrasound (EUS) imaging has proved useful for all of the following except:
A Staging esophageal tumors
B Diagnosis of common bile duct stones
C Detecting portal vein invasion by pancreatic cancer
D Identifying small pancreatic tumors not seen with CT
E Assessing metastatic disease to the liver
Ref.: 1, 2
Comments
Endoscopic ultrasound imaging is useful for all of the applications described in this question except for the assessment of metastatic disease to the liver. EUS is a minimally invasive technique in which a high-frequency transducer is placed into the gastrointestinal tract. Frequency, EUS techniques allow the identification of small lesions (<2 cm), detection of lymphadenopathy, detection of vascular involvement, and the ability to perform guided fine-needle aspiration (FNA). Staging of esophageal tumors by EUS identifies patients with advanced tumors who may benefit from preoperative therapy. Pancreatic tumors as small as 3 mm may be seen on EUS. The accuracy of EUS without FNA averages 85% for determining T stage and 70% for determining N stage disease. Percutaneous biopsy of pancreatic tumors has been used primarily in patients with unresectable pancreatic cancers or in those with cancer for whom neoadjuvant protocols are being considered. Nevertheless, EUS has become the preferred technique, when possible, in either situation. EUS has a complication rate lower than that of endoscopic retrograde cholangiopancreatography (ERCP) and is as accurate as ERCP in detecting common bile duct stones.
Answer
E
16 Which of the following statements regarding the safety of diagnostic ultrasound and possible adverse effects on scanned tissues is false?
A As sound propagates, energy is converted to heat.
B Bone absorbs sound; therefore, an elevation in temperature is more likely at a bone-tissue interface.
C Significant tissue damage can occur with an increase of 2.5° C (4.5° F).
D Fetal tissue is less tolerant than adult tissue.
E None of the above.
Ref.: 3
Comments
Attention to the acronym “ALARA” (as low as reasonably achievable) will help minimize any possible bioeffects: decrease the power and decrease the time of exposure as much as possible. “…There are no confirmed biological effects on patients or instrument operators by exposures from present diagnostic ultrasound instruments. Although the possibility exists that such biological effects may be identified in the future, current data indicate that the benefits to patients of the prudent use of diagnostic ultrasound outweigh the risks, if any, that may be present.” Ultrasound does generate heat and therefore warms tissue, but the degree is so slight that it is clinically undetectable in most routine applications and the physiologic effect appears to be negligible. Fetal tissue appears to be more susceptible than adult tissue.
Answer
E
17 Which of the following is not true regarding radiofrequency ablation (RFA)?
A It may be used for benign conditions such as neuralgia and cardiac arrhythmias.
B It cannot be applied topically for the treatment of metastatic cutaneous tumors.
C It may be used endoscopically to treat gastroesophageal reflux disease.
D It results in coagulation necrosis, protein denaturation, and tissue desiccation from thermal injury.
E It is synonymous with microwave ablation.
Ref.: 4
Comments
Radiofrequency ablative therapy or radiofrequency ablation involves the transmission of a high-frequency alternating current via electrode application into the tissue of interest. The main application of RFA is for the ablation of malignant tumors, including liver, lung, kidney, adrenal, breast, thyroid, and pancreatic tumors. Probes applied to the skin or too close to the surface of the skin can cause a thermal burn. Microwave ablation involves the transmission of microwave energy via a probe to create a rapidly alternating electrical field that induces motion of polar molecules within the lesion; generates kinetic energy, which in turn is dissipated as heat; and causes coagulation necrosis of the target. Microwave ablation may be used for liver lesions and to treat cardiac arrhythmias, prostatic hyperplasia, and endometrial bleeding, but it is limited by the very small volume of tissue treated with current equipment.
Answer
E
18 Regarding cryotherapy, which of the following is true?
A It is not associated with significant risk for coagulopathy.
B It is a relatively inexpensive modality.
C It is usually performed with the patient under local anesthesia.
D It is used for interstitial applications only.
E It is less efficacious for lesions adjacent to major blood vessels.
Ref.: 4-6
Comments
Cryotherapy is the freezing and thawing of tissue either topically or interstitially with liquid nitrogen or argon circulating through a probe. Ice crystals form in the target tissue during freezing and the tissue degrades during thawing, thereby resulting in cell death from tissue ischemia, fluid and electrolyte shifts, and protein denaturation. Freezing of all areas of the target to at least −40° C, with an additional surrounding 1-cm margin, and repeated treatment cycles are advisable to ensure that no viable tumor cells remain. Its major application has been for the treatment of unresectable primary or secondary liver tumors, as well as kidney tumors.
A major disadvantage is that cryotherapy equipment is quite expensive, and major complications of treatment include “cryoshock,” coagulopathy, myoglobinuria, and hypothermia. Frequently, significant bilateral pleural effusions develop, and a severe systemic inflammatory response syndrome can even occur. Additionally, the procedure is time-consuming, patients usually require general anesthesia, and its efficacy is limited for lesions near large vessels secondary to the heat-sink effect of circulating blood.
Answer
A
19 With regard to ablative therapy for malignant tumors, which of the following is true?
A RFA is best suited for the treatment of smaller hepatocellular carcinomas (HCCs), whereas percutaneous ethanol injection (PEI) is better suited for treating larger lesions.
B PEI is more efficacious for the treatment of septated HCC than is percutaneous injection of acetic acid.
C Real-time ultrasound is the only imaging modality suitable for guiding percutaneous ablation.
D During treatment with cryotherapy, the formed frozen area (ice ball) denoting the treated area is visualized easily with real-time ultrasound.
E During treatment with RFA, the ablation zone denoting the treated area is visualized accurately with real-time ultrasound.
Ref.: 4, 5, 7, 8
Comments
Initially, radiofrequency ablation was limited to the treatment of smaller lesions (or required multiple overlapping probe placements). Currently available larger probes (configured with retractable multiple electrode tips that extend in a radiating pattern) can now treat areas as large as 7 cm with a single ablation. Percutaneous ethanol injection is usually reserved for the treatment of smaller HCCs in patients not candidates for resection. Recent data suggest that RFA is superior to PEI for limited HCC in terms of local tumor control but not in terms of overall survival. Similarly, surgical resection appears to be superior to laparoscopic RFA in terms of local control of HCC, but it does not appear to improve overall survival. Because of its strong necrotizing properties, acetic acid injection has been demonstrated to be more effective than PEI for the treatment of septated lesions. Percutaneous ablations can be done with CT, MRI, or ultrasound guidance. A drawback of RFA is that treatment cannot be monitored precisely by ultrasound because gas microbubbles form in the tissue during treatment and create markedly hyperechoic areas that only roughly correspond to the treatment area. The ice ball (or cryolesion) created with cryotherapy can be monitored with real-time ultrasound. The cryolesion appears as a hypoechoic area during and after treatment, whereas edema in the surrounding tissue creates a distinctive hyperechoic halo.
Answer
D
20 A 59-year-old man is found to have an elevated carcinoembryonic antigen (CEA) level 3 years after resection of a T3N0 carcinoma of the sigmoid colon. CT of the abdomen reveals bilobar metastatic liver disease. The largest lesion is 4 cm. Preoperative positron emission tomography (PET) demonstrates four fluorodeoxyglucose (FDG)-avid lesions corresponding to the findings on CT and no evidence of extrahepatic disease. The patient previously underwent partial hepatectomy for trauma. The consensus opinion from your multidisciplinary tumor conference is that this patient would best be treated by RFA, followed by systemic therapy. Which of the following is true regarding the care of this patient?
A Laparoscopy before RFA may diagnose unsuspected extrahepatic disease in up to 30% of patients.
B Chemotherapy converts unresectable disease to resectable in more than 50% of patients.
C Systemic therapy may cause hepatic toxicity, bleeding, and hypercoagulability.
D The efficacy of RFA depends on the size but not the location of the metastatic lesions.
E Randomized controlled clinical trial data support the use of RFA over other treatment modalities for unresectable colorectal liver metastases.
Ref.: 6, 9, 10
Comments
Liver metastasis will already be present at initial evaluation or will develop in approximately one half of patients with colorectal cancer. Although these patients are all considered to have stage IV disease, they are a heterogeneous group. Treatment recommendations depend on both tumor and patient characteristics. Factors reported to be of significant prognostic and predictive value, either singly or within a scoring system, include patient age, CEA level, primary tumor grade, T and N stages, size of the largest metastasis, number of metastases, presence of bilobar metastases, and the presence of extrahepatic disease. Although patients initially seen with metastatic disease should be evaluated for resection, the majority of patients are not candidates because of tumor features, performance status, or limited hepatic reserve. Increasingly over the past decade, RFA has been used to treat these patients. Percutaneous, laparoscopic, and open approaches have all been used. Because laparoscopy or celiotomy may disclose extrahepatic disease in approximately 10% of patients and because laparoscopic or open intraoperative ultrasound may identify more disease than diagnosed by preoperative imaging, as well as for technical reasons, either of these operative approaches is considered superior to percutaneous ablation of hepatic metastases from colorectal cancer. Aggressive systemic therapy is variably reported to convert 10% to 30% of patients from unresectable disease to potentially resectable disease. However, the commonly used agents oxaliplatin and camptothecin-11 (CPT-11; irinotecan) frequently cause hepatic steatosis, which may decrease functional hepatic reserve. Moreover, bevacizumab can cause both coagulopathy and thrombosis, and thus surgical treatment should be delayed until at least 6 weeks after the cessation of therapy. Both tumor size and location affect the success of RFA; complete ablation of tumors near large blood vessels may be limited by the inability to achieve target temperatures in the tumor. A recent systematic review of evidence about the efficacy and utility of RFA for hepatic metastases from colorectal cancer by an American Society of Clinical Oncology panel noted that the data were insufficient to form a practice guideline and that the large body of literature is composed of single-arm, retrospective, and prospective trials; no randomized control trial data exist. Their review concluded that overall survival of patients without extrahepatic disease was improved by hepatic resection. Contemporary series of appropriately selected patients report a 5-year survival rate of 25% to 58% for these patients. With RFA, reported 5-year survival rates vary widely from 14% to 55%, as do reported local recurrence rates of 4% to 60%.
Answer
C
21 After successful treatment by RFA, which of the following is the most appropriate recommendation for follow-up?
A Ultrasound examination 1 week postoperatively and then at 3-month intervals
B MRI 2 weeks after surgery and then at 6-month intervals
C MRI every 3 months after surgery
D CT 1 week postoperatively and then at 3-month intervals
E PET-CT every 3 months after surgery.
Ref.: 6
Comments
Although intraoperative ultrasound is used to facilitate proper placement of the radiofrequency ablation probe and for intraoperative monitoring, it is not sensitive for distinguishing the difference between treated tissue and tumor recurrence. CT or MRI best visualizes the adequacy of ablation following treatment. The appropriate follow-up imaging schedule is either CT or MRI 1 week postoperatively, followed by repeated studies at 3-month intervals thereafter. Tumor marker studies are usually done at 3-month intervals as well. After RFA, peritumoral hyperemia is seen on cross-sectional imaging as rim enhancement around the ablation zone, which is indistinguishable from tumor enhancement. Persistent rim enhancement, months after treatment, is diagnostic of recurrent (or residual) disease. PET may also help diagnose recurrence, but findings in the treated area or areas in the perioperative period are usually nonspecific.
Answer
D
22 Which of the following ablative modalities is approved by the Food and Drug Administration (FDA) for the treatment of biopsy-proved breast fibroadenomas?
A RFA
B High-frequency ultrasound ablation
C Cryoablation
D Laser ablation
E Microwave ablation
Ref.: 11
Comments
Cryoablation is currently approved by the FDA for the treatment of core needle biopsy–proved fibroadenomas. The use of ablative technology for or as an adjunct to the treatment of small invasive breast cancers is an area of active investigation.
Answer
C
23 With regard to ablative therapy for breast cancer, which of the following is true?
A RFA, cryotherapy, and laser ablation can all be performed with ultrasound guidance.
B Laser ablation and RFA create similar-size zones of ablation.
C Similar information regarding margin status and tumor size and histology can be obtained after treatment with ablation alone or surgical excision.
D The ablation zone created by RFA cannot be distinguished from residual carcinoma on postablation MRI.
E In the majority of cases, no viable tumor cells are found after complete RFA.
Ref.: 11
Comments
Laser ablation requires that the lesion be targeted with MRI or stereotaxis, whereas cryoablation and RFA can be done with real-time ultrasound guidance. With current technology, laser ablation creates a smaller coagulation zone than RFA does, 2.5 to 3 cm versus 3 to 7 cm, respectively. Histopathologic information on tumor size, grade, and histology is not obtained when the tumor is ablated, although some of this information may be obtained from the preprocedure diagnostic core needle biopsy. On MRI, the zone of ablation differs in signal intensity from residual carcinoma. Thus, MRI can be used as a follow-up imaging modality. Pilot safety and efficacy studies of radiofrequency ablation followed by excision for small breast cancers report residual viable tumor cells detected in 5% to 35% of cases and complication rates (predominantly skin or muscle burns) of less than 10%. Intraoperative RFA of the lumpectomy cavity has been proposed as a one-step technique to avoid reexcision of positive or close margins, improve cosmesis, decrease treatment cost, and possibly substitute for postoperative adjuvant brachytherapy (partial breast irradiation).
Answer
E
References
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11 Klimberg VS. Ablative techniques in the treatment of benign and malignant breast disease. In Cameron JL, editor: Current surgical therapy, ed 9, St. Louis: CV Mosby, 2007.