Intraoperative Abdominal Ultrasound: Animals Need Ultrasound Too - Research Paper Example

? Intraoperative Abdominal Ultrasound of the Under the guidance of Format: AMA style Word count: Intraoperative Abdominal Ultrasound Intra-abdominal ultrasound has become an indispensable evaluating tool for surgeons especially in the field of surgery related to the hepatobiliary system (Patel and Roh, 2004). Infact, as of now, there is no such preoperative study that can have sensitivity and specificity similar to intraoperative ultrasound (Patel and Roh, 2004). The procedure is very useful in not only defining the extent of the disease, but also in providing guide to various hepatic resections and also for percutaneous ablative and laparoscopic techniques. According to Machi et al (2004), "being safe, quick, accurate, and versatile intraoperatively, IOUS is a valuable technique that surgeons are recommended to master to improve intraoperative decision making and surgical procedures." In this research essay, intraoperative abdominal ultrasound and its clinical implications will be discussed. Intraoperative ultrasound is mainly useful to image liver, pancreas and bile ducts (Charnley, and Hardcastle, 1990). It is the only method by which it is possible for a surgeon to ascertain the conformation of anatomy of the hepatic veins. Through the knowledge of such anatomy, it is possible to allow localization of the lesion to the particular segment involved, thus providing information for segmental resection and thereby avoiding the need for hemihepatectomy. It is also possible to image the portal vein branch that feeds the particular segment under study and can be cannulated using a fine needle (Charnley, and Hardcastle, 1990). The concept of performing intraoperative ultrasound was introduced first in 1960s and it was introduced mainly to evaluate stones in the bile duct. Limitations in the technology of ultrasound prevented further use of the application until 1980s when more advanced forms of ultrasound applications were introduced (Patel and Roh, 2004). The main limiting factors were poor image quality and bulky transducers (Patel and Roh, 2004). Resolution and the amount of information provided by ultrasound depends on the attenuation of the tissue and the transducer frequency (Charnley, and Hardcastle, 1990). The first modern concept of intraoperative ultrasound came into vogue for adjunct application during pancreatic and hepatobiliary surgery, especially hepatectomy. Since then, the application of intraoperative ultrasound has grown exponentially. As of now, intraoperative abdominal ultrasound in the mainstay in all hepatobiliary procedures related to tumors and cancers (Patel and Roh, 2004). In surgeries related to hepatobiliary system, intraoperative ultrasound is useful to ascertain the resectability and the characteristics of the tumor and these are based on the appearance of the tumor on sonography and also the relationship of the tumor with intrahepatic vasculature. There are several approaches for imaging hepatic tumors in the preoperative period. Transabdominal ultrasound is not only a fast method of imaging, but also noninvasive, cheap and the imaging modality of choice for distinguishing non-obstructive from obstructive causes of jaundice. Transabdominal ultrasound also helps in providing general information with regard to the overall condition of the hepatic parenchyma. In current day practice, CT can of the pelvis and the abdomen is used rampantly because of the valuable information it provides anatomically and also helps in evaluation of the presence of extrahepatic disease. However, the sensitivity of detection of lesions is modest, i.e., only 34- 76 percent (Patel and Roh, 2004). With regard to sensitivity, spiral CT scan is better. The sensitivity is about 86 percent. The sensitivity can be improved by using adjunct arterial portography, but it is an invasive procedure and even that cannot detect lesions less than 20mm diameter. The portography also has high false positive values. When compared to these imaging modalities, MRI is more specific and sensitive and is useful in the detection of very small lesions too. It also helps in delineating the type of lesion, like solid mass or hemangioma. However, it is fraught with certain disadvantages like longer scanning duration and expense. Despite all these advances on the technology side, preoperative evaluation and detection of lesions of the liver is only 60- 80 percent and has several short comings like false negative rates and expense. All these disadvantages are overcome by intraoperative abdominal ultrasound (Patel and Roh, 2004). Liver being the largest organ in the body varies considerably in size and configuration from person to person. Ultrasound is a useful means of assessing internal structures of the liver and evaluating both diffuse and focal parenchymal abnormalities (Scanning protocol for abdominal ultrasound, CUHK). It is useful in diagnosing conditions where there is gross disruption of normal echo pattern. The examination must be performed using 5MHz curved or sector transducers. Hepatic lesion localization on ultrasound is done by Courinaud's anatomical classification of portal segments. There are basically 8 segments defined. Each segment has its own blood supply including arterial, portal, hepatic venous and biliary drainage. The most frequent generalized liver disease detected on ultrasound is cirrhosis where there is overall increased echogenecity of the parenchyma on both A- and B- modes. In addition to these findings, decreases in both normal beam penetration and vascularity of the liver also are seen in cirrhosis. In intrahepatic obstruction cases of jaundice, ultrasound reveals dilatation of the intrahepatic biliary radicles (Kurtz 1980). In pathologically minimal acute and chronic hepatitis, the ultrasound scans may be normal. The findings in acute hepatitis include overall decrease in echogenecity of the liver. In chronic hepatitis the overall echopattern is coarsened due to the increased amount of fibrous tissue and inflammatory cells surrounding the hepatic lobules. This is because; in acute hepatitis the major pathological changes are in the intralobular portion of the liver causing swelling of the liver cells. In chronic hepatitis, the pathological changes are more in the periportal and portal regions (Kurtz 1980). Though definitions related hepatic territories and segments differ among different institutions, individual relation to vascular structures is consistent. It is also important to be aware of the normal variants to anatomic relations. For example, in most individuals, hepatic veins are present in the fissures between hepatic segments and do not follow the distribution of bile ducts, portal veins or hepatic arteries., normal variants conditions, the 3 veins can enter the large vein, inferior vena cava as a single trunk. Such and other variations must be acknowledged before assessing anatomy through imaging modalities like intraoperative ultrasound abdomen (Patel and Roh, 2004). Ultrasound imaging is a valuable tool for imaging liver both in the preoperative period and intraoperative period. The scanning technique is important in the analysis of both acute and chronic hepatitis. In acute hepatitis a single scan is recommended particularly along the long axis of the right lobe because the predominant finding is prominence of the portal vein radicles and the walls are large, specular and angle-dependent reflectors. Hence the purpose is to allow the transducer to be as perpendicular to the vein radicle walls as possible. In chronic hepatitis, one must note that the technique is more affected by changes in the power and TGC curve and inordinate increase in either would produce a false overall brightness similar to true coarsening (Kurtz 1980). This is because in chronic hepatitis, the liver parenchyma consists of small, diffuse and non-angle dependent reflectors. Hence the differentiation is mainly made by evaluating the intrahepatic blood vessels wherein in true coarsening, the vessels will remain echo free (Kurtz 1980). Ultrasound is a safe, effective first-line screening test for cirrhotic patients with clinically suspected neoplastic transformation. It is infact the least expensive choice of screening. The ultrasound appearance of HCC is actually variable and the quality depends upon the examiner. Also, the sonologist must take special precaution to look at the whole liver because HCC can present as a small mass and can be easily missed out. Sensitivity of ultrasonography for detection of small nodules is actually low (Stuart, 2006). A suspicious lesion on a sonogram generally requires additional imaging studies to confirm the diagnosis and the stage of the tumor (Stuart, 2006). The 3 different ultrasound patterns observed in hepatocellular carcinoma are increased reflectivity, decreased reflectivity, and mixed echo pattern. (Cottone, 1983). Small masses of HCC are hypoechogenic and the larger masses have mixed echogenicity. The sensitivity of US for the detection of lesions in a cirrhotic liver is limited (Jacobson, 2007). Doppler imaging may have an advantage that it be performed at the same time to determine the patency of the portal vein (Stuart, 2006). The diagnosis of HCC using ultrasound is enhanced by using contrast agents. In a study by Nicolau and colleagues (2004), they used SonoVue, a second generation ultrasound contrast agent to study the appearance of HCC. They reported that contrast-enhanced ultrasound using coherent-contrast imaging and SonoVue revealed enhancement in the arterial phase in >95% of HCCs, with a few well-differentiated cases not being diagnosed due to the absence of enhancement. They also suggested that echogenicity in the portal and late phases correlated with cellular differentiation. In some cases biopsy may be necessary to confirm the diagnosis. Contrast-enhanced sonography before percutaneous focal liver lesion biopsy improves the diagnostic accuracy of the procedure. It provides important intralesional information for differentiating viable, denaturalized, or necrotic tissue (Wu 2006). The only chances of cure in HCC are surgical resection and liver transplantation. But as mentioned earlier, surgery can be performed in only 20% of cases and cure by surgery is possible in only 5% of cases. Other modalities of treatment are systemic chemotherapy, chemo-embolization and local tumor ablation (Stuart, 2006). The treatment of HCC depends upon the size, number, and location of tumors and also presence or absence and extent of cirrhosis. Other factors which influence treatment are patency of portal vein and presence of metastatic disease (Stuart, 2006). Ultrasound is a valuable tool in evaluating these factors. It is very easy to identify liver tumors by intraoperative ultrasound abdomen because of echogenecity that is altered when compared to the normal parenchyma of the liver. Lesions which are difficult to identify are those which are homogenous and they such lesions can be identified only through the mass effect they exert on the surrounding structures. Characterization of lesions is done as hypoechoic or hyperechoic when compared with normal liver parenchyma (Patel and Roh, 2004). Tumors which are anechoic are those like simple biliary cysts which are round and have a thin and regular wall. These cysts have intensification on the posterior aspect of the cysts. Even hydatid cysts are sonoluscent, but they are multilayered, thick and have multiple compartments that are filled with liquid. These are known as daughter cysts. Intraoperative abdominal ultrasound will be able to detect the communication between the hydatid cysts and the biliary tree. Tumors which are hyperechoic are usually benign tumors, like angiomas or are metastases from gastrointestinal tract. Rarely, hepatocellular cancer masses also may appear to be hyperechoic. Hypoechoic lesions are always malignant lesions like hepatocellular carcinoma or are metastatic lesions from extra-abdominal areas like lung. These lesions are extensive locally and thrombosis in the branch of portal vein draining the corresponding segment is usually evident. Heterogenous lesions of hepatocellular carcinoma are often difficult to identify because, in many circumstances they appear in livers with cirrhosis which are heterogenous too (Patel and Roh, 2004). Intraoperative ultrasound is superior to simple palpation and in about 30- 40 percent cases, new lesions, not detectable through palpation can be identified (Patel and Roh, 2004). In one study by Gruenberger et al (cited in Patel and Roh, 2004), ultrasound appearance of hepatic metastases correlated with prognosis related to colorectal cancer resection. It is possible to perform complete evaluation of the hepatic region through most of the incisions and with only minimal mobilization of liver. There are several systems of intra-operative abdominal ultrasound systems. The best system to perform intraoperative abdominal ultrasound is by using a realtime B-mode electronic scanner with a 5 or 7.5 MHz electronic scanner system that has a probe that is linear and T-shaped (side-fire) or a convex- array probe (end-fire). Either of the probes can be applied to the liver surface directly without the need to apply any acoustic coupling agent or gel. Convex probe is better, in the sense, it allows better visualization of even deeper aspects of liver when compared to linear array. It is very important to use a systematic and methodological approach in examination of the liver along with study of overlapping fields from left to right side. To study the posterior regions, the probe can be placed in the posterior aspect of the liver. It is very important that through the study, the transducer is in the hand of the surgeon and the surgeon must never lose contact with the liver surface and must be aware of the tactile perception of the position of the transducer in order to prevent missing of examination of any areas (Patel and Roh, 2004). Whenever a lesion is visualized, all aspects of the lesion must be examined, like longitudinal and transverse direction for determination of the full extent of the lesion. The proximity of the lesion to neighboring structures and also the extension of the lesion must be determined especially when ablation and biopsy are planned. Superficial lesions can go missing with 5MHz probe and this can be prevented by using probes with higher frequency. It is actually difficult to image lesions that are located in the subscapular region (Patel and Roh, 2004). Intraoperative abdominal ultrasound is useful in evaluating the patency of the vessels in the liver, presence of thrombi related to tumor and invasion of the tumor. The type of resection and extent of resection is largely based on the proximity and also the extension of the tumor mass into the vascular system. These aspects need to be considered especially for those with hepatocellular cancer because of the risk of propagation of the tumor through branches of the portal vein supplying the tumor and development of daughter lesions. In these cases, it is important to perform radical resection that includes the entire portal region supplying the tumor mass. This is difficult in cirrhosis cases and the job is done easier with application of intraoperative abdominal ultrasound (Patel and Roh, 2004). Rifkin et al (1985) conducted a study in which patients who underwent surgeries for liver or other disease processes were examined using special ultrasound transducers. In 55 percent of the patients, there was no new information available through intraoperative ultrasound abdomen. In the remaining individuals, new information was available. In 14 percent of them, there was no change in therapeutic approach. In 12 percent, therapeutic change was possible and benefitted the patient. One study by Makunchi et al (cited in Charnley, and Hardcastle, 1990) reported that intraoperative ultrasound was more sensitive than preoperative sonography, computed tomography or angiography in detecting tumors less than 5 cm in the liver and that intraoperative sonography was more accurate in detecting thrombi related to tumors and intrahepatic metastases (Charnley, and Hardcastle, 1990). Biopsy of lesions that are suspicious can be done using biopsy gun under the guidance of ultrasound (Charnley, and Hardcastle, 1990). In unresectable lesions, local ablation of the tumor is a therapeutic option and ablative procedures include cryoablation, injection with ethanol, photocoagulation, radiofrequency coagulation and microwave coagulation. the success and precision of application of these techniques, especially the radiofrequency ablation is enhanced by intraoperative application of abdominal ultrasound (Patel and Roh, 2004). During laparoscopic procedures, it becomes difficult to evaluate the liver because of the limited ability to palpate lesions and structures. Thus, laparoscopic ultrasound has an important role to play in laparoscopic surgeries, especially those related to resection of colon cancer and before elective hepatic resection. There is some evidence that is known liver disease cases, 64 percent of patients had sparing of laparotomy incision based on laparoscopic ultrasound. There are certain advantages of employing laparoscopic ultrasound while ablating liver lesions and they are detection of lesions that are occult, direct visualization of the organs and the peritoneal cavity and decreased injury risk to surrounding structures (Patel and Roh, 2004). Lin et al (2003) reported a case wherein they used laparoscopic ultrasound for isolation and surgical removal of myoma. Intraoperative ultrasound helps in localizing renal stones accurately during surgery. It also helps in determining the invasion extent of stomach cancers, thus guiding the surgeon about the extent of lymphnode dissection and also the line of dissection for gastrectomy. Some researchers are of the opinion that intaoperative ultrasound is not as accurate as palpation in the detection of gastrinomas, but it is useful in the diagnosis of palpable nodules that are suspicious (Charnley, and Hardcastle, 1990). Intraoperative ultrasound for renal stones is not used much because of advances in percutaneous lithotripsy. Currently, it is mainly used for delineation of biliary, hepatic and pancreatic tissue. Machi et al (1993) reported that intraoperative abdominal ultrasound provided appropriate information in various abdominal surgeries and is superior to various screening tests. It is useful for diagnosis hepatic metastasis secondary to colon cancer, for diagnosisng metastatic liver tumors, for common bile duct calculi screening and for diagnosis invasion of portal vein in pancreatic carcinoma. In pancreatic cancer, imaging pancreas in the preoperative period is often difficult and palpation of the organ during surgery provides a useful extent of the cancer mass. Intraoperative ultrasound provides supplementary diagnosis in these cases and they also help in establishing the diagnosis in non-palpable cases (Charnley, and Hardcastle, 1990). Intraoperative ultrasound is useful in the investigation of some endocrine tumors related to pancreas. There is some evidence that intraoperative ultrasound can detect 100 percent of the insulinomas (Charnley, and Hardcastle, 1990). As far as diseases of the common bile duct are concerned, common method for detection of stones appears to be palpation and it is actually an unreliable method. Operative cholangiography is useful for detection of stones, but is fraught with high false positive values and negative exploration of the ducts. Studies which have evaluated intra-abdomen ultrasound with cholangiography opine that the accuracy of intraoperative abdominal ultrasound is much higher than chalangiography. The researchers also opined that ultrasound was quicker to perform and was much cheaper when compared to cholangiography. It is also non-invasive and does not require any cannulation or isolation of the cystic duct. One major disadvantage of ultrasound abdomen is that air in the duodenal region can cause degradation of the image. Air in the biliary tree can resemble calculi and can obstruct the image of the surgeon with regard to biliary tree anatomy. The airbubbles hinder the images pertaining to passage of contrast to from the stomach to the duodenum. Air also makes it difficult to identify stones within the intrahepatic ducts (Charnley, and Hardcastle, 1990). Intraoperative ultrasound abdomen is useful in detecting metastases in liver related to cancer of the colon or rectum, during resection of the bowel. There are reports that metastases as low as 5 mm can be detected using ultrasound. Thus, it is thoiugh that ultrasound done intraoperatively must be able to detect a great proportion of occult metastases which are not palpable during surgery either due to their small size or because they lie in that part of the liver that cannot be palpated (Charnley, and Hardcastle, 1990). Thus intraoperative ultrasound of the abdomen is a very useful tool in imaging intra-abdominal structures, especially the liver and biliary tract during open surgeries and laparoscopic surgeries. As far as liver cancer is concerned, intraoperative abdominal ultrasound has become one of the essential components of the surgery. This evaluation helps in ascertaining the characteristics of the tumor and also its resectability based on the appearance on sonography and also its relationship to the vasculature of the liver. The procedure is easy, cheap, sensitive, specific and reliable. References Charnley, RM, Hardcastle, JD. Intraoperative abdominal ultrasound. GUT. 1990; 31(4): 368–369. Jacobson, DR. Hepatocellular Carcinoma. eMedicine from WebMD. 2007. http://www.emedicine.com/radio/topic332.htm. Accessed July 20, 2011. Kurtz, AB, Rubin, CS, Cooper, HS, et al. Ultrasound Findings in Hepatitis. Radiology. 1990; 136: 717-723. Lin, PC, Thyer, A, Soules, MR. Intraoperative ultrasound during a laparoscopic myomectomy. Fertility and sterility. 2004; 81(6): 1671- 1674. Machi, J, Oishi, AJ, Furumoto, NL, Oishi, RH. Intraoperative ultrasound. Surg Clin North Am. 2004; 84(4): 1085-111. Machi, J, Sigel, B, Zaren, HA, Kurohiji, T, Yamashita, Y. Operative ultrasonography during hepatobiliary and pancreatic surgery. World J Surg., 1993; 17(5): 640-5. Nicolau, N, Catala, V, Vilana, R, Gilabert, R, Bianchi, ., Sole, M, et al. Evaluation of hepatocellular carcinoma using SonoVue, a second generation ultrasound contrast agent: correlation with cellular differentiation. European Radiology. 2004; 14(6): pp. 1092-1099. Patel, NA, Roh, MS. Utility of intraoperative liver ultrasound. Surg Clin N Am. 2004; 84: 513–524. Rifkin, MD, Rosato, FE, Branch, HM, et al. . Intraoperative ultrasound of the liver. GUT. 1987; 4(4): 22-41. Stuart, KE, Stadler, ZK. Hepatic Carcinoma, Primary. eMedicine from WebMD. 2006. http://www.emedicine.com/med/topic2664.htm. Accessed July 20, 2011. Scanning protocol for abdominal ultrasound. CUHK. http://www.droid.cuhk.edu.hk/web/service/ultrasound/exam_protocol/us_exam_abdomen.htm Accessed July 20, 2011. Wu, F, Wang, Z, Chen, W, Zou, J, Bai, J, Zhu, H, et al. Advanced Hepatocellular Carcinoma: Treatment with High-Intensity Focused Ultrasound Ablation Combined with Transcatheter Arterial Embolisation. Radiology. 2005; 235(2): 659- 667. Read More