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Holzheimer RG, Mannick JA, editors. Surgical Treatment: Evidence-Based and Problem-Oriented. Munich: Zuckschwerdt; 2001.

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Surgical Treatment: Evidence-Based and Problem-Oriented.

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Intra-operative and laparoscopic ultrasound

, M.D.

Department of Surgery, University of Virginia Health Sciences Center, Charlottesville, U.S.A.

Abstract

General surgeons are increasingly using advanced technology to accomplish operative procedures or assist in determining the need for such procedures. Ultrasound is currently used by surgeons to varying degrees based on geographic location, practice patterns, traditional delegation of use, and evolving procedures. While competence in ultrasound is currently a required part of training for board certification in surgery in Germany, it does not constitute part of that testing process in the United States. In Japan, ultrasound machines are commonly available on the intermediate care units of hospitals for use by residents; in many other countries they are limited to being located in the area of radiologic studies with restricted use by radiologists only.

This chapter will present the evidence for the benefit of ultrasound in the treatment of surgical disease in both the intraoperative open as well as the intraoperative laparoscopic setting. In such situations, the location and nature of the procedures lend themselves to the surgeon becoming facile and competent in the use of ultrasound, rather than continuing to rely on supporting personnel to interpret the images. Indeed, the intraoperative setting is a location in which the surgeon has a favorable milieu for learning ultrasound use and interpretation, since the surgeon is already uniquely familiar with the anatomy to be assessed using ultrasound imaging. While surgeons may also use intraoperative ultrasound in treating problems of the vascular system, obtaining central venous access, or localizing soft tissue lesions, this chapter will be limited to the evidence for the use of ultrasound for abdominal operative procedures.

Equipment and technique

Transducers

Ultrasound transducers function to convert electrical energy to sound wave energy via piezoelectric crystals. The sound waves are disseminated in a parallel (linear transducers) or radial (sector transducers) pattern. The ultrasound waves variably penetrate tissues and tissue interfaces, with some energy being reflected back to the transducer at such interfaces. The transducer converts the signal of such reflected waves to continuous gray scale images on the ultrasound monitor. This is B-mode scanning.

Transducers are designed to produce ultrasound waves of different frequencies. The higher the frequency of the waves, the greater resolution of the image conveyed to the screen. Thus a 10 MgHz transducer will produce a significantly more clear image than a 5 MgHz transducer. The disadvantage to higher MgHz transducers is that the ultrasound waves of higher frequencies are more rapidly attenuated with tissue penetration. 10 MgHz transducer cannot penetrate more than approximately 5 cm into the parenchyma of a solid organ such as the liver, and does not yield satisfactory images of intraabdominal structures if it is applied transabdominally. Intraoperative use of an ultrasound probe, where the abdominal wall thickness is not an issue, allows the use of higher MgHz ultrasound transducers since the transducer is placed directly on the surface of the organ to be imaged. Therefore, intraoperative ultrasound images are much sharper and well defined than those obtained through a transabdominal approach.

Technique

Assessment of an intraabdominal organ must be done from two separate planes. Ultrasound images are subject to potential artifact from refraction and mirror images from nearby solid surfaces (such as the diaphragm), and only through the imaging of a finding in two planes can one confirm it is really present. This requires the ultrasonographer to image the organ in both a longitudinal and transverse plane. With open surgery during intraoperative ultrasound (IUS), this biplanar imaging is readily accomplished due to the unlimited access. However, with laparoscopic surgery port sites must be placed strategically to allow the laparoscopic ultrasound probe to be inserted for biplanar examination during laparoscopic ultrasound (LUS). In the case of the liver, this usually requires an epigastric or umbilical port for longitudinal imaging and a lateral abdominal port for transverse imaging.

The entire structure to be assessed should be slowly and carefully imaged in two planes. Intraoperative ultrasonography of the liver involves identifying the three major hepatic veins as well as the two major branches of the portal vein so that lobar anatomy is clearly defined. One then scans each lobe in a progressive and orderly fashion to determine if any pathology exists.

The pancreas is best visualized by opening the lesser sac for direct placement of the probe on the pancreatic parenchyma. If this is not practical, transgastric imaging is possible only if the stomach is completely decompressed. Pancreatic parenchyma is often best initially identified by its relationships to the major vessels coursing underneath it. Laparoscopic ports are usually needed in the umbilicus and right lateral abdominal area.

The biliary tree is best imaged by use of intraperitoneal saline to submerge the porta hepatis area. Then the ultrasound probe can be placed directly on the area overlying the common bile duct. The technique for LUS of the bile ducts has been described in detail by several sources. Transverse scanning in the area of the mid common bile duct produces cross sectional images of the duct, hepatic artery, and portal vein which are typically described as the “Mickey Mouse” pattern (Figure 1).

Figure 1. Schematic view of the structures of the hepatoduodenal ligament illustrating the normal anatomy and the characteristic views of laparoscopic sonography.

Figure 1

Schematic view of the structures of the hepatoduodenal ligament illustrating the normal anatomy and the characteristic views of laparoscopic sonography.

Performing intraoperative biopsy of suspicious lesions must be a part of the practicing surgical ultrasonographers armamentarium. Intraoperative biopsy during celiotomy is best done with dynamic alternating longitudinal and transverse imaging of the structure to confirm needle placement in the correct three dimensional plane. Laparoscopic biopsy has been more difficult and cumbersome, but there is now a laparoscopic transducer with inline biopsy capability. This may allow more advanced procedures such as energy-directed ablation of hepatic metastases to be more commonly done under LUS rather than IUS guidance.

Biliary tree imaging

Laparoscopic cholecytectomy is now the standard procedure for treating symptomatic cholelithiasis. Intraoperative imaging of the biliary tree during this operation is done variably. While arguments exist to justify its routine use versus its selective use, it is not the aim of this chapter to provide the evidence for those arguments. Suffice it to say, it is appropriate for biliary tract surgeons to be competent in imaging the biliary tree intraoperatively. Currently, when imaging the biliary tree during laparoscopic cholecystectomy, most surgeons perform intraoperative cholangiography. However, intraoperative laparoscopic ultrasound has now been established as equal to cholangiography in experienced hands for defining choledocholithiasis.

Several studies have compared the accuracy of LUS to laparoscopic intraoperative cholangiography (LIOC) in the detection of common bile duct stones (14). Although there was some discrepancy between studies, the overall sensitivity of LUS was high (71–100%) and comparable to LIOC (Table I).

Table I. Sensitivity of laparoscopic ultrasound and cholangiography in the detection of common bile duct stones.

Table I

Sensitivity of laparoscopic ultrasound and cholangiography in the detection of common bile duct stones.

Specificity of 90–100% was reported for both modalities.

Advantages of LUS are that it usually takes less time and requires less dissection than LIOC. Disadvantages are that LUS has a decreased sensitivity in detecting stones in the intra-pancreatic portion of the common bile duct, and a decreased ability to identify abnormal ductal anatomy, when compared to cholangiography. Most experts agree LUS is complementary to LIOC as a method of evaluating the biliary tract during laparoscopic cholecystectomy, depending on the specific information desired. However, at least one center with significant experience in both methods has now adopted LUS as the standard procedure since it takes less time to perform (4).

Another potential use of LUS is for specific imaging of the gallbladder if there is any question of gallbladder carcinoma. Also, LUS has been used to assist in the diagnosis and staging of proximal bile duct tumors.

Liver

The efficacy of intraoperative ultrasound (IUS) in determining resectability of hepatic tumors was first described by Makuuchi et al. Most hepatomas are not amenable to resection when discovered due to coexisting hepatic disease or additional tumor precluding resectability. The determination of resectability preoperatively, despite the continued improvement in the technologies and imaging capabilities of computed tomography (CT scan) and magnetic resonance imaging (-MRI), has generally been, at best, in the 50 to 80% range. IUS can more accurately determine the extent of tumor involvement of the liver, confirming resectability, than any preoperative method including CT portography. IUS has been shown to be more accurate than either preoperative ultrasound, CT, CTAP, or surgical exploration in the detection of liver metastases from colorectal carcinoma. Machi and Sigel reported their experience in confirming the superiority of IOUS with other screening tests for 250 patients (table II). In patients with known hepatomas, laparoscopy and LUS has been clearly shown to be of value in limiting the number of patient subjected to unnecessary laparotomy for unresectable disease. In two series, patients with apparently resectable hepatocellular carcinoma by preoperative studies underwent this combination of examinations and 63% and 64% of the patients were found to have unresectable disease, sparing them unnecessary laparotomy (8).

Table II. Accuracy of screening methods for detecting liver metastases from colorectal carcinoma (reproduced with permission from Machi J, Sigel B (1996) Operative ultrasound in general surgery. Am J Surg 172: 15–20).

Table II

Accuracy of screening methods for detecting liver metastases from colorectal carcinoma (reproduced with permission from Machi J, Sigel B (1996) Operative ultrasound in general surgery. Am J Surg 172: 15–20).

IUS is particularly helpful in evaluating hepatic lesions seen on preoperative imaging studies that are suspicious as possibly being metastatic tumors. For the patient undergoing hepatic resection for tumor, IUS has been shown to alter the operative plan, when that plan was based on preoperative imaging, in 38 to 49% of cases in several reports. In most series reporting assessment of colorectal metastatic disease by various imaging studies, 5–12% of patients have been found to have metastatic disease detectable only through IUS. These lesions are usually small, yet often change the operative plan (10).

IUS is also the best method to clearly define the hepatic resection plane intraoperatively and achieve clear margins during tumor resection.

The weakness of IUS is in detecting lesions just under the surface of the liver which are less than 1.0 cm in diameter. However, intraoperative palpation of the liver detects such lesions with a high sensitivity. Clarke et al demonstrated that IOUS allowed surgeons to detect an additional 25–35% of hepatic lesions beyond those detected by simple intraoperative exploration and palpation of the liver when performing surgical resection and staging for colorectal carcinomas. The combination of intraoperative liver palpation and IUS are significantly more accurate in detecting hepatic lesions than any single modality.

Pancreas

LUS is often used in the staging of patients with adenocarcinoma of the pancreas. Laparoscopy with LUS has been shown to identify unresectable pancreatic cancer in 19–62% of patients who were thought to be resectable by preoperative imaging, thus often saving an unnecessary laparotomy when other palliative procedures are available (8). During operations for pancreatic carcinoma, IUS may be used as a helpful intraoperative tool to quickly assess tumor resectability with respect to portal vein involvement. IUS can detect portal venous invasion by tumor with a 92% sensitivity and specificity. In one recent report it found venous involvement in 42% and arterial involvement in 38% of cases of pancreatic carcinoma at staging, resulting in a treatment change for 14% of patients (6).

IUS is highly effective for localizing primary endocrine neoplasms of the pancreas and surrounding tissues. These tumors are often small in size, making preoperative detection difficult even with a combination of transabdominal ultrasound, CT, MRI, and venous sampling of secretory products. IUS has been shown to successfully locate insulinomas in 85% of cases. When combined with intraoperative palpation, the detection rate can be in the 95 to 100% range. IUS was shown to detect 83% of gastrinomas in one series, including 100% of intrapancreatic lesions. In patients with MEN-I syndrome, preoperative tumor imaging has a low yield, and IUS is the indicated procedure for optimal tumor localization. Pancreatic islet cell tumors are now also being localized by LUS prior to laparoscopic resection.

Other intraoperative uses of ultrasound to treat pancreatic disease include the use of IUS to locate the pancreatic duct for drainage procedures, and the use of IUS or LUS to drain pancreatic pseudocysts.

Esophagus and stomach

Laparoscopy with LUS can be used to stage gastric and distal esophageal carcinoma, but exerts less impact on disease management than with hepatic or pancreatic tumors. Laparoscopy with LUS helped avoid unnecessary laparotomy in only 5–16% of patients with gastric or distal esophageal cancer thought to be resectable by preoperative imaging. It was less helpful for esophageal than gastric carcinoma in one study (5). This may be in part because many patients with advanced disease of these organs still require resection or another procedure for palliation via an open laparotomy. For cancer of the stomach or distal esophagus, laparoscopy with LUS is likely best used on a selective basis.

IUS may be helpful in determining margins for resection of primary gastric carcinomas, while it is less helpful for determining appropriate extent of surgical margins for recurrent gastric carcinomas or for gastric lymphomas.

Other uses of laparoscopic ultrasound

LUS with Doppler ultrasound may be valuable to assess blood flow and viability of bowel during procedures for diagnosis of acute pain or lysis of adhesions for small bowel obstruction. During laparoscopic procedures for drainage and decortication of symptomatic kidney cysts, LUS can help localize the cysts and detect previously unidentified cysts. Similarly, LUS can guide laparoscopic drainage of lymphoceles following renal transplantation. Gynecologists have used LUS to evaluate complex adrenal masses and uterine myomata. LUS may be useful in selected cases of laparoscopic adrenalectomy to locate the gland and vein and confirm the presence of abnormalities.

Summary

The basic advantages of intraoperative ultrasound include realtime imaging, avoidance of ionizing radiation, rapid determination of fluid versus solid lesions, extremely sharp images of solid organ structures determining the presence of small pathologic changes, and the use of Doppler ultrasound to detect blood flow. These advantages are present using either open or laparoscopic ultrasound. There is extensive evidence to document the superiority of intraoperative ultrasound in diagnosing and staging for malignancy, and it is also effective for imaging structures such as the biliary tree for calculus disease. Surgeons are well advised to adopt this technology into their practice. Certain residency training programs have responded to the foreseen need of future surgeons to understand and use ultrasound by establishing it as part of the curriculum and training.

References

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Copyright © 2001, W. Zuckschwerdt Verlag GmbH.
Bookshelf ID: NBK6975

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