Intraoperative diagnostic techniques

Evaluation of the liver

IOUS of the liver was first introduced into clinical practice in the early 1980s and rapidly became routine practice for the management of malignant liver disease. Early reports demonstrated the advantages of IOUS, which in some cases altered the operative management of hepatic malignancy not only by delineating the proximity major vascular and biliary structures but also by detecting hepatic tumors not revealed on preoperative imaging ( Fig. 24.1 ). In a study of 100 consecutive patients undergoing preoperative imaging for colorectal liver metastases, contrast-enhanced and unenhanced IOUS identified an additional 47 liver nodules that were not viewed using MRI, and these new findings resulted in the modification of a previously planned procedure. In a similar study of 102 patients with colorectal liver metastases, contrast-enhanced IOUS altered 22% of planned surgical procedures because of the additional diagnosis of nodules or more accurate visualization of vascular invasion. The yield of IOUS is highly dependent on the type and quality of preoperative imaging obtained and although additional intraoperative findings may not influence all planned resections, it remains an integral adjunct to parenchymal assessment and operative planning.

When evaluating the liver parenchyma, the sonographer must first evaluate the extent of intrahepatic disease and then assess for vascular occlusion or invasion. Sonographic features of liver tumors vary. The surgeon should anticipate the need for assistance in the case of ambiguous or challenging lesions and communicate with radiologists preoperatively so that personnel and equipment are readily available.

The sonographer should be familiar with the characteristics of common parenchymal lesions (see Chapter 13, Chapter 14, Chapter 15 ). Hemangiomas are typically soft when palpated and either lack any visible flow or demonstrate minimal flow compared with the adjacent liver parenchyma. They typically appear hyperechoic with well-demarcated margins and may demonstrate posterior echo enhancement. In contrast, colorectal liver metastases are usually hyperechoic or isoechoic with adjacent liver parenchyma and are frequently surrounded by an ill-defined hypoechoic rim that may give the lesion a bull’s-eye or target appearance. Mucinous variant colorectal cancer metastases may contain calcification that produces acoustic shadowing. Hepatocellular carcinoma (HCC) frequently invades major vascular structures and may be associated with portal lymphadenopathy.

Technical considerations

Examination of the liver should always start with inspection of the organ and the entire peritoneal cavity followed by palpation. IOUS is then applied with increasing pressure to accurately delineate the spatial relationship of hepatic tumors to major vascular and biliary structures. Intraoperative transducers appropriate for liver surgery include high-frequency (6–10 MHz) T-shaped linear- or curvilinear-array transducers. These probes provide excellent high-resolution images and can identify lesions as small as approximately 1 to 2 mm in size at depths of penetration of approximately 10 to 12 cm. Transducers with color-flow Doppler imaging enable further discrimination of tumors and normal hepatic vasculature.

Techniques for IOUS continue to evolve, with some units now routinely performing laparoscopic IOUS. Particular attention must be given to port placement in this scenario. Typically, no coupling gel is required because of the natural surface moisture of the liver. The transducer is initially held in a transverse position, and the survey of the liver begins by first identifying the confluence of the right and left portal pedicles. Next, all segmental pedicles on the right are visualized, followed by those on the left. Each hepatic vein is visualized by scanning peripherally and then by traversing toward the vena cava. Identifying the hepatic veins can be achieved by placing the transducer cranially in a midline position and angling towards the heart. The confluence of the left and middle vein has a characteristic appearance and should be observed in all sonographic examinations. Only light pressure should be applied to the liver. If the entire liver is to be scanned (e.g., to search for metastases), sequential overlapping sagittal strokes are made sweeping from superior to inferior, beginning at the most lateral margin of segment II and traveling toward the right. More focal scanning can be used to localize impalpable lesions situated deep within the liver parenchyma. Special care must be taken when imaging the superior portion of the right liver, the posterior subdiaphragmatic bare area, and surface lesions, such as hamartomas, because these areas are particularly challenging to completely visualize. Once the lesion has been delineated and measured, photographic documentation should be obtained and saved.

The planned surgical margin of the lesion may be outlined using electrocauterization of the liver capsule because it will produce acoustic shadowing. The depth of the lesion can be estimated using its relationship to other structures or direct measurement.

Evaluation of the biliary tree

As laparoscopic cholecystectomy has become the standard of care for gallbladder disease, the use of laparoscopic US (LUS) during this procedure has emerged as an alternative to cholangiography (see Chapters 37 and 38 ). In this scenario, IOUS has a reported sensitivity and specificity over 90% for detecting choledocholithiasis and is recommended as the primary screening modality for evaluating bile duct calculi because of its safety, efficiency, and overall cost-effectiveness. IOUS is at least as good as cholangiography, if not better, at detecting stones during laparoscopic cholecystectomy. LUS in particular has the added advantage of reducing the risk for biliary and vascular injury. A recent systematic review compared LUS with intraoperative cholangiography (IOC) during laparoscopic cholecystectomy and found that routine LUS reduced bile duct injuries to almost 0% and resulted in a reduced procedure time when compared with IOC. However, proficiency with IOUS requires some time to develop and has a longer learning curve, which may explain why it is not used more liberally for biliary disease.

LUS is a useful adjunct for staging gallbladder carcinoma and cholangiocarcinoma (see Chapter 49, Chapter 50, Chapter 51 ). Sonographic findings not only reveal subtle liver metastases but also may help to define the local extent of these tumors and their relationship to the ductal system. ^, Doppler and color flow images may help distinguish biliary sludge from polyps and other intraluminal tumors. Other applications of LUS include evaluating biliary strictures and malignant biliary obstructions in the planning of surgical reconstructions, such as biliary bypass procedures.

Technical considerations

The biliary tree and gallbladder are imaged best from a right subcostal port or from the periumbilical port. Sonographic examination of the gallbladder is approached through the liver by using a 5- or 7-MHz transducer. A nasogastric or orogastric tube should be placed for decompression. The bile ducts can be visualized through a compressed duodenum or gastric antrum using a 7-MHz transducer, but placing the transducer directly on the ducts should be avoided because reverberation artifact limits its sensitivity. Color flow images are helpful for distinguishing the common bile duct (CBD) from the portal vein, for identifying the insertion of cystic duct into the CBD, and for identifying any aberrant biliary anatomy during surgery.