20 Endoscopic Ultrasonography
Endoscopic ultrasonography (EUS) has become indispensable and unavoidable in the diagnostic and the treatment of the digestive diseases. It is a demanding technique and learning remains long, tedious, and difficult. A prior initial experience in diagnostic and therapeutic digestive endoscopy is required in order to understand this procedure better. The high diagnostic accuracy of the technique especially in cancerous pathologies and the recent popularization of the EUS-guided sample using fine-needle aspiration (FNA) have led to the integration of this technique at the center of care in digestive oncology. This is therefore the recommended first-line investigation for the histologic diagnosis of solid and cystic pancreatic tumors and for evaluation of their locoregional extension. Nevertheless, a wide range of pathologies can be advantageously evaluated by the EUS from submucosal tumors through esophageal motility disorders or endometriosis. EUS also benefits from the latest technologies in ultrasound with exceptional resolution, elastography, and contrast EUS now possible to significantly improve the diagnostic capabilities in many fields. Recently EUS moved progressively to a unique interventional modality that offers a minimally invasive alternative to various surgical interventions with an excellent safety profile. The drainage of pancreatic pseudocysts is the historical example. However, improving the equipment now allows considering a multitude of drainage techniques sometimes see hybrid like for biliary or pancreatic duct and digestive anastomosis. A very exciting future expects this technique which is now mature. This text presents the basic principles of EUS, its validated indications, and its main outcomes.
20.2 Overview of the Procedure
EUS is a technology allowing the use of ultrasound within the upper and lower digestive lumen. The transducer is placed at the tip of the endoscope which keeps a video view of the gastrointestinal (GI) tract. The close contact with the intestinal wall allows the use of high frequency which brings the best compromise between image resolution and depth of field. This specificity makes it the technique of choice for the analysis of the bowel wall (esophagus, stomach, duodenum, rectum, and anus) and organs in contact (mediastinum, liver, biliary ducts, gallbladder, pancreas, vagina, bladder). The quality of the results of the procedure depends directly on the operator’s experience.
20.3 General Diagnostic and Therapeutic Techniques
20.3.1 Conditions of Implementation
EUS allows the analysis of the upper digestive part from the esophagus to the distal duodenum and adjacent organs. The exploration of the lower part of the digestive tract is limited to anus, rectum, and sigmoid. A bowel preparation based on enema is required for the anorectal exploration. The procedure could be routinely performed under propofol sedation, but conscious sedation is still widely used in Europe and Asia. 1 The outpatient management is the rule in case of diagnostic procedure including the EUS-guided sample using FNA. 2 Room air or CO2 insufflations are suitable for diagnostic EUS and EUS-FNA, but CO2 is required for therapeutic process due to the risk of perforation especially in case of EUS-guided digestive anastomosis. Periprocedural antibiotic prophylaxis is suggested by international guidelines for EUS-FNA of pancreatic cysts. 3 Prophylactic antibiotics have not been studied in case of interventional EUS procedures (i.e., pseudocyst and biliary or pancreatic duct drainage, tumor destruction, vascular treatment, fiducial placement). Nevertheless, this prophylaxis is usually performed, with infectious complication infrequently reported. As recommended, no withdrawal or modification of antiplatelet agents and anticoagulation therapy are required for diagnostic EUS. 4 Aspirin alone is allowed during EUS-FNA in case of solid tumor. All antiplatelet or anticoagulation treatment should be stopped when therapeutic EUS is performed or when EUS-FNA on cystic lesion is expected.
20.3.2 Endoscopes and Probe
The radial scanning or curved linear array endoscope is used depending on local expertise, but only linear probe allows a therapeutic approach and FNA due to the large working channel (3.7–3.8 mm) and the presence of an elevator. If imaging capability of each techniques is compared, curved linear array seems to be superior in the exploration of the pancreatic head–body transition, the pancreatic tail, the hepatic hilum, and the vascular bifurcation whereas radial scanning allows a better major duodenal papilla and gallbladder delineation. 5 High frequencies (5–12 MHz) and Doppler analysis are now available in all echoendoscope. Endorectal ultrasonography could be accomplished using rigid or flexible devices: rigid linear probe presents a limited insertion but are more practical for rectal cancer staging and anal functional disorders (▶Fig. 20.1). 6 , 7
20.3.3 EUS Semiology of the Bowel Wall
The stratification of the bowel wall with EUS could be described in five, seven, or nine layers according to the type of frequency used. In low frequency (5–7.5MHz), five layers are usually visible as described in ▶Fig. 20.2. The fourth hypoechoic layer is an essential marker since it corresponds to the muscular layer. The appearance in nine layers is possibly observed with very high-frequency probes (20 MHz) which are less used and available. These probes help to identify the muscularis mucosae (fourth hypoechoic layer with these) and its potential involvement by tumor, increases risk of cancerous lymph nodes.
The patient is placed in prone or left lateral position. Insufflation during the procedure and the introduction of the endoscope needs to be minimized in order to reduce artifact. The instillation of water should be considered to improve the resolution of the picture especially for the GI wall analysis. A close contact between probe and the target area is mandatory using the up handle of the scope.
Usually, the procedure for biliopancreatic investigation starts from the second/third duodenum to allow the inspection of the interest area with a slow withdrawal and rotation of the scope. The head of pancreas, papilla, and the distal part of common bile duct is accurately investigated by a transduodenal approach. The proximal part of the bile duct with hepatic hilum, the arterial and venous axis (portal vein, superior mesenteric artery and vein) could be explored by transduodenal and transgastric approach. The body and tail of the pancreas, the celiac trunk, and the splenic artery/vein are analyzed only by a transgastric view.
The endoscope is pushed into the sigmoid (aorta bifurcation and spine in posterior view) under video control and then the EUS exploration phase is performed after fulfilling the digestive lumen with water with a slow withdrawal of the scope.
20.4 Accessory Devices and Techniques
It is a noninvasive method that can be used in combination with conventional EUS which is a measure of tissue stiffness evaluated by the application of slight pressure to the target with the ultrasonography probe (▶Fig. 20.3). It has been demonstrated to differentiate between benign and malignant solid pancreatic masses and lymph nodes with a high accuracy, as well as normal pancreatic tissues from early chronic pancreatitis. 8
20.4.2 Contrast-Enhanced EUS
Contrast-enhanced EUS (CE-EUS) is the intravenous use of microbubble blood pool agents to allow the real-time imaging of tumor vascularization and perfusion. The evaluation of microvascularity by CE-EUS was useful, especially for the discrimination between pancreatic adenocarcinoma (hypoenhancement) and inflammatory nodules in chronic pancreatitis. 9
20.4.3 Needles and EUS-Guided Sample
EUS-guided needles of various diameters (19, 20, 22, and 25 gauge) are commercially available. Specific designs have been proposed to allow core tissue acquisition which provides a more representative sample and tissue architecture of the lesion with capability for immunohistochemistry or vital stains: 19-gauge Trucut needle and side port (reverse cutting bevel) at the tip of the needle in different caliber (EUS–fine needle biopsy [FNB]) are available. Nevertheless, the Trucut needle did not show any improvement comparing with other needles due to a lack of flexibility and high failure rate in duodenum (40%). 10 No significant difference between the EUS-FNB and standard FNA needles is observed for sample adequacy, diagnostic accuracy, or acquisition of a core specimen. 11 However, a reduction in passes to establish the diagnosis is demonstrated with it and a higher diagnostic yield has been suggested for nonpancreatic lesion. 12
The usual technique for EUS-FNA implicates several steps which are presented in ▶Fig. 20.4. The fanning technique should be considered for each EUS sample. 13 This technique is based on the change of the axis of the needle in different areas within the mass by using the up–down dial of the echoendoscope when moving back and forth. Other variants have been described to improve the tissue acquisition including the EUS-FNA without stylet (reduction of the procedure time and the risk of accidental needlestick injuries), the capillary or “slow-pull” technique (slow withdrawal of the stylet), and the wet–suction technique (column of air replaced by 5 mL of saline solution in the needle).
The classical suction technique improved the diagnostic yield and the adequacy of the specimen. The high negative pressure (50/60 mL) is certainly better to obtain a significant higher rate of adequate sample for histologic analysis. 10 The use of stylet does not impact the EUS-guided sampling result. 2
Air flushing in a slow and controlled fashion is the best way to express the material from the needle. Stylet reinsertion is only required if the aspirates cannot be expelled due to clotting or drying. The collection of histopathologic specimens could be performed using smear, liquid-based cytology, and/or cell block (▶Fig. 20.5). The cell block improves the diagnostic yield as it provides histologic analysis and should be considered when possible.