Gastrointestinal imaging: Endoscopic ultrasound☆
Section snippets
Instrumentation
EUS is performed using either dedicated echoendoscopes or standard endoscopes through which miniprobes are passed. Two main types of echoendoscopes are used in clinical practice—radial and curvilinear array.1, 2, 3 Radial imaging uses a rotating 360° transducer and provides an image in a plane perpendicular to the direction of insertion of the echoendoscope. The image obtained is thus analogous to that of cross-sectional computed tomography (CT) and is more easily interpretable as a rule than
The gut wall
Standard EUS is able to show 5 layers of the gastrointestinal wall of alternating hyperechoic and hypoechoic layers as described in Table 2.With higher-frequency probes, 7 or more layers can be seen.5, 6
Cancer staging
Cancer staging is probably the most common indication for EUS. Because it can delineate the component layers of the gut wall, EUS is very well suited to classifying gastrointestinal cancers arising from the mucosa using the widely accepted TNM classification.3 It is also useful for some
Esophageal cancer
There are a variety of therapeutic options for esophageal cancer including surgery, radiotherapy, chemotherapy, photodynamic therapy, palliation, and multimodal combination therapy.18 The appropriate treatment for esophageal carcinoma is particularly dependent on accurate staging, and EUS plays an increasingly pivotal role in this staging, which uses the TNM classification. Superiority of EUS over CT for local staging of esophageal cancer has been shown in several studies,19, 20 and the
Pancreatic carcinoma
The advent of newer imaging modalities over the last decade has improved the detection rate for pancreatic cancers, but the ideal diagnostic tool should allow detection of small, potentially curable lesions. Some consider EUS to be the gold standard in imaging of tumors of the pancreas, and it appears to be superior to several other imaging modalities including endoscopic retrograde cholangiopancreatography (ERCP), angiography, and spiral CT, particularly for small masses less than 2–3 cm in
Rectal carcinoma
There is a growing body of literature describing the use of EUS in staging of rectal carcinoma, but there are many conflicting results and no apparent uniform consensus. Accurate staging of rectal cancer is important to guide appropriate resection (Figure 11) because lesions that are confined to the mucosa can be resected transanally.17Distal, invasive tumors require an
Mediastinal masses
There is growing interest and experience in the use of EUS FNA for the evaluation of mediastinal masses (Figure 12A and B).The middle and posterior mediastinum are inaccessible to percutaneous ultrasound,114 and, traditionally, lesions in these locations have been imaged and biopsies performed using CT, MRI, bronchoscopy
Interventional EUS
The number of therapeutic procedures being attempted under EUS is rapidly growing, and the introduction of EUS-guided FNA systems has led to many advances in the field of intervention. Following is a review of some of the procedures performed under EUS, some of which are still essentially under development (Table 4).Celiac plexus blocks FNI for achalasia EUS directed endoscopic resection FNI of tumors with immunotherapeutic, chemotherapeutic, gene
Future developments
There are many exciting developments in the field of interventional EUS. EUS-guided fine needle injection of tumors with immune modulators is under study as described earlier.135 It is likely with advances in tumor therapy and echoendoscope technology that EUS fine needle injection may also deliver chemotherapeutic agents, gene therapy, and radionuclide preparations directly into tumors.5 Delivery of radionuclide agents by EUS would require a shielded delivery system.15
Another exciting
Summary
EUS is now firmly established as the investigation of choice in the locoregional staging of several gastrointestinal tumors and submucosal masses. In some situations, it is recommended that combination of information from other imaging modalities with EUS findings is needed to maximize accuracy. However, the increasing use of EUS-guided FNA should improve the accuracy of EUS as a stand-alone investigation.
Other advances have been made in the diagnosis of chronic pancreatitis with EUS,
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Address requests for reprints to: Michael F. Byrne, M.D., MA (Cantab), MRCP, Box 3189, Duke University Medical Center, Durham, North Carolina 27710. e-mail: [email protected]; fax: (919) 684-4695.