What is the anatomy visualized during an Endoscopic Ultrasound (EUS)?

From the Guidelines

Endoscopic ultrasound (EUS) anatomy is characterized by a 5-layer pattern of the gastrointestinal tract wall, which is essential for the diagnosis and management of subepithelial lesions (SELs) 1. The layers of the GI tract wall, as visualized by EUS, are numbered from the lumen out and include the mucosa, submucosa, muscularis propria, and serosa or adventitia.

• The first and second layers represent the mucosa, including the muscularis mucosa.
• The third layer is the submucosa.
• The fourth layer is the muscularis propria (MP).
• The fifth layer is the serosa or adventitia. EUS serves two primary roles in the diagnosis and management of SELs: characterization of the lesion and tissue acquisition 1.
• Characterization involves determining whether the lesion is intramural or extramural, its layer of origin, size, echogenicity, and presence of blood vessels on Doppler flow.
• Tissue acquisition is crucial for definitive diagnosis and can be performed using EUS-guided fine needle aspiration or biopsy. The echogenicity of the lesion is also an important feature in EUS, with anechoic lesions often representing fluid-filled structures, hypoechoic lesions representing a range of pathologies, and hyperechoic lesions usually representing lipomas or fibrolipomas 1. Understanding the EUS anatomy and the characteristics of SELs is vital for accurate diagnosis and management, as well as for performing EUS-guided interventions safely and effectively.

From the Research

Endoscopic Ultrasound Anatomy

• Endoscopic ultrasound (EUS) is a diagnostic modality that uses high-frequency sound waves to produce detailed images of the digestive tract and surrounding tissues 2.
• EUS echoendoscopes can be categorized into radial and linear configurations, with radial devices used for diagnostic imaging and linear echoendoscopes facilitating image-guided tissue sampling and intervention 2.
• The anatomy visualized by EUS includes the esophagus, stomach, duodenum, pancreas, bile duct, and surrounding lymph nodes and vascular structures 3.
• EUS is particularly useful for evaluating the pancreas, including the detection of pancreatic lesions, chronic pancreatitis, and pancreatic cancer 4.
• The high resolution of EUS allows for detailed imaging of the gastrointestinal tract and surrounding tissues, making it an essential tool for diagnosing and staging various gastrointestinal disorders 2, 3.

Clinical Applications

• EUS has a wide range of clinical applications, including the diagnosis and staging of gastrointestinal cancers, such as esophageal, gastric, pancreatic, and rectal cancer 2, 3.
• EUS is also used to evaluate pancreatic lesions, including cystic lesions and solid tumors, and to guide fine-needle aspiration (FNA) and fine-needle biopsy (FNB) for tissue diagnosis 4, 5.
• The anatomy visualized by EUS is critical for guiding therapeutic interventions, such as celiac plexus neurolysis and pancreatic pseudocyst drainage 2.

Training and Education

• EUS training requires both cognitive and technical abilities, including an understanding of the appropriate indications, performance of evaluations, and management of procedure-related complications 6.
• Acquiring EUS skills often requires training beyond the scope of a standard GI fellowship program, and regular short-term intensive EUS training programs can help practitioners improve and maintain their skills 6.