Endoscopic ultrasound

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Endoscopic ultrasound (EUS) is a procedure that combines endoscopy with ultrasound to image organs inside the chest, abdomen, and colon. A small ultrasound probe is passed through the mouth into the esophagus, stomach, or duodenum, allowing doctors to see the walls of these organs and nearby structures, and to evaluate blood vessels with Doppler imaging. It is most commonly used in the upper digestive tract and in the respiratory system.

The test is performed by gastroenterologists or pulmonologists who have special training. For the patient, it feels similar to a regular endoscopy, unless ultrasound-guided biopsy of deeper tissues is needed.

During an EUS of the upper GI tract, the probe is used during an esophagogastroduodenoscopy to study the esophagus, stomach, and duodenum. It helps screen for cancers of the pancreas, esophagus, and stomach, and can evaluate benign tumors. It also allows biopsy of focal lesions by guiding a needle through the stomach lining to the target. Less commonly, it can identify problems in the bile ducts and pancreatic ducts.

EUS is performed with the patient sedated. The endoscope is guided to the area of concern, and from different positions between the esophagus and duodenum, doctors can image organs inside and outside the GI tract and biopsy them with fine needle aspiration. Organs such as the liver, pancreas, and adrenal glands, as well as abnormal lymph nodes, are easily sampled. The GI wall can also be checked for abnormal thickening that may indicate inflammation or cancer.

EUS is highly sensitive for detecting pancreatic cancer, especially when a mass or jaundice is present. For staging pancreatic cancer, it mainly looks for local spread; when used with CT, it provides a strong method for diagnosis and staging.

EUS can be used with ERCP to locate gallstones in the common bile duct, which can block drainage and cause back pain, jaundice, or pancreatitis. Echo-endoscopy can also image the rectum and colon, primarily for staging rectal or anal cancer, and may sample lymph nodes with EUS-guided aspiration. It can assess the anal sphincters during lower EUS.

An esophageal EUS can visualize chest lymph nodes around the airways, important for lung cancer staging, and ultrasound can also be performed inside the bronchi (endobronchial ultrasound). Image quality improves with higher frequency, which gives better detail but less penetration, while lower frequency penetrates deeper but with less detail.