Endoscopy is a medical procedure that uses a flexible tube with a camera to visualize the interior surface of the digestive system. Ultrasonography is an imaging technique that utilizes high-frequency sound waves to obtain images of internal organs such as the liver, gallbladder, and pancreas.

Endoscopic Ultrasonography (EUS) is an advanced diagnostic method that combines these two technologies. By integrating endoscopy with ultrasonography, EUS allows for a detailed examination of the deeper layers of the digestive tract wall and surrounding structures, offering superior resolution compared to conventional imaging methods.

EUS plays a critical role in various clinical applications:
* Cancer Diagnosis and Staging: It is highly effective in diagnosing and staging cancers of the esophagus, stomach, rectum, biliary tract, and pancreas.
* Biopsy Procedures: Facilitates precise biopsy collection from suspicious lesions.
* Early Cancer Detection: Aids in the early identification of malignancies.
* Post-Treatment Monitoring: Useful for evaluating recurrence in post-operative follow-ups and assessing tumor response (regression) after pre-operative radiotherapy.
* Assessment of Local Invasion: Enables detailed examination of cancer involvement in adjacent organs (e.g., prostate, bladder, vagina), lymph nodes, and blood vessels, particularly around the rectum.
* Tumor Grading: Essential for determining the extent and stage of a tumor (T1, T2, T3, T4).