Endoscopy is a flexible instrument used to examine the digestive system. Ultrasonography is a device that uses high-frequency sound waves to obtain images of organs such as the liver, gallbladder, and pancreas. Endosonography combines endoscopy and ultrasonography, allowing examination of the deeper layers of the digestive system and surrounding tissues.

Endoscopic ultrasonography can be used in the diagnosis of esophageal cancer, stomach cancer, rectal cancer, bile duct cancer, and pancreatic cancer; obtaining biopsies; early detection of cancer; post-surgical follow-up to investigate recurrence; investigating tumor regression after radiotherapy before surgery; examining cancer involvement in neighboring organs around the rectum (prostate, bladder, vagina), lymph nodes, and blood vessels; and determining the tumor stage (T1, T2, T3, T4).