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The information on this page was reviewed and approved by

Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on October 27, 2021.

Colonoscopy and endoscopic procedures for colorectal cancer

A gastroenterologist uses a colonoscopy to examine the inner lining of the colon and rectum, which make up the large intestine. In this endoscopic procedure, a colonoscope—a long, flexible, lighted tube with a tiny camera attached to the end—is inserted into the rectum. The gastroenterologist guides the colonoscope through the colon, looking for polyps, signs of bleeding, inflammation or other abnormalities.

If the gastroenterologist finds polyps, or small growths, inside the colon or rectum, a polypectomy may be performed during the colonoscopy. The polyps are then analyzed in a laboratory for signs of cancer.

A patient may have a colonoscopy as an outpatient. The procedure typically takes 15 to 60 minutes, but patients usually remain onsite for two to three hours, including preparation and recovery time. Patients are often sedated during the procedure to help them relax and tolerate discomfort. They may experience pressure, bloating or cramping during or after the procedure, but rarely do patients experience pain.

In addition to a colonoscopy, endoscopic procedures used to diagnose colorectal cancer include:

Flexible sigmoidoscopy: For this procedure, a gastroenterologist uses a lighted tube with a tiny camera attached to its end to examine the rectum and lower part of the colon (the sigmoid colon) for polyps or other abnormalities. The gastroenterologist may also perform a biopsy to collect samples of tissues or cells for further investigation. This colorectal cancer detection test is an outpatient procedure that does not typically require pain medication or sedative anesthesia.

Endoscopic ultrasound (EUS): This diagnostic procedure, which combines an endoscopy and ultrasound, is used to examine the digestive tract as well as other organs, including the colon, pancreas, liver, gallbladder and bile duct. This high-resolution imaging technology helps detect potential tumors and identify lymph nodes where the cancer may have spread. A very thin needle is used to obtain tissue samples, which are analyzed to determine whether cancer cells are present. Sometimes, doctors use an EUS to stage rectal cancer and determine an appropriate treatment plan.

With an EUS, sound waves bounce off of the patient’s internal structures, creating detailed images that a doctor can see in real time. The two types of EUS are: upper endoscopic ultrasound and lower endoscopic ultrasound.

An upper EUS examines:

  • The walls of the gastrointestinal tract
  • The esophagus
  • The small intestine
  • Nearby organs and structures

A lower EUS examines:

  • The wall of the rectum and colon
  • The bladder
  • The prostate or uterus
  • Other nearby structures

For both procedures, sedation or general anesthesia is given intravenously to avoid discomfort. The patient’s vitals are monitored and oxygen is typically administered.

During an upper EUS, a long, thin tube with an ultrasound probe, camera and light on one end is threaded through the mouth and stomach and into the small intestine. To protect the patient’s teeth and the endoscope, a bite block is placed inside the mouth.

For a lower EUS, the endoscope is inserted through the anus and into the colon so that the inside lining of the GI tract may be examined.

Next topic: What are the lab testing options for colorectal cancer?

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