From the Guidelines
Lower endoscopy, also known as colonoscopy, visualizes the entire large intestine (colon) and the terminal portion of the small intestine (terminal ileum). This procedure allows for the examination of the rectum, sigmoid colon, descending colon, transverse colon, ascending colon, cecum, and often the terminal ileum, as supported by the US Preventive Services Task Force recommendation statement published in JAMA in 2021 1. The examination begins at the anus and advances through the rectum, proceeding through all segments of the colon to the cecum, which is identified by the presence of the ileocecal valve and appendiceal orifice. Some key points to consider about the procedure include:
- The ability to visualize the entire colon, making it valuable for detecting colorectal polyps, cancer, inflammatory bowel disease, diverticular disease, and other pathologies affecting the lower gastrointestinal tract.
- The potential to examine the terminal ileum, typically up to 5-20 cm of the distal small intestine, by passing the endoscope through the ileocecal valve.
- The requirement for bowel preparation to clear the intestine of stool, allowing for optimal visualization of the mucosal surface, as implied by the discussion of direct visualization tests in the context of screening for colorectal cancer 1. In many cases, the endoscope can be passed through the ileocecal valve to examine the terminal ileum, providing a comprehensive visualization of the lower gastrointestinal tract. The US Preventive Services Task Force recommendation statement published in JAMA in 2021 1 highlights the importance of direct visualization tests, including colonoscopy, in screening for colorectal cancer, further emphasizing the significance of lower endoscopy in visualizing the intestine.
From the Research
Parts of the Intestine Visualized with Lower Endoscopy
The parts of the intestine that are visualized with lower endoscopy include:
- The colon
- The terminal ileum
- The rectum
- The sigmoid colon
- The descending colon
- The transverse colon
- The ascending colon
- The cecum
Visualization of Specific Colonic Segments
Studies have shown that:
- Cap-assisted colonoscopy (CAC) significantly extends visualization in the right colon 2
- The improvement of visualization by CAC is only significant for the right colon, but not for the rectum, sigmoid or descending colon 2
- Satisfactory bowel preparation of the right colon was more frequently reported for a low-volume (2-L) polyethylene glycol regimen compared to a single-dose (4-L) regimen 3
- The split-dose regimen had a better quality of preparation in the right colon compared to the low-volume regimen 3
Diagnostic Capability of Lower Endoscopy
Lower endoscopy is the gold standard for visualization and diagnosis of conditions involving the colon and terminal ileum, and facilitates screening and prevention of colorectal cancer 4