The small intestine joins the large intestine in the right lower quadrant. The ileocecal valve separates the small from the large intestine. The first part of the large intestine is called the cecum. The appendiceal orifice also enters into the cecum and has its own characteristic appearance. Identification of the ileocecal valve and the appendiceal orifice can help an endoscopist confirm that he/she has completed the colonoscopy and visualized the entire colon. The ascending colon (i.e., right colon) transforms into the transverse colon at the hepatic flexure. The hepatic flexure is the region of the large intestine located in the right upper quadrant near the liver. The end of the transverse colon is marked by the splenic flexure. The splenic flexure is the region of the large intestine located in the left upper quadrant near the spleen.
These anatomical landmarks are used by clinicians, particularly when communicating regarding the locations of lesions. The flexures can be identified during colonoscopy but are less reliable as landmarks particularly in the setting of prior surgery or very redundant colonic anatomy. The descending colon (i.e., left colon) joins the sigmoid colon to empty into the rectum. The rectum also has a very characteristic appearance that aides in its identification and localization of lesions.
Endoscopists try to describe the locations of lesions based on visual clues obtained during colonoscopy; characteristic appearance of colonic folds may also aid in localization. For example, the folds of the transverse colon are somewhat triangular in appearance. Endoscopists may also cite the distance from the rectum in centimeters. This is less reliable in the setting of redundant colon as the colon may telescope over the colonoscope thus making the measurement inaccurate. Injecting tattoo is very helpful for marking lesions. The tattoo is usually visible from both the inside of the colon for repeat colonoscopies and on the outside of the colon by the surgeon during an operation. Clips that are radiolucent can be placed to mark an area of concern, but these clips may be knocked off the tissue by the passage of stool.
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Image courtesy of: Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. CC BY 3.0. Blausen 0604 LargeIntestine2.png
