The sigmoid colon is located in the lower left abdomen between the rectum and the descending colon. Its name is derived from its S shape (sigma = the Greek letter S). The sigmoid colon is completely intraperitoneal, attached and supplied by its own mesentery (mesosigmoid) to the posterior abdominal wall. Due to its intraperitoneal position, the sigmoid colon is usually highly mobile. However, previous lower abdominal surgery, especially gynecological operations and inflammation (e.g., diverticular disease), can cause adhesions, fixing it to the abdominal wall, making passage difficult, and in rare cases even impossible. The length of the sigmoid colon can vary greatly; usually 15-30 cm long, it can be significantly longer (a so-called elongated sigmoid, not considered a pathology), which can lead to looping, and create significant problems for advancing the endoscope. As already mentioned, there is no clear anatomical demarcation at the distal end between the sigmoid colon and the rectum, though the rec
tosigmoid junction is usually rather sharply angled. The sig-moid-descending junction is often acutely angled, particularly in slender patients, making passage difficult. This is because the back wall of the descending colon is fixed retroperitoneally to the posterior abdominal wall, while the sigmoid colon distal to it is mobile. Advancement of the instrument thus pushes the sigmoid colon upward, causing unwanted angling.
The mucosa is shiny and smooth and the blood vessels clearly visible, though less prominent than in the rectum (Fig. 6.6). The lumen is round or oval-shaped (Fig. 6.7). The sigmoid is usually comprised of a series of curves, making visualization into the haustra more difficult (Figs. 6.8, 6.9). The sigmoid colon often is marked by strong contractions, which can also obstruct the view into the haustra. Figure 6.10 shows an example of the previously mentioned acute angling of the sigmoid-descending junction, as can be seen, for instance, in slender patients.
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