Читать книгу Successful Training in Gastrointestinal Endoscopy - Группа авторов - Страница 115

The colonic anatomy can be broken down into various segments, each with some defining characteristics that can help the endoscopist keep track of the scope's location in the colon (Figure 6.1) (Video 6.1). The anal canal is lined with squamous mucosa. Inside the internal sphincter and puborectalis muscles, the anus transitions to the rectum at the dentate line. This line represents the transition between the anal squamous mucosa and the columnar epithelium found throughout the intestines and stomach (Figure 6.2). The rectum progresses posteriorly in the retroperitoneum. Within the rectum, there are three semicircular folds called the valves of Houston (Figures 6.2 and 6.3). These folds differ from the rest of the colon in that they are not circumferential but rather span roughly 50% of the circumference of the lumen. At the peritoneal reflection, the colon leaves the retroperitoneal space and moves into the peritoneum. At this reflection, the sigmoid colon begins and deflects anteriorly, inferiorly, and to the left in the peritoneal space. This portion of the colon varies in length and configuration from one individual to the next and accounts for a majority of the looping and difficulty with scope advancement encountered during colonoscopy, due to its mobile and circuitous nature. As one moves more proximally, the sigmoid continues toward the left flank and again progresses posteriorly to its junction with the descending colon. The descending colon rises up the left posterior abdomen in a fairly straight manner. This segment of the colon, along with the ascending colon, is partially fused to the posterior peritoneum along the colonic gutters and as a result is relatively nonmobile. In rare instances, however, these segments may be freely mobile, making endoscopic advancement quite difficult. At the splenic flexure, the colon acutely deflects anteriorly and to the right, marking the transition between the descending colon and the transverse colon. Like the sigmoid, the transverse colon is mobile in the peritoneal space attached only by the mesentery. It too can be quite variable in length and redundant, leading to difficult scope advancement. The lumen of the transverse colon also differs from the other segments of the colon in that the three tinea coli running the length of the colon produce a triangular appearance as opposed to the circular appearing folds elsewhere in the colon (Figure 6.4). As the transverse colon sweeps to the right side, it again moves posteriorly, and at the hepatic flexure, the colon deflects posteriorly and downward, becoming the ascending colon. This segment is normally fixed to the right posterior gutter of the peritoneal cavity. At the hepatic and splenic flexures, external organs such as the liver or spleen can often be seen through the wall of the colon as bluish‐gray discoloration (Figure 6.5). The ascending colon proceeds down along the right posterior flank to the cecum. The cecum marks the most proximal portion of the colon and is the location where the three tinea coli come together along the external surface of the colon and meet at the appendix. From the luminal view, this appears in the cecal base as three longitudinal folds coming together adjacent to the appendiceal orifice (Figure 6.6). These folds are often referred to as the “crow's foot” or “Mercedes sign” as it resembles the clawed foot of a crow or the emblem of the well‐known automaker. The cecum transitions to the ascending colon at the level of the ileocecal valve that rests on the first major haustral fold above the appendiceal orifice. The valve can be identified by the asymmetric prominence of this first fold and with careful inspection, torque, and dial control, the valve os can be directly visualized and intubated.

Table 6.1 Listed are the core motor and cognitive skills trainees must acquire to be minimally competent in colonoscopy. These are broken down into early and intermediate skills to ensure the foundation of basic skills is established before building upon this with more complex abilities.

	Motor	Cognitive
Early	Correct holding of the scopeUse of the scope controlsScope insertionScope advancementBasic tip controlTorque steeringLumen identificationWithdrawal/mucosal inspection	AnatomyPreparationScope selectionSedation managementAssessment of indication and risks
Intermediate	Loop reduction	Pathology identification
Angulated turns	Therapeutic devices
TI intubation	Complication management

Figure 6.1 Colon anatomy. This illustration demonstrates the anatomy of the colon.

(Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)

Figure 6.2 Rectal anatomy. Just inside the anal sphincter muscles, the dentate line marks the transition from the squamous mucosa lining the anal canal to the columnar epithelium of the rectum. The rectum is notable for its semilunar (half‐circle) folds called the Valves of Houston.

(Copyrighted and used with permission of Mayo Foundation for Medical Education and Research.)

Figure 6.3 Endoscopic view of the rectum. This endoscopic view shows the semilunar folds of the rectum (Valves of Houston).