The rectum is a distinct part of the colon situated between the peritoneal reflection and the anus.  The rectum is involved in maintaining normal passage of feces, and is frequently involved with tumors.

The featured move in this edition shows the rectum in a male patient, in an orientation which would be similar to that seen using a linear array echoendoscope (Video Clip 1, narrated). The structures that move through the plane of vision include the bladder, the prostate, and the sacrum. The peritoneal reflection marks the proximal extent of the rectum. It can be seen just over the bladder in the movie. A link to the Visible Human dataset is found with Figure 1 for those who wish to interrogate this region. Figures 2 and 3 show the female rectum.  In the female, the peritoneal reflection can be seen over the uterus. 

Video Clip 1: A rotational view of the male pelvis. Larger Versions (Contain Audio): Low Resolution (512 KB) High Resolution (920 KB)	Figure 1: Click here to launch Interactive Atlas	Figure 2	Figure 3

Although it is difficult to determine where the peritoneal reflection is during colonoscopy or endoscopic ultrasonography, one can sometimes identify the approximate location based on a knowledge of where the reflection lies relative to other pelvic structures.  Colorectal cancer staging by EUS is often used to help decide whether or not one should employ neoadjuvant therapy or whether one should proceed directly to surgery. One is more likely to recommend neoadjuvant therapy for tumors below the peritoneal reflection. An example of this dilemma is shown in the video of a rectal tumor seen through a forward viewing and an oblique viewing endoscope in a female patient (Video Clip 2, narrated). By EUS, the tumor appeared to be proximal to the uterus and bladder (Video Clip 3, narrated), suggesting it was in the sigmoid colon. The patient went directly to surgery and the location of the tumor in the distal sigmoid colon was confirmed.