Chapter 25 Low Anterior Resection
INTRODUCTION
Surgical resection of all or part of the rectum with a primary anastomosis is referred to as a low anterior resection. This procedure is most commonly performed for rectal cancer. However, on occasion, the rectum is removed for a variety of other benign and malignant conditions. When done for mid and low rectal cancers, the operation includes a total mesorectal excision1,2 with an anastomosis at the level of the pelvic floor. For upper rectal cancers, a partial mesorectal excision with a 5-cm distal and mesorectal margin is probably adequate.3 In this circumstance, the anastomosis is usually done in the midrectum. When done for cancer, obtaining a negative circumferential margin is critical to decrease the likelihood of local recurrence.4,5 Therefore, the dissection must stay outside the fascia propria and closer to the pelvic sidewall. This may increase the likelihood of complications, including bleeding and autonomic nerve injury. For benign disease, there is no circumferential margin, so violation of the fascia propria has no significant implications. Therefore, in benign disease, it is probably better to veer the dissection closer to the rectum to decrease the probability of these other complications. For the purpose of this discussion, it is assumed that the indication for surgery is cancer and the technical points will stress adequate oncologic technique. These principles are generally applicable to benign conditions as well. However, on occasion, there are differences in patients with benign disease, and this is noted in the text.
INDICATIONS
OPERATIVE PROCEDURE
Patient Positioning
Peripheral Nerve Injuries
• Consequence
• Prevention
Incision
Bladder Injury
• Consequence
• Repair
• Prevention
Colon Mobilization and Ligation of the Mesenteric Vessels
In order to perform a low anterior resection of the rectum, the sigmoid colon must be fully mobilized. Furthermore, in most instances, complete mobilization of the descending colon and splenic flexure is also required to perform a tension-free anastomosis (see later). Most mishaps that can occur during this portion of the procedure are similar for any left-sided colonic operation and are well described in Chapter 24 (Left Colectomy: Open and Laparoscopic). These complications are briefly reviewed here.
Bleeding
• Consequence
• Repair
• Prevention
Ureteral Injury
An intra-abdominal injury to the ureter is possible when the sigmoid and descending colon is mobilized. This is fully described elsewhere in the text so it is only reviewed here. Clearly, proper identification of the ureter is essential to preventing injuries. The ureter is usually identified as it crosses the iliac vessels but must be followed superiorly and swept posteriorly to prevent injury when ligating the IMA and IMV. It is important to remember that the ureter lies beneath the gonadal vessels, so if the dissection is above the gonadal vessels, the ureter should also be posterior and out of harm’s way. Sometimes, the ureter is difficult to clearly identify and is most often confused with the gonadal vessels. Under these circumstances, it is important to remember several principles. The ureter runs longitudinally through the retroperitoneum. It never branches, as do blood vessels, and when manipulated, it should show evidence of peristalsis (Fig. 25-8). If the ureter cannot be identified secondary to inflammation or tumor, the ureter should be identified higher in the abdomen, where the anatomy may be more normal, and followed distally. If it is anticipated that ureteral identifica tion will be difficult, placing ureteral stents preoperatively can be quite helpful.
Splenic Injury
When the splenic flexure is mobilized, the spleen can be injured and cause troublesome bleeding.15 This complication is possible with any intra-abdominal colon operation and is reviewed in detail elsewhere. Most splenic injuries originate from omental attachments to the splenic capsule. With downward retraction on the colon, these attachments are torn off the splenic capsule, causing bleeding from the injured spleen. Fortunately, these attachments are unusual, but when identified, they need to be carefully divided (Fig. 25-9). If the splenic flexure is torn, troublesome bleeding will ensue. Most of the time, this bleeding is well controlled with simple packing, but on occasion, bleeding will persist. Although other maneuvers to control bleeding are available, the surgeon should not hesi-tate to perform a splenectomy if the bleeding is not well controlled.
Rectal Mobilization
An understanding of rectal anatomy is critical to proper rectal mobilization. The rectum is surrounded by a large amount of fat containing the mesentery and lymphatics to the rectum itself. This tissue is enveloped by a thin layer of fascia, known as the fascia propria. An avascular plane exists between the fascia propria and the presacral fascia, which is adherent to the periosteum of the sacrum. The retrorectal fascia, or Waldeyer’s fascia, is a thick layer of fascia connecting the presacral fascia to the fascia propria of the rectum. Division of this fascia is necessary to mobilize the distal rectum, and when divided, the rectum will lift from the sacral hollow and begin a more anterior approach. This greatly lengthens the rectum, especially posteriorly. For this reason, a low-lying posterior tumor may elevate significantly after division of the retrorectal fascia, allowing for a low anterior resection. Anteriorly, the rectum is more fixed and will not lengthen as much with mobilization. Therefore, a low-lying anterior tumor will more likely require an abdominal perineal resection than would a posterior-based tumor at the same preoperative level.
Rectal mobilization begins by entering the retrorectal space at the level of the sacral promontory (see Fig. 25-5). Division of the peritoneum at this level will identify the avascular plane between the mesorectum and the presacral fascia. The peritoneum lateral to the rectum is then incised toward the anterior cul-de-sac bilaterally. Finally, the anterior peritoneum also needs to be divided, which will allow entrance into the proper plane to mobilize the vagina in a woman, or the seminal vesicles and prostate in a man. Once the peritoneum is completely incised, the rectum is further mobilized by dividing the areolar tissue that exists between the fascia propria of the rectum and the fascia of the pelvic sidewall, collectively referred to as the endopelvic fascia. This dissection is greatly facilitated by proper deep pelvic retractors and anterior retraction of the rectum (Fig. 25-10). This dissection should be continued posteriorly and in the midline as deep as possible (Fig. 25-11). This will help identify the proper lateral plane, which should continue just adjacent to the mesorectum. Finally, the anterior plane needs to be developed, separating either the vagina or the prostate from the rectum (Figs. 25-12 and 25-13). This is greatly facilitated by using a lipped pelvic retractor and anterior traction on the vagina or prostate while using the hand for posterior traction of the rectum. Whereas this description implies that the posterior, lateral, and anterior dissections are done sequentially, in reality the surgeon needs to constantly adjust her or his retractors to dissect the area that is currently best exposed and continue this dissection circumferentially all the way to the pelvic floor. When this is done properly, there should be no mesorectum at the pelvic floor, thus completing a total mesorectal excision. Therefore, all that should be left is the rectum itself as it enters the rectal ampulla between the muscles of the pelvic floor. Division of the rectum at this level can almost always be done with one fire of a 30-mm transverse stapling device. Figure 25-14 shows the final appearance of the sacral hollow after complete removal of the rectum and the associated mesorectum.
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