The mobilization is extended to the root of the mesentery, and the inferior mesenteric artery is identified at its takeoff from the aorta (Fig. 25-2, A). Branches of the sympathetic nerves, which lie deep to the IMA, are protected by keeping close to the fascia of the mesocolon as it wraps around the IMA, if necessary sweeping nerve branches dorsally and away from the vessel (Fig. 25-2, B). The IMA is isolated, clamped, and ligated. The left colic artery and the inferior mesenteric vein are divided and ligated at the level of the IMA (Fig. 25-2, C). The mesentery is divided perpendicularly to the level of the marginal artery, just proximal to the 1st sigmoidal branch. Unlike in low anterior resection, where extra length is needed for a tension-free colorectal anastomosis, mobilization of the splenic flexure is not required unless the patient is morbidly obese and extra length is needed for stoma construction.

FIGURE 25–2 Arteries and nerves of pelvis and rectum.

The colon is divided proximal to the 1st sigmoid branch, and pulsatile arterial flow is confirmed in the marginal artery.

Approach for Rectal Dissection

The patient is placed in the Trendelenburg position and a self-retaining retractor is inserted. It is helpful to place a figure-of-eight absorbable suture in the uterine fundus, retracting it anteriorly, and securing the suture to the self-retaining retractor (Fig. 25-3, A). In open surgical cases, the dissection is greatly facilitated by the use of lighted, deep pelvic retractors.

FIGURE 25–3 Approach for rectal dissection.
IMA, Inferior mesenteric artery.

Mobilization of the rectum and its investing mesorectum and fascia begins behind the inferior mesenteric vessels, in the loose areolar tissue between the mesorectal fascia and the presacral fascia. The lateral peritoneum overlying the mesorectum is then scored (Fig. 25-3, B). Unless an extended resection is being performed, the ureters are generally easily protected because they lie deep to the fascia of the retroperitoneum. Nevertheless, the ureters’ location is verified throughout the dissection (Fig. 25-3, C). The right and left hypogastric nerves are identified and swept posteriorly and are carefully avoided. The dissection continues posteriorly to the pelvic floor with the use of electrocautery (Fig. 25-3, D).

Dissection of the pelvis proceeds posteriorly, then laterally, and finally anteriorly. By lifting the rectosigmoid junction anterior and cephalad and indenting the mesentery, this avascular plane can be identified and entered, anterior to the nerves. If in the proper plane, cautery is adequate for hemostasis. Posteriorly, the dissection is continued through the filmy, avascular plane until the dissection reaches the rectosacral (Waldeyer’s) fascia. While the dissection proceeds posteriorly, its direction will tilt more anteriorly, above the level of the coccyx (Fig. 25-3, E).

Laterally, the presacral parasympathetic nerves (nervi erigentes) can be seen along the pelvic side wall at approximately the level of the lateral stalks and middle rectal arteries (Fig. 25-3, F). The mesorectum is retracted medially and the dissection is continued on the right and left, and the nervi erigentes are allowed to fall laterally as the dissection ensues. This procedure is continued until the pelvic floor and levator muscles are reached.

The anterior dissection is now begun. The peritoneum in the cul-de-sac is scored just anterior to the fold at the peritoneal reflection. Denonvilliers’ fascia is reflected posteriorly to keep the mesorectum intact on the specimen. The surgeon must keep in mind the location of the pelvic plexus of nerves that overlies the seminal vesicles anteriorly in the male. It is important to avoid skeletonizing the vesicles to prevent nerve injury. Also to avoid injury, the proximity of the ureters to the apex of the seminal vesicles must be considered (Fig. 25-4). The anterior dissection is continued to the pelvic floor.

FIGURE 25–4 Prostate and seminal vesicles.

In women with a bulky, anteriorly based tumor, en bloc posterior vaginectomy is typically performed. The uterus and ovaries can be mobilized en bloc with the rectum if a hysterectomy has not been performed. The round ligaments are divided and ligated on the lateral side walls. The gonadal vessels are taken distal to the pelvic brim after identification and preservation of the ureters. The bladder is separated from the vagina anteriorly. The uterine vessels are serially clamped and suture-ligated directly adjacent to the cervix, to avoid the ureters. The anterior vagina is then opened, and the lateral borders of the vagina are divided with the cautery, leaving the posterior vagina en bloc with the rectum. Once at the pelvic floor, the abdominal dissection is complete.

It should be emphasized that the common error of creating a narrow waist of tissue just proximal to the pelvic floor should be avoided. Because the mesorectum naturally tapers above the levator muscles, the surgeon must avoid “coning in” on the specimen and compromising the circumferential margin. This error must be consciously avoided throughout the distal pelvic dissection to complete an oncologic extra-levator dissection, more recently called a “cylindrical resection” by some authors.

After the abdominal dissection is completed, two options exist for the perineal dissection. The stoma can be created, the abdomen closed, and the stoma matured, followed by subsequent turning of the patient to the prone jackknife position. Some surgeons believe that this approach greatly facilitates the perineal dissection. Alternatively, the patient’s legs can be moved to high lithotomy position and the perineal dissection completed with the surgeon seated between the legs.

Regardless of positioning, the margins of dissection are determined by tumor location. In general, the posterior margin is determined by palpation of the coccyx, the lateral margins by palpation of the ischial tuberosities, and the anterior margin by the urethra in the male and the posterior vaginal wall in the female. As noted, posterior vaginectomy is typically performed for any bulky, anteriorly based lesion.

After outlining margins, the skin is scored. The amount of skin that needs to be taken is not great, and usually the anal verge suffices, except with a larger squamous lesion. The dissection is continued until the ischiorectal fossa is entered circumferentially (Fig. 25-5, A). Usually, the posterior dissection is performed first because it has the clearest landmarks. The dissection proceeds to join the abdominal dissection, just above the coccyx. The surgeon continues the lateral dissection up to the lateral origin of the levator muscles, staying in an extra-levator plane. A finger is placed in the patient’s pelvis and hooked behind the levators, and cautery is used to divide the left and right muscles (Fig. 25-5, B).