During embryologic development, the colon starts off as a midline structure. As the embryo develops, the colon rotates laterally and fuses with the retroperitoneum. The white line of Toldt represents the lateral fusion line between the colon and the retroperitoneum (Fig. 3.9a, b). Regardless of type of dissection approach (medial to lateral vs. lateral to medial) one uses during a laparoscopic colectomy, the ultimate goal is to separate the colon and its mesentery away from the retroperitoneal structures and develop the colon as a midline structure. When performing the lateral-to-medial approach, the dissection must be started along or just medial to the white line of Toldt (Fig. 3.10a, b). Dissection in this area will allow an entry into the appropriate plane between the colon mesentery and the retroperitoneum. On the other hand, dissecting lateral to the white line will likely lead directly into the retroperitoneal space and will increase the likelihood of causing unwanted bleeding and injury to the retroperitoneal structures. When performing medial-to-lateral dissection, the mesenteric vessels are isolated and ligated before gaining an access into the retroperitoneum (Fig. 3.10a, b). Because there is no fusion plane between the colon mesentery and the retroperitoneum in the midline, closest to the named vessels, there is a tendency to veer off from the proper dissection plane (Fig. 3.11a). The surgeon has to make a conscious effort to stay within the appropriate surgical plane (Fig. 3.11b). The mantra “purple goes down” is useful to remind ourselves from getting too deep into the retroperitoneal space.

The ureters lie under the parietal peritoneum and rest on the anterior surface of the psoas muscle (Fig. 3.12). The right and left ureters both follow a straight path from the renal pelvis to the pelvic, 4–5 cm laterally to the IVC and the aorta, respectively (Fig. 3.13). The ureters then cross over the iliac vessels to enter the pelvic brim. The right ureter classically traverses the external iliac artery (Figs. 3.16 and 3.17), whereas the left ureter lies slightly more medial and typically crosses the common iliac artery. The ureters then run posterior and inferior on the lateral pelvic sidewall. In males, the ureters continue to course medially and pass between the vas deferens (anterior) and the seminal vesicles (posterior). In females, the ureter descends posterior to the ovary and into the base of the broad ligament passing under the uterine artery. In males and females, the ureter enters the posterolateral surface of the bladder and travels at an oblique angle for approximately 2 cm until it forms the trigone [3].

In the course of performing laparoscopic right colectomy, the right ureter is typically not encountered when dissecting the right colon mesentery away from the retroperitoneal structures. Rather, the right ureter is typically visualized when the terminal ileum mesentery is sharply dissected away from the retroperitoneum over the pelvic brim (Fig. 3.19).

When performing a laparoscopic left colectomy or pelvic dissection, the ureters may be encountered in two locations: (1) where they cross over the common iliac vessels and (2) the lateral walls of the pouch of Douglas as they course beneath either the vas deferens or the uterine artery (Fig. 3.20). When dissecting behind the IMA into the retroperitoneal space, the left ureter is located medial to the gonadal vessels (Fig. 3.21). When developing the plane anteriorly, theoretically the ureters should not be seen at this level [4, 5].

Pearls :

The gonadal arteries typically arise from the anterior aorta just below the renal artery. Unlike the ureter, the gonadal vessels travel oblique toward the pelvic inlet. The gonadal arteries cross the abdominal ureters approximately halfway between the pelvic inlet and the renal pelvis. The ovarian vessels enter the broad ligament of the ovary at the pelvic brim. The testicular vessels cross the pelvic brim between the sacroiliac joint and the inguinal ligament to enter the deep inguinal ring. After traveling their respective courses, the right ovarian and testicular vein generally join the inferior cava while the left gonadal vein commonly joins the left renal vein [3].

The posterior compartment of the pelvis is comprised of the presacral fascia, rectum with its associated mesorectum, and surrounding fascia propria (Fig. 3.20). The presacral fascia overlies the concavity of the bony sacrum and coccyx (Figs. 3.18 and 3.23). It contains the middle sacral artery, the autonomic nerves, and the presacral veins known for causing perilous bleeding during a pelvic dissection [6, 7]. The rectum is enclosed by the fascia propria of the rectum, an investing extension of the endopelvic fascia. It encloses the mesorectum, fat, nerves, and the blood supply along the lateral extraperitoneal stalks of the rectum. The rectogenital septum marks the anterior border of the posterior pelvic compartment. The septum is clearly marked by the visceral pelvic fascia or Denonvilliers fascia that separates the extraperitoneal rectum anteriorly from the vagina (Figs. 3.24 and 3.25) or prostate and seminal vesicles [8]. Developing the plane anterior to the fascia propria or extramesorectal plane may lead to resection of Denonvilliers fascia and is associated with an increased risk of bladder and sexual dysfunction due to sacrifice of branches of the pelvic plexus of the hypogastric nerves.

Pearls :

The colon and rectum are innervated by the sympathetic and parasympathetic systems. The sympathetic supply of the left colon and the rectum arises from L1 to L3 and is distributed through the lumbar splanchnic nerves via the aortic and inferior mesenteric plexuses and the sacral splanchnic nerves through the superior and inferior hypogastric plexuses (Fig. 3.28). The preganglionic fibers synapse in the preaortic plexus, while postganglionic fibers travel along the IMA and superior rectal artery to the intestine. These nerves typically overlie the aorta, and care must be taken to identify and preserve these during dissection and ligation of the IMA off the aorta. The lower rectum is innervated by presacral nerves formed by the fusion of the lumbar splanchnic nerves and the aortic plexus. Subsequently, these nerves combine to form the hypogastric plexus located just below the sacral promontory (Figs. 3.29 and 3.30). The hypogastric plexus gives rise to two main hypogastric nerves which travel along the lateral sacrum and pelvic sidewalls into the pelvic plexus located in the lower rectum adjacent to what are typically conceived as the lateral stalks of the mesorectum [9, 10].