Robotic Rectal Resection for Rectal Cancer: State of the Art

Abstract

Surgical resection with total mesorectal excision (TME) represents a crucial milestone in the treatment of rectal cancer. Conventional open procedures have been gradually replaced by minimally invasive techniques. To date, laparoscopic and robotic resection associated with neoadjuvant chemo-radiotherapy, represent the gold standard for rectal malignancies. Robotic surgery, when performed by an experienced surgeon, can offer advantages in case of difficult anatomical conditions, such as in male patients with a narrow pelvis. Higher costs remain a matter of debate in the diffusion of robotic platforms in general surgery. However, encouraging surgical outcomes and a shorter learning curve for the surgeon counterbalance the associated expense. Different surgical approaches are available for rectal cancer, according to the extension of the tumor and its location. The cornerstone of the different approaches is represented by TME, both transabdominally and transanally. Adequate TME, associated with neoadjuvant therapy, is pivotal in the success of the oncological treatment, in terms of curative results and reduced recurrence. Current different approaches are low anterior resection, abdominoperineal resection, and intersphincteric resection. They can all be performed with the robotic system and their surgical steps are described in this chapter.

1. Introduction

In the multimodal approach to rectal cancer, surgical resection is the gold standard for curative therapy. Early-stage rectal cancer, which does not spread further than the mucosa, can be treated by curative endoluminal resection. When rectal tumor spreads beyond the mucosa and the submucosa into the perirectal tissue, the transanal endoscopic resection is not curative and a multimodal approach with systemic and local therapies associated with surgical resection is required [1]. The initially proposed regimen was combined chemo-radiotherapy following surgical resection, as adjuvant therapy [2]. The German Rectal Trial in 2004 demonstrated, however, that chemo-radiotherapy is associated not only with improved compliance of patients but also with reduced toxicity and a potential preoperative downstaging of the tumor that can increase the number of sphincter-preserving resections in patients with low rectal tumors when administered preoperatively [3]. This trial analyzed about 800 patients and changed the systemic approach to locally advanced rectal cancer, thus making neoadjuvant radio-chemotherapy the standard of care. The optimal time of surgery after neoadjuvant radio-chemotherapy is still under debate. Many studies have been published on the topic, often reporting controversial results and no consensus has been reached yet. Historically, a time interval of 6–8 weeks was related to good oncological results and an increased rate of sphincter-preserving procedures [4]. After the publication of the results of the research by Habr-Gama in 2004, this time interval was revised, and the opportunity to consider longer intervals before surgery became a field of interest [5]. The attention of most researchers, indeed, focused on the optimization of the time interval and obtaining the highest pathological complete response. A recently published study from a high-volume center in China identifies a longer period of 10 weeks as the ideal time interval between neoadjuvant radio-chemotherapy and surgery, in terms of longer recurrence-free survival in 5-year follow-up [6]. Moreover, a time interval beyond eight weeks has been reported as protective for anastomotic dehiscence [7]. The most important limitation of these studies is their retrospective design. To date, several randomized trials, some unpublished, are ongoing to better define the optimal time interval in the search for tailored multimodal treatment for those patients suffering from local-advanced rectal cancer [8, 9].

Introduction of total mesorectal excision (TME) in the 1980s by Heald et al. represents the most relevant development in rectal cancer surgery [10]. And the standard procedure in the case of mid-to-low rectal cancer. TME addresses the mesorectum including the vascular and lymphatic structures, that are removed en-bloc with the involved rectum. Mesorectal and inferior mesenteric artery nodes are removed, which are the most common site of node metastasis. The dissection occurs along embryological planes, preserving the autonomic nerves involved in urinary and sexual function. Heald described the dissection plane as the avascular interface between the mesorectum and the surrounding somatic structures, identified as the “holy plane”. Surgical plane and completeness of TME remain the most important prognostic factors. Dissection is performed circumferentially, until reaching the plane of the levator ani muscles. The gross appearance of the specimen, with a bilobed tissue block together with the involved rectum, is accurate proof of a proper TME. For mid-to-low rectal cancer, low anterior resection (LAR) with TME reduces locoregional recurrences. For tumors located at a distance >10 cms from the anal verge, whether a distal margin of 5 cm can be achieved, the mesorectum can be safely sectioned at the same level as the rectum, with outcomes similar to TME [11].

The advantages of laparoscopic TME versus open surgery have been demonstrated in several studies. In 2013, the COLOR II trial demonstrated that laparoscopic rectal surgery resulted in comparable oncologic outcomes, with the well-known advantages of laparoscopic surgery, in terms of faster recovery and decreased postoperative pain [12]. Valid oncologic outcomes were also confirmed in long-term follow-up, in terms of overall survival, disease-free survival, and local recurrence [13]. Nevertheless, laparoscopic surgery has different limitations and technical difficulties, especially in challenging anatomical conditions. A narrow pelvis, obese male patients, as well as bulky low tumors, represent a continuous challenge for the laparoscopic surgeon. In addition to the anatomical characteristics, specific drawbacks of laparoscopic procedures have been spotted such as a two-dimensional visualization, a restricted range of movement with instruments, suboptimal field exposure, and the amplification of hand tremor. Hence, with the development of robotic surgical platforms, several studies have been conducted to explore the potential benefits of robotic-assisted rectal surgery versus the laparoscopic approach. The robotic surgical platform offers the surgeon an increased range of motion, a stable surgical view, a three-dimensional visualization, and a more comfortable procedure. Short-term advantages have been widely demonstrated. Robotic rectal resection versus laparoscopic approach leads to less blood loss, inferior conversion rate, and reduced overall complication rate [14]. Moreover, recent meta-analysis on seven studies including more than 2500 patients, demonstrated the non-inferiority of long-term oncologic outcomes of robotic TME versus laparoscopic TME [15]. The ROLARR trial, showed that Robotic TME was beneficial for men and patients with low rectal tumors [16]. Despite the encouraging findings, two main concerns against robotic rectal surgery have been raised: the longer operative time and the elevated costs. Being the latter the most relevant limitation to the diffusion of the robotic surgical platforms in surgical departments, more recent data does not support the former one. It has been demonstrated that when robotic TME is performed by an experienced surgeon, the operative time is not higher than the laparoscopic procedure, especially when docking time is excluded. In addition, robotic TME may reduce the rate of diverting ileostomy, likely thanks to the option to reinforce the anastomosis or make a robot-assisted hand-sewn anastomosis, and postoperative pain, granted by the small dimensions and the wide range of motion of the robotic instruments and by the reduction of the fulcrum effect [17]. Robotic TME presents a shorter learning curve than laparoscopy, from about 30–50 cases per surgeon in laparoscopy to about 20 cases for robotic procedures. According to these data, fewer cases are needed for the surgeon to acquire the experience needed [18].

In conclusion, robotic surgical platforms are expanding and promising tools for TME and oncologic rectal surgery, with demonstrated advantages for the surgeon and for the patients compared to open surgery and laparoscopic approach. High costs are still the most relevant limitation that hampers its diffusion worldwide.

1.1 The da Vinci surgical platform

The da Vinci robot is currently the most widespread robotic surgical system, with thousands of units sold worldwide and thousands of peer-reviewed publications [19]. The first model of the da Vinci surgical platform was released in 1999 and since then, four different generations have been developed. In 2009 the daVinci Si surgical platform was released, consisting of four arms, while in 2014 Intuitive Surgical (Sunnyvale, CA, USA) developed and promoted the da Vinci Xi surgical platform, the current versinoe fo this robotic platform, which provides easier docking, as well as a wider range of motion with smaller arms on a rotating beam [20].

Numerous studies have been published after the introduction of the da Vinci Xi Surgical Platform, which was compared to the da Vinci Si Surgical Platform in colorectal surgery, in terms of surgical outcomes and surgeon’s preference. In 2021, a meta-analysis including six studies for a total of 610 patients found that operative times significantly decreased using the da Vinci Xi, while no differences resulted in terms of conversion and complication rates compared to the daVinci Si [21]. Similar results were described more recently, confirming the advantages of the latest generation of the da Vinci platform, which present a more user-friendly design [22]. Interestingly, the reduction of the operating time when performing sphincter-saving TME in mid-low rectal cancer patients with the da Vinci Xi system has been correlated to a decrease in general costs. Lower operative room hours and shorter interventions, indeed, can be translated into lower expenses [23].

At the beginning of 2022, another retrospective analysis has been published, comparing the perioperative and postoperative outcomes of the third (da Vinci Si) and the fourth (da Vinci Xi) generation platforms on a single surgeon experience. This study confirmed significantly shorter operation time with the Xi system compared to Si system when performing sphincter-saving TME in mid-low rectal cancer patients [24].

Regardless of the different advantages that the da Vinci Xi shows over the Si, surgical steps and procedures are equivalent, except for trocar placement. Therefore, no difference in the description of the surgery itself nor any preference is reported. Trocar positioning is differently described according to the robotic platform.

2. Low anterior resection (LAR): surgical procedure

Low Anterior Resection is the most common surgical approach for rectal cancer. It is indicated for rectal cancer from distal to very low localization. In case of tumor invasion of the mesorectum, neoadjuvant chemo-radiotherapy is recommended to decrease long-term recurrence [25]. In the preoperative setting, the site of the diverting ileostomy is marked.

2.1 Surgical steps of robotic LAR with the daVinci robotic system for low or ultra-low rectal tumor

The procedure is performed under general anesthesia. Patient is in supine modified lithotomy position. A nasogastric tube is inserted before surgery.

Induction of pneumoperitoneum is performed, with the preferred technique. In our institution, the Veress needle technique is carried out, inserting the needle in the left hypochondrium (Palmer’s point). Then, the trocars are placed accordingly to the type of robotic system available.

Exploratory laparoscopy is firstly performed to exclude carcinosis or undetected metastases. Cytologic examination is carried out in case of peritoneal effusion in searching for malignant cells. The small bowel is displaced with laparoscopic forceps to expose the left colon and the neoplasia.

When the daVinci Xi Surgical Platform (Intuitive Surgical Inc., Sunnyvale, CA, USA) is used, trocars are placed following the Universal Port Placement Guidelines provided by Intuitive Surgical for left lower abdominal procedures: an 8-mm port in the right iliac fossa, a 12-mm assistant trocar in the right flank, and two 8-mm robotic ports in the periumbilical region and the left hypochondrial space, in a line joining the right hip joint and the left subcostal margin at the level of the mid-clavicular line, at a distance of 6–8 cm from one another. Alternatively, the trocar line can be totally on the right side of the patient, being more vertical than in the first scenario, with Arm 1 in epigastrium up to Arm 4 in right iliac fossa. The daVinci Xi robotic system is targeted toward the left iliac fossa at the level of the sacral promontory. With the use of the laser pointer, the overhead boom is centered on the camera port. The boom is rotated to grant a better exposition of the robotic arms and instruments. A 12 mm-AirSeal-trocar system is placed on the right flank, for assistance.

The monopolar scissors are inserted through Arm 4, and placed in the right iliac fossa. A bipolar forceps is inserted through Arm 2, placed cranially and laterally off of the umbilicus on its left. A ProGrasp grasper is inserted through Arm 1 at the left hypochondriac space and is used for counter-traction and lifting. The endoscope is inserted through Arm 3 positioned between the umbilicus and the lower trocar (in the right iliac fossa). For performing the TME, the camera can be placed in a different arm or change its anatomical target. Alternatively, instruments’ position and types can be the same as for the first phase.

The Xi robotic platform provides several “technical” advantages: torpedo-shaped robotic arm that are mounted on a rotating beam, universal arms where camera can be docked onto any arm, longer instruments, a new vision architecture with chip-at-the-tip technology and camera, endoscope, and cable integrated into one handheld design, an adapted user interface offering more assistance with robotic setup and installation, integrated energy with a single device for mono- and bipolar energy, a standard integration of Firefly Fluorescence Imaging. All these features help the surgeon to better perform the procedure and to access a greater field of surgery without the need to reinstall the robotic system (single docking approach).

When the daVinci Si Surgical Platform (Intuitive Surgical Inc., Sunnyvale, CA, USA) is used, four robotic trocars and one laparoscopic trocar for the assistant are used (AirSeal). The robotic trocar for the camera is placed 3 cm upward and 2 cm rightward to the umbilicus. Two robotic trocars are placed at the intersection of the midclavicular line and the spinoumbilical line, on both sides. The other two robotic trocars are positioned at the level of the midclavicular line in right and left hypochondrium. On the right flank, laterally to and between the two robotic trocars, the laparoscopic trocar for the assistant is placed (Figure 1).

Figure 1.

Position of trocars in LAR with the da Vinci Si surgical platform.

The robotic docking is performed with the robot on the left side of the patient placed following an imaginary line connecting the left anterosuperior iliac spine of the patient, the umbilical scar, and the shoulder of the patient. The robotic camera is placed in the umbilical trocar. The first arm with monopolar scissor (Arm 1) is introduced through the trocar in the right iliac fossa. Arm 2 is placed in the right hypochondrium with bipolar forceps (Figure 2).

Figure 2.

Operating room setting (a) and trocars used (b) for splenic flexure mobilization.

With the daVinci Si, two alternative approaches can be adopted for the mobilization of the splenic flexure, the first step of the procedure: a supramesocolic and a submesocolic approach. The two approaches are equivalent, and the choice is solely based on surgeon’s preference.

In the supramesocolic approach, the patient is firstly positioned with a 5 degrees anti-Trendelenburg and a 15 degrees right tilt.

The procedure starts with the dissection of the gastrocolic ligament in a medial-to-lateral direction, starting from the Bouchet area. The assistant pulls the transverse colon caudally with laparoscopic forceps and the surgeon pulls the omentum in the opposite direction with Arm 2. Starting from the middle transverse colon, the dissection continues laterally, preserving the contralateral gastro-epiploic arcade. This maneuver allows the opening of the omental bursa. Splenocolic and phrenocolic ligaments are sectioned. Previous identification of the inferior pancreatic edge and the root of the mesocolon, dissection reaches the splenic flexure, and the descending colon is mobilized from the left parietocolic gutter. The assistant can now pull the splenic flexure downward and rightward, opening the avascular dissection plane between the Gerota’s and the Toldt’s fascia. Along this avascular plane the root of the mesocolon is exposed and the origin of the inferior mesenteric vein (IMV) is identified. Mobilization of the splenic flexure is now complete. The robotic system is removed, and patient’s position is changed, with 25–30 degrees of Trendelenburg and 15 degrees of right tilt. Robotic docking is performed again adding the third arm. Arm 1 is docked to the trocar in the right iliac fossa mounting the monopolar scissors; Arm 2 is placed in the left hypochondrium/left middle quadrant mounting ProGrasp forceps; Arm 3 is placed in the right hypochondrium mounting bipolar forceps. The ProGrasp pulls the mesocolon upward, exposing the IMV and the inferior pancreatic margin. Locoregional perivascular lymphadenectomy is performed, the IMV is isolated, and it is cut between clips. The surgeon proceeds mediolaterally beneath the IMV toward the parietocolic gutter, dissecting the descending mesocolon. During this maneuver, it is important to preserve the left ureter and the gonadic vessels. At the level of the renal artery, the peritoneum is sectioned under the iliac bifurcation, and the inferior mesenteric artery (IMA) is exposed. The ProGrasp in Arm 3 pulls the IMA and locoregional lymphadenectomy is performed between the aorta and the IMA. Periaortic nerves and the mesenteric nervous plexus should be identified and preserved. The IMA is then sectioned between clips, about 2 cm distal its origin from the aorta [26].

The dissection planes of IMA and IMV are now rejoined, and the perivascular lymphadenectomy is completed.

Mobilization of sigmoid colon from the parietocolic gutter, until the sacral promontory and upper rectum is now performed. During this step, the assistant pulls the descending colon rightward, exposing the left parietocolic gutter and helping the surgeon to identify and preserve the left ureter throughout its course. Once the promontory is reached, the mesorectum starts and TME can be performed. Robotic arms are switched, with Arm 2 positioned in the left iliac fossa mounting the ProGrasp, and Arm 3 in the left hypochondrium mounting the bipolar forceps. Two laparoscopic trocars are available for the assistant, which will use the lateral one for the laparoscopic forceps and the medial one for the laparoscopic aspirator. Initially, the laparoscopic forceps pull the sigmoid colon and proximal rectum cranially and leftward. The ProGrasp pulls the visceral peritoneum of the rectum on the right side and the TME starts. Circumferential mesorectal excision starts from the right posterolateral side, preserving the presacral fascia and the hypogastric nerves underneath. The dissection proceeds until the Waldeyer ligament. Now, the assistant switches the position of the laparoscopic forceps and aspirator, to pull the rectum cranially and rightward. TME continues from right to left side, reaching the anterior compartment. The peritoneum is sectioned at this point reaching the extraperitoneal rectum and the TME continues anteriorly along the plane between the rectum and the bladder-prostate complex in men and along the recto-vaginal septum in female. The laparoscopic forceps pull the rectum cranially and downward, while the ProGrasp pulls upward the peritoneum of the urinary bladder and the prostate to expose the Denonvillier’s fascia at this level. During dissection of the Denonvillier’s fascia, it is important to preserve the seminal vesicles in men. In female, a vaginal manipulator can be introduced trans-vaginally, for a more efficient separation of the recto-vaginal septum. Mesorectal excision is now completed by sectioning the Waldeyer ligament posteriorly and reaching the levator ani fascia anteriorly and laterally. TME can be considered accurate at this point (Figure 3). Indocyanine green (ICG) is administered intravenously to confirm correct vascularization of the rectal stump. The assistant performs the resection of the distal rectum with laparoscopic linear mechanical stapler. Alternatively, the robotic stapler can be positioned on Arm 1.

Figure 3.

Operating room setting (a) during vessel ligation and total mesorectal excision. Trocars used during inferior mesenteric vessels ligation and perivascular lymphadenectomy (b). Trocars used during total mesorectalexcision (c).

A suprapubic Pfannenstiel incision is performed, and pneumoperitoneum is deflated. A wound protector is usually inserted at this point to avoid contact between the abdominal wall and the colon. The resected colon is extracted. The inferior mesenteric artery peduncle previously cut is identified, and the operator can complete the resection of the sigmoid mesocolon along the artery line to obtain an accurate lymphadenectomy. Once the area of the descending colon is identified for resection, ICG test is performed to confirm the correct vascularization and the colon can be sectioned. Colorectal anastomosis will be performed using a circular stapler. The anvil of the stapler is inserted in the colic lumen, and it is secured by using a purse string suture technique. The colon is reinserted intra-abdominally and pneumoperitoneum is inflated. The operator moves between patient legs and inserts the circular stapler transanally. The mechanical colorectal Knight-Griffen anastomosis is fashioned. The ICG test can be performed up to surgeon’s preference. The air leak test is advisable to exclude possible anastomosis leakage. The surgical procedure is now completed (Figure 4). Washing of the abdominal cavity is performed, and a drainage is usually placed in the Douglas space. In case of medium-to-low rectal tumors and in case of neoadjuvant chemo-radiotherapy, a temporary loop ileostomy is recommended.

Figure 4.

Rectal specimen after LAR with visible vascular pedicle.

In the submesocolic approach, that is the same for both the two robotic platforms, the patient is positioned in a 25–30 degrees Trendelenburg and 15 degrees right tilt. The robot docking is performed, and the robotic camera is placed in the umbilical trocar. When the Si is used, three Arms are placed from the beginning of the procedure. Arm 1 is introduced through the trocar in the right iliac fossa mounting the monopolar scissors; Arm 2 is placed in the left hypochondrium/left middle quadrant mounting ProGrasp forceps; Arm 3 is placed in the right hypochondrium mounting bipolar forceps.

All the following steps are carried out in a similar manner to the two robotic platforms.

The ProGrasp pulls the mesocolon upward, exposing the IMV and the inferior pancreatic margin. The IMV is isolated, perivascular lymphadenectomy is performed and then the vein is cut between clips. Dissection continues mediolaterally inferiorly to the IMV. The left colon is mobilized from the parietocolic gutter in a caudo-cranial direction and the splenic flexure is reached. Now the assistant can pull medially the descending colon, while the surgeon pulls contralaterally the omentum with the ProGrasp in Arm 3. Latero-medial dissection is performed, completing the mobilization of the splenic flexure.

Both supramesocolic and submesocolic approaches lead to the complete mobilization of splenic flexure and left colon. The following steps of the procedure will not be repeated, and they can be found in the section above.

3. Abdomino-perineal resection (miles’ operation): surgical procedure

Abdomino-perineal resection was developed by Sir William Miles to reduce the burden of local recurrence in rectal cancer surgery. For decades, Miles’ operation was considered the standard of care for all rectal cancer, being the only therapeutic option for these patients. However, the development of perioperative local and systemic therapies, a better understanding of the pathologic tumor dissemination mechanisms [27], and thanks to the development of less mutilating techniques, such as sphincter preservation, TME and LAR, the indication for abdomino-perineal resection have consistently decreased in the decades [28]. First indication of Miles’ procedure is ultra-low rectal tumors in which a negative distal margin cannot be obtained. The concept of negative resection margin in rectal surgery has been widely debated among the surgical community. The milestone concept of the “5-cm margin” was challenged by the development of neoadjuvant therapy and the development of TME. To date, a distal resection margin of 1 cm is considered acceptable in case of ultra-low rectal cancer, in the context of a multimodal treatment plan [29]. Moreover, Miles’ procedure is indicated in case of involvement of external sphincter or levator ani complex. The abdomino-perineal resection is also the treatment of choice for anal squamous cell carcinoma, when chemoradiation therapy fails [30].

3.1 Surgical steps of miles’ operation

The intraperitoneal steps of the abdomino-perineal resection are equivalent to the steps of LAR; hence, you can refer to the appropriate section for it.

Once the dissection reaches the extraperitoneal rectum, TME is performed circumferentially, until the levator ani fascia is reached. It can be recognized because the mesorectum with adipose yellow tissue ends and the white appearance of the levator ani fascia becomes visible. The left colic vein is identified at its confluence in the IMV, and it is sectioned. From this point, the sigmoid mesocolon is sectioned. Now, the proximal section of the colon can be performed with the laparoscopic or robotic mechanical stapler, and the perineal phase can start. The surgeon and the assistant move to the perineal area, which is exposed by lifting patients’ legs upward.

A retractor system is positioned, commonly the Lone Star (Lone Star Medical Products Inc., Houston, TX, USA) is used. The perianal region is sectioned circumferentially, 1 cm from the external sphincter margin. It is paramount for the oncological outcome of this procedure to remove the sphincter complex en bloc. The dissection is performed along the pelvic floor and the levator ani fascia. Posteriorly, the surgeon can start form the perineal raphe, from the coccyx along the margin of the sacrum, reaching the plane that was previously dissected in the intra-abdominal phase of the intervention. The dissection proceeds laterally by sectioning the levator ani muscles, and anteriorly, where the vagina or the prostate and urethra are found, in female and male, respectively. At this point, the circumferential perineal dissection is complete, and the surgical specimen can be extracted through the perineum. After accurate washing of the perineal area, the perineum is closed by layers. This is a crucial step, because abdomino-perineal resection often results in perineal wound defects. In addition to risk factors related to wound healing defects, such as smoking, advanced oncologic status and alcohol consumption, the introduction of neoadjuvant radiotherapy significantly increased the rate of wound defects [31] and neoadjuvant chemoradiation and wound complications are predictors of long-term perineal pain [32]. Wound dehiscence in Miles’ procedure is the topic of numerous studies, searching for a valid standard closure method of the perineum. However, no ideal solution currently exists, and different approaches have been attempted with more or less success. Primary closure, with levator ani muscles reapproximated with multiple absorbable stitches, remains the most frequent technique. When this closure cannot be obtained, the use of biological or synthetic mesh can be considered [33]. Biological mesh appears to be a valid option, especially in terms of hernia prevention. Its role in preventing wound infections and dehiscence is less clear. Moreover, reconstruction with myocutaneous flap can be considered in selected cases [34]. Regardless the different options, abdomino-perineal resection results often in wound defects that deeply affect patient’s quality of life and morbidity, as well as hospitalization and healthcare-associated costs. When the wound fails to heal, a conventional negative pressure wound therapy (NPWT) device can be considered. In a recent systematic review, the use of NPWT represents an encouraging tool in reducing surgical site infection and wound dehiscence in these patients [35].

Once the perineum is sutured, pneumoperitoneum is reinduced. After accurate hemostasis, a surgical drain is placed in the pelvic cavity, the colic stump is brought to the abdominal wall – in the area identified and marked before surgery – and the colonostomy is created.

4. Intersphincteric rectal resection

Sphincter preservation in patients with low rectal cancer is feasible reducing the distance between the tumor and the resection margin. In this way continence can be preserved, but still the oncological radicality of the procedure must be guaranteed.

A conservative procedure can be performed under the following condition:

• Integrity of the sphincter complex: the integrity of the external sphincter (Debray’s reflex) and the preservation of the levator ani muscle is essential to maintain normal continence. In particular, the levator ani muscle accentuates the angle of the rectum (Parks mechanism) through the contraction of the puborectal bundles. The rectal resection must therefore fall above the elevator plane and should not damage the external sphincter nerves. The integrity of the mucosal membrane of the anal canal and of the distal end of the rectum are not necessary for a good continence, as the sphincter motor activity is regulated by receptors placed in the external sphincter [36]

• Well vascularized rectal stump [36]

• Transposition of the colon above the pelvic and perineal plane without the risk of traction or lack of perfusion. The impediment to lowering is generally due to the presence of a short Riolano arch or of an accessory middle colic artery [36]

When a free resection margin cannot be obtained without sphincter involvement, an abdomino-perineal resection must be performed.

In ultra-low rectal resections, it is possible to perform a manual coloanal anastomosis or proceed with the intersphincter resection, with partial or total removal of the internal sphincter. This technique aims to obtain appropriate longitudinal and radial margins [37], thanks to the presence of the Debray’s reflex and the Parks mechanism, which would guarantee adequate continence [36].

The low rectal cancer can be classified in four groups according to Rullier [38]:

• type I supra-anal (> 1 cm from the anal ring)

• type II juxta-anal (< 1 cm from the anal ring)

• type III intra-anal (internal anal sphincter invasion)

• type IV transanal (external anal sphincter or levator ani invasion)

Type I patients are eligible for ultra-low anterior resection, type 2 for partial intersphinteric resection, type 3 for total intersphinteric resection and type 4 need abdomino-perineal resection. Postoperatively, only 50% of patients presents a good fecal continence; 11% suffers from severe fecal incontinence and 6% of patients requires a definitive colonostomy due to severe postoperative fecal incontinence [38]. Performing a very low colorectal anastomosis can lead to anterior resection syndrome, characterized by involuntary loss of stool, urgency and multiple defecation, due to the loss of the rectal reservoir. Due to these disfunctions, some studies report that patients undergoing an ultra-low anterior resection present a lower quality of life than those undergoing abdominal-perineal amputation, despite the loss of the physiological possibility of defecating and the presence of a definitive ostomy. For these reasons, sphincter preservation procedures must be considered only for those patients who have an adequate sphincter function demonstrated by a manometric examination, and for those who accept a suboptimal functional result [37, 38].

There has been a progressive reduction in Mile’s procedures, in favor of LAR which is currently the most used procedure even in cases of ultra-low lesions. Abdominal-perineal amputation is preferred only when disease-free resection margins cannot be guaranteed without resecting the sphincters, or in case of their infiltration [39]. According to Rullier, an intersphinteric rectal resection is performed in two different surgical times: the intraabdominal and the transanal one. The former follows the usual steps of LAR. The transanal time starts with the exposure of the anal canal, using a retractor like Lone Star; for limiting the tumor seeding it is recommended to introduce a gauze into the rectum. The resection starts 1 cm below the tumor with a circular incision that transect the internal anal sphincter by both the mucosa and the muscular layer. Performing a partial or total resection of the internal sphincter depends on the level of the incision (on the dentate line or 1–2 centimeters below). The dissection continues upward between the two sphincters through an avascular plane and can be performed with scissors or an electric scalpel. The resection should start posteriorly and laterally where the external anal sphincter is more visible and proceeds anteriorly. The rectum is closed with a suture as soon as the upper edge of the anal ring is reached in order to avoid intraoperative tumor seeding; then dissection follows the levator ani fibers to reach the previous intrabdominal dissection or a transanal TME (TaTME) is performed [40].

4.1 Transanal total mesorectal excision

In recent years, many efforts have been made to reduce surgical trauma and obtain better operative and postoperative results for patients, but despite the latest technological and surgical advances, rectal cancer surgery is still very complex especially in obese patients, with a narrow pelvis and low tumors. For these reasons, a new surgical approach has recently gained particular attention: the TaTME [41], which according to preliminary results of many centers, has proved to be safe and feasible [42]. The development of this technique resulted from the experience acquired through the different minimally invasive techniques in colorectal surgery: transanal endoscopic microsurgery (TEM) [43], transabdominal transanal (TATA) proctosigmoidectomy [44], transanal minimally invasive surgery (TAMIS) [45] and natural orifice transluminal endoscopic surgery (NOTES) [46, 47]. TaTME is a colorectal resection performed with laparoscopic instruments through a natural orifice: the anal canal [48]. TaTME can facilitate surgery in patients who require anterior resection for low and medium rectal tumors, where intraabdominal insertion of an endoscopic stapler could be limited by the anatomical conformation, such as in obese patients and in males with a narrow pelvis, allowing to achieve complete excision of the mesorectum with clean distal and circumferential resection margins [48, 49]. The TaTME technique developed by Lacie (Cecil Approach) involves the use of a double surgical team, one for the abdominal time and one for the transanal time. Abdominal time coincides with the previously described LAR and involves mobilization of the splenic flexure and of the left colon, identification with section of the inferior mesenteric vein below the inferior margin of the pancreas, identification, and section of the inferior mesenteric artery at its origin. The transanal time begins when the inferior mesenteric artery is sectioned. A transanal surgical device (Buess Rectoscope or Gel Point Platform) is placed and the pneumorectum is performed, with a target pressure of 12–15 mmHg. A purse-string suture of the rectum is performed clockwise distal to the tumor, to prevent tumor spillage, from the anterior wall. The rectal wall is resected by a monopolar hook, with a full-thickness perpendicular transaction, following the holy plane, upwardly. The anterior and posterior planes are dissected at first, because easier to identify than the lateral ones; the lateral resection should be performed following the imaginary line that completes the circumference. Before the communication between transanal and abdominal field, a second purse string suture is performed in the free open edge of the distal stump; this suture will serve to tighten the stapler rod before the anastomosis. When the transanal surgical team is close to the peritoneal reflection, the two teams work together until the rendezvous is completed and the specimen is resected. The specimen can be extracted transanally if the dimension of the pelvis allows it, or transabdominally through a Pfannenstiel incision. The anastomosis could be a handsewn coloanal or a stappled end-to-end one, depending on the resulting stump length. The stapler anvil could be reinserted by the abdominal team if the specimen is extracted transabdominally or by the transanal team if extracted transanally. After tiding the distal purse-string suture around the circular stapler rod, the two parts can be connected, and it is possible to fire the stapler. At this point, the transanal device should be inserted again to verify the anastomosis. The side-to-end hand-sewn anastomosis is performed by pulling the colon wall near the distal rectal margin [50].

5. Conclusions

Surgical resection is a crucial milestone in the multimodal treatment of rectal cancer. A proper and accurate TME represents the most important factor for the postoperative oncological outcome. With the development of minimally invasive techniques in general surgery, the open approach to rectal cancer surgery has been progressively abandoned. More recently, the robotic surgical platform has gained consent in the surgical community. In addition to the well-known advantages of the robotic system over laparoscopy in terms of surgeon’s comfort and 3-D visualization, robotic-assisted rectal resection can overcome technical difficulties related to anatomical conditions, such as a narrow pelvis in males and obese patients. Moreover, a learning curve for robotic TME is shorter than for laparoscopic TME. When experienced surgeons perform robotic rectal surgery, the actual operating times do not significantly exceed the laparoscopic ones. Advantages of the robotic technique are counterbalanced by still-elevated costs that hamper its diffusion in surgical centers. No difference in terms of oncological outcomes is reported in the two different minimally invasive approaches.

Different surgical procedures can be offered to the patient affected by rectal cancer, according to its distance from the anal verge and its local extension. The most frequent procedure is low anterior resection. When feasible, a sphincter-preserving procedure should be preferred, and only in case of sphincter involvement or unachievable negative resection margins, abdomino-perineal resection with permanent colonostomy be performed. Different sphincter-preserving techniques have been described, and intersphincteric resection can offer the maintenance of fecal continence. In recent years, transanal TME has been developed, to reduce surgical trauma and improve postoperative results for patients. In this chapter, the currently available options in rectal surgery are reported and the robotic techniques are explained in detail.

Conflict of interest

The authors declare no conflict of interest.