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Rectal Cancer Microsurgery
Introduction
Colorectal malignancies are considered the third most common cancer for both male and female individuals. Moreover, they are the second most common cause of malignancy-related mortalities in the United States.[1] However, it should be noted that the distinct rectal cancer prevalence might not be simply concluded from the current cancer registry and is mostly combined with colon cancer data sets.[2]
Histological diagnosis of invasive adenocarcinoma should be confirmed before surgical planning for rectal cancers because in the management of rectal neoplasms of other histologies, including squamous cell carcinomas, non-surgical or different multimodality options are indicated.[3]
Operative management with excisional biopsy is typically not indicated unless it is feasible to perform with adequate radial margins and curative intentions. Local excision in the management of rectal cancer is an acceptable surgical option with curative intent and is limited to the highly selected patients with cT1N0. Moreover, the patient should have favorable clinical and histological characteristics. Accordingly, transanal excision may be indicated in patients with more advanced cT disease who do not meet the eligibility criteria for radical cancer surgery.[4][5]
Local excision in treating rectal cancers provides several advantages, including limited operative risk and minimal functional morbidities. However, it does not adequately excise the tumor, and the mesorectal lymph nodes' pathological staging is less than optimal.[6]
Determining the exact depth of tumoral invasion (Tis, T1, or T2) may be complicated using MRI only. Therefore, endoscopic ultrasonography (EUS) may be applied as a complementary tool for more precise staging.[7]
The optimal approach for managing rectal adenocarcinoma depends on several factors, of which the tumor location in the rectum and tumoral extension are the most important. The surgical approach remains the only curative treatment for rectal cancer. Curative resection demands a wide resection with histologically negative margins and total mesorectal excision (TME). Total mesorectal excision includes local lymph node resection via transabdominal approach. The trans-abdominal approach in the management of rectal cancer refers to low anterior resection or abdominoperineal resection.[8]
Rectal microsurgery is a form of minimally invasive surgery used in the treatment of early rectal cancers, defined as an adenocarcinoma invading the rectal wall up to the submucosa.[4] Traditionally, rectal resection combined with total mesenteric excision (TME) was the gold standard for all rectal cancers.[9] Unfortunately, this procedure is associated with high morbidity and functional sequelae, which may not be considered acceptable in early disease.
Transanal excision (TAE) using a conventional retractor was one method of managing benign neoplasia and early rectal cancer. This technique is significantly limited by exposure and visibility, making it incredibly difficult to achieve high-quality oncological resections. High lesions in the proximal two-thirds of the rectum are also not reachable by TAE, leaving transabdominal resection the only curative option.[10]
Widespread use of screening programs has led to a significant increase in the detection of rectal cancers, which has propagated greater interest in developing organ-preserving techniques. Transanal endoscopic microsurgery (TEMS) was established in the 1980s as a minimally invasive procedure capable of performing full-thickness excision of rectal tumors down to the perirectal fat under general or spinal anesthesia. Current evidence supports using TEMS as a curative method for T1 rectal cancers.[11] However, in the context of more advanced rectal cancer, TEMS should only be considered a compromise and used sparingly in selected patient groups.[12]
Transanal minimally invasive surgery (TAMIS) was introduced more recently as an alternative to TEMS. TAMIS works on the same principles as TEMS but uses a slightly different platform on which to operate. As a technique, TAMIS has gained considerable international experience since its inception but remains relatively infantile compared to TEMS.[13]
Endoscopic submucosal dissection (ESD) is an endoluminal technique that can also remove lesions within the rectum and other parts of the colon. ESD is not covered in the scope of this article but is considered another viable option for treating pre-malignant and early rectal cancer, depending on locoregional experience and expertise.
Anatomy and Physiology
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Anatomy and Physiology
Rectal anatomy and physiology are incredibly complex, and a clear understanding of relevant landmarks, key structures, and neurovascular supply is crucial in rectal surgery.[14][15][16]
Anatomical Landmarks
The rectum is a distinct structure from the rest of the colon and bridges the last 15cm of the alimentary canal before reaching the anal orifice. The partition between the sigmoid colon and rectum is marked by the coalescence of tenia coli and loss of appendices epiploicae, normally found at the level of the sacral promontory. From an anatomical perspective, the rectum can be arbitrarily divided into three parts - upper (12 to 15 cm from the anal verge), middle (7 to 11 cm from the anal verge), and lower (up to 6cm from the anal verge). Functionally, the rectum has two parts - the upper part acting in a propulsive manner similar to the sigmoid colon. In contrast, the lower part is dilated and forms a reservoir for storage purposes.[17][18][19]
Relationship to Other Structures
The upper two-thirds of the rectum is covered in the pelvic peritoneum (continuation of parietal peritoneum), which thickens and reflects anteriorly and laterally to protect the ureters and posterior bladder in both sexes. This forms the rectovesical pouch in men and the pouch of Douglas in women. The pelvic peritoneum covers the uterus and fallopian tubes (broad ligament) before extending posteriorly over the cervix and vaginal fornix to form the rectouterine pouch.[20]
Denovillier's fascia is the rectoprostatic fascia that lies between the anterior surface of the rectum and the prostate and seminal vesicles. Within this fascia, it may be possible to identify the hypogastric nerves and small vessels supplying the male reproductive organs, although this is often not easily recognized.[21]
Waldeyer's fascia is found on the posteroinferior side of the rectum as a thickening of the presacral fascia that descends to meet the mesorectal fascia about 3 to 5 cm from the anorectal junction. This fascia appears to act as an anchor tethering the rectum to the sacral bone.[22]
Mesorectum
The rectum is enveloped in a layer of adipose tissue known as the mesorectum, surrounded by mesorectal fascia. The mesorectum contains the descending branches of the superior rectal artery, corresponding venous tributaries, and draining lymphatics and nodes. The site of surgical dissection in total mesorectal excision lies in a relatively avascular areolar plane between the mesorectal fascia and parietal pelvic fascia.[23][24]
Neurovascular Supply
The vascular supply to the rectum comes from three main arteries - the superior rectal artery, middle rectal artery, and inferior rectal artery. The inferior mesenteric artery gives off the superior rectal artery, which supplies the upper part of the rectum and provides approximately 80% of the total blood supply. The remainder comes from the anterior division of the internal iliac artery, below the level of the pelvic floor, giving rise to the middle rectal artery and internal pudendal artery. The inferior rectal artery is a branch of the internal pudendal artery and supplies the anorectal junction, internal and external anal sphincters, and peri-anal skin.
Similar to artery supply, the venous drainage of the rectum occurs via three veins - superior, middle, and inferior rectal veins. The superior rectal vein drains into the inferior mesenteric vein as part of the portocaval system. Meanwhile, the middle and inferior rectal veins drain back into the systemic venous system via the internal iliac and internal pudendal veins, respectively. The lymphatic drainage for the upper third of the rectum follows the superior rectal vessels from the pararectal lymph nodes to the inferior mesenteric nodes. The lower aspect of the rectum drains along the middle rectal vessels directly into the internal iliac lymph nodes.[25]
The autonomic supply to the rectum is provided by sympathetic and parasympathetic systems. The sympathetic nerves reach the rectum via the lumbar splanchnic nerves and superior and inferior hypogastric plexuses. The parasympathetic supply is delivered by the pelvic splanchnic nerves (S2, S3, and S4), traveling down into the pelvis to become the inferior hypogastric plexus on either side of the rectum. The inferior hypogastric plexus is an important network of nerves that controls the function of pelvic organs. Injury to the plexus can therefore lead to significant urinary and sexual dysfunction.[26]
Indications
Transanal excision of rectal cancer is indicated for treating benign polyps or early-stage cancers in selected patients.[27] Lesions suitable for local excision are typically small (less than 3 cm in size), mobile, and involve less than a third of the rectal circumference to allow enough space to work. Larger lesions can certainly be removed using TEMS or TAMIS by an experienced surgeon, although the risk of complications would increase. If the technique is used for curative purposes in cancer, there should also be no evidence of local-regional spread, such as enlarged visible or palpable mesenteric lymph nodes.
For malignant lesions, local excision using transanal microsurgery is accepted for T1N0 rectal cancers. T1 rectal cancers are further subdivided into sm1 (submucosal invasion of fewer than 1000 micrometers), sm2, and sm3 (submucosal invasion of greater than 1000 micrometers), depending on the depth of submucosal invasion. Nodal involvement in sm1 is 0 to 1.8% compared with 12.8 to 13.8% in sm2 or sm3, thereby significantly increasing the chance of recurrence. As a result, the European Society for Medical Oncology recommends local excision for T1 sm1 rectal cancers and rectal resection with total mesorectal excision for sm2 and sm3.[28]
Furthermore, rectal microsurgery can treat a variety of benign or premalignant lesions, including rectal polyps, solitary rectal ulcers, rectal stenosis, and prolapse.[29]
Contraindications
Transanal microsurgery is often limited by technical factors, including the location and size of the tumor. Lesions low down in the rectum (<5 cm from the anal verge) may not be easily excised due to being obscured by the transanal port. Tumors occupying >30% of the luminal circumference or >3 cm in size may also be considered contraindications, although this depends on surgeon experience. Nonetheless, if the lesion possesses one of these attributes, excision will be difficult and lead to worse oncological outcomes.[30][31]
Equipment
Transanal Endoscopic Microsurgery (TEMS)
TEM was the first rigid platform created in 1983. The proctoscope has a flat or beveled end with a diameter of 40mm and a length of 12 or 20 cm. Once introduced into the rectum, the proctoscope is sealed with a faceplate that contains multiple ports for inserting the stereoscopic optics system and surgical instruments. The stereoscopic optics system provides depth perception by allowing the surgeon to see in three dimensions. Penumorectum is maintained by an insufflation system, while a roller pump drives suction irrigation. The entire platform is secured to the operating table using a support arm.[32][33]
Transanal Minimally Invasive Surgery (TAMIS)
TAMIS was introduced in 2010 after single incision laparoscopic ports became widely available. The TAMIS platform was adapted from the SILS Port and GelPOINT PATH and incorporated a flexible port with multiple channels for the insertion of conventional laparoscopic camera scopes and instruments.[34][35]
Insufflation
Maintaining a stable pneumorectum is essential in both TEMS and TAMIS to maintain a clear operative field and space in which to work. Generally speaking, pressures of 12 to 15 mmHg is used in rectal microsurgery. In TEMS, a multifunctional endosurgical unit regulates CO2 insufflation and suction while monitoring intrarectal pressure. Meanwhile, TAMIS uses a gel seal cap with a port that allows the insufflation of CO2. More recently, Airseal has been introduced in TAMIS, which is a tri-lumen filtered tube set that optimizes gas flow by insufflating CO2 and extracting smoke simultaneously.
Personnel
The essential theatre team is composed of the surgeon, surgical assistant, anesthesiologist, and scrub nurse. Other members may also present to help position the patient, assist in the anesthetic process and retrieve equipment intraoperatively.
Preparation
Pre-operative Work-up
The standard of care for rectal microsurgery can be variable across different centers due to a lack of uniformity and standardization. The work-up and decision-making process are the same for TEMS and TAMIS. Once a rectal lesion has been identified and considered suitable for localized surgery, a full colonoscopy should be performed to exclude any synchronous tumors elsewhere in the colon. The rectal lesion must be accurately localized, with its position and orientation carefully documented.
Staging is performed using a combination of magnetic resonance imaging and endoscopic ultrasound to characterize the lesion with computed tomography of the chest, abdomen, and pelvis to ensure there is no evidence of metastatic disease. Biopsy of the rectal lesion is a contentious topic as there is a risk of fragmentation and seeding of cancer. Furthermore, any disruption to the tissue will lead to scarring and make mucosal resection more difficult.
Nonetheless, without histological analysis, it is difficult to appreciate the exact nature of the lesion and the extent of invasion. Transanal microsurgery can be used as a curative method for low-risk T1 (sm1) rectal cancers, but patients with poor histological features or deeper submucosal invasion (sm2 and sm3) have a high risk of recurrence.[36] Consequently, the decision to perform either an initial biopsy or proceed straight to an excision biopsy should be discussed at a multidisciplinary meeting involving surgeons, radiologists, and histopathologists.
If the patient has been diagnosed with early rectal cancer, then cancer nurse specialists should be made available to provide patient support and detailed information about the operation and recovery. A stoma nurse consultation may also be deemed necessary to give advice and reassurance to patients even though the likelihood of a stoma is low.
Pre-operative Preparation
Patients are typically given full bowel preparation the day before surgery to empty the bowel and provide optimal exposure and access to the tumor. Prophylactic antibiotics and venous thromboembolism prophylaxis are administered at the surgeon's discretion at the time of the procedure.
Post-operative Care
After the operation, patients tend to stay one or two days in the hospital. Most people will complain of discomfort or some pain in the back passage, but this should resolve quickly. Oral intake is encouraged, and although there is no consensus, solid food can usually be started immediately. Bowel movements will be quite loose initially and can take a few weeks to normalize. In certain scenarios, the patient may need the help of dieticians to adjust their dietary intake for a short period postoperatively to ensure nutritional needs are met.
Technique or Treatment
Positioning for TEM
For the rigid platform, the patient needs to be positioned so that the lesion is 'down' relative to the angled stereoscopic optic system, which is fixed to the proctoscope with the bevelling facing downward. Depending on the location of the lesion, the patient may need to be in a prone position for anterior lesions, supine or lithotomy for posterior lesions, and right or left-sided tilt for lateral lesions.
Positioning for TAMIS
Less positioning is required in TAMIS as the port allows for 360 degrees of movement and visualization. The patient is placed in the lithotomy position regardless of the orientation and location of the lesion. In certain circumstances, some surgeons may prefer the lithotomy position for distal and mid rectal lesions but the prone position for proximal anterior lesions.[34]
Resection
Diathermy is used to mark out a margin of 10 to 15 mm around the lesion. Dissection is typically started on the lower edge of the lesion, working superiorly in a circumferential manner. Malignant lesions require full-thickness excision of the rectal wall down to the mesorectal fat. The defect in the rectal wall is transversely closed with absorbable sutures to prevent lumenal stenosis. The specimen is orientated, kept in formalin, and sent for histological assessment. The risk of entering the peritoneal cavity is much higher for proximal anterior lesions. Perforations can generally be closed without entry into the abdomen. Full-thickness excision is typically recommended even for benign neoplasms as these lesions can harbor an invasive component.[34][37][38]
Complications
Patients who undergo local excision using rectal microsurgery generally have better functional outcomes than transabdominal procedures. Nonetheless, fecal incontinence remains a possible complication often attributed to using a large-diameter proctoscope. Other potential sequelae include post-operative rectal bleeding, proctalgia, rectal stenosis, and pelvic inflammation or abscess.
In certain cases, free perforation into the abdominal cavity may occur, leading to peritonitis and the need for major transabdominal surgery. Generally, rectal microsurgery is considered very safe and far superior in terms of hospital stay and recovery compared to traditional mesorectal excision.[39][40]
Clinical Significance
The indications, techniques, platforms, and complications of rectal microsurgery are discussed in this article. Overall awareness of different platforms and techniques enables health professionals to select patients correctly and provide adequate clinical information and aftercare for those undergoing this procedure. Recognizing normal post-operative recovery versus potential complications will also prevent unnecessary investigation or delay in diagnosis and treatment.
Enhancing Healthcare Team Outcomes
An interprofessional approach to colorectal cancer is crucial for achieving good patient outcomes. Rectal microsurgery is an emerging technique. Knowledge of patient selection and procedural steps are essential for good postoperative care and early identification of potential complications utilizing clinicians (MDs, DOs, PAs, and NPs), nursing staff, and in some cases, pharmacists. Teamwork and open communication are necessary to establish effective communication and advancement of clinical knowledge aimed at optimizing care for patients and reducing unnecessary hospital stays.
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