Laparoscopic Total Mesorectal Excision

Antonio M. Lacy

Beatriz Martín-Pérez

INDICATIONS/CONTRAINDICATIONS

Total mesorectal excision (TME) is defined as the en bloc removal of the rectum and its entire mesentery as indicated for the oncologic treatment of rectal tumors. After removing the rectum and the mesorectum, the bowel continuity may be restored through an anastomosis and a temporary diverting ostomy may be indicated in cases of high-risk anastomosis.

Each patient with rectal cancer should be individually evaluated because the management of rectal cancer has become increasingly complex, from diverse technical options to combination with different neoadjuvant treatments. The technical plan for the resection is customized to stage, gender, age, body habitus, prior radiation history, and other variables. With these issues in mind, the technical choices for a radical resection are discussed subsequently.

At present, a surgeon has three major surgical curative options: local excision, sphincter-saving abdominal surgery, and abdominoperineal resections (APRs). High rectal tumors and mid rectal tumors will benefit from sphincter-sparing procedures in general terms, except when an anastomosis is contraindicated and a stoma is performed. Conversely, low rectal cancers would undergo APRs as described by Miles. Sphincter-sparing procedures for resection of mid and some distal rectal cancers have become increasingly prevalent, because their safety and efficacy have been established in lieu of APR. The advent of circular stapling devices is largely responsible for their increasing popularity and utilization. Body habitus, adequacy of the anal sphincter, encroachment of the tumor on the anal sphincters, and adequacy of the distal margin are all factors in determining the applicability of a sphincter-sparing operation. According to Rullier et al. (Fig. 39-1), APRs are indicated when the tumor invades the external sphincter (Table 39-1).

FIGURE 39-1 Standardization of low rectal cancer, according to Rullier. Type I: supra-anal; type II: juxta-anal; type III: intra-anal; type IV: transanal.

TABLE 39-1 Surgical Classification of Low Rectal Cancer According to Rullier’s Classification

Classification	Definition	Surgical procedure
Type I	Supra-anal tumor >1 cm from anal ring	Coloanal anastomosis
Type II	Juxta-anal tumor <1 cm from anal ring	Partial intersphincteric resection
Type III	Intra-anal tumor Internal sphincter invasion	Total intersphincteric resection
Type IV	Transanal tumor External sphincter invasion A: levator ani muscles B: external sphincter C: levator ani and external sphincter	Abdominoperineal resection

In summary:

Tumors in the high rectum may undergo a partial mesorectal excision (PME) with a high colorectal anastomosis.
Tumors in the mid rectum will be treated by TME with a low colorectal anastomosis.
Low tumors lying 1 cm above the anorectal ring will benefit from TME with a coloanal anastomosis.
Juxta-anal tumors lying in less than 1 cm from the anorectal ring will undergo TME with partial intersphincteric dissection.
Tumors invading the internal sphincter will be subjected to TME with total intersphincteric dissection.
Tumors invading the external sphincter will not be candidates for TME with a sphincter-preserving procedure, but for an APR.

Principles of Total Mesorectal Excision

Richard “Bill” Heald defined the concept of TME in 1982, establishing the principles of the modern era for rectal surgery. He proposed that the excision of all the tissue surrounding the rectum would improve the oncologic control of the rectal disease. Since his pioneering work, removing the mesorectum has been considered the gold standard in rectal cancer surgery.

The mesorectum is the layer composed of adipose and lymphovascular tissue covering the rectum. Thus, the mesorectum is found between the rectal wall and the visceral layer of the pelvic fascia, which will anteriorly continue as the Denonvilliers’ fascia in men and the rectovaginal septum in women. The mesorectum is developed mainly laterally and posteriorly rather than anteriorly, where it is a thinner layer of tissue, and extends distally up to 2-3 cm of the anorectal junction.

TME can be achieved either by a low anterior resection or during an APR. Regardless of the procedure performed, the entire mesorectum should be dissected sharply, including the mesorectum distal to the tumor, as an intact unit. Before the advent of the TME description, the visualization of the rectal dissection was limited to the pelvic anatomy characteristics and the mesorectum was excised mainly bluntly. Residual mesorectum was left behind because the circumference was routinely violated along undefined planes, leaving viable tumor burden within the pelvis, reflected by a higher recurrence rate in conventional surgery. In addition, a significant incidence of sexual and urinary dysfunction was described, related to the damage of the autonomic parasympathetic and sympathetic nerves by blunt dissection.

Thanks to the spread of the minimally invasive techniques, the mesorectum is sharply removed under direct visualization, following the same key principles described by Heald of autonomous innervation preservation while maintaining hemostasis, and avoiding mesorectal envelope violation. Lower anastomoses between 3and 6 cm from the anal verge are preferred to APR. Recent comparative studies between the open and the laparoscopic approaches show similar disease-free survival and overall survival.

Total Mesorectal Dissection Extent

Lymphatic Spread of Rectal Cancer

The importance of the mesorectum lies in the lymphatic extension from the rectum into the mesorectum, as it is a well-established prognosticator. Therefore, if the mesorectal envelope is removed en bloc, every path of spread of the tumor into the mesorectum will also be removed.

The extent of the rectal cancer resection remains controversial. On the basis of the spreading pathway described in several articles from the 20th century, the extension is mainly upward along the lymphatic course. However, tumors below the peritoneal reflection spread distally also by intra- and extramural routes. Summarizing, the spread will occur mainly as follows:

Upwards, which is the main route of invasion along the lymphatic course, and justifies the en bloc excision of the mesorectal region containing the upper rectal pedicle.
Downwards, up to 4 cm below the distal border of the tumor, translating into the average 5-cm distal margin for the mesorectum accepted traditionally, which is reduced to 2 cm for the lower rectal tumors for those well-differentiated according to recent studies.
Laterally, reflected on the circumferential resection margin (CRM). If the lymphatic invasion threatens the circumferential margin, there is a higher chance of locoregional recurrence.

Distal Margins

Traditionally, a 5-cm distal margin was the minimum requirement for a safe surgery, because early surgeries demonstrated that the downward extension of the tumor reached up to 4 cm below the distal border of the tumor. More recent pathologic studies described that intramural extension occurs within 2 cm of the tumor, unless the tumor is poorly differentiated or widely metastatic. Extramural retrograde lymphatic dissemination is a poor prognostic factor even with more radical surgeries. Recent studies demonstrated no significant differences in survival or local recurrence when comparing distal rectal margins of <2, 2-2.9, and >3 cm. As a result, a 2-cm distal margin has become acceptable for resection of rectal carcinoma, although a 5-cm proximal margin is still recommended.

However, smaller distal margins, even 1 mm, may be acceptable to avoid APRs in patients who have received neoadjuvant chemoradiation.

Partial and total intersphincteric resections have been widely accepted. According to Rullier et al., juxta-anal tumors lying less than 1 cm from the anorectal ring are best treated by partial intersphincteric dissection, but those invading the internal sphincter will be subjected to TME with total intersphincteric dissection.

Radial Margins

On the basis of studies of Quirke et al., local recurrence is intimately related to a radial spread (Fig. 39-2). These studies demonstrated that approximately 90% of patients with positive radial margins would develop a local recurrence. A CRM < 1 mm is an independent predictor of a poor outcome in patients whether they received neoadjuvant treatment or not. Patients with an R1 CRM have a risk of up to 26% for local recurrence at 5 years and an overall survival of 43%.

FIGURE 39-2 Magnetic resonance imaging for rectal cancer. Imaging is essential to determine the invasion of the tumor into the rectal wall. A. Axial view. B. Sagittal view.

Magnetic resonance imaging (MRI) has shown relatively high diagnostic accuracy for preoperative T staging and CRM assessment and should be reliable for clinical decision making. Endorectal ultrasound can provide additional assessment of CRM for mid or distal rectal lesions, increasing the accuracy of the staging when combined with MRI. Patients undergoing neoadjuvant treatment before surgery should be restaged. Accurate restaging of locally advanced rectal cancer by MRI, computed tomography (CT), and endoluminal ultrasound is still a challenge. Identifying a complete pathologic response by imaging is not completely accurate. It is difficult to predict the presence of metastatic lymph node disease. Further studies to correlate the radiologic findings and the final pathology results are required.

Lateral Lymph Node Dissection

Lateral lymph node dissection for low rectal cancers with suspected lateral lymph node metastasis is a routine practice in Japan. Prior studies have shown up to a 16.4% incidence of lateral lymph node involvement because of the lateral lymphatic drainage of the rectum from the lower rectum through the lateral ligaments ascending along the internal iliac arteries and inside the obturator spaces. However, even if the oncologic control may be improved, lateral dissection increases urinary and sexual dysfunction. Studies have compared local recurrences after lateral lymph node dissection (6.9%) versus radiation and TME treatment (5.8%). This questions the indication for extended lymph node dissection and the consequent morbidity, when neoadjuvant treatment can achieve similar oncologic outcomes. More comparative studies will need to address this issue to assess the benefit of the lateral lymph node dissection in patients without clinical disease along the pelvic sidewall or the iliacs.

Nerve Dissection

Nerve preservation is essential during TME to maintain optimal functional results after surgery. From the inferior mesenteric artery (IMA) pre-aortic plexus down to Denonvilliers’ periprostatic plexus, dissection should be carefully performed to avoid nerve injuries. These complications during TME can occur at different levels and are well recognized:

During the dissection of the IMA close to this aorta, the pre-aortic plexus can be injured to cause retrograde ejaculation.
At the level of the sacral promontory, the presacral sympathetic plexus bifurcates to each side of the pelvis. The nerves should be left intact near the promontory to avoid retrograde ejaculation or bladder dysfunction.
The nervi erigentes (parasympathetic plexus) can be potentially damaged when dissecting the lateral stalks in the lower part of the mid rectum dissection, resulting in erectile dysfunction.
Mixed sympathetic and parasympathetic injury is encountered when dissecting under the sacral promontory into the lateral pelvic sidewall, outside of the lymphovascular bundle, lateral to the seminal vesicles in men and the cardinal ligaments in women, leading to erectile dysfunction and bladder dysfunction.
Dissection anterior to Denonvilliers’ fascia can damage the periprostatic plexus, developing into erectile dysfunction and/or a neurogenic bladder.

Neoadjuvant Therapies

Associated with the oncologic improvement because of the advent of TME, adjuvant therapies including radiotherapy and chemotherapy have also been established to improve outcomes. Patients with node-positive disease benefited the most in terms of disease-free survival after neoadjuvant treatment. Accordingly, patients with Stage II and III disease should be considered for adjuvant therapy before TME surgery. Preoperative neoadjuvant treatment associated with TME has demonstrated in a randomized trial a significant decrease in the rate of local recurrence at 2 years without increasing complications. Conventional chemoradiation enhances pathologic response and improves local control in resectable Stage II and III rectal cancer when compared to short-term radiotherapy. There are contradictory results regarding the impact on the mid- or long-term disease-free survival results.

Short-course radiotherapy followed by immediate surgery is as effective as long-course radiotherapy with delayed surgery in terms of overall survival, disease-free survival, local recurrence, distant metastasis, sphincter preservation, R0 resection, and late toxicity. Long-course radiotherapy may increase the pathologic response rate at the expense of increasing acute toxicity.

In addition, those patients preoperatively treated with chemoradiation may achieve a complete clinical response according to MRI, CT, and/or endorectal ultrasound and clinically by rectoscopy.
These patients may benefit from a “watch and wait” approach or from local resection as opposed to a radical surgery, with similar oncologic outcomes. The “watch and wait” approach is complete predicated on clinical and radiologic disappearance of the lesion. Close surveillance to detect any recurrence early on is required. If recurrence is detected, the patient can still undergo radical surgery without compromising the long-term oncologic results.

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