Overview

Most decisions about type of anastomosis or the need for permanent colostomy for a patient with rectal cancer should be made before entering the operating room both because there is no substitute for advanced preparation and since this influences the risk-benefit discussion with the patient. In most situations, the decision to proceed with a sphincter-preserving procedure rather than an abdominoperineal resection (APR) is based on history, physical examination, imaging studies, response to chemoradiation, tumor histology, and the ability to obtain clear surgical margins. Additional patient factors including age, comorbidities, body habitus, continence status, and patient desires must be considered.[1] A good quality magnetic resonance imaging (MRI) with careful interpretation is important to identify any absolute indications for APR, including involvement of the levators or external anal sphincter.[2]

The surgeon must always be mindful that sound oncologic principles call for clear radial and distal margins. The relationship of the tumor to the sphincters on physical examination and high-resolution rectal MRI will dictate surgical options. In general, if the tumor is not directly involving or abutting the sphincters, a low anterior resection (LAR) with a total mesorectal excision (TME) with either stapled or hand-sewn reconstruction offers good disease control and, for many patients, a good functional outcome. Figure 1 is a diagram of a TME plane for a LAR. In situations where the tumor is abutting the internal sphincter, the options are limited to intersphincteric resection (ISR; Figure 2) or APR (Figure 3). When the sphincters are involved, APR is generally the procedure of choice.[3] Table 1 provides an overview of the features of LAR, ISR, and APR.

Figure 1. TME Plane for a LAR

TME, total mesorectal excision

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Figure 2. TME Plane for an APR

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Figure 3. APR

APR, abdominoperineal resection

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Table 1. Features of LAR, ISR, and APR

APR = abdominoperineal resection; ISR = intersphincteric resection; LAR = low anterior resection

In difficult situations, examination under anesthesia, second assessment by a colleague, or referral to a high-volume specialty center may be warranted to determine the best operation as it relates to safety, oncological outcomes, and quality of life. Despite the surgeon’s best intentions, in rare occasions often owing to body habitus, tumor size, or pelvic dimensions, the final decision to spare the anus can only be made at the time of surgery. In this scenario, the patient must be counseled about all of the possible procedures and the surgeon must be flexible and have very precisely defined the goals of surgery.[4]

As previously discussed, mesorectal tumor involvement can extend distal to the luminal tumor margin, and a 4–5 cm mesorectal margin (or all of the distal mesorectum in the case of a TME) is required to ensure complete removal of at-risk nodal tissue.[5][6] Accordingly, a tumor-specific mesorectal excision is recommended for tumors located in the upper third of the rectum, preserving rectal length and function without compromising cure rates. When the tumor is located in the distal third of the rectum—that is, ≤5 cm from the anorectal ring—TME is required to remove all nodal tissue.[5][6][7][8]

If the tumor is located in the distal third of the rectum where a TME is mandated, a 2-cm distal mural margin is generally desirable although a margin of < 1 cm may be acceptable, particularly following chemoradiation.[9][10][11][12]

Although a stapled anastomosis results in better function and less morbidity, mucosectomy and hand-sewn anastomoses can provide sphincter preservation in select cases. Mucosectomy and hand-sewn anastomoses are reasonable options when the distal aspect of the tumor approaches, but does not involve, the internal sphincter; in these cases, a circular stapler should generally not be used as the stapler donuts may incorporate removing a portion of the internal sphincter.[13]

When the cancer invades the sphincters but is confined to the internal sphincter, an ISR may be performed in highly selected patients when a radial margin of >1 mm at resection can be anticipated based upon preoperative high-resolution rectal MRI. Similar tumors exhibiting a poor response to neoadjuvant treatment or other tumors with a threatened (≤1 mm) radial margin are best managed with APR. Patients who can be considered for ISR are likely best managed at a specialized center where the procedure is more commonly performed. Fecal incontinence is common after these procedures; therefore, ISR should be reserved for patients highly motivated to avoid colostomy and willing to accept imperfect bowel function. Levator or external sphincter muscle involvement requires APR.[14][15][16]

At the time of operation, every effort should be made prior to rectal division to ascertain whether the distal margin will be adequate. When the decision to proceed with an APR is made during the operation, it should be made as soon as possible to avoid unnecessary moblilzation fo colon and to maximize the circumferential resection margin using a cylindrical dissection (Figure 4). When sphincter preservation seems possible and the rectum has been resected, the specimen should be examined on a back table; frozen section analysis is performed when the radial or distal margin appears suspect for involvement. If the distal mural margin is inadequate, or the radial margin is involved, and no more rectum can be resected, an APR will be required.[3][17]

A combination of bulk tumor and mesentery in a relatively small pelvis can create difficulty with direct vision of the lateral and distal dissection. This potential difficulty is especially true in obese men and can make sphincter preservation more challenging. These patients also experience a higher conversion rate to open surgery.[18][19] Further, some studies note an increasing trend on non–sphincter-sparing surgery, while others do not.[1][20][21][22][23] With the advent of robotic surgery, some of these challenges may be mitigated in the hand of a skilled surgeon.[24][25]

Figure 4. Coronal View of Extralevator APR

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Transanal TME is a promising technique that can augment a technically difficult distal dissection and that facilitates the distal TME. The distal margin and lower mesorectum are transanally dissected under direct vision or via transanal minimally invasive surgery (known as TAMIS). This approach is combined with an open or minimally invasive transabdominal TME. While the initial case series are promising, this technique is not universally adopted because peer-reviewed oncologic results are not mature, indications and contraindications remain to be refined, and the learning curve his quite steep.[26][27][28]

Metaanalysis of prospective and randomized trials from high-volume centers have shown equivalent short-term outcomes comparing transanal TME with traditional TME dissection.[29][30] However, real-world data have demonstrated unusual complications (especially urinary and vaginal injuries and carbon dioxide embolism), inconsistent and sometimes poor functional outcomes (bowel and sexual), and a significant learning curve.[31][32][33][34] Therefore, it is recommended that transanal TME be performed with caution outside outside specialty centers experienced with this technique.[35][36]

Regardless of whether sphincter preservation is planned, the overall success of a sphincter-preserving resection requires the patient to demonstrate a thorough understanding of anticipated functional outcomes, including potential complications with fecal frequency, urgency, and incontinence, and the potential permanency of a stoma. The surgeon’s discussion with the patient about their preferred approach should make clear the expectation of early postoperative dysfunction and that with adaptation there can be a degree of functional improvement over time.

Patient education and sharing of honest opinions regarding the expected outcomes following a restorative procedure will help to appropriately select patients for sphincter preservation and will help avoid the need for reoperation with diversion because of poor function or impaired quality of life.[37]

Patients with poor preoperative anal sphincter or bowel function and who would be an oncologic candidate to undergo an LAR with coloanal anastomosis may be offered a stapled closure of the upper anal canal (low Hartmann’s procedure) and creation of a colostomy. While this latter approach obviates the need for a perineal wound with its attendant risks of nonhealing and a chronically draining sinus tract, a low Hartmann’s procedure is sometimes complicated by breakdown of the stump closure and chronic pelvic sepsis.[38] This option is preferably used in the elderly patient where neoadjuvant radiation was omitted.

Overall, the decision to perform an LAR, ISR, or APR is first and foremost dictated by the need for uninvolved resection margins. The decision-making process also needs to be balanced with a preoperative assessment of a patient’s baseline sphincter function, their mobility, and their overall health status.