Indications for LAR Versus Intersphincteric Resection Versus APR
Most decisions about type of anastomosis or the need for permanent colostomy for a patient with rectal cancer should be made prior to entering the operating room because there is no substitute for advanced preparation. 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. A good quality MRI with careful interpretation is important to identify any absolute indications for APR including involvement of the levators or external sphincter.
The surgeon must always be mindful that sound oncologic principles call for clear margins related to the mesorectum and rectal wall in both radial and distal directions. The relationship of the tumor to the sphincters on physical examination and high-resolution rectal MRI can help predict the procedural options. In general, if the tumor is not directly involving or abutting the sphincters, a low anterior rection (LAR) total mesorectal excision (TME) procedure has a high likelihood of success with either stapled or hand-sewn reconstruction (Figure 5.1). In situations where the tumor is abutting the internal sphincter, then the options are limited to intersphincteric resection (Figure 5.2) or abdominoperineal resection (Figure 5.3). If the sphincters are involved, abdominoperineal resection is generally the procedure of choice.
In difficult situations, an 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, rare occasions exist due to body habitus, tumor size, or pelvic shape, where the final decision can only be made at the time of surgery. In this scenario, the patient must be appropriately counseled about all of the possible procedures and the surgeon must be flexible and have very precisely articulated goals of care.
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, whichever is a shorter distance, is required to ensure complete removal of at-risk nodal tissue., 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. When the tumor is located in the distal third of the rectum, 5 cm or less from the anorectal ring, a TME procedure is required to remove all nodal tissue.,,, For tumors in the middle third, especially in obese patients, it may be prohibitively difficult to perform a tumor-specific mesorectal excision and save 2-3 cm of viable rectum above the pelvic floor. Consequently, it is often technically easier and safer to extend the resection for an additional 2-3 cm to complete a TME. The decision in this situation is primarily based on the technical feasibility of dissecting through the distal mesorectum at the appropriate level while preserving the viability of the rectal stump.
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 < 1 cm may be acceptable, particularly following chemoradiation. However, a higher risk of local recurrence exists for very close distal margins, so that poorly differentiated tumors or those with other unfavorable characteristics are not good candidates for LAR with very close margin.
Although a stapled anastomosis results in better function and less morbidity, a mucosectomy and hand-sewn anastomosis can provide sphincter preservation in selected cases. A mucosectomy and hand-sewn anastomosis is considered when the distal aspect of the tumor approaches but does not involve the internal sphincter, and a circular stapler should not be if the donuts will incorporate removing a portion of the upper internal sphincter.
When the cancer invades the sphincters but is confined to the internal sphincter, an intersphincteric resection may be performed in selected individuals if 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 others with a threatened (≤1 mm) radial margin are best managed with an abdominoperineal resection. These patients considered for intersphincteric resection are likely best managed at a specialized center where the procedure is more commonly performed. Fecal incontinence is common after these procedures, and they should be reserved for patients highly motivated to avoid colostomy and willing to accept imperfect bowel function.,, Levator or external sphincter muscle involvement typically requires an abdominoperineal resection.
Determining the role for aggressive sphincter-preserving procedures requires the patient to demonstrate a thorough understanding of functional outcomes including potential problems with fecal frequency, urgency, and incontinence. Additionally, the individual must have appropriate expectations and appreciate that early postoperative dysfunction is normal, but long-term improvement is common secondary to adaptation. Education of the patient and sharing of honest opinions regarding the expected outcomes following a restorative procedure will further help to appropriately select patients for sphincter preservation and avoid the need for reoperation to establish diversion because of poor function or impaired quality of life.
At the time of operation, every effort should be made prior to rectal division to ascertain if the distal margin will be adequate so that steps can be taken to extend the resection to an uninvolved plane as necessary. If the decision to proceed with an APR is made during the operation, it should be made as soon as possible to halt the abdominal dissection above the levators and maximize the circumferential resection margin using a cylindrical dissection (Figure 5.4). If sphincter preservation seems possible and the rectum has been resected, it 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 and no more rectum can be resected or the radial margin is involved, an abdominoperineal resection and colostomy is required. In the obese male with a bulky tumor and relatively small pelvis, distal mesorectal dissection under direct vision and sphincter preservation may be impossible using standard open or laparoscopic techniques; in this case, an abdominoperineal resection and colostomy might be required to obtain clear margins.
Transanal TME is a promising technique to augment a technically difficult distal dissection. The distal margin and lower mesorectum are transanally dissected under direct vision and the approach extends the distal limits of dissection in these patients when combined with an open or minimally invasive TME. While the initial case series are promising, this technique is not ready for universal adoption as the oncologic results are not mature, indications and contraindications remain to be refined, and the learning curve has yet to be established.,,
Patients with poor preoperative anal sphincter or bowel function who would normally have a low anterior resection with coloanal anastomosis may be better managed with a stapled closure of the upper anal canal (low Hartmann’s procedure) and creation of a colostomy. While this obviates the need for a perineal wound with its attendant risks of nonhealing and chronically draining sinus tract, a low Hartmann’s procedure is occasionally complicated by breakdown of the stump closure and chronic pelvic sepsis. This option is preferably used in the elderly patient where neoadjuvant radiation was omitted.
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