The cancer-related and functional goals of operations for rectal cancer are integrally related. Although the goals of cancer treatment are cure and local control, careful selection of the planes of pelvic dissection can help preserve both sexual and urinary function. Even the long-term goal of local control affects the success of sphincter preservation. The single greatest cause for the creation of a colostomy remote from the initial treatment site is pelvic recurrence. Successful treatment is defined by the achievement of all these goals in concert. This article will focus on sphincter preservation and the preservation of anorectal function.
On lateral view of the pelvis, the rectum may be divided into three levels: the low, mid-, and high (or upper) rectum (Figure 1). Due to variations in body habitus, height, and individual anatomy, it is difficult to assign exact measurements, but, as a general rule, the following statements are true: (1) The rectum may be regarded as the distal 6 inches of the large bowel. (2) A more accurate reflection of rectal anatomy is the extraperitoneal portion of the large bowel situated within the pelvis. A working definition of the rectum adopted by numerous authors and the cooperative groups is the distance of 0 to 12 cm from the anal verge in the left lateral Sims' position on rigid proctoscopy.
The low rectum is generally regarded as 0 to 5 cm from the anal verge; the mid-rectum, 6 to 10 cm from the anal verge; and the upper rectum, 11 or 12 cm from the anal verge (Figure 1A). Cancers of the low rectum may be intimately associated with the voluntary sphincters, anal canal, or levator ani, and are usually below the coccyx (Figure 1B). Cancers of the mid-rectum are usually situated proximally, within the sacral hollow between the tip of the coccyx distally and the peritoneal reflexion (Figure 1C). Cancers situated more than 12 cm from the anal verge tend to manifest a local recurrence rate equal to that of colonic cancers (6%), as compared with the 30% rate traditionally observed in rectal cancer.
The American College of Surgeons includes cancers up to 15 cm from the anal verge as part of the "upper rectum." This enhances the apparent rates of local failure by including some lesions less prone to recur locally. Various studies[1-5] consider the 12-cm upper limit to be a more stringent criterion.
During the past few decades, numerous pathologic studies have confirmed that the mesorectum, ie, the integral mesentery surrounding the rectum, is the regional site of either direct extension or spread from a primary rectal cancer. Such regional spread can manifest as lymph node metastases, separate foci of tumor implanted in the mesorectum, lymphatic vascular or perineural invasion, or extracapsular nodal penetration, among other presentations.[6-9]
The rectum and the mesorectum form a single unit that is contained within the envelope of the visceral pelvic fascia. The parietal layer of the pelvic fascia covers the sacrum, presacral fascia, musculoskeletal boundaries of the pelvic side walls, internal iliac vessels, pelvic autonomic nerves, and plexuses controlling both sexual and urinary function.
Utilizing sharp dissection along an areolar plane that separates the parietal from the visceral fascia, the affected rectum and mesorectum can be completely excised as an intact unit with negative circumferential margins, achieving high rates of cure and low rates of local failure. This recently introduced practice is now known as total mesorectal excision (Figure 2). By contrast, conventional surgery is associated with blunt dissection along undefined planes and often violates the integral mesorectum, leaving tumor behind and accounting for a worldwide local recurrence rate of 30%. Local recurrence has been pathologically related to involved circumferential margins and really represents the clinical manifestation of persistent disease.
The 45% to 50% 5-year survival rate achieved by conventional surgery compares poorly to the 75% rate attained with total mesorectal excision (in T3, N0 or T3, N, any M0 disease). In contrast to the worldwide local failure rate of 30% associated with conventional surgery, total mesorectal excision is associated with a local failure rate on the order of 4% to 8% for T3, N0, M0 and T3, N1-2, M0 disease.
The past 2 decades have witnessed extraordinary progress in the implementation of sphincter-preserving operations for rectal cancer. Although first introduced in 1938, sphincter-preserving operations for rectal cancers (deep within the narrow confines of the pelvis) remain technically demanding and have been less rapidly adopted by the surgical community than have sphincter-preserving operations for cancers of the rectosigmoid (more than 12 cm from the anal verge). Indeed, still widely prevalent are the outdated belief and practice that the operation of choice for all rectal cancers within reach of the examining finger is abdominoperineal excision of the rectum and permanent colostomy.
Patients with cancers of the mid-rectum (6 to 10 cm) or above are candi- dates for sphincter-preserving operations. Patients may be selected for a sphincter-preserving operation based on the distance of the tumor from the anal verge, mobility, and, in cases which border on the low rectum, early T-stage. Adjacent organ involvement, size or shear bulk of the primary tumor, or depth of penetration may influence the complexity of a given operation but are not contraindications to sphincter preservation. In cases where a tumor may be resected with negative circumferential margins and the rectum fully mobilized, creating an adequate distal margin (vide infra), sphincter preservation is generally indicated.
In 1974, Stearns compared the results of a large series of patients who underwent sphincter-preserving operations for mid-rectal cancer with results in patients with mid-rectal cancer who underwent abdominoperineal resection of the rectum on technical grounds alone. Sphincter preservation did not compromise either cure or local control. Numerous studies have since confirmed these results. Thus, whenever possible, cancers of the mid-rectum should be treated by sphincter preservation.
Types of Sphincter-Preserving Operations
A sphincter-preserving operation may be classified as (1) a standard low anterior resection, (2) a low anterior resection with a coloanal anastomosis, or (3) a low anterior resection or coloanal anastomosis with a J-pouch colonic reservoir. By definition, all low anterior resections represent a resection and an anastomosis between the serosalized colon and the extraperitoneal nonserosalized rectum. A standard low anterior resection usually involves an intrapelvic anastomosis situated within the sacral hollow proximal to the floor of the pelvis (Figure 3).
A coloanal anastomosis is an extrapelvic anastomosis situated at the apex of the anal canal or lower in the anal canal at the dentate line. In a standard low anterior resection, the amount of the remaining distal rectal segment may be variable, while in a coloanal anastomosis, there is no remaining distal rectal pouch (vide infra).
Low Anterior Resection--A low anterior resection is accomplished by the complete mobilization of the rectum and mesorectum down to the levator ani by using sharp dissection along the planes previously described. With complete mobilization, the rectum, which was previously situated along the sacral curvature, straightens upward, producing a new 4- or 5-cm length of rectal wall distal to the lowest edge of the primary tumor. This distance provides a safe margin that allows for transection of the bowel and reconstruction.
The majority of low anterior anastomoses are performed using circular stapling devices (Figures 3A-3C). Two concentric rows of staples are placed through the walls of the rectum and colon, which have been brought together over the shaft of the circular anastomotic stapling device. Either of two methods of anastomosis is generally employed:
- The "purse-string" or "whip-stitch method." In this method, a suture is sewn along the cut edge of the distal rectal stump. A similar stitch or an automatically placed purse-string suture is placed proximally along the edge of the colon to be anastomosed (Figure 3A). Both ends are tied down, gathering the bowel wall to the shaft of the intact stapler (Figure 3B), and the instrument is then closed (the cartridge and the anvil are approximated to each other) and fired (Figure 3C).
- The double-staple technique. In this method, the rectum to be resected is completely mobilized, and the point at which the rectum will be divided is determined (Figure 4A). A transverse or horizontal staple line is created by applying a linear stapler to the rectum at the chosen level for division (Figure 4B). The rectum must be cleared of all surrounding fat at this point. The rectum is divided above this staple line, and the specimen is removed, leaving the distal stump of the rectum sealed by a linear transverse staple line (Figure 4C).
The anvil from the circular stapling device is introduced into the sigmoid colon and the purse-string suture is tied down along its shaft. The cartridge of the stapling device is now introduced transanally. In contrast to the purse-string method, the cartridge is introduced without the anvil attached. Utilizing a sharp plastic spike specially designed for the purpose, the shaft is gently advanced through the apex of the rectal stump, immediately adjacent to the horizontal staple line (Figure 4D). The anvil and the cartridge are reunited, closed, and fired through the apex of the rectal stump (Figure 4E). With the firing of the instrument, the circular concentric rows of staples intersect with the horizontal row of staples (Figure 4F).
Both methods have been found to be relatively safe. The double-staple technique seems to be more applicable to higher rectal lesions, requiring a wider pelvis or a more proximal tumor in order to have room to manipulate the transverse linear stapling device.
Low Anterior Resection With Coloanal Anastomosis--Coloanal anastomosis is utilized under various circumstances (Figure 5). Technically, the coloanal anastomosis may be hand sewn via a perianal approach or it may be a stapled anastomosis situated within the anal canal anywhere between the dentate line and the anorectal junction or ring (Figures 5A and 5B).
The coloanal anastomosis may be utilized under any of the following circumstances:
- In mid-rectal cancer when a patient is oncologically suited to having a sphincter-preserving operation, but it is technically difficult or impossible to accomplish a standard anastomosis; eg, in the obese or stocky male patient with a narrow pelvis and an enlarged prostate.
- As a substitute for abdominoperineal resection of the rectum in selected early stages of low rectal cancers.
- When used in combination with radiation therapy or both chemotherapy and radiation as an experimental, protocol-based substitute for an abdominoperineal resection of the rectum.
Low Anterior Resection With J-Pouch Reservoir--In addition, a low anterior resection, with or without a coloanal anastomosis, may be combined with an anastomosis from the colon to the anus or with a small colonic J-pouch serving as a reservoir (Figure 6).
Optimally, the coloanal anastomosis will be used as a means of reconstruction when a traditional low anterior resection is technically impossible.[11,13] Paty and coworkers have reported on the oncologic results of low anterior resection with coloanal anastomosis. Rates of survival and local control at 5 years were equivalent to figures observed after standard low anterior resection.