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Sphincter-Preserving Operations for Rectal Cancer

Sphincter-Preserving Operations for Rectal Cancer

ABSTRACT: Sphincter-preserving operations represent an important model for integrating the goals of surgery for rectal cancers. These goals--the achievement of cure and local control and the preservation of autonomic visceral pelvic functions--are inherently related. Sphincter-preserving procedures are possible for patients with mid-rectal cancers (6 to 10 cm from the anal verge) and for highly selected patients with distal rectal cancers (£ 5 cm from the anal verge). Total mesorectal excision, a new concept in resection with negative circumferential margins, dramatically enhances both cure and local control. Total mesorectal excision can be combined with sphincter preservation. Perioperative adjuvant therapy protocols have been combined with sphincter-preserving operations in many investigative settings. Functional outcomes and recent survival data seem to favor preoperative over postoperative radiation therapy. The currently changing standards of surgery for rectal cancer, which result in improved local control, should enhance long-term sphincter preservation in the future. [ONCOLOGY 10(11):1673-1689, 1996]

Introduction

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.

Defining the Rectum Anatomically

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.[1]

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.

Principles of Adequate Resection

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.[2]

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.[2]

Sphincter-Preserving Operations

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.

Patient Selection

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.[10] 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:

  1. 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
    ).
  2. 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:

  1. 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.[11]
  2. As a substitute for abdominoperineal resection of the rectum
    in selected early stages of low rectal cancers.
  3. 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.[12]

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.[13]
Rates of survival and local control at 5 years were equivalent
to figures observed after standard low anterior resection.

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