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246 Mesenteric component of sigmoid colectomy
Inferior mesenteric artery
Clamping of
inferior
mesenteric
artery
(a)
(b
)
(c)
Division
Ligation
Figure 17.12 Inferior mesenteric vessel after skeletonization (a), clamping (b), division, and ligation (c).
Open mesosigmoidectomy 247
until the left mesocolon has been fully free up to the splenic
flexu e (Figure 17.13). In fact, the mesenteric component
of the splenic flexu e can also be mobilized in this manner.
Ultimately, the surgeon enters the lesser sac where he/she
will be impeded by the apposition of the greater omentum
to the cephalad aspect of flexur l and transverse mesentery.
Mobilization of the left colon proceeds as far as the
splenic exure by dividing the left peritoneal reection and
congenital adhesions. e latter can be prominent just distal
to the exure. It is usually possible at this point to insinu-
ate the ngers of the right hand underneath the splenocolic
reection and then diathermy divide the latter onto one’s
nger. is action divides the peritoneal component of
theexure. Peritonotomy exposes the underlying colo- and
mesofascial planes. Separation of planar components com-
pletes mobilization of the splenic exure.
Increasing volumes of visceral adiposity mean that omen-
tal mobilization from the transverse mesocolon and colon is
required to achieve complete mobilization of the splenic ex-
ure. To achieve this, the surgeon stands between the legs and
the patient is placed in the slight head up position. e perito-
neal reection between the greater omentum and transverse
colon is divided and adhesions between the greater omentum
and transverse colon divided (Figure 17.14). While applying
downward traction on the transverse colon/mesocolon and
upward traction on the greater omentum, separation of both
is continued laterally as far as the splenocolic reection. At
the exure, the greater omentum and splenocolic reection
Mesofascial interface between the left mesocolon and underlying fascia
Left
mesocolon
(undersurface)
Left mesocolon
(undersurface)
Mesofascial
interface
Mesofascial
interface
Mesocolic
(Toldt’s )
fascia
Mesocolic
(Toldt’s )
fascia
(b)
(a)
Figure 17.13 (See also QR 6/2.) The mesofascial interface between the left mesocolon and underlying fascia before (a) and
after (b) hemostatic mesofascial separation. In (a) the mesocolic fascia (Toldt’s fascia) is pulled up onto the undersurface
of the leftmesocolon. In (b) the fascia has been separated from the mesocolon and the latter mobilized. By repeating this
process the left mesocolon is fully mobilized.
248 Mesenteric component of sigmoid colectomy
coalesce to variable degrees. It is always possible, however,
despite this coalescence, to gently introduce the index n-
ger of the left hand beneath the splenocolic reection and
use diathermy onto one’s nger to divide the reection. In
the past, this activity was conducted via sharp dissection
and any bleeding controlled by packing at the hilum with a
swab. Fully hemostatic division of the splenocolic reection
is feasible and should invariably be the aim.
When this is completed as far lateral as possible, the
peritonotomy of the left peritoneal reection meets that of
the splenocolic reection and the peritoneal component
of exural mobilization completed. Both the colo- and
mesofascial interface are then identiable. If the colic com-
ponent of the splenic exure is retracted toward the right
iliac fossa, this transmits tension to the fascial interface
and exaggerates the latter. Sharp diathermy division allows
mesofascial separation until the colic and mesenteric com-
ponents of the splenic exure have been completely freed
from the retroperitoneum. At this point, all components
of the splenic exure (i.e., peritoneal, colic, and mesen-
teric) have been fully mobilized. One will notice that the
mesentery converges toward the root region of the superior
Omento-colic peritoneal reflection
Omento-colic
peritoneal
reflection
Greater
omentum
Transverse
colon
Peritonotomy
of omento-c
olic
peritoneal
reflection
Transverse
colon
Greater omentum
(a)
(b)
Figure 17.14 (a, b) The omento-colic reection between the greater omentum and the transverse colon.
References 249
mesenteric artery, where the middle colic artery originates.
isimpedes further mobilization.
Examination of the mobilized left mesocolon and splenic
exure will readily demonstrate the IMV, which is skeleton-
ized, clamped, and suture ligated. IMV division, coupled
with mesocolic mobilization, guarantees sucient colo-
mesenteric reach for low pelvic anastomoses such as a colo-
anal anastomosis.
e division of the mesentery in preparation of the
proximal resection margin of the intestinal tract has been
dealt with earlier in the section describing laparoscopic
mesosigmoidectomy. e division of the mesorectum has
also similarly been dealt with; however, certain additional
points should be made in relation to the open surgical
approach. Inthe fi st case, it is important to fully skeleton-
ize the mesorectum off the serosal surface of the rectum
at the level at which the anastomosis is to be conducted.
eimportance of this lies in the fact that once the rectum
has been divided the rectum and the mesorectum will retract
down into the pelvis. ereaer, the mesorectum cannot be
directly grasped, as doing this will lead to extensive bleeding.
SPECIAL CONSIDERATIONS: UNABLE
TO IDENTIFY THE CORRECT ANATOMIC
PLANE FOR MOBILIZATION
It is not uncommon, in surgery for diverticular disease or
Crohn’s disease, for the correct plane of mobilization to have
been obliterated by the pathologic process [21–23]. is fre-
quently aris es where a perforation has sealed over and brosed .
In the acute setting, one encounters this with a phlegmon (see
Chapter 7). e adhesive inammatory and brotic processes
cause a fusion of adjacent structures and the normal meso-
fascial demarcation is lost. One approach in this setting is to
temporarily ignore the region in question, identify, and mobi-
lize in the correct interface around it, and then return to the
region in question as a last step (i.e., “circling the enemy” as
described by Victor Fazio in Cleveland). is approach relies
on identication of correct planes circumferentially, which
helps in the diffe entiation of structures and usually has the
added benet of partially freeing up the area in question. e
anatomic “positional sense” provided permits a resection that
minimizes damage to adjacent structures.
Rarely, one must resect adjacent anatomic structures.
Itisimportant to have anticipated this preoperatively and
have urologic or vascular expertise available. Irrespective
of one’s level of expertise, unexpectedly encountering an
unplanned multivisceral resection is unsettling for the
surgical team and dangerous for the patient.
FUTURE DIRECTIONS
Mesosigmoidal detachment and disconnection are the
cornerstone of safe resection of the descending colon, the sig-
moid colon and proximal rectum. Standardization of thesteps
involved could help improve post-operative outcomes. As
it is unlikely that a randomized control trial will ever be
conducted to determine this, future eff rts should focus on
international standardization of the techniques involved in
open, robotic, and laparoscopic sigmoid resection.
SUMMARY
e surgical activities required in open, laparoscopic, and
robotic mesosigmoidectomy are based on mesenteric, peri-
toneal, fascial, and intestinal continuity as well as their
contiguity. e primary goals are intact mesosigmoidal
detachment and disconnection and can be achieved through
peritonotomy, mesofascial separation, mesenterotomy, and
mesenterectomy.
REFERENCES
1. Coffey, J.C. etal., Terminology and nomencla-
ture incolonic surgery: Universal application of
a rule-based approach derived from updates on
mesenteric anatomy. Tech Coloproctol, 2014.
18(9):789–794.
2. Culligan, K. etal., Review of nomenclature in colonic
surgery—Proposal of a standardised nomenclature
based on mesocolic anatomy. Surgeon, 2013.
11(1):1–5.
3. Gledhill, A. and M.F. Dixon, Crohn’s-like reaction in
diverticular disease. Gut, 1998. 42(3):392–395.
4. Hobson, K.G. and P.L. Roberts, Etiology and
pathophysiology of diverticular disease. Clin Colon
Rectal Surg, 2004. 17(3): 147–153.
5. Shelley-Fraser, G. etal., The connective tissue
changes of Crohn’s disease. Histopathology, 2012.
60(7): 1034 –1044.
6. Kredel, L.I. and B. Siegmund, Adipose-tissue and
intestinal inammation—Visceral obesity and
creeping fat. Front Immunol, 2014. 5: 462.
7. Coffey, J.C. et al., The mesentery in Crohn’s disease:
Friend or foe? Curr Opin Gastroenterol, 2016. 32(4):
267–273.
8. Coffey, J.C. etal., Mesenteric-based surgery exploits
gastrointestinal, peritoneal, mesenteric and fascial
continuity from duodenojejunal exure to the
anorectal junction—A review. Dig Surg, 2015. 32(4):
291–300.
9. Beck, D.E. etal., The ASCRS Manual of Colon
and Rectal Surgery. Springer, New York, 2014,
pp.777–786, 831–843.
10. Chand, M. etal., Laparoscopic surgery for rectal
cancer. J R Soc Med, 2012. 105(10): 429– 435.
11. Delaney, C.P. etal., Operative Techniques in
Laparoscopic Colorectal Surgery. Wolters Kluwer
Health, Philadelphia, PA, 2013, pp. 85–96, 200 –209,
217–221.
12. Karandikar, S. and S. Abbott, Open resection for
colorectal cancer. Surgery, 32(4): 190 –196.
13. Milsom, J.W. etal., Laparoscopic Colorectal Surgery.
Springer, New York, 2006, pp. 145–169.
250 Mesenteric component of sigmoid colectomy
14. Beraldo, S. etal., The prophylactic use of a ureteral
stent in laparoscopic colorectal surgery. Scand
JSurg, 2013. 102(2): 87–89.
15. da Silva, G., M. Boutros, and S.D. Wexner,
Roleofprophylactic ureteric stents in
colorectalsurgery. Asian J Endosc Surg, 2012.
5(3):105–110.
16. Speicher, P.J. etal., Ureteral stenting in
laparoscopic colorectal surgery. J Surg Res, 2014.
190(1): 98–103.
17. Culligan, K. etal., The mesocolon: A prospective
observational study. Colorectal Dis, 2012. 14(4):
421–428; discussion 428–430.
18. Coffey, J.C. et al., Mesenteric-based surgery exploits
gastrointestinal, peritoneal, mesenteric and fascial
continuity from duodenojejunal exure to the anorec-
tal junction—A review. Dig Surg, 2015. 32(4): 291–300.
19. Culligan, K. et al., The mesocolon: A prospective
observational study. Colorectal Dis, 2012. 14(4):
421–428; discussion 428–430.
20. Mimica, Z. etal., Effect of surgical incision on pain
and respiratory function after abdominal surgery:
Arandomized clinical trial. Hepatogastroenterology,
20 0 7. 54(80): 2216–2220.
21. Johnson, E.K. and B.J. Champagne, Diverticular
disease and the obese patient. Clin Colon Rectal
Surg, 2011. 24(4): 253–258.
22. Abcarian, H. and R.K. Pearl, A safe tech-
niqueforresection of perforated sigmoid
diverticulitis.DisColon Rectum, 1990. 33(10):
905–906.
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187–193.
251
18
Mesenteric component of rectal resection
J. CALVIN COFFEY AND JONATHON EFRON
A plane is the interface between two contiguous
surfaces.
Bill Heald
AIM
e aim is to demonstrate the mesenteric and peritoneal
principles of total mesorectal excision of the rectum.
INTRODUCTION
e terminology total mesorectal excision (TME) is
relatively recent and denotes removal of the entire
mesorectum. Implicit in the terminology is a complete
mesenterectomy (and removal of the rectum) in a manner
that ensures an intact mesorectal package. Although the
terminology partial mesorectal excision is not as widely
applied, this modication of “total mesorectal excision”
implies adoption of the same principles (i.e., the mesen-
tery is maintained intact, until one reaches a predeter-
mined level of transection). “Total mesorectal excision”
is gradually substituting the terminology “anterior resec-
tion” in Europe but not in North America, where the term
proctosigmoidectomy is mostly used. “Anterior resection”
historically replaced the terminology “posterior resec-
tion” as earlier approaches to the rectum involved a pos-
terior parasacral approach [1–4].
ANATOMY
e rectum is a continuation of the colon and hence intestinal
tract. In keeping with this, it is suspended during embryo-
logic development via the dorsal mesentery [5,6]. Inthe adult,
the mesorectum is a downward extension of the mesentery
and the apex of the mesorectum is the termination of this
extension. At a macroscopic level, the mesorectum is bulky
posterolaterally with a slight gully in the posterior midline.
Collectively, these features generate a contoured appearance.
In most individuals, the mesorectum continues around the
lateral aspect of the rectum to reach the anterolateral and
anteromedial aspects of the latter. At the anteromedial and
lateral aspects, it is reduced in bulk. Anterolateral and medial
mesorectal bulk correlates with the patient’s level of obesity,
being negligible in thin individuals. In the obese, the meso-
rectum extends around the anterolateral and medial aspect
of the rectum to meet (but not fuse) in the midline. ese
anatomic relationships can be conrmed using the Visual
Human Project (VHP) in which the full color data set enables
one observe structures as one might in a cadaver [2,7–10].
One can then reconstruct these in a 3D format (Figure 18.1).
In this manner, the mesorectum can be delineated in its
undisturbed format (Figure 18.1). e value of this lies in
the fact that once mobilized, the fatty mesorectum adopts a
conformation that has very little resemblance to that which it
had insitu. Inall individuals, the mesorectum tapers toward
the anorectal junction.
Aim 251
Introduction 251
Anatomy 251
Mesenteric principles of total/partial mesorectal
excision 254
Technique: Laparoscopic/Robotic 255
Open total or partial mesorectal excision 264
Video recording of open mesorectal excision 264
Techniques 264
Special considerations: Coloanal anastomosis 273
Special considerations: Mesorectal obesity in a
narrow male pelvis 273
Future directions 275
Summary 275
References 275
252 Mesenteric component of rectal resection
e mesorectum is separated from the posterior and lat-
eral pelvic sidewall by Toldt’s fascia. is is a continuation of
the fascia that separates the entire mesocolon from the retro-
peritoneum. Several terms are used interchangeably for Toldt’s
fascia in this region. ese include mesorectal fascia, visceral
pelvic fascia, Waldeyer’s fascia, and endopelvic fascia[3,4].
Outside Toldt’s fascia, a further fascial layer overlies the bony
pelvis (i.e., the parietal or presacral fascia). In the distal pel-
vis, and at the level where the mesorectum ends, Toldt’s fas-
cia condenses into what is referred to as Waldeyer’s fascia.
is occupies the space created between the termination of
the mesorectum and the surrounding pelvis. Toldt’s fascia
Development of digital model of mesorectum
Visible human project (VHP)
(a)
Point cloud
derived from VHP
(b)
3D digital model
Cavity where
rectum has
been removed
Anterior
mesorectum
Distal mesorectum
Upper mesorectum
(c)
Upper mesorectum
Posterior mesorectum
3D digital model
sagittal section
Anterior
mesorectum
(d)
Figure 18.1 Panel demonstrating (a) the mesorectum as seen in the full color dataset of the Visual Human Project.
(b)Points can be placed around the mesorectum in each plane, within the Visual Human Project. Collectively they gener-
ate a “point cloud” as demonstrated here. (c, d) The point cloud can be imported into a digital sculpting environment to
generate a 3D digital sculpture. As this is digital it can be sectioned to present any view required.
Anatomy 253
is readily identiable posterior to the mesorectum where
it isareolar in appearance and has been aptly described as
“angel hair.” e fascia is a distal continuation of the meso-
sigmoidal fascia (i.e., Toldt’s fascia beneath the attached
component of the mesosigmoid) (see earlier). Laterally, and
anteriorly, the fascia is more dicult to identify, where, due
to pressure eff cts arising between the mesorectum and
surrounding pelvis, it is attenuated. In addition, the meso-
rectum becomes densely attached to the lateral pelvic side-
wall, in what is increasingly referred to as the T zone (or
zone of adherence). Here, the anatomy of the fascia is poorly
characterized [3,4]. e fascia is disrupted at the zone of
adherence, but regathers around it.
As mentioned in previous chapters, in the pelvis the
fascia is areolar in nature and certainly less dense than
elsewhere. An exception occurs in the distal pelvis where
it condenses as Waldeyer’s fascia. In some individuals, an
anatomic space occurs in the very distal reaches of the rec-
tum, just above the pelvic oor.
e upper rectum is covered anteriorly and laterally
(but not posteriorly) by peritoneal reections. e right
and left pararectal reections are a distal continuation of
reections associated with the mesosigmoid (Figure 18.2).
e left lateral mesosigmoidal reection continues distally
as the left pararectal reection. e right lateral mesosig-
moidal reection continues distally as the right pararectal
reection. Both meet in the anterior midline where the
peritoneal reection marks the anatomic end point for the
peritoneal cavity (Figure 18.2). Debate persists in relation
to peritoneal anatomy at this point. Denonvilliers’ fascia
refers to the caudal extension of the peritoneal reection
from the anterior midline. e fascia (where present) overlies
the anterior mesorectum and extends distally for a variable
distance. It is interposed between the anterior mesorectum
(posteriorly) and the fat posterior to the seminal vesicles,
vas deference, and prostate. As Denonvilliers’ fascia is not
an anatomic constant, it is likely to continue as a source
of debate for colorectal surgeons and anatomists [11–13].
Notwithstanding this, there is always a plane between semi-
nal vesicles/prostate anteriorly and mesorectum posteriorly.
As is the case for the mesofascial plane in general, this plane
is comprised of an areolar and attenuated fascia posteriorly,
with seminal vesicles and prostate located anteriorly.
Controversy also occurs in relation to the lateral ligaments
in which the middle rectal artery is classically described as
conveyed to the mesorectum. e experience of many is
not consistent with this nding as oentimes (though not
invariably) one is able to separate the mesorectum from the
lateral pelvic side wall until a zone of “adherence” is identi-
fi d anterolaterally. e latter is variable in position and
vertical extent and corresponds to the “T” zone described
by some authors. “Lateral ligaments” are not apparent when
Rectum
(a)
Left
pararec
tal
peritoneal
re˜ec tion
Sigmoid colon
Right
pararectal
peritoneal
re˜ec tion
Anterior
peritoneal
re˜ec tion
Pararectal peritoneal re˜ec tions
Figure 18.2 (See also QR 2d/5-7.) The pararectal peritoneal reections. (a) Digital imagery demonstrating the right and left pararec-
tal reections and the manner in which these coalesce in the anterior midline as the peritoneal reection in the pouch of Douglas.
(Continued )
254 Mesenteric component of rectal resection
the mesorectum is examined in the Visual Human Project
[2,7–10]. Examination of most cases of laparoscopic mobiliza-
tion of the mesorectum demonstrates absence of lateral liga-
ments and shows how circumferentia l mobiliz ation is possible
so long as one adheres to embryologic and anatomic planes.
Although this is consistent with the absence of an embryo-
logic precursor for these, it does not explain the manner in
which the middle rectal artery, where present, gains access to
the mesorectum. On the other hand, contemporary studies
suggest that the middle rectal artery is infrequently present
[14,15]. In addition, recent studies suggest that the zone of
adherence is a region where the mesorectum is tangentially
approached by nerves and vessels, which then gain access to
the mesorectum. e “zone of adherence” (or T zone), where
vessels and nerves tangentially approach and gain access to
the mesorectum, was previously termed a “ligament.”
In the female, the rectum is separated anteriorly from the
vagina by the rectovaginal septum. In general, this is com-
prised mainly of connective and adipose tissue and can be
quite vascular.
Many of the controversies related to rectal and mesorec-
tal anatomy may be resolved using the Visual Human Project
[7,8,16]. As mentioned earlier, the full color version of the
VHP permits identication and characterization of the meso-
rectum in the undisturbed state in both the male and female.
When this utility is adopted in evaluating mesorectal anat-
omy, a structure is apparent posterior to the seminal vesicles
and prostate, and anterior to the rectum. is may represent
Denonvilliers’ fascia. However, lateral rectal ligaments are
not apparent. Although appearances on the VHP cannot be
extrapolated to the general population, they can be correlated
with corresponding magnetic resonance (MRI) and comput-
erized axial tomographic (CT) images [9]. e latter can in
turn be compared with corresponding MRI and CT imagery
in general. is represents an avenue for future study and may
provide denitive answers in relation to both Denonvilliers’
fascia and the lateral rectal ligaments [2,9,10].
MESENTERIC PRINCIPLES OF TOTAL/
PARTIAL MESORECTAL EXCISION
In the following, we will describe the mesenteric principles
of the laparoscopic/robotic and open mesorectal excision
for both male and female.
Preoperative multidisciplinary assessment is of primary
importance in total or partial mesorectal excision (TME or
PTME). e mesofascial interface is radiologically identi-
able and provides an important anatomic landmark for sur-
gical planning. Extension of pathology beyond the interface
is signicant both technically and oncologically. If extra-
mesorectal extension occurs in the posterior midline, it may
be feasible to resect the sacrum beyond S2 but not proxi-
mally. If extension occurs into the lateral pelvis, this may be
unresectable outside settings where vascular, urologic, and
orthopedic supports are available. Vascular support may be
required to control external and internal iliac vessels, while
urologic support is required to safeguard or reconstruct
structures as appropriate. Anterior extension of pathology
can be dealt with more readily albeit with a multivisceral
resection. In keeping with this, it may be necessary to excise
(b)
Left
pararec
tal
re˜ec tion
Uterus
Anterior
re˜ec tio
n
Right
pararec
tal
re˜ec tion
Rectum
Figure 18.2 (Continued ) The pararectal peritoneal reections. (b) Robotic view of the pararectal and anterior peritoneal
reections. The uterus is held anteriorly thereby providing unimpeded access to the pararectal reections and underlying
mesofascial planes.
Technique: Laparoscopic/Robotic 255
the posterior wall of the bladder or vagina. Involvement of
the membranous urethra, prostate, or seminal vesicles may
require a pelvic exenteration. It is always best if extra- mesorectal
extension is identifi d preoperatively and appropriate sup-
port measures put in place at the outset, rather than discov-
ering these intraoperatively. As a result, the plane formed
by the mesorectum and mesorectal fascia (i.e., Toldt’s fascia
within the pelvis) is of considerable clinical signicance.
e principles of preparing the operative fi ld to maximize
mesenteric access are detailed in the preceding chapter but will
be reemphasized here. In laparoscopic and robotic surgery cor-
rect port placement is essential to permit access to the distal
pelvis and ensure that an intact and extensive mesenterectomy
is technically feasible. Most place ports as they might for total
or partial mesosigmoidectomy, that is, 10/12mm port in the
right lower quadrant, 5mm port in the right upper quadrant,
and 5mm port in the left lower quadrant to further assist in
retraction. Although a 30° lens is preferable, it is not essential.
TECHNIQUE: LAPAROSCOPIC/ROBOTIC
e operation commences as one would a mesosigmoidec-
tomy (see Chapter 17) with mesosigmoidal mobilization. e
steps will be briey summarized here. e rst stage of meso-
sigmoidectomy involves mobilizing the adipovascular pedicle
of the inferior mesenteric artery (IMA) within the mesosig-
moid (Figure 18.3). Next, left mesocolic mobilization is com-
pleted up to and including the splenic exure (Figure 18.4).
is ensures the colon and mesocolon have been mobilized
from the origin of the middle colic adipovascular pedicle to
the rectosigmoid level. Although some do an extensive mobi-
lization as routine, that is not an absolute prerequisite (Figure
18.4). It does however guarantee sucient reach for a distal
anastomosis, and it simultaneously provides a valuable edu-
cational and practical opportunity for the trainee.
e mesorectal dissection is commenced by dividing the
pararectal peritoneal reection on either side of the meso-
rectum (Figure 18.5). e mesothelium of this reection is
then grasped and retracted using an atraumatic grasper. It is
important not to grasp mesorectum directly as this leads to
bleeding that obscures the operative fi ld and can be limiting.
By grasping the peritoneal mesothelium with an atraumatic
device, one can generate traction toward the pelvic side wall.
Countertraction on the mesorectum places the mesorectal
plane under stretch, thereby exaggerating interface compo-
nents (Figure 18.6). e surgeon then dissects through the fas-
cia, sweeping it forward toward the mesorectum, ensuring an
intact mesorectal package. It is feasible, technically, to deect
the mesorectum in diffe ent directions using the opened jaws
of the atraumatic grasper. Some use the suction apparatus to
achieve this to good eff ct. At no point should one directly
grasp the mesorectum as it will bleed (Figure 18.6).
Once le-sided and posterior mobilization have been
competed as far distally as possible, right-sided mobiliza-
tion commences via peritonotomy of the right pararectal
reection (Figure 18.7). e interface between mesorectum
and fascia becomes apparent, and the combination of lateral
traction on pelvis, and medial traction on the rectum, keeps
the interface under stretch. e rectum/mesorectum is then
deected anteriorly and the plane of dissection between
Mesosigmoidal mobilization
Peritonotomy of
medial aspect of
mesosigmoid
Peritoneal reflection at
right medial aspect of
mesosigmoid
Mesosigmoid
Peritonotomy
Sigmoid colon
(a) (b)
Figure 18.3 Mesosigmoidal mobilization. (a) Robotic view of the peritonotomy through peritoneum at the rightside of the
mesosigmoid. The mesosigmoid has been retracted away from the posterior abdominal wall to emphasize the groove in the
peritoneal reection. (b) (See also QR 2/11.) Corresponding digital image demonstrating the peritoneal, mesenteric, and
facial regional anatomy. In this image, the mesosigmoid has not been retracted away from the posterior abdominal wall but
instead is in its usual position. This demonstrates the orientation of the peritonotomy created. (Continued )