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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_699_Библиотеки_им_академика_М_И_Перельмана.pdf
Radiographic appearance of the
mesenteryandperitoneum
J. CALVIN COFFEY AND MARTIN SHELLY
8
Aims 109
Introduction 109
History of mesenteric imaging 109
Reappraisal of the radiologic appearance of the
mesentery andperitoneal reection 110
Difculties encountered in establishing aradiologic atlas 110
Recent advances permit generation of avalidated
atlas of mesenteric and peritoneal radiology 110
The Visual Human Project: Collating fullcolor and
radiologic images 110
Learn to see things as they really are, not as
weimagine they are.
Vernon Howard
AIMS
e rst aim is to summarize the historical development
of the eld of mesenteric and peritoneal reection radiology. e second aim is to present an atlas of the radiologic
appearance of the mesentery and associated peritoneal
reection, based on recent developments in our understanding of their anatomy.
INTRODUCTION
Radiologic investigation is a noninvasive means of visualizing structures. It is a key adjunct in the diagnosis and
management of diseases. Given recent developments in our
understanding of mesenteric and peritoneal reection anatomy, it is important to reappraise the radiologic appearance
of these in normality and disease states.
e radiologic appraisal of intraperitoneal or intra-
abdominal structures is invaluable in the assessment of
intra-abdominal diseases. e development of computer
tomography (CT) and magnetic resonance (MR)–based
imaging modalities transformed abdominal imaging
OsiriX: Enhancing visualization and model generation 112
Point cloud 112
Reference atlas 116
Implications for the radiologic appraisal of abdominal
disease 117
Future studies: Assembling a comprehensive model
of abdominal anatomy 117
Summary 117
References 117
generating real-time snapshots of structures inside and outside the intestine. For decades, the emphasis in abdominal
imaging was delineation of the intestinal tract itself using
contrast-based techniques. With CT and MR and the collation of axial, sagittal, and coronal views, extra-intestinal
structures could be identied and reconstructed to provide
an improved appraisal of diseases [1]. It is interesting that
despite this renaissance in noninvasive imaging, the resolution of fatty structures has remained relatively underdeveloped even to the present.
HISTORY OF MESENTERIC IMAGING
With the development of CT- and MR-based imaging
modalities, radiologists realized that the appearances of
mesenteric regions were dicult to reconcile with prevailing anatomic teaching. As classic interpretations of mesenteric anatomy emphasized a discontinuous and fragmented
structure, it is not surprising that this was described as a
complex eld [2,3]. e current and simpler principle of
mesenteric anatomy, which emphasizes continuity throughout, is a recent development and has yet to penetrate the
general body of radiologic literature [3–9].
In 1982, Oliphant proposed that the CT appearances of
the mesentery could be explained by a continuity between
mesentery and retroperitoneum (Figure 8.1) [10]. e retro-
peritoneum was called “the posterior central core” and the
109
110 Radiographic appearance of the mesenteryandperitoneum
sim
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lt
ghl
anorectal junction (Figure 8.3a and b) [4,5]. Crucially, it fans
out from a root region at the SMA origin, to span the entire
intestine from duodenum to anorectal junction. Although it
attaches to the retroperitoneum in several regions, it remains
separated from this by Toldt’s fascia. While a vascular continuity occurs at the superior and inferior mesenteric vascular
pedicles, there is no adipose contiguity [3,6,25–28].
gsl
dcl
im
Figure 8.1 Schematic illustration of the subperitoneal space
and posterior abdominal core, as described by Oliphant.
pcl
tm
srl
continuous space called the “subperitoneal space of Oliphant.”
Several publications emerged, which adapted this concept
tothe CT appearance of intra-abdominal pathology [11–17].
In 1986, Willie Dodd commented on how the CT appraisal
of intra-abdominal pathology was dicult to reconcile with
anatomic concepts [18]. He presciently suggested that CT
appearances may be better understood by considering the
mesenteric organ as fully outside the retroperitoneum (i.e.,
extra-retroperitoneal) (Figure 8.2). Although this suggestion
resonated with the earlier anatomic descriptions of Carl Toldt
(see Chapter 1), there was little uptake of this concept [19].
In 1993, Charnsangavej etal. reappraised the radiologic
appearance of the mesocolon using vascular markings to
identify separate mesocolic regions [20,21]. is greatly
simplied identication of mesocolic segments in normality
and disease states. e practicality of this approach led to its
widespread adoption [20–23]. However, they did not reconcile radiologic appearances with then prevailing concepts of
mesocolic anatomy. In the most recent review of the topic,
Ramachandran etal. commence their review by stating that
the radiologic appearance of the mesentery and peritoneal
reections remains a dicult eld [24]. eir interpretation
of the mesentery is based on classic interpretations of mesenteric anatomy (i.e., the mesentery is discontinuous).
Recent anatomic ndings (see Chapter 2) resonate with
the suggestions of Dodd and Toldt, that is, the mesocolon
persists throughout its length into adulthood as an entirely
extra-retroperitoneal organ [18]. As is seen in the preceding
chapters, Culligan etal. demonstrated, using a combination
of dierent investigatory modalities, that the adult mesentery is continuous from the duodenojejunal exure to the
REAPPRAISAL OF THE RADIOLOGIC
APPEARANCE OF THE MESENTERY
ANDPERITONEAL REFLECTION
Difculties encountered in establishing
aradiologic atlas
Ideally, for radiologists to interpret the radiologic appearance of the mesentery, a reference atlas should be developed,
which collates anatomic and radiologic images. Several factors hampered the development of one such atlas for the
mesentery. First, the shape of the mobilized mesentery bares
little if any resemblance to that occupied in the undisturbed
state. As a result, it is impossible to infer mesenteric shape
from resected specimens. In turn, this has implications for
related structures such as the peritoneal reection.
Second, the fascia separating the mesentery from underlying retroperitoneum is exquisitely thin (see Chapter 5) and
thus subject to obliteration during xation processes. In addition, the resolution of current imaging is such that the fascia
is extremely dicult to identify in nonpathologic settings.
Finally, as the boundary of the mesentery is mesothelial,
it is not possible to identify it on current CT or MRI images.
is in turn means that it is dicult to dierentiate mesocolic from small intestinal mesenteric regions of the mesenteric organ. If one is overlying the other, then one cannot
determine where the interface between both occurs.
Recent advances permit generation
of avalidated atlas of mesenteric and
peritoneal radiology
Fortunately, a number of recent advancements converged to
permit development of a reference atlas for mesenteric radiology. ese include digitalization of radiologic imagery,
the Visual Human Project (VHP), and the development of
sowares that permit 3D reconstruction (e.g., OsiriX) [28].
e combination of these facilities, with recent advances in
mesenteric anatomy and histology, has enabled the development of the rst, validated reference atlas of mesenteric
and peritoneal radiology. Before describing this atlas, the
instruments involved in its generation will be described.
The Visual Human Project: Collating
fullcolor and radiologic images
Key in the development of a reference atlas was identifying
an archive in which cadaveric anatomy (in the undisturbed
Mesenteric root region
(a)
Vasculature on CT at mesenteric root region Higher-magnification view of mesenteric root region(c) (d)
Reappraisal of the radiologic appearance of the mesentery andperitoneal reection 111
Retroperitoneum
Aorta
Mesenteric
root region
Superior
mesenteric
artery
Retroperitoneum
(b)
Mesenteric
root region
Figure 8.2 (a) Axial section through the full color male dataset of The Visual Human Project at the level of the origin of
the superior mesenteric artery (SMA). The mesentery converges on (or diverges from) the SMA root. Otherwise, a direct
mesenteric continuity does not occur with the retroperitoneum. Importantly, this (the “root region”) is the origin of the
mesenteric organ distal to the fourth part of the duodenum. (b) Wider eld view of the same region as in (a) demonstrating the relationship of the mesenteric root region to adjacent structures. Coronal computerized axial tomographic illustration of the root of the mesentery under low (c) and high (d) magnication, respectively.
112 Radiographic appearance of the mesenteryandperitoneum
(a) (b)
The mesenteric organ
Mesentery and intestine
Figure 8.3 2.5D snapshots of 3D digital sculpture demonstrating the mesenteric organ and associated intestine distal to
the SMA root region. (a) (See also QR 1/1.) Mesentery and intestine. (b) Mesentery without intestine.
state) could be collated with CT-based imaging. e VHP
is a remarkable archive that permits this form of collation
[29–31]. e VHP is housed at the U.S. National Library of
Medicine and is a digital archive of human anatomy derived
from cryosectioning of a male and female cadaver [32]. Full
color photographs are available of each cryosection and
stored at a pixel resolution that permits identication of
subtle fascial planes and peritoneal reections. As these are
full color photographs, it means that mesenteric, mesocolic,
peritoneal, and fascial structures can be observed as one
might in a cadaveric dissection. Crucially, however, they
occur in the undisturbed and insitu state.
e scale of the opportunity represented by the VHP
increases further given the provision of corresponding
axial CT and MRI images (Figure 8.4a through c). As a
tissue leaving all remaining fascia, vessels, and peritoneal
reections (Figure 8.5). Serial axial sections can then be
stacked conceptually to generate a complete 3D model corresponding to the invivo mesentery, associated fascia, and
peritoneal reections. is is invaluable in demonstrating
insitu and undisturbed mesenteric, fascial, and peritoneal
anatomy in general.
By way of example, this process has been applied to
demonstrate the region where the small intestinal mesentery continues laterally as right mesocolon (Figure 8.5).
is region was rst identied in the VHP and then on the
corresponding CT image. CT images were next imported
into OsiriX. In the later, all mesenteric fat was conceptually
subtracted to retain only the associated vessels, peritoneal
reection, and underling fascia [7].
Mesentery without intestine
result, if one identies a particular structure in full color
images, then one can identify the same structure in the corresponding CT and MRI images. e VHP thus provides a
unique and invaluable opportunity to develop a CT-based
(or MRI-based) reference atlas of mesenteric anatomy and
radiolog y [7,31].
Point cloud
Nonexural mesenteric regions (i.e., the le and right
mesocolon) are readily identiable in the VHP. Flexural
regions (i.e., ileocolic, hepatic, splenic, sigmoid, and rectosigmoid) are more dicult to interpret. is diculty
OsiriX: Enhancing visualization and model
generation
can be overcome using a “point cloud”–based approach.
First, in the VHP, boundaries of the mesentery are demarcated by a series of points. is is repeated for serial images
e data contained in the VHP digital imagery are such
that once imported into soware such as OsiriX (Pixmeo,
Switzerland), then the corresponding axial, coronal, and
sagittal images can be generated from full color, CT, and
MRI datasets (Figure 8.4) [28,33]. e versatility of OsiriX
is considerable and by utilizing a custom lookup table
(i.e.,CLUT), one can articially subtract mesenteric adipose
in the axial, coronal, and sagittal views, and the overall
point cloud is imported into a soware to “join the dots”
and create a 3D shape (Figure 8.6). e resultant model
is in a digital format, which means it can be imported
into a range of soware such as Cinema 4D, Z-Brush, and
OsiriX. e model can also be used to generate 3D printed
models of the mesentery [7,28,34].
Reappraisal of the radiologic appearance of the mesentery andperitoneal reection 113
Toldt’s fascia and peritoneal reflection
Retroperitoneum
(a)
(c)
Toldt’s fascia
Left mesocolon
Retroperitoneum
Peritoneal reflection
Toldt’s fascia
Left mesocolon
Toldt’s fascia
Retroperitoneum
Left
peritoneal
reflection
Left mesocolon
Figure 8.4 (a) Axial view of left mesocolon as seen in full color version of the visual human project. (b) Corresponding
appearance on the computerized tomographic section at the same level and (c) image in OsiriX. In the OsiriX image, the
fat has been removed, leaving only the peritoneal reection for visualization. When axial images are stacked in OsiriX,
then a 3D model of the reection is apparent. This is the left peritoneal reection.
114 Radiographic appearance of the mesenteryandperitoneum
Small intestinal mesentery(c)
Mesenteric regions
Right mesocolon
Small intestinal mesentery Small intestinal mesentery(b)(a)
Right mesocolon
Left mesocolon
Right mesocolon
Left mesocolon
Figure 8.5 Panel demonstrating (a) region of continuity between small intestinal mesentery and right mesocolon in the
visual human project (VHP), (b) corresponding appearance on computerized tomographic imaging in the VHP and
(c)corresponding appearance once (b) has been imported in OsiriX.
Reappraisal of the radiologic appearance of the mesentery andperitoneal reection 115
Point cloud
derived from point cloud
(c)
Development of 3D printed model of mesorectum
g
CT appearance of mesorectum
(a)
3D digital print
of mesentery and
intestine
Corresponding appearance of mesorectum
Points around
mesorectal margin
Extraction of all
points as point cloud
(b)
Points correspondin
3D digital sculpture
to above
Figure 8.6 Flow chart demonstrating the process whereby (a) the mesentery is outlined in the visual human project,
(b)theoutline (in point format) is exported in the form of a point cloud, and (c) a 3D model of the mesorectum is
developed from the point cloud.
116 Radiographic appearance of the mesenteryandperitoneum
(c)
(a)
Flexures
REFERENCE ATLAS
Using the soware and archive described earlier, we
recently developed a reference atlas for the CT appearance
of the mesentery, as well as associated fascia and peritoneal reections. e atlas refers to the mesentery from the
duodenojejunal level to the junction between the rectum
and anus. Each panel includes (1) a full color image (highlighting either exural or nonexural mesentery, underlying fascia, and associated peritoneal reection) and (2) the
Hepatic flexure
corresponding CT image. is enables the viewer to identify, within the CT, the shapes corresponding to mesentery,
fascia, and peritoneum [7].
To test the utility of this atlas, we determined rates at
which exural and nonexural mesentery could be identied in normality. Radiologists rst examined the atlas and
then serially reviewed abdominal CT scans, which were
known to lack intra-abdominal pathology. Regions corresponding to exural and nonexural mesentery were consistently identiable in all patients (Figure 8.7a throughd).
Hepatic flexure
(b)
Splenic flexure
Figure 8.7 Images taken from the reference atlas of mesenteric radiology. (a) Right mesocolon (coronal view). This is
a nonexural region of the mesocolon (i.e., the mesocolon is attached to the retroperitoneum). (b) The hepatic exure
(axial view). The right mesocolon, hepatic exure, and transverse mesocolon are seen. Continuity is apparent between all
three. (c) Splenic exure (coronal view). The transverse and left mesocolon are evident as is the exural region interposed
between both (i.e., the splenic exure). (d) Left mesocolon on axial view.
Splenic flexure(d)
References 117
e rate of identication of exural and nonexural regions
of the mesentery increased as one proceeded distally from
the ileocecal to the mesosigmoidal and mesorectum
level[7].
Ideally, all mesenteric (exural and nonexural) regions
should be identiable in all patients. is did not hold in the
study in question and while there was good general agreement between radiologists, there was discordance in a considerable proportion of cases. Future studies should aim to
improve the rates of identication of exural and nonexural
regions based on current anatomic appraisals. is should
initially be conducted in states of normality (prior to proceeding to disease states) and could employ the reference as a
guide to identication of exural and nonexural regions [7].
IMPLICATIONS FOR THE RADIOLOGIC
APPRAISAL OF ABDOMINAL DISEASE
ere are several implications for the developments
described above. In the rst instance, the reference atlas
generated provides a standard that should aid radiologists
in identifying separate mesenteric regions from the SMA
origin to the anorectal junction. It remains to be validated
in this context. By better identifying normality, one can
improve the radiologic appraisal of abnormality. In keeping
with this, the eects of benign and neoplastic processes may
be better staged by taking into account the manner in which
they aect the mesentery, underlying fascia, and adjacent
peritoneal reections.
FUTURE STUDIES: ASSEMBLING
A COMPREHENSIVE MODEL
OFABDOMINAL ANATOMY
The ability to reliably identify mesenteric, fascial, and
peritoneal structures on standard abdominal CT enables
one assemble a highly accurate and comprehensive
model of intra-abdominal anatomy in the undisturbed
state. For example, the mesentery (once correctly delineated) could serve as a starting point around which retroperitoneal, omental, intestinal, fascial, and peritoneal
structures can be assembled. It would then be a simple
matter to digitally add or subtract components to the
resultant model.
is process could then be repeated in disease settings.
If pathology were present, then it would be feasible for the
radiologist to generate a 3D reconstruction of the intestine,
associated mesentery, retroperitoneum, and greater omentum (and other structures). He or she could then sequentially subtract individual structures to better demonstrate
the 3D features of the pathology in question. In the rst
instance, this would be an invaluable educational tool. In
addition, however, it would also represent a clinical utility
as it would facilitate planning of interventional radiologic
procedures such as the drainage of an abscess or obtaining
tissue for biopsy.
SUMMARY
e radiologic appearance of the mesenteric organ distal
to the duodenojejunal exure requires reappraisal in view
of recent clarications in structure. In completing one
such appraisal on the CT appearance, a radiologic atlas
was developed for reference in normality. is provides a
reference against which the radiologic appearance of intraabdominal disease can be compared. Future studies should
aim to interpret the appearance of intra-abdominal disease
based on comparisons with this standard.
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