Peritoneum
The peritoneum is the extensive serous membrane
that, in general, lines all borders of the abdominopelvic cavity and reflects
from the body wall onto the organs that are contained within it. A general
concept that one might have of the pleura or the serous pericardium can be
carried over to the peritoneum. In all of these situations, the serous membrane
lining the body wall is continuous with that on the surfaces of the viscera contained
within the portions of the body cavity involved, and although one refers separately
to parietal and visceral portions of the serous membrane, they are continuous.
Also, under normal circumstances, the organs fill the respective portion of the
body cavity so completely that the visceral and parietal portions of adjacent
structures are separated from each other by only a thin film of fluid. The
peritoneal cavity of the female is the only place where an organ’s lumen is in
direct contact with the peritoneal space, as the opening of each uterine tube
is open to the peritoneal cavity.
The peritoneum is much more complicated in its arrangement than either
the visceral pleura or the serous pericardium. This is essentially due to the
fact that parts of several viscera deform the peritoneal serous membrane to
various degrees in the course of fetal development. The rotations of the gut,
combined with the propensity of one free peritoneal surface to fuse with
another free surface, result in complex changes of the arrangement that lead to
the mature appearance of the abdominal organs. The stomach (to cite only one
example of the manifold rearrangements in the visceroperitoneal relations) in
its primary vertical position was attached by one double layer of peritoneum,
the ventral mesogastrium, to the ventral body wall, and by another double
layer, the dorsal mesogastrium, to the posterior wall. When the stomach
rotated, its original left side became the anterosuperior surface and the
original right side the posteroinferior surface; the dorsal mesogastrium was
swept toward the left to form an outpouching of the peritoneal cavity, which
presents itself at an early developmental stage (6 weeks) as the omental bursa
(lesser sac), communicating with the rest of the peritoneal cavity (greater
sac) by only a small opening, the omental foramen (of Winslow), located a
little to the right of the midline posteroinferior to the liver.
The best way to obtain a general concept of the arrangement of the
peritoneum is to trace it in three planes, a midsagittal plane and two
horizontal planes, one at the level of the pylorus and the other at the level
of the umbilicus, in a preferably fresh specimen at the autopsy table. Lacking
this opportunity, the use of these three planes still remains methodically the
most informative approach for
studying the peritoneal continuity and its relationship to the abdominopelvic
viscera.
In the midsagittal plane, the greater and lesser peritoneal sacs must be
pursued separately, because they are not continuous anywhere in this plane. In following
the cut edge of the greater sac, one can start with the parietal
peritoneum on the inner surface of the anterior wall at the level of the
umbilicus. Progressing superiorly, the peritoneum
continues onto the inferior surface of the diaphragm and along it until
it is reflected to the liver as the superior (anterior) layer of the left
triangular ligament. From here it extends along the anterosuperior surface
of the liver, around the free margin of the liver, and onto its visceral
surface, until it is reflected toward the lesser curvature of the stomach as
the anterior layer of the lesser omentum, which then advances onto the
anterior surface of the stomach, leaving the latter as the anterior surface of the greater omentum.
At the free margin of the greater omentum, this layer turns superiorly to
become the posterior surface of the greater omentum, which proceeds superiorly
to the transverse colon, where it appears to continue onto the posterior
surface of the transverse colon and then as the posterior layer of the transverse
mesocolon. From the posterior layer of the transverse mesocolon, the peritoneum
turns interiorly from the lower border of the pancreas across the
anterior surface of the third portion of the duodenum and becomes the
right (superior) layer of the intestinal mesentery. At its free margin the
mesentery entirely (except for the area of mesenteric attachment) surrounds the
small intestine and continues to the posterior body wall as the left (inferior)
layer of the mesentery. On reaching the body wall, it runs as the parietal
peritoneum of the posterior wall interiorly on the anterior surface of the
aorta and then on the vertebral column to about the second sacral level, where
it comes to lie on the anterior surface of the rectum, from which, in the male,
it is reflected onto the posterosuperior surface of the bladder, bounding the rectovesical
pouch. In the female, the peritoneum passes from the anterior surface of the rectum to the posterior vaginal
fornix, bounding the rectouterine pouch (of Douglas). It passes up the
posterosuperior aspect of the uterus, over the fundus of the uterus, and down
on its anteroinferior aspect to about the junction of the body and cervix, from
whence it reflects onto the posterosuperior aspect of the bladder, bounding the
vesicouterine pouch. In both the male and the female, the peritoneum passes
from the superior surface of the bladder to the inner surface of the
anterior body wall, a variable distance above the symphysis pubis, depending on
the degree of distention of the bladder. From here it continues superiorly to
the point at which this tracing of the peritoneum was started.
In following the cut edge of the omental bursa’s peritoneum in a
midsagittal plane, a start can be made on the anterior surface of the pancreas,
and the peritoneum can be traced superiorly from here onto the surface of the
diaphragm until it reflects from the diaphragm to the liver as the inferior
(posterior) layer of the left tri- angular ligament. From here it can be traced
along the posterior and then inferior surfaces of the liver to the point at
which it leaves the liver to go to the lesser curvature of the stomach as the
posterior layer of the lesser omentum, which continues onto the posteroinferior
surface of the stomach and to the greater curvature, where it leaves the stomach to extend for a variable distance into
the greater omentum. This distance depends on the degree of fusion of the
peritoneum which has taken place, typically not reaching beyond the transverse
colon. The peritoneum turns superiorly on the anterior surface of the
transverse colon, and then, in the adult, it usually forms the anterior layer
of the transverse mesocolon if the fusion of the primitive dorsal mesogastrium
with the primitive mesentery of the transverse colon has been complete. The
transverse mesocolon comes to the posterior body wall just inferior to the
point at which the tracing of the lesser sac peritoneum was started.
In tracing the peritoneum in a horizontal section at the level of the
omental foramen, a start can be made with the greater sac peritoneum on the
inner surface of the anterior abdominal wall in the midline. Following the cut
edge of the parietal peritoneum to the left along the inner surface of the
anterolateral wall to the region of the posterior wall, it will pass onto the
anterolateral surface of the left kidney, from where it reflects to the
hilar area of the spleen, forming the external layer of the splenorenal
ligament, and then completely surrounds the spleen except at the hilar
area. From the anterior margin of the hilum of the spleen, the peritoneum
passes to the stomach as the external layer of the gastrosplenic ligament. The peritoneum can then be
followed along the anterosuperior surface of the stomach to the lesser curvature,
where it leaves the stomach as the anterior layer of the lesser omentum, which
can be followed to the right until the free margin is reached a short distance
to the right of the midline. Here the peritoneum passes around the free margin
of the lesser omentum (anterior boundary of the omental foramen) to become the
peritoneum of the omental bursa, which continues to the left, as the posterior
layer of the lesser omentum, to the lesser curvature of the stomach, where it
continues onto the posteroinferior surface of the stomach, which it follows
until it leaves the stomach to form the internal (lesser sac) layer of the
gastrosplenic ligament. From the spleen the peritoneum forms the internal layer
of the splenorenal ligament and then travels to the right anterior to the aorta
and the inferior vena cava. At the right margin of the inferior vena
cava, the peritoneum again becomes continuous with the greater sac and
continues to the right onto the anterior aspect of the right kidney. From here
the tracing of the peritoneum could differ, depending on whether the bare area
of the liver were to extend down just
far enough to be encountered in the plane of the tracing or whether the plane
of tracing passes just inferior to the bare area of the liver. In the former case,
the peritoneum would pass from the kidney as the inferior layer of the coronary
ligament to the liver, and would follow around the liver to its anterosuperior
surface, where it would leave the liver as the left layer of the falciform
ligament, to go to the inner surface of the anterior body wall and to the
left to the point from which the tracing started. To complete the tracing in
this plane, one must follow the peritoneum from the right layer of the falciform
ligament onto the anterosuperior surface of the liver, and to the right along
this surface to the superior layer of the coronary ligament, along this to the
diaphragm, and then anteriorly to the right layer of the falciform ligament. If
the plane of section passes just inferior to the bare area of the liver as the
peritoneum leaves the anterior surface of the inferior vena cava (the posterior
boundary of the omental foramen), it passes across the anterior surface of the
right kidney, then to the diaphragm, and forward on the inner surface of the body
wall to the falciform ligament.
In tracing peritoneum in a horizontal section at about the level of the umbilicus, one can start
at the midline of the inner surface of the anterior abdominal wall and follow from this point the parietal
peritoneum to the left along the inner surface of the wall to the posterior
wall, where it reflects onto the left side of the descending colon to
cover also the anterior surface and right side of this structure, from which it
passes to the posterior body wall. In early development the descending colon
was suspended by the primitive dorsal mesentery, but peritoneal fusion during
embryologic development brings it into the adult relationship to the peritoneum
just described. The peritoneum continues to the right on the posterior body
wall to about the midline, where it reflects forward to form the left
(inferior) layer of the intestinal mesentery. The small intestine is completely
surrounded (except at its mesenteric attachment) in the free margin of the mesentery;
from here the peritoneum is traced posteriorly to the posterior body wall as
the right (superior) layer of the mesentery. Thereafter, the peritoneum can be
followed to the right onto the posterior body wall, until it reflects from here
to cover the left, anterior, and right surfaces of the ascending colon. This
structure was also suspended originally by the primitive dorsal mesentery. From
the right side of the ascending colon, the peritoneum passes to the posterior
body wall and then forward on the inner surface of the anterolateral abdominal
wall until it reaches the midline, from where the tracing was started. Also in
a section at about the level of the
umbilicus, one would expect to find the greater omentum cut, which is present
as an island of peritoneum not connected in this section to the rest of the
peritoneum. If the transverse colon is hanging low enough, it too would be cut
as an island with its peritoneum continuous with that of the greater omentum.
Worthwhile additions to the general concept of the distribution of the
peritoneum, gained by tracing it in several planes as done above, can be
obtained by careful study of a view of the posterior half of the abdominopelvic
cavity, in which all of the viscera (except the bladder and rectum) that
invaginate the peritoneum to any degree have been removed, cutting the
peritoneum along its lines of reflection from the posterior body wall or the
anterior surfaces of the viscera and vessels that do not project into the
peritoneum. The right and left kidneys, the pancreas (except
for the tip of its tail), the second, third, and most of the fourth
parts of the duodenum, and the aorta and inferior vena cava do
not project into the peritoneal cavity to a significant degree. The peritoneum
covers the inner surface of the abdominopelvic body walls as parietal
peritoneum, except where it is lifted away from them by the structures just
listed (the bare area of the liver against the diaphragm, the ascend- ing and
descending colon, the roots of the mesentery, the transverse mesocolon and
sigmoid mesocolon, the ureters and inferior mesenteric vessels, and the rectum
and bladder and, in the female, the uterus and broad ligaments, other folds in
the pelvis, and folds on the inner surface of the anterior abdominal wall). The
folds on the inner surface of the anterior abdominal wall are the falciform
ligament of the liver (a remnant of the ventral mesentery, ventral to where
the liver grew into it), running superiorly and a little to the right from the
umbilicus, with the ligamentum teres (obliterated umbilical vein) of the liver
in its free margin; the median umbilical fold, projecting from the
superior aspect of the urinary bladder, running superiorly up the midline to
the umbilicus; the medial umbilical folds, also running to the umbilicus
and containing the obliterated right and left umbilical veins; and the right
and left lateral umbilical folds, containing the inferior epigastric
artery and vein on each side (which may produce a slight elevation
remindful of a fold by pulling the peritoneum a little away from the body
wall). The depression between the median and medial umbilical folds is
called the supravesical fossa,
whereas the one between each medial and lateral umbilical fold is the
epigastric fold. Lateral of the lateral umbilical fold is the lateral inguinal
fossa. Parietal peritoneum is thus seen to be applied to practically the entire
extent of the inner surface of the anterolateral abdominal wall, and virtually
any incision through this wall will open into the peritoneal cavity.
Much of the diaphragm has parietal peritoneum on its abdominal surface,
but much less of the muscular portion of the posterior abdominal wall is
directly lined by peritoneum on its
inner surface. This is because several viscera, major vessels, and a significant
amount of adipose tissue lie behind the peritoneum and most of the abdominal
viscera project from the posterior wall into the peritoneal cavity.
From the preceding description it is obvious that the degree to which the
various abdominal viscera are covered by peritoneum (visceral peritoneum)
varies along a spectrum in which peritoneum may cover just part of one surface
of the viscus in question to the other extreme
in which peritoneum covers the viscus entirely, except for the area of
attachment of a suspending double-layered fold of peritoneum. “Retroperitoneal”
is a very commonly used descriptive term having the general meaning of “behind
the peritoneum,” which is well agreed upon, but some authors refer to certain
organs as retroperitoneal that other authors would not designate in this
fashion. Generally, “primarily retro- peritoneal structures” (e.g., ureter,
kidney) are those that develop posterior to the peritoneal lining and never
develop a mesentery. “Secondarily retroperitoneal structures” once had a
mesentery but lost it when the organ was laid back along the body wall and the
mesentery fused to a degree with the parietal peritoneum (e.g., ascending colon,
second portion of the duodenum). “Intraperitoneal structures” are those that
are suspended from the posterior body wall by a mesentery containing blood
vessels and nerves associated with the organ (e.g., stomach, ileum). Additional
details will be given in the sections dealing with each organ or region.
The mesentery
is commonly taken to mean the mesentery of the small intestine (i.e., the
jejunoileal portion of the small intestine which is the portion having a
mesentery or a double-layered fold of peritoneum suspending it from the
posterior abdominal wall). The root of the mesentery is about 15 cm in
length, and its line of attachment varies a bit with the shape of the duodenum,
but, in general, it courses from a little to the left of the second lumbar
vertebra inferiorly and to the right, crossing the third part of the duodenum,
the aorta, the inferior vena cava, the right ureter, and the right psoas major
muscle to reach a point near the right sacroiliac joint. The free or unattached
border, which contains the loops of the small intestine, is frilled out to such
an enormous degree that it may attain a length varying from 3 m to more than 6
m. The distance from the attached border to the free border measures 15 to 22
cm; it may definitely increase with age, probably owing to stretching of the
mesentery due to laxity of the anterior abdominal wall. Between the two layers
of peritoneum on the two surfaces of the mesentery are the superior
mesenteric artery and its branches, the accompanying veins, lymphatics,
approximately 100 to 200 lymph nodes, autonomic nerve plexuses, connective
tissue, and varying amounts of adipose tissue, which is present in greater
amounts near the root. The mesentery divides the area below the transverse mesocolon
into two compartments, which are important in determining collections of fluid and the localization of infection.
The transverse mesocolon is the broad peritoneal fold suspending
the transverse colon from the posterior body wall. The root of the
transverse mesocolon crosses the anterior surface of the right kidney, the
second portion of the duodenum, and the head of the pancreas, and then passes
along the lower border of the body and tail of the pancreas superior to the
duodenojejunal flexure, to end on the anterior surface of the left kidney. It contains the middle colic artery, branches
of the right and left colic arteries, accompanying veins, lymphatic structures,
autonomic nerve plexuses, as well as a considerable thickness of connective
tissue.
The sigmoid mesocolon is the mesentery of the sigmoid colon. When
the peritoneum begins to surround the large intestine near the crest of the
ilium, the attachment of the sigmoid mesocolon follows a fairly straight line
from the posterior part of the left iliac fossa inferiorly and medially to
reach the third sacral segment.
If, as is the case in the other extreme of the range of variation, the
colon is closely bound down in the iliac fossa, the line of attachment of the
sigmoid mesocolon goes posteriorly along the pelvic brim until it crosses the
anterior side of the sacroiliac joint, and then descends along the anterior aspect
of the sacrum to the level of its second to third segment. The sigmoid colon is
enwrapped by the free margin of the sigmoid mesocolon, which has its greatest
width (distance from attached to free border) at its attachment to the first
sacral segment. This width varies from about 5 to 18 cm, although it
occasionally may be as much as 25 cm between the layers of the sigmoid
mesocolon through which run the sigmoidal and superior rectal arteries,
accompanying veins, lymphatics and autonomic nerve plexus, and connective
tissue, which, of course, includes varying amounts of adipose tissue.
The greater omentum is the largest peritoneal fold; it may hang
down like a large apron from the greater curvature of the stomach in front of
the other viscera as far as the brim of the pelvis or even into the pelvis. It
may even extend into an inguinal hernia, most commonly on the left side. It
also may be much shorter than this, appearing as just a fringe on the greater
curvature of the stomach, or it may be of some length and found folded in
between coils of the small intestine, tucked into the left hypochondriac area
or turned superiorly just anterior to the stomach. The superior end of the left
border is continuous with the gastrosplenic ligament, and the superior end of
the right border extends as far as the beginning of the duodenum. The greater
omentum is usually thin, with a delicate layer of fibro- elastic tissue as its
framework, and somewhat cribriform in appearance, although it usually contains
some adipose tissue and may accumulate a large amount of fat in an obese
individual. In the make-up of the greater omentum, the peritoneum of the
omental bursa on the posteroinferior surface of the stomach and the greater sac
peritoneum on the anterosuperior surface of the stomach meet at the greater
curvature of the stomach and course inferiorly to the free border of the
greater omentum, where they turn superiorly to the transverse colon. Early in
development, these two layers of elongated dorsal mesogastrium course superiorly
in front of the transverse colon and transverse mesocolon to the anterior
surface of the pancreas. Owing to fusions of these two layers of peritoneum to
each other and to the peritoneum
on the transverse colon, and the anterior surface of the primitive
transverse mesocolon, it appears, in the fully developed state, as though the
“two layers” of peritoneum, running superiorly as the posterior layer of the
greater omentum, separate from each other to surround the transverse colon and
continue as the two layers of the transverse mesocolon. Frequently, there is
enough fusion in the four-layered primitive greater omentum inferior to the
transverse mesocolon that no extension of the omental bursa is present between
layers. Close to the greater curvature of the stomach, the right and left
gastroomental vessels course, anastomosing with each other in the greater
omentum. The greater omentum, if of any length, has a great deal of mobility
and can shift around to fill what would otherwise be temporary gaps between viscera
or to build up a barrier against bacterial invasion of the peritoneal cavity by
becoming adherent at a potential danger spot.
The lesser omentum, which can be subdivided into hepatogastric and
hepatoduodenal ligaments, extends from the posteroinferior surface of
the liver to the lesser curvature of
the stomach and the beginning of the duodenum. It is extremely thin,
particularly the part to the left, which is sometimes fenestrated. The right
side is thicker and ends in a free, rounded margin, which contains the common
bile duct to the right, the hepatic artery to the left, and the portal vein
posterior to these two, and forms the anterior border of the omental foramen.
In addition to the structures just listed, the lesser omentum contains the
right and left gastric arteries (close to the lesser curvature of the stomach)
and the accompanying veins, lymphatics, and autonomic nerve plexuses. The
lesser omentum reaches the liver at the porta hepatis, and to the left of the
porta hepatis it extends to the bottom of the fossa for the ligamentum venosum,
the obliterated ductus venosus, which carried oxygenated blood from the
umbilical vein to the inferior vena cava.
The omental bursa (lesser sac of the peritoneum) is a large fossa,
or outpouching, from the general peritoneal cavity. It is bounded in front,
from superior to inferior, by the caudate lobe of the liver, lesser omentum,
posteroinferior surface of the stomach, and anterior layer of the
greater omentum (at least in part). Posteriorly, from inferior to superior,
are the posterior layer of the greater omentum (the amount of this depends on
the variable inferior extent of the bursa), transverse colon, anterior layer of the transverse
mesocolon, anterior surface of the pancreas, left suprarenal gland, superior
end of the left kidney, and, to the right of the esophageal opening into
the stomach, that part of the diaphragm supporting the caudate lobe of the
liver. The horizontal extent of the bursa stretches from the omental foramen at
the right to the hilum of the spleen at the left, where it is limited by the splenorenal
and gastrosplenic ligaments. Inferiorly, the bursa may extend about
as far as the transverse colon, its cavity having originally reached as far
down as the free margin of the greater omentum before becoming obliterated by
fusion of its layers. The portion of the bursa between the caudate lobe of the
liver and the diaphragm is called the superior recess, and the narrow portion
from the omental foramen across the head of the pancreas to the gastropancreatic
fold is called the vestibule of the bursa.
The omental foramen (of Winslow) is the opening by which the
omental bursa communicates with the general peritoneal cavity (greater sac). It
is somewhat circular and is usually large enough to admit one or two fingers.
Anterior to the foramen is the free margin of the lesser omentum, containing
the common bile duct, hepatic artery, and portal vein. Its
posterior border is the peritoneum covering the inferior vena cava; superior to it is the peritoneum on the caudate
process of the liver, and its inferior boundary is the peritoneum that covers
the beginning of the duodenum and the hepatic artery. Many extremely variable
and inconstant fossae or recesses have been described which are of interest to the
surgeon because of the possibility of herniation of a loop of intestine into
any one of them. The more common ones are located either in the region of the
fourth portion of the duodenum or in the region of the cecum and ileocecal
junction. A relatively common “intersigmoid recess” is found on the left side
of the line of attachment of the sigmoid mesocolon at the angle that is present
in this line when the colon is tightly
bound down in the iliac fossa.
A characteristic of the peritoneum covering the surfaces of the various
parts of the colon is the presence of little outpouchings of peritoneum
containing adipose tissue, which are called omental appendages (appendices
epiploicae).
The parietal peritoneum is supplied by the nerves to the adjacent body wall and is thus pain sensitive. The visceral
peritoneum is insensitive to ordinary pain stimuli but does respond to
ischemia, distention, and inflammation. When moist surfaces of peritoneum which
are in contact become irritated, adhesions tend to form that often become permanent.
