DOI:10.2214/AJR.05.0644
AJR 2006; 186:703-717
© American Roentgen Ray Society
Review of Internal Hernias: Radiographic and Clinical Findings
Lucie C. Martin1,
Elmar M. Merkle1 and
William M. Thompson1
1 All authors: Department of Radiology, Duke University Medical Center, Box
3808, Durham, NC 27710.
Received April 14, 2005;
accepted after revision August 9, 2005.
Address correspondence to W. M. Thompson
(thomp132{at}mc.duke.edu).
Abstract
OBJECTIVE. Internal hernias, including paraduodenal (traditionally
the most common), pericecal, foramen of Winslow, and intersigmoid hernias,
account for approximately 0.5-5.8% of all cases of intestinal obstruction and
are associated with a high mortality rate, exceeding 50% in some series. To
complicate matters, the incidence of internal hernias is increasing because of
a number of relatively new surgical procedures now being performed, including
liver transplantation and gastric bypass surgery. A significant increase in
hernias is occurring in patients undergoing transmesenteric, transmesocolic,
and retroanastomotic surgical procedures. It is important for radiologists to
be familiar with and to understand the various types of internal hernias and
their imaging features so that prompt and accurate diagnosis of these
conditions can be made.
CONCLUSION. This article illustrates the imaging findings of
internal hernias, with emphasis placed on the CT findings, especially in
transmesenteric, transmesocolic, and retroanastomotic types of internal
hernias.
Keywords: colon • CT • gastrointestinal radiology • hernia • small bowel
Introduction
Although internal hernias have an overall incidence of less than 1%, they
constitute up to 5.8% of all small-bowel obstructions, which, if left
untreated, have been reported to have an overall mortality exceeding 50% if
strangulation is present [1,
2]. Over the past decade, their
incidence has been increasing because of the more frequent performance of
liver transplantations and gastric bypass surgery for bariatric treatment. In
this subset of patients, internal hernias account for just over half of all
cases of small-bowel obstruction, almost equal to those caused by adhesions in
one study [3,
4]. Without a heightened
awareness and understanding of these hernias, they can often be misdiagnosed,
with subsequent significant morbidity and mortality. The purpose of this
article is therefore not only to review the definition and types of internal
hernias, but also to describe the clinical and radiographic findings, with an
emphasis placed on the CT features, because CT is rapidly becoming the
first-line imaging technique in these patients.
Definition
Hernias are of two main types, external and internal
[1]. External hernias refer to
prolapse of intestinal loops through a defect in the wall of the abdomen or
pelvis, and internal hernias are defined by the protrusion of a viscus through
a normal or abnormal peritoneal or mesenteric aperture within the confines of
the peritoneal cavity. The orifice can be either acquired, such as a
postsurgical, traumatic, or postinflammatory defect, or congenital, including
both normal apertures, such as the foramen of Winslow, and abnormal apertures
arising from anomalies of internal rotation and peritoneal attachment.
In the broad category of internal hernias are several main types, as
traditionally described by Meyers
[5], based on location.
Specifically, using historical data, these consist of paraduodenal (53%),
pericecal (13%), foramen of Winslow (8%), transmesenteric and transmesocolic
(8%), intersigmoid (6%), and retroanastomotic (5%)
(Fig. 1), with the overall
incidence of internal hernias being 0.2-0.9%. The other 7% described by Meyers
included paravesical hernias, which are not true internal hernias and thus are
not described in this article. In general, internal hernias have no age or sex
predilection. With more new surgical procedures being performed using a Roux
loop, the number of transmesenteric, transmesocolic, and retroanastomotic
internal hernias has been increasing. These are probably more common than the
traditional incidence of the various types of internal hernias reported by
Meyers (Table 1).
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Fig. 1 —Diagrammatic illustration shows various types of internal hernias: A
= paraduodenal, B = foramen of Winslow, C = intersigmoid, D = pericecal, E =
transmesenteric, and F = retroanastomotic.
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General Clinical Findings
Clinically, internal hernias can be asymptomatic or cause significant
discomfort ranging from constant vague epigastric pain to intermittent colicky
periumbilical pain [1,
5]
(Table 1). Additional symptoms
include nausea, vomiting (especially after a large meal), and recurrent
intestinal obstruction [1,
2,
5-7].
Symptom severity relates to the duration and reducibility of the hernia and
the presence or absence of incarceration and strangulation
[6]. These symptoms may be
altered or relieved by changes in patient position
[5,
7]. Because of the propensity
of these hernias to spontaneously reduce, patients are best imaged when they
are symptomatic [5,
7].
General Imaging Findings on Radiography and CT
Imaging studies often play an important role in the diagnosis of internal
hernias because they are often difficult to identify clinically. In the past,
these hernias were most frequently assessed with small-bowel oral contrast
studies. However, CT has become the first-line imaging technique in these
patients because of its availability, speed, and multiplanar reformatting
capabilities. General radiographic features with barium studies include
apparent encapsulation of distended bowel loops with an abnormal location,
arrangement or crowding of small-bowel loops within the hernial sac, evidence
of obstruction with segmental dilatation and stasis, with additional features
of apparent fixation and reversed peristalsis during fluoroscopic evaluation
[1,
5]
(Table 1). On CT, additional
findings include mesenteric vessel abnormalities, with engorgement, crowding,
twisting, and stretching of these vessels commonly found and providing an
important clue to the underlying diagnosis
[6].
Paraduodenal Hernias
In the classic older literature, paraduodenal hernias were the most common
type of internal hernia, accounting for approximately 53% of all cases
[1]. Unlike most types of
internal hernias, this subtype does have a sex predilection, being found more
commonly in men by a ratio of 3:1
[1,
2,
6]. There are two main types,
left and right, with the former consisting of most (75%) cases
[1,
6-8].
Left Paraduodenal Hernia
Left paraduodenal hernias have an overall incidence of approximately 40% of
all internal hernias. They occur when bowel prolapses through Landzert's
fossa, an aperture present in approximately 2% of the population
(Fig. 1). These hernias
therefore can be classified as a congenital type, normal aperture subtype.
Landzert's fossa is located behind the ascending or fourth part of the
duodenum and is formed by the lifting up of a peritoneal fold by the inferior
mesenteric vein and ascending left colic artery as they run along the lateral
side of the fossa. Small-bowel loops prolapse posteroinferiorly through the
fossa to the left of the fourth part of the duodenum into the left portion of
the transverse mesocolon and descending mesocolon
(Fig. 2).
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Fig. 2 —Graphic illustration of a left paraduodenal hernia depicts loop of
small bowel prolapsing (curved arrow) through Landzert's fossa,
located behind inferior mesenteric vein and ascending left colic artery
(straight arrow). Herniated bowel loops are therefore located lateral
to fourth portion of duodenum.
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Clinically, in addition to the aforementioned symptomatology, these
patients will also often present with postprandial pain, typically chronic in
nature, with symptoms dating back to childhood
[5].
On radiography or oral contrast studies, these hernias will present as an
encapsulated circumscribed mass of a few loops of small bowel (usually
jejunal) in the left upper quadrant, lateral to the ascending duodenum
[1,
5,
9]
(Fig. 3A). These loops may have
mass effect, depressing the distal transverse colon and indenting the
posterior wall of the stomach
[1,
5] (Figs.
3B and
3C). Mild duodenal dilatation
often occurs, and the efferent loop often shows an abrupt caliber change
[5]. With CT, similar findings
of encapsulated bowel loops are noted, either at the duodenojejunal junction
between the stomach and pancreas to the left of the ligament of Treitz; behind
the pancreatic tail itself, displacing the inferior mesenteric vein to the
left; or between the transverse colon and the left adrenal gland
[5-7,
9-12]
(Figs. 4A,
4B,
4C, and
4D). Evidence of small-bowel
obstruction with dilated loops and air-fluid levels is also commonly seen
[5]
(Fig. 4E). There is associated
mass effect with displacement of the posterior stomach wall anteriorly, the
duodenojejunal junction inferomedially, and the transverse colon inferiorly
[6,
7,
10]. Mesenteric vessel
abnormalities, including enlargement, stretching, and anterior displacement of
the main mesenteric trunks, especially the inferior mesenteric vein, to the
left, are also helpful findings
[10,
11]. If the vasculature is
optimally visualized, one can often see additional findings of engorged
vessels grouped together at the entrance of the hernia sac, with the proximal
jejunal arteries showing an abrupt change of direction posteriorly behind the
inferior mesenteric artery [6,
7]
(Fig. 4F). The inferior
mesenteric vein and ascending left colic artery lie in the anterior and medial
border of the left paraduodenal hernia and may be displaced laterally (Figs.
2 and
4C).
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Fig. 3A —Left paraduodenal hernias shown on upper gastrointestinal series,
and barium enema in one patient and lateral view of upper gastrointestinal
series from different patients. 55-year-old man with gastrointestinal
bleeding. Anteroposterior projection of oral contrast small-bowel study shows
cluster of small-bowel loops in left upper quadrant, lateral to fourth portion
of duodenum (arrow).
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Fig. 3B —Left paraduodenal hernias shown on upper gastrointestinal series,
and barium enema in one patient and lateral view of upper gastrointestinal
series from different patients. Barium enema study (anteroposterior
projection) from same patient as in A depicts inferior displacement of
distal transverse colon and splenic flexure (arrow) caused by mass in
left upper quadrant that was later revealed to be left paraduodenal
hernia.
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Fig. 3C —Left paraduodenal hernias shown on upper gastrointestinal series,
and barium enema in one patient and lateral view of upper gastrointestinal
series from different patients. Lateral radiograph from upper gastrointestinal
series in 35-year-old woman with abdominal pain shows small-bowel loops
(arrow) causing mass effect and indentation on posterior aspect of
stomach (S), displacing it anteriorly.
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Fig. 4B —CT scans from six patients with left paraduodenal hernia. Axial
contrast-enhanced CT scan in 28-year-old man shows small-bowel loops
(white arrow) behind pancreas (P) itself. Black arrow indicates
stomach.
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Fig. 4C —CT scans from six patients with left paraduodenal hernia. Axial
contrast-enhanced CT scan in 36-year-old man shows small-bowel loops
(arrows) displaying inferior mesenteric vein (arrowhead) to
left.
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Fig. 4D —CT scans from six patients with left paraduodenal hernia. Coronal
reconstruction of contrast-enhanced CT data set in 28-year-old man shows
small-bowel loops between transverse colon (T) and left adrenal gland
(arrow).
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Fig. 4E —CT scans from six patients with left paraduodenal hernia. Unenhanced
axial CT scan in 35-year-old man shows evidence of small-bowel obstruction of
herniated contents as multiple loops of dilated small bowel (arrow)
with fluid-fluid levels noted.
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Fig. 4F —CT scans from six patients with left paraduodenal hernia. Axial
contrast-enhanced CT scan in 23-year-old man shows multiple engorged and
prominent vessels (arrow) in herniated sac caused by vascular
congestion and obstruction.
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Right Paraduodenal Hernia
Right paraduodenal hernias have an overall incidence of approximately 13%
and occur when bowel herniates through Waldeyer's fossa (representing a defect
in the first part of the jejunal mesentery), behind the superior mesenteric
artery and inferior to the transverse or third portion of the duodenum
(Fig. 5). This normal yet
uncommon recess is found in less than 1% of the population and, like left
paraduodenal hernias, the right paraduodenal hernia can be classified as
congenital type, normal aperture subtype
[1,
9]. In these situations, the
herniated contents are located in the right half of the transverse mesocolon
and behind the ascending mesocolon. This type of hernia occurs more frequently
in the setting of nonrotated small bowel
[6,
8]. When compared with the left
paraduodenal hernias, those on the right are usually larger and are more often
fixed [5].
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Fig. 5 —Graphic illustration of right paraduodenal hernia shows loop of
small bowel prolapsing (curved arrow) through Waldeyer's fossa,
behind superior mesenteric artery (straight arrow) and inferior to
third portion of duodenum (asterisk).
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Clinically, these hernias present in a similar manner to the left
paraduodenal hernias with chronic postprandial pain
[5].
On a standard barium gastrointestinal examination, a larger and more fixed,
encapsulated, ovoid collection of bowel loops is noted lateral and inferior to
the descending duodenum, in the right half of the transverse mesocolon, or
behind the ascending mesocolon
[1,
5,
9]
(Fig. 6A). As opposed to the
left paraduodenal hernias, both the afferent and efferent loops of bowel are
closely opposed and narrowed
[1,
5]. With CT, an encapsulated
cluster of small-bowel loops is noted in the right mid abdomen, with looping
of the small bowel around the superior mesenteric artery and vein at the root
of the small-bowel mesentery being seen occasionally
[5,
8]
(Fig. 6B). Small-bowel
obstruction may be present with dilated loops containing air-fluid levels.
Because right-sided paraduodenal hernias are thought to be congenital, related
to abnormalities of embryologic midgut rotation, there may be additional clues
such as small-bowel nonrotation, as evidenced by the superior mesenteric vein
occupying a more ventral and left-ward position and the absence of a normal
horizontal duodenum [5,
8,
9]. The cecum, however, remains
in its normal position. Vascular findings include jejunal branches of the
superior mesenteric artery and superior mesenteric vein looping posteriorly
and to the right of the parent vessel to supply the herniated loops
[1,
5,
8,
9]. Additional vascular
findings include the presence of the superior mesenteric artery, ileocolic
artery, and right colic vein in the anterior margin of the neck of the hernial
sac, displaced anteriorly if there is sufficient mass effect by the encased
small-bowel loops [8]. Again,
vessel engorgement may also be present and provide a clue to the
diagnosis.
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Fig. 6A —23-year-old man with abdominal pain. Anteroposterior projection from
oral contrast small-bowel study reveals cluster of small-bowel loops
(asterisk) posterior and lateral to second and third portions of
duodenum (arrow).
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Pericecal Hernias
Historically, pericecal hernias account for 13% of all internal hernias.
The pericecal fossa is located behind the cecum and ascending colon and is
limited by the parietocecal fold outward and the mesentericocecal fold inward
[9]. Although there are
actually four subtypes (ileocolic, retrocecal, ileocecal, and paracecal) of
pericecal hernias, most commonly the herniated loop consists of an ileal
segment protruding through a defect in the cecal mesentery and extending into
the right paracolic gutter [1,
9]
(Fig. 7). These hernias can
therefore be subcategorized as either acquired or congenital defects in the
cecal mesentery.
Clinically, patients with pericecal hernias present in a similar manner to
those with all other types of internal hernias except for the location of
symptoms, which tends to be in the right lower quadrant, so that pericecal
hernias are sometimes mistaken for appendiceal abnormalities
[1,
9]. A higher incidence of
occlusive symptoms with rapid progression to strangulation is also commonly
found, with a mortality rate reported to be as high as 75%
[9,
13].
Imaging studies, including both barium and CT, show similar findings. These
hernias can often be confidently diagnosed as a cluster of bowel loops
(usually ileal) located posteriorly and laterally to the normal cecum,
occasionally extending into the right paracolic gutter
[1,
9] (Figs.
8A and
8B). Again, there will be
evidence of small-bowel obstruction and mass effect displacing the cecum
anteriorly and medially.
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Fig. 8A —60-year-old man with right lower quadrant pain. Single
anteroposterior radiograph from barium enema study shows retrograde filling of
herniated distal ileum (arrows) as loops of ileum pass posterior to
cecum (C) through defect of ileocecal mesentery to reach right paracolic
fossa. (Reprinted with permission from
[1])
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Fig. 8B —60-year-old man with right lower quadrant pain. Contrast-enhanced
axial CT scan shows loops of small bowel (arrow) posterior and
lateral to cecum (asterisk) in right paracolic gutter, producing
small-bowel obstruction. (Courtesy of Ghahremani GG, San Diego, CA)
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Foramen of Winslow
The foramen of Winslow is a normal communication between the greater and
lesser peritoneal cavities, located beneath the free edge of the lesser
omentum, the hepatoduodenal ligament (Fig.
9). The posterior, superior, and inferior boundaries of this
foramen include the inferior vena cava, caudate lobe, and duodenum,
respectively [14]. This hernia
can therefore be subcategorized as a congenital type, normal aperture subtype.
It constitutes 8% of all internal hernias, with approximately two thirds
containing small bowel alone, and the remaining one third containing
additional cecum and ascending colon and occasionally gallbladder, transverse
colon, and omentum [1,
5,
6,
9,
14]. Risk factors for this
type of hernia include an enlarged foramen of Winslow, an abnormally long
small-bowel mesentery, persistence of the ascending mesocolon allowing marked
mobility of bowel, and an elongated right hepatic lobe (such as a Riedel's
lobe), which is thought to direct the mobile intestinal loops toward the
foramen of Winslow [1,
5,
6,
9,
14,
15].
The typical patient is middle-aged, with acute onset of severe, progressive
pain and signs of small-bowel obstruction
[1]. Patients also often
present with symptoms of a proximal bowel obstruction, which are caused by a
pressure effect on the stomach by the herniated contents
[14]. Symptom onset is often
preceded by a change in intraabdominal pressure, such as parturition or
straining [1,
5]. Occasionally, forward
bending provides some relief
[1]. Rarely, patients will
present with jaundice or a distended gallbladder, again from pressure or
stretching of the common bile duct by the herniated colon
[5].
When the small bowel herniates, conventional radiographs may reveal a
circumscribed collection of gas-filled loops in the upper abdomen, medial and
posterior to the stomach, which may progress to a location anterior to the
hepatic flexure [1,
5,
9]. Evidence of small-bowel
obstruction will probably be seen
[1,
5]. With barium studies,
additional mass effect will likely be shown because the stomach and the first
and second parts of the duodenum will shift anteriorly and laterally
[1,
5,
14] (Figs.
10A and
10B). On occasion, this type
of hernia can have the appearance of a cecal volvulus if the herniated sac
contains cecum [1,
5,
14] (Figs.
11A and
11B). The zone of transition
of the obstruction is usually located near the hepatic flexure
[1]. On CT, multiple gas-filled
loops are located in the lesser sac, posterior to the liver hilum, anterior to
the inferior vena cava, and between the stomach and pancreas, with tapering of
the herniation through the foramen of Winslow
[9]
(Fig. 10C). There may be
anterior and lateral displacement of the stomach and stretching of the
mesenteric vessels through the foramen of Winslow
[6]. Complications can arise if
defects exist in the gastrocolic or gastrohepatic omentum, allowing reentry of
herniated loops into the greater peritoneal cavity.
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Fig. 10A —54-year-old woman with abdominal pain. Anteroposterior radiograph
from upper gastrointestinal series shows abnormal cluster of small-bowel loops
located in lesser sac, representing foramen of Winslow internal hernia.
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Fig. 10B —54-year-old woman with abdominal pain. Oblique lateral view from
same gastrointestinal series shows abnormal cluster of small-bowel loops
posterior to stomach (asterisk), indenting (arrows) and
displacing stomach anteriorly.
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Fig. 11B —70-year-old man with severe epigastric pain. Barium enema
(anteroposterior view) shows large, air-filled structure in upper abdomen
(arrows), originally thought to represent a distended stomach but
surgically confirmed to be cecum involved in foramen of Winslow hernia.
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Foramen of Winslow hernias often present a similar radiographic appearance
to that of left paraduodenal hernias. One key feature that can be useful in
distinguishing between these entities is the presence of an encapsulating
membrane seen with left paraduodenal hernias and not with those involving the
foramen of Winslow. In addition, if the entry point can be identified, it will
be slightly inferior and to the left of the spine, delineated anteriorly by
the inferior mesenteric vein and the left colic artery with left paraduodenal
hernias, whereas with foramen of Winslow hernias, the entry point will be
relatively superior and to the right of the spine, delineated by the liver
hilum anteriorly. Along the same lines, mass effect on the transverse colon
more commonly indicates a left paraduodenal hernia, again because of its more
inferior location. Occasionally, left paraduodenal hernias can be supracolic.
Finally, prominent, congested blood vessels have more commonly been described
with paraduodenal hernias, although not exclusively.
Sigmoid-Related Hernias
Two or three main types of sigmoid-related hernias are seen, depending on
the degree of adherence to the definition of internal hernia
[5,
16]. The most common and most
disputable, the intersigmoid type, develops when herniated bowel, usually
ileum, protrudes into the intersigmoid fossa, formed between two adjacent
sigmoid segments and their respective mesenteries
[9]. Although this fossa is
found at 65% of autopsies [1],
it is debatable whether the opening of this fossa truly is an aperture. These
hernias are often easily reducible
[1]. A second type, the
transmesosigmoid hernia, occurs when small bowel herniates through a complete
defect involving both layers of the sigmoid mesocolon to lie in a position
posterolateral to the sigmoid itself
[1,
9,
16]
(Fig. 12). In this type of
hernia, the orifice is usually a long slit with its edge bounded by branches
of the inferior mesenteric artery
[5]. The third and least common
type, the intramesosigmoid hernia, is herniation of viscera through an
incomplete defect involving only one of the layers (usually the left leaf) of
the mesosigmoid [1,
9,
16]. The third type therefore
consists of a hernial sac that lies within the sigmoid mesocolon
[16]. Both the second and
third types are acquired subtypes of internal hernia, whereas the first is a
normal congenital subtype. However, these three types are radiographically
difficult to distinguish, and differentiation is not so important because they
are treated surgically in a similar manner
[9].
Clinically, these hernias present as described, with no distinctive or
characteristic findings on history or physical examination.
If the patient has no evidence of obstruction, these hernias can be
diagnosed with postevacuation barium enema radiographs, which will show
sacculated ileal loops occupying the left lower quadrant and elevation and
displacement of the sigmoid colon to the right
[17]. If obstruction is
present, however, CT findings include a cluster of Y- and X-shaped dilated
small-bowel loops entrapped behind the left posterior and lateral aspect of
the sigmoid colon, with the defect most commonly located between the sigmoid
colon and the left psoas muscle, or between sigmoid loops if it is an
intersigmoid type [4,
17]
(Fig. 13). These bowel loops
often cause mass effect, displacing the sigmoid colon anteromedially
[17]. Additional findings of
mesenteric vessel congestion and stranding of the fat, suggesting
strangulation, may be seen
[17].
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Fig. 13 —85-year-old man with abdominal pain. Axial CT scan of
sigmoid-related hernia (type 2, transmesosigmoid) reveals small-bowel loops
(arrow) protruding through defect in sigmoid mesocolon, which usually
occurs between left psoas muscle (arrowhead) and sigmoid colon (S),
to lie posterior and lateral to sigmoid colon itself.
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Transmesenteric Hernias
Although previously an uncommon type of hernia, transmesenteric hernias are
increasing in incidence and surpassed the frequency of paraduodenal hernias in
one study [4,
7,
10]. These hernias have a
bimodal distribution, occurring in both pediatric and adult patients. In
children, transmesenteric hernias are the most common type of internal hernia,
occurring in 35% of this patient population
[1,
5,
9,
18]. In this age group, they
are thought to arise from a congenital defect in the small-bowel mesentery,
near the ileocecal region or ligament of Treitz
[1,
5,
9]. One popular theory relates
the cause to prenatal intestinal ischemia and subsequent thinning of the
mesenteric leaves because the prenatal intestinal ischemia is associated with
bowel atresia in 5.5% of the pediatric population
[1,
2,
5,
18]. Other causes postulated
include intraperitoneal inflammation, trauma, partial development regression,
and fenestration of the mesentery by the colon during the embryologic
displacement into the umbilical cord
[6].
However, there is a second peak of occurrence in the adult population, and
in this subset of patients, the cause is iatrogenic, usually related to prior
abdominal surgery, especially with Roux-en-Y anastomosis, trauma, or
inflammation [1,
5,
6,
9,
18]. Both liver
transplantation and the most common type of gastric bypass surgery involve the
formation of a Roux-en-Y loop at the choledochojejunostomy site, and these
procedures are increasing in frequency
(Fig. 14). If the Roux loop is
placed anteriorly to the transverse colon, referred to as antecolic, there
will be no defect created in the transverse mesocolon; however, this procedure
is less commonly performed because of the required long segment of bowel
needed to travel around the transverse colon to finally be anastomosed to the
remaining gastric pouch. A more direct route involves creating a defect in the
transverse mesocolon, allowing a shorter Roux limb length. However, this
second surgical procedure, also known as a retrocolic type, is more associated
with the potential complication of internal hernia
(Fig. 14). Interestingly,
internal hernias also appear to occur more commonly after laparoscopic
Roux-en-Y gastric bypass than after open Roux-en-Y gastric bypass, for reasons
unknown [15].
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Fig. 14 —Diagrammatic illustration shows retrocolic Roux-en-Y procedure, with
loop of small bowel about to herniate through transverse mesocolon
(arrow) at surgically created defect, in keeping with transmesocolic
internal hernia.
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Three main types of transmesenteric internal hernias are seen. The first
and most common is the transmesocolic, which has been documented to occur in
0.7-3.25% of patients after laparoscopic Roux-en-Y gastric bypass surgery
[15]. The second type of
transmesenteric internal hernia occurs when bowel prolapses through a defect
in the small-bowel mesentery. Finally, the third type, known as the Peterson
type, has also been described and involves the herniation of small bowel
behind the Roux loop before the small bowel eventually passes through the
defect in the transverse mesocolon
[4].
Several predisposing factors have been postulated. Although surgeons
attempt to close the defects created, they can be incompletely closed or can
have a breakdown or a pulling of the suture material through the mesocolic fat
[3,
15]. Enlargement of the
mesenteric defect can occur with repeated herniation. An additional possible
predisposing factor may be the rapid weight loss and decreased intraperitoneal
fat that occurs in bariatric patients, causing enlargement of the defect
[4]. Transmesenteric hernias
are more likely than other subtypes to develop volvulus and strangulation or
ischemia, the incidence of which is reported to be as high as 30% and 40%,
respectively, with mortality rates of 50% for the treated groups and 100% for
the nontreated subgroups
[5-7,
18]. Volvulus and
strangulation or ischemia may be partly caused by the usual small aperture of
the defect (2-5 cm) in addition to the lack of encapsulation of the herniated
loops, allowing a large length of small bowel to herniate through the
mesenteric defect [5,
18].
Clinically, in both the pediatric and adult populations, patients present
with signs and symptoms of small-bowel obstruction, with periumbilical, crampy
pain, nausea, and distention
[1,
7,
10]. Vomiting can be a less
prominent feature than with other types of internal hernias because of fewer
gastric and enteral secretions from the proximal gastric pouch or Roux limb
that can accumulate above the level of obstruction
[15]. Overall, however,
symptom onset is often more acute than with other types of hernias
[6]. Most (93%) transmesenteric
internal hernias in the adult postoperative population occur more than 1 month
after surgery (mean, 235 days), and the most common cause of obstruction
during the first postoperative month is adhesions
[4]. On physical examination,
the "Gordian knot of herniated intestine" has been described,
representing a tender abdominal mass
[1].
Transmesenteric hernias are more difficult to diagnose on imaging studies
because their appearance and location are more variable. This is partly
because of the lack of a confining sac and therefore their potential location
anywhere in the peritoneal cavity, although they tend to occur more commonly
in the right mid abdomen [6,
9,
10]. Most commonly, it is the
Roux loop itself that herniates with a cluster of a few loops of dilated small
bowel in the expected location of the Roux loop
[4]
(Fig. 15). On radiography,
there may be signs of small-bowel obstruction, occasionally with a closed loop
appearance [18].
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Fig. 15 —40-year-old woman with nausea and vomiting. Contrast-enhanced axial
CT scan of transmesenteric internal hernia 19 months after Roux-en-Y procedure
shows dilated loops of duodenum (large black asterisk) and jejunum
(white asterisk) in expected location of Roux loop. Note that Roux
limb (arrowhead) is compressed. Straight arrows, curved arrow, and
small black asterisk represent colon. (Reprinted with permission from
[19])
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Although the transmesenteric hernia often causes obstruction of the limb
proximal to the enteroenterostomy site, if the hernia is distal, an important
clue may be the presence of significant air in the gastric remnant, which is
only a normal finding in the early postoperative course
(Fig. 16). Otherwise, this
finding is of concern for a distal obstruction at or beyond the
enteroenterostomy site.
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Fig. 16 —36-year-old man with sudden onset of abdominal pain. Radiograph
(anteroposterior projection) shows distended air-filled gastric remnant, which
is normal finding in recently postoperative patient. However, in this patient
several months after surgery, this finding is most worrisome for obstruction
at distal anastomosis of Roux-en-Y loop.
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Oral contrast material and cross-sectional studies will provide a variable
appearance, depending on the type of transmesenteric hernia and the segment
and length of herniated bowel. If the hernia is of the first type, through the
mesocolon and consisting of only a few loops of small bowel, oral contrast
studies may show a beaked appearance of both the afferent and efferent loops
and resultant mass effect on the stomach and transverse colon, simulating a
left paraduodenal hernia [5].
With CT as with barium studies, these hernias can often be mistaken for or
occur concomitantly with a small-bowel volvulus and closed loop obstruction,
including a beaklike appearance of the closely opposed afferent and efferent
loops [9,
18]. Again, there may be mass
effect on the stomach and transverse colon.
On the other hand, a slightly different radiographic picture will emerge if
the herniated segment is much longer or is of the second type, through the
small-bowel mesentery. On CT, more typical findings have been described, in
addition to the usual findings of small-bowel obstruction with transition
point [6]. As described by
Blachar and Federle [6] and
Blachar et al. [7], the
presence of clustered bowel loops in the periphery of the peritoneal cavity,
lateral to the colon (a reversal of the normal pattern), with central,
inferior, and posterior displacement of the transverse colon is one clue
(Fig. 17A). Because, as
previously mentioned, the herniated bowel is located more commonly on the
right, it is often the hepatic flexure that is displaced inferiorly and
medially [6].
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Fig. 17A —CT scans in two different patients with transmesenteric internal
hernias. Contrast-enhanced axial CT scan of 84-year-old woman showing
transmesenteric internal hernia after Roux-en-Y procedure shows dilated,
fluid-filled loops of small bowel lateral to ascending colon (arrow)
and displacing omental fat because loops of bowel lie directly beneath
anterior abdominal wall (arrowheads).
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The second described finding, again by the same authors
[6,
7], involves displacement of
the overlying omental fat, with the obstructed loops compressed and directly
abutting the abdominal wall (Fig.
17B). It has been suggested that these two findings of
peripherally located small bowel and lack of omental fat between the loops and
the anterior abdominal wall might be the most helpful CT signs, with an
overall sensitivity of 85% and 92% for each respective finding
[7]. The mesenteric vasculature
may also show an abrupt change in the course of the superior mesenteric
artery, which is often displaced to the right, with crowding, stretching,
engorgement, and displacement of its visceral branches
[5,
6,
10,
18]. However, further studies
concluded that the only statistically significant signs were relatively
nonspecific findings of small-bowel dilatation with transition point,
clustering of small-bowel loops, and mesenteric vessel abnormalities
(including displacement of the main mesenteric trunk to the right), obtaining
an overall average sensitivity of 63%, specificity of 73%, and accuracy of 77%
[10]. Again, a "closed
loop" sign, twisting of the mesenteric vessels and the whirl sign if
volvulus is present, may also be seen
[1,
6,
9]. Occasionally, there may
even be evidence of ischemia with ascites and bowel wall thickening present
[7].
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Fig. 17B —CT scans in two different patients with transmesenteric internal
hernias. Axial contrast-enhanced CT scan at level of transverse mesocolon in a
40-year-old woman shows dilated loop of jejunum directly abutting anterior
abdominal wall (white asterisk). In addition, note compression of
pancreaticobiliary limb (straight arrows), whereas Roux limb
(small arrowhead) is barely visible. Large arrowhead, black asterisk,
and curved arrow indicate colon. (Reprinted with permission from
[19])
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With the third type of transmesenteric hernia associated with Roux-en-Y
surgery, known to surgeons as the Peterson type, little has been described in
the imaging literature other than nonspecific findings of partial small-bowel
obstruction and crowding of the mesenteric vessels.
As previously mentioned, because of their variable imaging appearances,
transmesenteric hernias are often confused with either right paraduodenal or
pericecal hernias. One helpful distinguishing feature for the former includes
the presence of an encapsulating membrane, which should be seen only with
right paraduodenal hernias. Differentiating a pericecal hernia from a
transmesenteric hernia can be more problematic. Location of herniated bowel
loops (in the right upper quadrant for transmesenteric and right lower
quadrant for pericecal) can sometimes provide a clue, although usually a
history of surgery is the most helpful information.
Retroanastomotic Hernias
Retroanastomotic hernias occur when small-bowel loops herniate posteriorly
through a defect related to a surgical anastomosis; they are therefore by
definition considered an acquired type, abnormal aperture subtype of internal
hernia. Specifically, these hernias have been most commonly described with the
Roux-en-Y formation and are ever increasing in incidence as liver
transplantations and gastric bypasses for bariatric surgeries continue to
become more frequent and widespread. If the surgery is of the antecolic type,
the borders of the aperture consist of the transverse mesocolon superiorly,
the ligament of Treitz inferiorly, and the gastrojejunostomy site and afferent
limb of the jejunum anteriorly; hence the term "retroanastomotic"
[5]
(Fig. 18). The most common
herniated loop consists of the efferent jejunal segment, which occurs in
approximately 75% of cases [1].
However, controversy exists in the literature as to whether this occurs more
commonly with the antecolic [5]
or retrocolic [1] form of the
surgery. Less commonly, a very long afferent limb, ileum, cecum, or omentum
can herniate into the retroanastomotic space. However, if antecolic surgery is
performed, the afferent loop will be the most commonly involved segment.
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Fig. 18 —Diagrammatic illustration shows retrocolic Roux-en-Y gastric bypass
procedure. Arrow indicates loop of small bowel protruding posterior to
enteroenterostomy, in keeping with a retroanastomotic internal hernia.
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As opposed to the transmesenteric type of internal hernia related to the
Roux-en-Y surgery, the retroanastomotic type tends to occur most commonly
during the first postoperative month, with half of all cases presenting during
this time [1,
5]. Of the remaining 50%, half
will occur after the first year, and the other half (or 25% of the total) will
occur between months 2 and 12
[5]. Also in contradistinction
to the transmesocolic type, the retroanastomotic hernia is more common with
the antecolic form of the surgery. Symptoms again depend on whether the
retrocolic or antecolic form of the surgery was performed. If retrocolic,
symptoms may be nonspecific findings related to a high small-bowel
obstruction, such as crampy abdominal pain and nausea
[1,
5]. Typically, there is less
vomiting because of the relative lack of fluid and secretions in the gastric
pouch or Roux limb [19]. On
physical examination, there may be a tender mass in the left upper quadrant
[1]. With the antecolic form of
the surgery, patients more commonly present with persistent epigastric pain
and tenderness, nonbilious vomiting, and increased amylase
[1]. Compared with other types
of internal hernias, these hernias are less likely to present with
strangulation because of the large aperture size. However, uncommonly,
complications can arise when the herniated loop reenters the greater
peritoneal cavity through the foramen of Winslow or a gastrohepatic or
gastrocolic ligament [5].
Diagnostic considerations include more common postoperative complications such
as gastric outlet obstruction, dumping syndrome, and postoperative
pancreatitis, with a delay in the diagnosis potentially leading to
strangulation (with mortality rates of 30% and 100% for the treated vs
nontreated groups, respectively)
[1,
5].
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Abstract
Introduction
