DOI:10.2214/AJR.04.1522
AJR 2006; 186:1368-1379
© American Roentgen Ray Society
MRI of the Peritoneum: Spectrum of Abnormalities
Khaled M. Elsayes1,2,
Paul T. Staveteig1,
Vamsidhar R. Narra1,
John R. Leyendecker3,
James S. Lewis, Jr.4 and
Jeffrey J. Brown1
1 Mallinckrodt Institute of Radiology, Washington University School of Medicine,
510 S Kingshighway Blvd., St. Louis, MO 63110.
2 Present address: Theodore Bilharz Institute, Giza, Egypt.
3 Department of Radiology, Wake Forest University School of Medicine,
Winston-Salem, NC.
4 Department of Surgical Pathology, Washington University School of Medicine,
St. Louis, MO.
Received September 27, 2004;
accepted after revision March 14, 2005.
Address correspondence to: K. M. Elsayes
(elsayesk{at}mir.wustl.edu).
Abstract
OBJECTIVE. Our objective was to detail peritoneal anatomy,
techniques for optimizing peritoneal MRI, and the MRI characteristics of
several disease processes that frequently involve the peritoneum.
CONCLUSION. Homogeneous fat suppression and dynamic
contrast-enhanced imaging, including delayed imaging, are critical technical
factors for successful lesion detection and characterization on peritoneal
MRI.
Keywords: abdominal imaging • MRI • peritoneum
Introduction
Diseases involving the peritoneum are frequently encountered in medical
practice. Primary abnormalities of the peritoneum are rare. However,
involvement of the peritoneal cavity and its specialized folds secondary to
infectious, neoplastic, and traumatic conditions that originate at other sites
within the abdomen and pelvis is frequent.
MRI, because of its excellent tissue characterization and multiplanar
abilities, is a powerful tool for disease characterization and anatomic
delineation. This article details peritoneal anatomy, techniques for
optimizing peritoneal MRI, and the MRI characteristics of several disease
processes that frequently involve the peritoneum.
Peritoneal Anatomy
The peritoneum is a serous sac consisting of a thin mesothelial membrane
that lines the abdominal and pelvic cavities and covers most of the abdominal
organs contained therein [1].
Although the peritoneum is a single continuous sheet, it is divided
arbitrarily into two types, the visceral peritoneum and the parietal
peritoneum.
The parietal peritoneum lines the abdominal and pelvic cavities. The
visceral peritoneum covers the external surface of most abdominal organs, or
viscera. The small and large intestines are suspended from the posterior
aspect of the peritoneal cavity by the mesentery, a double layer of parietal
peritoneum that has fused during embryologic development. The mesentery serves
as a conduit for the blood vessels, nerves, and lymphatic vessels going to and
from the abdominal organs.
The omentum is a double-layer extension of visceral peritoneum that extends
from the stomach. The lesser omentum, also known as the gastrohepatic
ligament, arises from the lesser curvature of the stomach and extends to the
liver. The greater omentum arises from the greater curvature of the stomach
and extends inferiorly in the peritoneal cavity. Other peritoneal ligaments,
such as the gastrosplenic ligament and splenorenal ligament, are also formed
by fused double layers of peritoneum.
The peritoneal cavity consists of several communicating spaces
[2]. Fused layers of peritoneum
form the transverse mesocolon, which is the mesentery suspending the
transverse colon. The transverse mesocolon divides the peritoneal cavity into
supramesocolic and inframesocolic components, as seen in
Figure 1A. As depicted, the
transverse mesocolon acts as the floor of the lesser sac. The transverse
mesocolon provides a pathway of spread for pancreatic disease to the
transverse colon.
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Fig. 1A —Schematics of peritoneal anatomy. In these sagittal (A),
axial (B), and coronal (C) views, pouch of Douglas and lateral
paravesicular spaces are seen to communicate (green arrows) with
peritoneal cavity. Peritoneum is shown in red. Ao = aorta, IVC = inferior vena
cava, Spl = spleen.
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Supramesolic Compartment
The supramesocolic compartment (Fig.
1B) is divided into right and left peritoneal spaces by the
falciform ligament.
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Fig. 1B —Schematics of peritoneal anatomy. In these sagittal (A),
axial (B), and coronal (C) views, pouch of Douglas and lateral
paravesicular spaces are seen to communicate (green arrows) with
peritoneal cavity. Peritoneum is shown in red. Ao = aorta, IVC = inferior vena
cava, Spl = spleen.
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The left supramesocolic peritoneal space is bound on the right by the
hepatic falciform ligament and consists of anterior and posterior perihepatic
components. The anterior and posterior perihepatic spaces communicate freely
below the lower border of the liver. This space can be affected by
abnormalities involving the left hepatic lobe, lesser gastric curvature,
anterior gastric and duodenal walls, and anterior wall of the gallbladder.
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Fig. 1C —Schematics of peritoneal anatomy. In these sagittal (A),
axial (B), and coronal (C) views, pouch of Douglas and lateral
paravesicular spaces are seen to communicate (green arrows) with
peritoneal cavity. Peritoneum is shown in red. Ao = aorta, IVC = inferior vena
cava, Spl = spleen.
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The right supramesocolic peritoneal space comprises an anterior perihepatic
region, bound medially by the falciform ligament, and a posterior component,
known as the lesser sac. The two right supramesocolic spaces communicate via
the foramen of Winslow. Morison's pouch (also known as the hepatorenal fossa)
is a recess between the liver and right kidney. Fluid collections in the right
perihepatic space are usually explained by abnormalities involving the right
hepatic lobe, gallbladder, and duodenum.
Inframesocolic Compartment
The inframesocolic compartment, depicted in
Figure 1C, is divided into two
spaces by the obliquely oriented small-bowel mesentery. The right
inframesocolic space is to the right of the small-bowel mesentery but medial
to the ascending colon. The left inframesocolic space is to the left of the
small-bowel mesentery.
The right and left paracolic gutters run laterally to the ascending and
descending colonic reflections, respectively. The right paracolic gutter is
continuous superiorly with the right perihepatic space. On the left, the
phrenicocolic ligament represents a barrier between the left paracolic gutter
and the left supramesocolic peritoneal space. Finally, the midline pouch of
Douglas and the lateral paravesicular spaces form the most dependent portions
of the peritoneal cavity, where infected fluid and malignant ascites usually
pool by means of gravity.
MRI Technique
MRI evaluation of the peritoneal cavity requires meticulous attention to
technique. Appropriate coil placement and homogeneous fat suppression are
essential. Oral contrast material and IV glucagon, although not routinely
used, can improve image quality.
Pulse sequences used for MRI examination of the peritoneum are similar to
those of standard abdominal MRI. Our standard protocol comprises four types of
sequences: a coronal T2-weighted single-shot fast spin-echo or HASTE sequence;
a turbo or fast spin-echo T2-weighted or long-TE inversion-recovery
breath-hold sequence in the axial plane (STIR eliminates field artifacts and
is usually performed as a fat-saturated T2-weighted pulse sequence); a
gradient-recalled-echo T1-weighted chemical-shift in-phase and out-of-phase
breath-hold sequence in the axial plane; and a 3D gradient-echo breath-hold
sequence, such as a volumetric interpolated breath-hold examination, which is
fat suppressed.
Dynamic gadolinium-enhanced images must be included, because peritoneal
disease typically enhances slowly after contrast administration
[3]. The arterial phase images
are acquired at 15-20 sec, the portal phase images at 60-90 sec, and the
delayed phase images at 5 min after IV contrast injection. Homogeneous fat
suppression is a critical feature of the sequence to eliminate competing
signal from fat adjacent to the peritoneum.
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Fig. 2A —45-year-old man with right indirect inguinal hernia
(arrows). Axial gradient-refocused-echo in-phase image (A) and
axial fast spin-echo T2-weighted image (B) show bowel loops and fat
herniating through right external inguinal ring.
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Fig. 2B —45-year-old man with right indirect inguinal hernia
(arrows). Axial gradient-refocused-echo in-phase image (A) and
axial fast spin-echo T2-weighted image (B) show bowel loops and fat
herniating through right external inguinal ring.
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Fig. 3 —51-year-old woman with left ventral incisional hernia. Axial
T1-weighted 3D volumetric interpolated breath-hold image shows left incisional
hernia containing mesenteric fat and small-bowel loops (arrow).
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Disorders of Peritoneal Confinement
Hernias are abnormal protrusions of intraabdominal contents through a
defect in the abdominal wall, usually as the result of a congenital defect, a
loss of tissue strength, or trauma. Hernias are typically described by
anatomic location. MRI characterizes hernias well on the basis of its ability
to differentiate tissue planes.
Indirect Inguinal Hernia
In indirect inguinal hernias (Figs.
2A and
2B), intraperitoneal contents
herniate through the internal inguinal ring lateral to the inferior epigastric
vessels and into the inguinal canal. Bowel strangulation, incarceration, and
obstruction may result from these and other types of hernias.
Spigelian Hernia
A spigelian hernia is a hernia through the lateral ventral abdominal wall
at the point where the semilunar and semicircular lines intersect at the
lateral border of the rectus abdominus, also known as the spigelian
aponeurosis. Classic spigelian hernias are cranial to the junction of the
inferior epigastric vessels and the spigelian aponeurosis. Visualization of a
spigelian hernia on physical examination can be difficult, particularly in
obese patients. Bowel may herniate through the spigelian hernia and become
incarcerated or strangulated. Omentum may also herniate through the spigelian
aponeurosis. Abdominal pain may result from omental infarction within a
spigelian hernia.
Incisional Hernia
An incisional hernia results during or after closure of anterior abdominal
wall incisions (Fig. 3).
Imaging may be useful for showing the size and location of the abdominal
defect, particularly in obese patients, and for differentiating hernia from
hematoma early after surgery. MRI provides excellent multiplanar tissue
resolution for hernia characterization
[4].
Peritoneal Inflammation and Intraperitoneal Fluid
Inflammatory peritoneal disease may result in acute or chronic peritonitis.
Peritonitis may be infectious and is typically seen in the setting of bowel
perforation, diverticulitis, appendicitis, or severe cholecystitis. Bacterial
peritonitis may also result from peritoneal instrumentation, such as
peritoneal dialysis, surgery, or penetrating abdominal trauma. Noninfectious
causes of peritonitis include pancreatitis and systemic diseases such as
systemic lupus erythematosus.
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Fig. 4A —36-year-old man with acute peritonitis. Axial T1
gradient-refocused-echo volumetric interpolated breath-hold images before
(A) and after (B) contrast administration show smooth linear
enhancement of peritoneum (arrows, B) with unenhanced
intraperitoneal fluid, representing acute peritonitis.
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Fig. 4B —36-year-old man with acute peritonitis. Axial T1
gradient-refocused-echo volumetric interpolated breath-hold images before
(A) and after (B) contrast administration show smooth linear
enhancement of peritoneum (arrows, B) with unenhanced
intraperitoneal fluid, representing acute peritonitis.
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Fig. 5 —42-year-old man with sarcoidosis. Axial enhanced T1-weighted
gradient-refocused-echo volumetric interpolated breath-hold image shows
irregularly enhancing omental soft tissue (arrows) secondary to
sarcoidosis.
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A dynamic, enhanced gradient-echo pulse sequence is particularly pertinent
for the diagnosis of peritonitis. The administration of IV contrast material
produces peritoneal enhancement in cases of peritonitis. The peritoneal
contour may remain smooth, in contrast to the nodular peritoneal contour more
typical of neoplastic disease
[5] (Figs.
4A and
4B).
Sarcoidosis is a granulomatous systemic disease of unknown cause that
infrequently involves the peritoneum
[6]. MRI characteristics
typical of sarcoid peritonitis include regions of enhancing peritoneum, with
soft-tissue infiltration of the omentum and mesentery
(Fig. 5).
Hemoperitoneum
Hemoperitoneum usually occurs secondary to abdominal trauma or tumor
rupture. Blood products evolve over time into deoxyhemoglobin, methemoglobin,
and other degradation products, with concomitant signal changes (Figs.
6A and
6B). The appearance of blood
products on MRI varies with their stage of evolution. Acute blood in the form
of deoxyhemoglobin is isointense on T1-weighted images and dark on T2-weighted
images. Subacute blood in the form of methemoglobin is hyperintense on
T1-weighted images. Initially, methemoglobin is intracellular and appears dark
on T2-weighted images. Subsequently, it becomes bright on T2-weighted images
as the red cells lyse and the methemoglobin becomes extracellular. An old
hemorrhage is dark on both T1- and T2-weighted images because of the presence
of hemosiderin. T1-weighted images with fat saturation are quite sensitive in
detecting methemoglobin. Gradient-echo images can magnify the susceptibility
effects of decreased signal intensity seen with hemosiderin and
deoxyhemoglobin, thereby increasing their conspicuity. Similarly, a lesion
that loses significant signal intensity on in-phase images compared with
out-of-phase images of shorter TE may contain blood products. Smooth
peritoneal wall enhancement is sometimes noted, likely from reactive
inflammation (Figs. 7A,
7B, and
7C).
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Fig. 6A —55-year-old woman with intraperitoneal subacute hematoma. Axial
T2-weighted inversion-recovery image (A) and axial
gradient-refocused-echo image (B) show subacute blood, best seen in
perihepatic space (arrows). Use of inversion recovery eliminates
near-field artifact.
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Fig. 6B —55-year-old woman with intraperitoneal subacute hematoma. Axial
T2-weighted inversion-recovery image (A) and axial
gradient-refocused-echo image (B) show subacute blood, best seen in
perihepatic space (arrows). Use of inversion recovery eliminates
near-field artifact.
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Fig. 7A —48-year-old man with infected intraperitoneal hematoma. Axial
T2-weighted image (A) and axial T1-weighted gradient-refocused-echo
volumetric interpolated breath-hold images before (B) and after
(C) IV administration of contrast material show linear smooth
peritoneal enhancement, with presence of intraperitoneal blood-intensity
signal.
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Fig. 7B —48-year-old man with infected intraperitoneal hematoma. Axial
T2-weighted image (A) and axial T1-weighted gradient-refocused-echo
volumetric interpolated breath-hold images before (B) and after
(C) IV administration of contrast material show linear smooth
peritoneal enhancement, with presence of intraperitoneal blood-intensity
signal.
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Fig. 7C —48-year-old man with infected intraperitoneal hematoma. Axial
T2-weighted image (A) and axial T1-weighted gradient-refocused-echo
volumetric interpolated breath-hold images before (B) and after
(C) IV administration of contrast material show linear smooth
peritoneal enhancement, with presence of intraperitoneal blood-intensity
signal.
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Pneumoperitoneum
Pneumoperitoneum (intraperitoneal air) usually results from instrumentation
or viscus perforation and is characterized by regions of signal absence on T1-
and T2-weighted images. Free intraperitoneal air can be a subtle MRI finding,
requiring a thorough search pattern. Gradient-refocused-echo sequences are the
most sensitive in depicting dephasing artifacts from free air due to
"blooming" associated with magnetic field inhomogeneities at
air-tissue interfaces [7]
(Figs. 8A and
8B).
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Fig. 8A —54-year-old man with pneumoperitoneum. Axial in-phase (A) and
out-of-phase (B) images show small amount of free air
(arrows). Conspicuity is increased on in-phase images because of
longer TE, resulting in greater susceptibility artifact.
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Fig. 8B —54-year-old man with pneumoperitoneum. Axial in-phase (A) and
out-of-phase (B) images show small amount of free air
(arrows). Conspicuity is increased on in-phase images because of
longer TE, resulting in greater susceptibility artifact.
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Intraperitoneal Bile Leak
A bile leak usually results from surgery and is clinically occult when the
leakage is present in small amounts. An active bile leak can be elucidated by
administration of mangafodipir trisodium (Teslascan, GE Healthcare), which
results in increased intraperitoneal T1 signal intensity on delayed enhanced
images (Figs. 9A,
9B, and
9C). This increased signal
results from biliary excretion of the contrast agent, which usually collects
in the right upper quadrant. Formation of a pseudocapsule results in biloma
formation. Other findings, such as peritoneal inflammation, likely related to
both recent surgery and inflammation secondary to bile leakage, are visualized
as smooth peritoneal contrast enhancement. Bilomas are typically cystic,
heterogeneously hypointense on T1-weighted images, homogeneously hyperintense
on T2-weighted images, and lacking internal enhancement (Figs.
10A and
10B)
[8].
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Fig. 9A —48-year-old woman with bile leak. Axial fat-suppressed T1-weighted
image (A) and axial (B) and coronal (C) fat-suppressed
T1-weighted images 1 hr after IV administration of mangafodipir trisodium show
hyperintense perihepatic fluid denoting bile leak (arrow,
C).
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Fig. 9B —48-year-old woman with bile leak. Axial fat-suppressed T1-weighted
image (A) and axial (B) and coronal (C) fat-suppressed
T1-weighted images 1 hr after IV administration of mangafodipir trisodium show
hyperintense perihepatic fluid denoting bile leak (arrow,
C).
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Fig. 9C —48-year-old woman with bile leak. Axial fat-suppressed T1-weighted
image (A) and axial (B) and coronal (C) fat-suppressed
T1-weighted images 1 hr after IV administration of mangafodipir trisodium show
hyperintense perihepatic fluid denoting bile leak (arrow,
C).
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Fig. 10A —52-year-old man with biloma. Axial T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold image (A)
and axial T2-weighted inversion recovery image (B) show lambda-shaped
fluid collection (arrows) adjacent to caudate lobe, representing
biloma.
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Fig. 10B —52-year-old man with biloma. Axial T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold image (A)
and axial T2-weighted inversion recovery image (B) show lambda-shaped
fluid collection (arrows) adjacent to caudate lobe, representing
biloma.
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Mangafodipir trisodium is a hepatocyte-selective contrast agent that is
partially eliminated via biliary excretion. Maximal hepatic parenchymal
enhancement occurs during the first 20 min after intravenous injection of this
agent. Delayed images acquired at about 60 min after injection can be used to
assess possible bile leaks. Unfortunately, Mangafodipir trisodium is no longer
available in the United States. Multi-Hance (Gadobenate dimeglumine, Bracco
Diagnostics) is also partially excreted by the biliary system, however,
further experience is needed to determine its efficacy in assessing bile
leaks.
Peritoneal Neoplasms
Benign Tumors
A variety of benign tumors of the peritoneum can manifest as soft-tissue
masses. These lesions include lipomas, neurofibromas, and other mesenchymal
tumors. Peritoneal and mesenteric neurofibromatosis is uncommon, seen most
often in patients with a diagnosis of neurofibromatosis type 1 (von
Recklinghausen's disease). Peritoneal and mesenteric neurofibromas have MRI
characteristics similar to those of neurofibromas in other anatomic locations.
Typically, neurofibromas are hypoto isointense to muscle on T1-weighted
images, are hyperintense to muscle on T2-weighted images, and show moderate to
brisk gadolinium enhancement
[9]
(Fig. 11). Both T2-weighted
and gadolinium-enhanced T1-weighted gradient-echo pulse sequences are useful
for the diagnosis of neurofibromatosis.
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Fig. 11 —39-year-old woman with neurofibromatosis type 1. Axial T1-weighted
volumetric interpolated breath-hold image obtained after IV administration of
gadolinium chelate shows heterogeneously enhancing mass (arrow)
involving small-bowel mesentery, representing neurofibromatosis.
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Cystic mesothelioma of the peritoneum is a rare benign neoplasm that occurs
predominantly in women and tends to recur locally. It is seen as a
multilocular mass that can be confused with other intraperitoneal cystic
lesions.
Malignant Tumors
Peritoneal mesothelioma—Primary peritoneal mesothelioma is a
rare neoplastic condition of the peritoneum, often associated with asbestos
exposure. Peritoneal mesothelioma spreads along the serosal surface and may
invade solid and hollow viscera directly. MRI of the peritoneum typically
reveals a peritoneal mass with delayed contrast enhancement, often in
association with sheets of enhancing peritoneal disease. Small nodules may be
seen in the early stages. Later, these nodules may coalesce to form large,
confluent masses or omental caking
[10] (Figs.
12A,
12B, and
12C).
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Fig. 12A —58-year-old man with mesothelioma. Gradient-refocused-echo
out-of-phase image (A) and enhanced axial T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold images (B
and C) show enhancing large mass (arrows, A and
B), representing mesothelioma, which is entangling bowel loops.
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Fig. 12B —58-year-old man with mesothelioma. Gradient-refocused-echo
out-of-phase image (A) and enhanced axial T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold images (B
and C) show enhancing large mass (arrows, A and
B), representing mesothelioma, which is entangling bowel loops.
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Fig. 12C —58-year-old man with mesothelioma. Gradient-refocused-echo
out-of-phase image (A) and enhanced axial T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold images (B
and C) show enhancing large mass (arrows, A and
B), representing mesothelioma, which is entangling bowel loops.
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Peritoneal metastases—Metastatic disease is the most
commonly encountered neoplastic process involving the peritoneum. Peritoneal
carcinomatosis is typically manifested by enhancing peritoneal nodules (Figs.
13 and
14) or a rind of enhancing
perihepatic soft tissue. In patients with ovarian neoplasms, gastrointestinal
malignancies, or pseudomyxoma peritonei, the peritoneal surfaces, including
the perihepatic ligaments and transverse mesocolon, are frequent sites of
tumor deposition [11]. These
neoplastic peritoneal nodules and sheets enhance gradually after gadolinium
administration. Distinguishing between simple perihepatic ascites and
perihepatic peritoneal neoplastic disease can be difficult with CT because
peritoneal disease may not enhance significantly with iodinated contrast
material. Gadolinium-enhanced MR images, on the other hand, are sensitive to
peritoneal enhancement, which is seen with inflammatory or malignant
peritoneal disease but not with simple ascites
[12]. The most common
locations of peritoneal metastases are the pouch of Douglas, ileocecal region,
right paracolic gutter, sigmoid mesocolon, greater omentum, and right
subdiaphragmatic parietal peritoneum
[13].
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Fig. 13 —44-year-old woman with metastases from ovarian cancer. Axial
enhanced T1-weighted 3D gradient-refocused-echo volumetric interpolated
breath-hold image shows nodular enhancement of peritoneum over liver surface
(arrows), representing metastases in patient with history of ovarian
cancer.
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Fig. 14 —41-year-old woman with ovarian cancer. Axial fat-suppressed
gradient-refocused-echo T1-weighted enhanced image shows peritoneal tumor
implants in perihepatic space (white arrow) and Morison's pouch
(black arrow).
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Mesenteric carcinoid—Intraabdominal carcinoid tumors,
although often arising from the foregut, midgut, and hindgut, may also arise
from neuroendocrine cells within Meckel's diverticulum, within cystic
duplications, and within the mesentery and peritoneum. Mesenteric carcinoid
tumors are usually seen as nodular masses associated with mesenteric
stranding. Ninety-four percent of carcinoid tumors are hypervascular and
exhibit low T1 signal intensity, high T2 signal intensity, and moderately
intense gadolinium enhancement
[14] (Figs.
15A,
15B, and
15C). Independent of site of
origin, aggressive carcinoid tumors typically spread to the mesentery,
mesenteric lymph nodes, liver, ovaries, and spleen. Bone metastases are not
rare.
Miscellaneous Diseases
Mesenteric Cysts
Mesenteric cysts are composed of a diverse group of fluid-filled lesions,
usually serous, sanguineous, or mixed. They are classified on the basis of the
tissue of origin and can be divided into lymphatic, mesothelial, enteric, or
urogenital types or may be related to prior infection or trauma. The typical
MRI appearance of mesenteric cysts is a multiloculated or uniloculated
well-defined abdominal mass, usually in the mesentery of the small bowel
[15]. The MRI signal intensity
of mesenteric cysts varies depending on the cyst contents. Serous cysts tend
to have a low T1 signal, whereas proteinaceous and hemorrhagic cysts have an
intermediate to high T1 signal. Mesenteric cysts show no internal enhancement
with gadolinium chelates (Figs.
16A and
16B).
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Fig. 16A —51-year-old man with mesenteric cyst. Axial enhanced T1-weighted 3D
gradient-refocused-echo volumetric interpolated breath-hold image shows large,
nonenhancing extrahepatic cystic structure (arrow) posterior to
portal vein and anterior to hepatic artery, representing mesenteric cyst.
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Endometrial Implants
Endometrial implants, the hallmark of endometriosis, are focal deposits of
functioning endometrial tissue outside the uterus (Figs.
17A,
17B, and
17C)
[16]. Endometriosis is a
common disorder of women of reproductive age. The ectopic endometrium is
responsive to ovarian hormones, resulting in a typical cyclic pattern of
symptoms. Endometrial implants commonly involve the serosal surface of the
ovary, where they can be cystic and are referred to as endometriomas or
chocolate cysts. The implants can incite an inflammatory reaction resulting in
adhesions and fibrosis. Because of cyclic hormonal stimulation, endometriomas
often exhibit varying stages of hemorrhage (most commonly increased T1 and T2
signal or increased T1 and decreased T2 signal). Chronic hemorrhage or
fibrosis can result in focal areas of signal void on both T1- and T2-weighted
images [17]. Fat-suppressed
T1-weighted imaging is the most sensitive MRI technique for depicting
endometriomas [18]. The use of
fat saturation helps to distinguish endometrial implants from fatty lesions,
such as ovarian teratomas. Common locations for endometrial implants, in
addition to the ovaries, include the peritoneal lining around the rectovaginal
pouch and the abdominal wall
[16].
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Fig. 17B —48-year-old woman with cystic liver lesion incidentally discovered
on CT. Unsubtracted (B) and subtracted (C) axial T1-weighted
gadolinium-enhanced images show capsule-based lesion (arrows)
secondary to endometriosis.
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Fig. 17C —48-year-old woman with cystic liver lesion incidentally discovered
on CT. Unsubtracted (B) and subtracted (C) axial T1-weighted
gadolinium-enhanced images show capsule-based lesion (arrows)
secondary to endometriosis.
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Conclusion
The peritoneum, including peritoneal reflections and spaces, is difficult
to visualize when it is healthy. However, knowledge of these peritoneal
reflections improves our interpretation of imaging studies of patients with
peritoneal disease, including hernias, peritonitis, and neoplasia.
Successful MRI of the peritoneum depends critically on imaging technique.
Homogeneous fat suppression and dynamic contrast-enhanced imaging, including
delayed imaging, are important technical factors for successful detection and
characterization of lesions.
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Abstract
Introduction
