1. Imaging of the peritoneum
and mesenteric lesions.
Dr/ ABD ALLAH NAZEER. MD.

2. The peritoneum is a thin, translucent, serous membrane and is the
largest and most complexly arranged serous membrane in the body. The
peritoneum that lines the abdominal wall is called the parietal
peritoneum, whereas the peritoneum that covers a viscus or an organ is
called a visceral peritoneum. The peritoneal cavity is a potential space
between the parietal peritoneum, which lines the abdominal wall, and
the visceral peritoneum, which envelopes the abdominal organs. In
men, the peritoneal cavity is closed, but in women, it communicates
with the extraperitoneal pelvis exteriorly through the fallopian tubes,
uterus, and vagina. Peritoneal ligaments, mesentery, and omentum
divide the peritoneum into two compartments: the main region, called
the greater sac, and a diverticulum, omental bursa, or lesser sac .
Peritoneal ligaments are double layers or folds of peritoneum that
support a structure within the peritoneal cavity; omentum and
mesentery are specifically named peritoneal ligaments. Most
abdominal ligaments arise from the ventral or dorsal mesentery.
Anatomic definitions.

4. Mesenteries
The visceral peritoneum lines all the organs that are intraperitoneal.
The parietal peritoneum lines the anterior, lateral and posterior walls
of the peritoneal cavity.
The deepest portion of the peritoneal cavity is the pouch of Douglas in
women and the retrovesical space in men, both in the upright and
supine position.
The mesentery is a double fold of the peritoneum.
True mesenteries all connect to the posterior peritoneal wall.
These are:
The small bowel mesentery
The transverse mesocolon
The sigmoid mesentery (or mesosigmoid)
Specialized mesenteries do not connect to the posterior peritoneal wall.
These are:
The greater omentum: connects the stomach to the colon
The lesser omentum: connects the stomach to the liver
The mesoappendix: connects the appendix to the ileum

6. Omentum:
The omentum is divided into the greater and lesser
omentum.
The greater omentum is subdivided into:
Gastrocolic ligament (yellow arrow): the largest
component
Gastrosplenic ligament: up to the hilus of the spleen
Gastrophrenic ligament: not shown on this illustration
The lesser omentum is subdivided into:
Gastrohepatic ligament: connects the left lobe of the liver
to the lesser curvature of the stomach.
Hepatoduodenal ligament (blue arrow): free edge of the
omentum, which contains the portal vein, hepatic artery
and common bile duct .

11. Peritoneal circulation:
These compartments enable the peritoneal cavity to have a normal
circulation for peritoneal fluid.
In the normal abdomen without intraperitoneal disease, there is a small
amount of peritoneal fluid that continuously circulates.
The movement of fluid in this circulatory pathway is produced by the
movement of the diaphram and peristalsis of bowel.
It predominantly flows up the right paracolic gutter which is deeper and
wider than the left and is partially cleared by the subphrenic lymphatics.
There are watershed regions in the peritoneal cavity that are areas of
fluid stasis:
Ileocolic region
Root of the sigmoid mesentery
Pouch of Douglas
When you are staging a patient for gastrointestinal malignancy you have
to look for disease in these areas of stasis.
Clearly the surgeons do better in finding subtle disease in these areas.

13. Peritoneal anatomy after intra-abdominal contrast injection.

14. Imaging Modalities.
US: may depict peritoneal collections or
ascites and is used to guide drainage of
ascites and large superficial fluid collections
CT : is the most common imaging modality
used to detect diseases of the peritoneum
to fully delineate peritoneal anatomy and
the extent of disease, we prefer to perform
isotropic imaging with coronal and sagittal
reformations.

15. Magnetic resonance (MRI).
Disadvantages of MR imaging include:
1- motion artifacts caused by respiration
and peristalsis
2- chemical shift artifacts at the bowel-
mesentery interface.
3-the spatial resolution of MR imaging is lower
than that of CT, a characteristic that may make
it difficult to assess small peritoneal lesions.
4-Patients who are ill may not tolerate prolonged
MR imaging examinations.

17. Pathology OF Peritoneum and Mesentery.
Cystic Masses
Mucinous Carcinomatosis
Pseudomyxoma peritonei
Mesenteric cyst - Lymphangioma
Enteric Duplication Cyst
Nonpancreatic Pseudocyst
Enteric cyst and mesothelial cyst
Peritoneal Inclusion Cyst
Tuberculosis
Echinococcal Cyst
Cystic teratoma

18. Solid Masses
Peritoneal metastases
Lymphoma
Carcinoid
Gastrointestinal Stromal Tumor - GIST
Inflammatory Pseudotumor
Mesenteric fibromatosis - Desmoid
Sclerosing Mesenteritis
Malignant mesothelioma
Primary Peritoneal Serous Carcinoma
Desmoplastic Small Round Cell Tumor
Retro-peritoneal liposarcoma.

21. Mucinous Carcinomatosis.
Mucinous carcinomatosis is the most common cystic
tumor to affect the peritoneal cavity.
Usually these metastases arise from mucinous
carcinomas of the ovary or of the gastrointestinal tract
(stomach, colon, pancreas).
The prognosis is poor.
However, when low-grade mucinous adenocarcinoma of
the appendix spreads to the peritoneal cavity, the
consequence is typically pseudomyxoma peritonei,
which is a distinct tumor with a better prognosis.
In peritoneal carcinomatosis we see tumor nodules
along the peritoneal lining (arrow), omental tumor
deposits, and bowel obstruction.

22. Mucinous Carcinomatosis with a tumor
nodule along the right paracolic gutter.

23. Peritoneal mucinous carcinomatosis that caused small bowel obstruction in a 40-year-old
man who complained of progressive abdominal pain, nausea, and vomiting. Intravenous
and oral contrast-enhanced CT scans show low-attenuation mucinous ascites that infiltrates
between the folds of the small bowel mesentery. There are low-attenuation mucinous
metastatic deposits in the greater omentum (arrows in a) and soft-tissue attenuation
deposits along the peritoneal surfaces and in the paracolic gutters (arrows in b).

24. Pseudomyxoma peritonei.
Pseudomyxoma peritonei is the result of a mucinous
adenocarcinoma of the appendix, which presents as a
mucocele and spreads to the peritoneal cavity.
It is a clinical syndrome, characterized by recurrent and
recalcitrant voluminous mucinous ascites due to surface
growth on the peritoneum without significant invasion
of underlying tissues.
A typical feature of pseudomyxoma peritonei is
scalloped indentation of the surface of the liver and
spleen.
Unlike peritoneal metastases, there are no tumor
nodules.
There may be some calcifications.

25. Pseudomyxoma peritonei in a 70-year-old woman who complained of
increasing abdominal girth. Longitudinal (a) and transverse (b) sonograms of
the abdomen show complex, hypoechoic ascites that contains nonmobile
echoes and centrally displaced small bowel that has a starburst appearance.

27. Pseudomyxoma peritonei with pronounced scalloping of the liver
and almost destruction of the spleen. Notice the calcifications.

28. Pseudomyxoma peritonei with thickened mesentery (arrow).

29. Mesenteric cyst – Lymphangioma.
Mesenteric cyst is a descriptive term for any cystic lesion
within the mesentery.
Usually it is a lymphangioma.
Other mesenteric cysts like enteric duplication cyst,
enteric cyst, nonpancreatic pseudocyst and mesothelial
cyst are very uncommon and have no specific features.
Lymphangioma is a benign lesion of vascular origin.
Most lymphangiomas are located in the neck, but 5% of
lymphangiomas are abdominal.
Lymphangioma has enhancing septa.
Unlike in cystic peritoneal metastases, ascites is not a
feature of lymphangioma.
When you see a septated cystic lesion without ascites
the most likely diagnosis is a lymphangioma.

30. (Lymphangioma).

32. (Lymphangioma).

33. Enteric Duplication Cyst.
Enteric duplication cyst is a cyst with a wall that has all
three layers of the bowel wall, i.e. mucosa, submucosa
and muscularis propria.
Although we commonly think of duplication cysts when
we see a cystic mass adjacent to the bowel, we have to
realize, that these are rare lesions. They may occur
anywhere in the mesentery, so either adjacent to or
away from the bowel.
On the left an enteric duplication cyst.
It is located in the transverse mesocolon.
This patient was suspected of having a cystic pancreatic
tumor.
The specimen demonstrates all the bowel wall layers

34. Enteric Duplication Cyst.

35. Enteric Duplication Cyst.

36. Nonpancreatic Pseudocyst.
Nonpancreatic pseudocyst is a residual of an old hematoma or infection.
Most of these patients have a history of prior abdominal trauma.
Often there is a thickened wall and there can be some debris within the lesion.

37. On the left a specimen and CT image of a nonpancreatic pseudocyst.
Notice the thick wall.
Probably this is an old hematoma or abscess.

38. Enteric cyst and mesothelial cyst.

39. Peritoneal Inclusion Cyst

40. Peritoneal inclusion cyst.

41. Tuberculosis.
T.B can produce very thick ascites, that can
be loculated in distribution.
Because of this, it can simulate a cystic
lesion.
Usually there is accompanying abnormality of
the terminal ileum and lymphadenopathy.
The lymph nodes most often are of low
attenuation (caseated).
So these are the things to look for.

42. TB the peritoneum is usually very thick (arrow).

43. Tuberculous peritonitis.

44. Tuberculous peritonitis.

45. Echinococcal Cyst.

46. Retro-peritoneal teratoma.

47. Solid Masses.
Peritoneal metastases
Peritoneal metastases are the most common
peritoneal solid masses.
Gastrointestinal and ovarian cancers are the
most common etiologies.
Usually there are omental metastases, i.e.
omental cake and ascites.
On the left a CT demonstrating omental cake in a
patient with ovarian cancer.

48. Peritoneal metastases.

49. Peritoneal metastases.

50. Serosal metastases.

51. Lymphoma.
NHL is the most common cause of
lymphadenopathy.
Usually there are other sites with lymphoma.
The CT attenuation at diagnosis is very
homogeneous in most cases with minimal to no
enhancement.
Heterogeneous attenuation is seen only in cases
with aggressive histology.
During treatment the attenuation becomes
heterogeneous as a result of necrosis and
fibrosis.
Calcification may occur

52. NHL located in the small bowel mesentery.

53. Primary
peritoneal
lymphoma.

54. Lymphomatosis. Intravenous and oral contrast-enhanced CT scan
shows soft tissue diffusely infiltrating through the peritoneum,
encasing the small bowel, and lining the folds of the small bowel
mesentery. Ascites and diffuse peritoneal thickening are present.

55. Carcinoid.
Carcinoid is a slow-growing neuroendocrine tumour
most commonly found in the small bowel.
Less than 10% of patients with carcinoid will develop
the carcinoid syndrome, caused by the
overproduction of serotonin, which can lead to
symptoms of cutaneous flushing, diarrhea and
bronchoconstriction.
Carcinoid metastasizes to the mesentery, which at
times is easier to appreciate than the primary tumor
in the small bowel. There is associated bowel wall
thickening due to a desmoplastic reaction.

56. Carcinoid with central calcification (blue arrow). Positive octreoscan in a patient with
carcinoid and liver metastases (blue arrows)

58. Gastrointestinal Stromal Tumor - GIST
Primary small bowel tumors can extend into
the mesentery and the typical example of that
is the GIST.
You can have a large mesenteric component
and such a small attachment to the bowel,
that you may not appreciate it.
On CT they are of mixed density due to
necrosis and hemorrhage and they tend to be
well vascularized, so they will enhance like the
case on the left.

59. Gastrointestinal Stromal Tumor - GIST

61. Mesenteric fibromatosis – Desmoid.
Mesenteric fibromatosis is also known as intra-
abdominal fibromatosis, abdominal desmoid
or desmoid tumor.
On the left a 33-year-old man who complains
of an increasing abdominal girth, abdominal
fullness, and a palpable abdominal mass.
First study the images on the left and continue
with the MR.
Look for some imaging features that are helpful
in the differential diagnosis.

62. Mesenteric fibromatosis.

63. Mesenteric fibromatosis – Desmoid
low density tumor located in the greater omentum (upper image)
and the gastrosplenic ligament (lower image).

64. Sclerosing Mesenteritis (panniculitis).
This disease has multiple synonyms reflecting the
wide histological spectrum: mesenteric panniculitis,
fibrosing mesenteritis and mesenteric lipodystrophy.
Pathologically it is a chronic inflammation of
unknown etiology.
This entity is more common than previously thought.
The signs and symptoms are variable.
Patients present with pain, a palpable mass or bowel
complications, but in many cases it is an incidental
finding on CT made for other reasons.

65. Sclerosing Mesenteritis(panniculitis).

66. Sclerosing Mesenteritis(panniculitis).

67. Sclerosing mesenteritis (Panniculitis).

68. Sclerosing encapsulating peritonitis.

69. Gliomatosis peritonei.

70. Retroperitoneal liposarcoma.

71. Retroperitoneal liposarcoma.

72. Dedifferentiated liposarcoma.

73. Malignant mesothelioma.

76. Primary Peritoneal Serous Carcinoma.
This tumor is also one of the primary peritoneal
malignancies. It occurs exclusively in women.
This tumor is histologically identical to malignant ovarian
surface epithelial tumors.
It was once thought to be very rare, but now almost one
third of tumors previously diagnosed as ovarian cancer are
diagnosed as primary peritoneal serous carcinoma.
Consider this diagnosis when:
Ovaries are normal or involvement of extraovarian sites is
greater than that of the ovarian surface or if ovaries are
involved, yet disease is confined to the surface epithelium
As a radiologist you should consider this diagnosis if you
think of metastatic ovarian cancer but the ovaries are
normal.

77. Primary peritoneal serous carcinoma.

78. Peritoneal mucinous carcinomatosis.

79. Desmoplastic Small Round Cell Tumor.
This tumor is also one of the primary peritoneal
malignancies.
It is a rare malignancy of uncertain origin.
It occurs primarily in young men with a mean
age of 19 years.
Consider this diagnosis if you see something that
looks like peritoneal carcinomatosis in a young
man that has no history of a primary malignancy.
It is a very aggressive tumor with a poor
prognosis.

80. Desmoplastic Small Round Cell Tumor.

82. Miscellaneous lesions of the peritoneum.
Peritoneal fluid: Ascites.

83. Ascites at CT and MRI images.

84. Shock bowel with hemoperitoneum.

85. Pneumoperitoneum at X-Ray chest.

86. Pneumoperitoneum at CT Scan.

87. Pneumoperitoneum of the abdomen.

88. Peritonitis with fluid collection and abscess at the pelvis.

89. Abscess from perforated diverticulitis.

90. Hydatid disease of the peritoneum.
Almostly secondary to hepatic disease.
The hydatid may be single or multiple.

91. Hydatid cyst at the pelvic peritoneum.

92. Torsion of the greater omentum with omental infarction.

94. CT images of missed towel within the peritoneum.