This document summarizes various pathologies that can present as cystic or solid masses in the peritoneum based on CT imaging findings. It describes mucinous carcinomatosis, pseudomyxoma peritonei, lymphangioma, enteric duplication cyst, tuberculosis, echinococcal cyst, peritoneal metastases, lymphoma, carcinoid tumors, gastrointestinal stromal tumors, inflammatory pseudotumor, desmoid tumors, sclerosing mesenteritis, malignant mesothelioma, primary peritoneal serous carcinoma and desmoplastic small round cell tumor. Key distinguishing imaging features for each condition are provided.

1. CT
DR SAKHER-ALKHADERI
CONSULTANT RADIOLOGIST AMC
IMAGING OF PERITONEAL
PATHOLOGY

3. Cystic Masses
Mucinous Carcinomatosis with a tumor nodule along the right paracolic
gutter

4. 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.
In peritoneal carcinomatosis we see tumor nodules
along the peritoneal lining (arrow), omental tumor
deposits, and bowel obstruction.

5. 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.
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.

6. Pseudomyxoma peritonei with a little bit of scalloping and
a mucocele of the appendix
Pseudomyxoma peritonei with thickened mesentery
(arrow)
Pseudomyxoma peritoni

7. Lymphangioma
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.

8. 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.
They may occur anywhere in the mesentery, so either adjacent to or away from the
bowel.
Case of 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.

9. Non pancreatic pseudocyst
Non pancreatic 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.

10. Enteric cyst & mesothelial
csyt
These are also mesenteric cysts. They are rare and have nonspecific imaging features.

11. Peritoneal inclusion cyst
Also called Multilocular peritoneal inclusion cyst or Benign cystic mesothelioma.
This is an uncommon benign primary peritoneal tumor that has no relation with the
malignant mesothelioma.
It occurs in premenopausal women with prior gynaecological surgery or infection that
results in peritoneal scarring.
The hormonally active ovaries secrete fluid that becomes loculated in the pelvis.

12. Peritoneal inclusion cyst
The imaging features of a
peritoneal inclusion cyst
are non-specific except
that it has to be located in
the pelvis:
-Multicystic pelvic mass
-Enhancing septa
-Peritoneal surfaces of
uterus, bladder
-May extend into upper
abdomen

13. Tuberculosis
Usually there is accompanying abnormality of the terminal ileum and lymphadenopathy.
The lymph nodes most often are of low attenuation (caseated).

14. Tuberculosis

17. Echinococcal cyst

21. Hemoperitoneum

25. Radiological Findings

28. Solid Masses
Peritoneal metastases
Omental cake (arrows) and ascites in a
patient with peritoneal metastases
Metastasis of a lung carcinoma
presenting as a solitary solid peritoneal
mass

29. 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 , solid masses
and ascites.

30. CT depicts multiple nodules and masses dispersed in the parietal
peritoneum and mesenteries. Note the "omental cake" sign (arrows)
Omental cake refers to infiltration of the omental fat by material of soft-
tissue density. The appearances refer to the contiguous omental mass
simulating the top of a cake.
Peritoneal metastases

31. Peritoneal metastases can range in appearance from
invisible to multiple large masses, and historically CT can
only detects 60-80% of peritoneal metastases later shown
to be present at surgery, although more recent studies
reported detection rates of 85-93% .
Appearances include :
-thickening and enhancement of peritoneal reflections
(especially if nodular)
-soft tissue nodules
-stranding and thickening of the omentum (omental cake)
-stranding an distortion of the small bowel mesentery
-ascites, especially if loculated
-calcifications 2 (particularly in cystadenocarcinoma of the
ovary)
nodular with non-calcified component are typical
nodal calcification
Peritoneal metastases

32. -Generalized lymphadenopathy is defined as enlargement of more
than 2 noncontiguous lymph node groups. A thorough history and
physical examination are critical in establishing a diagnosis. Causes
of generalized lymphadenopathy include infections, autoimmune
diseases, malignancies, histiocytoses, storage diseases, benign
hyperplasia, and drug reactions.
Lymphadenopathy
-Normal mesenteric lymph nodes may now be routinely identified at
the mesenteric root and throughout the mesentery .A recent report
has shown that mesenteric lymph nodes with a mean maximum
short-axis dimension of 4.6 mm may be seen in the normal
mesentery at CT.
-The most common malignancy resulting in mesenteric
lymphadenopathy is lymphoma Early in the course of the disease,
the lymph nodes may be small and discrete. As the disease
progresses, the nodes often coalesce, forming a conglomerate soft-
tissue mass.

33. Lymphoma
NHL located in the small bowel mesentery
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.

34. Gross mesenteric mass lesions consistent
with lymphadenopathy. Hodgkin
lymphoma.

35. Nodal metastasis from testicular teratoma.

36. 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.
Carcinoid
Clinical presentation
gastrointestinal tract carcinoid can present as vague
abdominal pain
carcinoid syndrome (in 8% of patients with a
carcinoid tumour 9)

37. Carcinoid
patient with typical carcinoid with
central calcification (blue arrow).
Notice the bowel retraction and wall
thickening.
There is a metastasis in the liver
(yellow arrow).

38. Positive octreoscan in a patient with carcinoid
and liver metastases (blue arrows)
Carcinoid

39. 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

40. Large exophytic soft tissue mass arising from
the greater curvature of the stomach.
GIST TUMOR
Common sites
of involvement
include:
stomach: 70%
small
intestine: 20-
25%
anorectum: 7%
oesophagus

41. Inflammatory
Pseudotumor
This disease can affect lung, orbit and mesentery.
Inflammatory pseudotumor is a diagnosis by exclusion.
Usually the diagnosis is made at surgery or biopsy.
It is the result of chronic inflammation with an unclear pathogenesis.
Probably it is an occult infection due to minor trauma or post surgical.

42. Mesenteric fibromatosis -
Desmoid
Mesenteric fibromatosis is also known as intra-abdominal fibromatosis,
abdominal desmoid or desmoid tumor.
Mesenteric fibromatosis or desmoid is a benign proliferative process that is
locally aggressive and can recur, but it does not metastasize.
The small bowel mesentery is the most common site.
13% of patients have familial adenomatous polyposis (FAP).
The lesion is well circumscribed with a low density on CT.
and appear hyperintense on MRI with moderate
enhancemment

43. Mesenteric fibromatosis - Desmoid

44. Sclerosing Mesenteritis
This disease has multiple synonyms reflecting the wide
histologic spectrum: mesenteric panniculitis, fibrosing
mesenteritis and mesenteric lipodystrophy.
Pathologically it is a chronic inflammation of unknown etiology.
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.
In a more advanced stage you can have significant
fibrosis resulting in retraction of the small bowel.
Within these masses dystrophic calcifications

45. Sclerosing Mesenteritis
Notice the retraction of
the bowel and also
notice the resemblance
to carcinoid.

46. Malignant mesothelioma
Suggestive features are a sheet-like peritoneal thickening and absence of
lymphadenopathy.
Just like pleural mesothelioma, it is associated with asbestos exposure.

47. In advanced cases you will see encasement of
the intra-peritoneal structures.
Malignant mesothelioma

48. Primary Peritoneal Serous
Carcinoma
This tumor is also one of the primary peritoneal malignancies. It occurs
exclusively in women.

49. 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
Primary Peritoneal Serous Carcinoma

50. Desmoplastic Small Round Cell
Tumor
It is a rare malignancy of
uncertain origin.
It occurs primarily in young
men with a mean age of 19
years.
NHL would be number
one in the differential
diagnosis

51. THE END