CT

DR SAKHER-ALKHADERICONSULTANT RADIOLOGIST AMC

IMAGING OF PERITONEAL PATHOLOGY

Cystic Masses

Mucinous Carcinomatosis with a tumor nodule along the right paracolic gutter

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.

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.

Pseudomyxoma peritonei with a little bit of scalloping and a mucocele of the appendix

Pseudomyxoma peritonei with thickened mesentery (arrow)

Pseudomyxoma peritoni

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.

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.

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.

Enteric cyst & mesothelial csyt

These are also mesenteric cysts. They are rare and have nonspecific imaging features.

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.

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

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

Tuberculosis

Echinococcal cyst

Hemoperitoneum

Radiological Findings

Solid MassesPeritoneal metastases

Omental cake (arrows) and ascites in a patient with peritoneal metastases

Metastasis of a lung carcinoma presenting as a solitary solid peritoneal mass

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. 

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

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 typicalnodal calcification

Peritoneal metastases

-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.

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.

Gross mesenteric mass lesions consistent with lymphadenopathy.  Hodgkin lymphoma.

Nodal metastasis from testicular teratoma. 

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 presentationgastrointestinal tract carcinoid can present as vague abdominal paincarcinoid syndrome (in 8% of patients with a carcinoid tumour 9)

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).

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

Carcinoid

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

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

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.

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

Mesenteric fibromatosis - Desmoid

Sclerosing MesenteritisThis 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 

Sclerosing Mesenteritis

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

Malignant mesothelioma

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

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

Malignant mesothelioma

Primary Peritoneal Serous Carcinoma

This tumor is also one of the primary peritoneal malignancies. It occurs exclusively in women.

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

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

THE END