Peritoneal and omental rule 3: Pathology

Intraperitoneal pathology:

1-Ascites:
Means presence of fluid in the peritoneal cavity such as serous fluid, blood or pus.
If the fluid is mucinous in nature, this cause a condition known as pseudo myxoma peritoni.
Pseudo myxoma peritoni appears as highly attenuated ascites causing scalloping of the visceral surfaces of the peritoneum covering liver, spleen and other organs.

2-Rotational abnormalities:
-Non rotation:
The large bowel is seen in the left side of the abdomen while the small bowel is seen in the right side.
Reversed position of the superior mesenteric artery and vein in relation to head of the pancreas(normal SMV is nearer to the head).
Mid gut volvulus:
A typical whirl sign around SMA. Note the high attenuation structure (arrow) in the whirld loops, representing SMA thrombosis.
-Partial rotation:
Here, the cecum is the only organ seen in abnormal position in the left side of the abdomen.


3-Vascular lesions:
-Due to SMA and SMV thrombosis seen as a filling defect or ring enhancement of the vessel.
-Effect of thrombosis on the bowel
Bowel wall thickening.
Bowel dilatation.
Decreased enhancement of the bowel wall.


4- Mesenteric panniculitis:
-It is an inflammatory condition of unknown etiology.
-CT findings:
Hazy mesenteric infiltration.
Relative sparing of perimesenteric fat.
Which means a mass abnormality seen in the mesentry but without any affection of surrounding fat with also non affection of the vessels seen inside this mass.


5-Mesenteric cysts:
If the mesenteric cyst contains septation, it will be a lymphangioma.
If contains most essentially fat in addition to calcium and soft tissue component, it will be cystic teratoma.
Other types of mesenteric cysts are simple cyst, or due to infection or trauma or simple duplication cyst.
Except lymphangioma with its septation and teratoma with its fat content, do not diagnose the other types of mesenteric cysts but just right it as a mesenteric cyst.

6-Peritoneal mesothelioma:
-Most common peritoneal neoplasm.
-Appears as omental cake or peritoneal carcinomatosis.


7-Peritoneal and retroperitoneal liposarcoma:
-Second most common.
-Contain fat and soft tissue components.
-D.D. from lipoma(lipoma contain fat only).
If you see an abdominal mass containing fat, you must diagnose it as a liposarcoma regardless you see a soft tissue component or not until prove otherwise by biopsy.

8-Intraperitoneal desmoid tumor:
-Occurs in patient with familial adenomatous polyposis syndrome (Gardner syndrome).
-It is also seen in abdominal wall and rectus muscle.




9-Mesenteric lymphoma:
-Seen as single or multiple discrete masses.
-Giving appearances of Sandwish sign:
It is the classic appearance giving rise to bulky adenopathy enveloping mesenteric vessels and fat.
Non Hodgkin lymphoma is  one of the most common mesenteric masses.


10-Metastases:
-Giving rise to omental cake.
-Peritoneal carcinomatosis.
-Ascites.