The omentum is a large sheet of fatty tissue inside the abdomen. The greater omentum hangs down from the stomach like an apron, draping over the intestines. A smaller sheet, the lesser omentum, connects the stomach to the liver.
The omentum is a fold of peritoneum filled with fat, blood vessels, and immune tissue. It cushions the organs, stores fat, and helps control infection. When part of the bowel is inflamed or perforated, the omentum can move toward the problem and wall it off. This is why it is sometimes described as the abdomen’s policeman.
What does the omentum look like under the microscope?
Most of the omentum is adipose tissue, meaning mature fat cells. Blood vessels and lymphatic channels run through it, and its outer surface is covered by a single layer of mesothelial cells. Scattered through the fat are small collections of immune cells called milky spots. These filter fluid from the abdominal cavity, and they are one reason tumor cells that reach the cavity so often lodge in the omentum.
Why is the omentum removed and examined?
The omentum is a favored landing site for tumor cells floating in the abdominal cavity, so it is frequently sampled or removed during cancer surgery. The operation to remove it is called an omentectomy.
This is standard practice in surgery for ovarian cancer, and it is common in surgery for cancers of the stomach, colon, appendix, and uterus. Even when the omentum looks completely normal to the surgeon, deposits too small to see are sometimes found under the microscope.
Radiologists sometimes use the phrase omental caking to describe an omentum thickened by widespread tumor. Patients often encounter this term on a scan report before any tissue has been examined.
What will my report say about the omentum?
An omentectomy report usually addresses three things: whether tumor was found, how much, and how it relates to the rest of the specimen.
- Negative for tumor. No tumor cells were found in the tissue examined. This is a favorable finding.
- Positive for tumor. Tumor deposits are present. The report may describe the size of the largest deposit, since this affects staging in some cancers.
- Acellular mucin only. In appendiceal and some other mucinous tumors, jelly-like material may be present without any tumor cells in it. See acellular mucin.
Because the omentum is large and tumor deposits can be small, pathologists examine multiple sections from different areas rather than the whole specimen.
Tumor in the omentum is counted as spread beyond the original organ, and in most cancers this places the disease at a more advanced stage. There are exceptions. For low-grade appendiceal mucinous neoplasms, the outlook is far better than the stage alone would suggest.
Questions to ask your doctor
- Was my omentum removed during surgery?
- Was any tumor found in it?
- How large were the deposits, and how many were there?
- Was the material found in the omentum mucin without tumor cells?
- How does this finding affect my stage?
- Does removing the omentum cause any long-term problems?
- Does this change the recommended treatment?
Related articles on MyPathologyReport.com
We are proud to partner with:
🔍 Search MyPathologyReport
Type what you see on your report — for example a diagnosis or test name