omentum
Meaning of omentum: Nicknamed the policeman of the abdomen for the way it migrates toward trouble and wraps around inflammation before it can spread further.
Definition of omentum
The omentum is a fatty apron of peritoneum, the thin membrane lining the abdominal cavity, that hangs from the stomach and drapes over the intestines. It carries blood vessels, lymphatic channels and clusters of immune cells within its fat, and it can shift position inside the abdomen, settling against areas of injury or inflammation.
What are the greater and lesser omentum?
| Greater omentum | Lesser omentum | |
|---|---|---|
| Hangs from | The greater curvature of the stomach | The lesser curvature of the stomach and the first part of the small intestine |
| Attaches to | The transverse colon, then falls free over the intestines | The undersurface of the liver |
| Size | Large, and often thickly fatty | Small and thin |
The two are separate structures with separate attachments, so a finding in one says nothing automatically about the other. Both are folds of the same membrane, the peritoneum, which lines the abdomen and wraps most of the organs inside it.
What does it do?
The fat is a store, but the omentum is not simply padding. Scattered through it are milky spots, small collections of immune cells that sample the fluid moving through the abdominal cavity and mount a response to what they find. Its generous blood supply and its mobility let it drift toward an inflamed appendix, a leaking bowel or a fresh surgical join and wrap around the area, sealing it away from the rest of the cavity. That behavior earned it the nickname policeman of the abdomen, and it is one reason a localized infection inside the abdomen sometimes stays walled off instead of spreading. The tissue also feeds the immune system more broadly, producing and holding immune cells rather than only reacting to arrivals.
Why does it matter in disease and surgery?
Cancers arising inside the abdomen, of the ovary and stomach in particular, spread across the peritoneal surfaces, and the omentum is a favored landing site. Deposits there can thicken the whole sheet into a mass visible on scanning, described as omental caking. Removal of the omentum is therefore a standard part of the operation for several abdominal cancers, both to take out disease and to establish how far it has traveled. Surgeons also put it to deliberate use: because it brings its own blood supply and immune tissue with it, a flap of omentum can be moved to cover a repair, fill a cavity left by removed tissue, or support healing at a site some distance away.
Used in a sentence
Imaging showed thickening of the omentum consistent with spread of disease within the abdomen.
Good to know
The greater omentum and the lesser omentum are distinct structures with different attachments, so a finding involving one does not automatically apply to the other.
Word origin
Where “omentum” comes from
From Latin omentum, the name for the fatty membrane covering the intestines.