[Echographic anatomy of the greater peritoneal cavity and its recesses]

The peritoneum of the great abdominal cavity and its recesses are a blind radiographical area which can however be easily outlined by US when it contains fluid. The anatomical study of these usually virtual cavities represents the purpose of this paper. The natural contrast of the peritoneal fluid as amplified by the mechanical effect produced by an adequate amount of fluid, allows a clear visualization of the anatomy of various peritoneal structures in either upper (subphrenic, subhepatic, lesser sac, etc.) or lower (pelvic) areas. The sovramesocolic and the infracolic compartments are in communication through the two external paracolic gutters which are the main passageways for the fluids between upper and lower compartments. In fact, peritoneal fluids are in constant movement due to different factors, such as gravity, statics, which causes the peritoneal fluids to flow into the lowest part of the peritoneal cavity, and hydrostatic pressure. Pressure differences are thought to convey fluids from various sites of the abdomen into different areas. In the lower abdomen, pressure is 3 times as much as in the upper abdomen, which causes the fluids to move into the subhepatic and subphrenic regions. The redistribution of fluids can be influenced by particular anatomical causes. The phrenicocolic ligament, eg, is a barrier to the advancing of fluids along the left paracolic gutter, which makes the right paracolic gutter the main passageway for the fluids. This pattern explains why abscesses are more frequent in the right than in the upper left abdominal regions. Another example is the tiny Winslow opening, which does not allow inflammatory material to pass into the lesser sac in case of inflammatory processes of the great peritoneal cavity and vice versa. Moreover, pointing out fluid collections and abscesses is important, since an early diagnosis and a topographic map are essential in order to plan treatment.