Overview
This lecture covers the anatomy of the peritoneal cavity, how it is divided into spaces, the organs it contains, and how to identify these on CT scans.
Structure of the Peritoneum
- The peritoneum is a thin membrane lining the abdominal cavity and covering abdominal organs.
- Parietal peritoneum lines the abdominal wall; visceral peritoneum covers the organs.
- Mesentery is a double layer of peritoneum connecting organs to the posterior abdominal wall.
- Four main mesenteries: transverse mesocolon, small intestine mesentery, sigmoid mesentery, and appendicial mesocolon.
- Omentum refers to double folds of peritoneum from the stomach to other organs (greater and lesser omentum).
Key Peritoneal Spaces
- The peritoneal cavity is divided into the greater sac (anterior) and lesser sac (posterior to stomach/liver).
- The epiploic foramen (of Winslow) connects the lesser and greater sacs.
- Supramesocolic space is above the transverse mesocolon; inframesocolic space is below it.
- Paracolic gutters are spaces lateral to the ascending and descending colon.
Organ Relationships and Retroperitoneal Structures
- Liver is on the right; spleen is on the left; stomach is J-shaped between them.
- Some organs are retroperitoneal (behind peritoneum): pancreas, duodenum (parts 2 and 4), ascending and descending colon.
- Intraperitoneal organs are within the peritoneal cavity and covered by mesentery.
Pelvic and Other Potential Spaces
- Right and left subphrenic spaces are between the diaphragm and liver/spleen.
- In females: pouch of Douglas (rectouterine pouch) is between the rectum and uterus; utero-vesicular space is between uterus and bladder.
- In males: rectovesical pouch is between rectum and bladder.
Imaging and Identification on CT
- Start CT abdomen review from thorax, identifying liver, spleen, stomach, intestines sequentially.
- Fluid accumulation makes potential spaces visible; examples include subphrenic, lesser sac, and paracolic gutters.
Key Terms & Definitions
- Peritoneum — membrane lining abdominal cavity and organs.
- Mesentery — double-layered peritoneal fold attaching intestines to the abdominal wall.
- Omentum — peritoneal fold extending from stomach to other organs.
- Greater sac — main peritoneal space (anterior).
- Lesser sac (omental bursa) — posterior space behind stomach/liver.
- Epiploic foramen — opening between lesser and greater sacs.
- Paracolic gutter — spaces lateral to colon.
- Pouch of Douglas — rectouterine pouch in females.
Action Items / Next Steps
- Review abdominal and retroperitoneal anatomy in additional lectures.
- Practice identifying peritoneal spaces and organs on CT images.
- Prepare for next week’s topic: retroperitoneum.