MRCS PART A · APPLIED BASIC SCIENCES
Peritoneal compartments & the epiploic foramen
Locate the space, trace its communication, then identify the boundary. Two selected abdominal anatomy objectives with four original SBAs. These are verbal spatial exercises, not diagnostic scans or instructions for operative access or drainage.
2 topics · 4 original SBAs
1 · Behind the stomach does not mean retroperitoneal
Your task: Distinguish the omental bursa from adjacent retroperitoneal tissue and from a fold of peritoneum.
What is the lesser sac?
The omental bursa: a recess of the peritoneal cavity behind the stomach and lesser omentum. The greater sac is the larger remainder; these names describe spaces, not two organs.
Is the lesser omentum the same thing?
No. An omentum is a peritoneal fold; a sac is a cavity or recess. Confusing a wall with the space it bounds leads to incorrect labels.
Which space lies between the posterior stomach and anterior pancreatic body?
In the conventional arrangement, the lesser sac. The peritoneal covering over the pancreas contributes to its posterior boundary; the space is not inside pancreatic tissue.
Is a space retroperitoneal simply because it lies behind the stomach?
No. Retroperitoneal means behind the posterior parietal peritoneum, not behind any named organ. A recess of the peritoneal cavity can have a retroperitoneal organ as a neighbour.
What changes if the label moves into tissue behind the posterior parietal peritoneum?
The compartment changes to retroperitoneal. Decide which side of the peritoneal boundary is meant, rather than applying 'posterior' as a compartment name.
Does fluid in this compartment prove a pancreatic cause?
No. Position identifies a compartment, not the origin of its contents. Nearby organs, peritoneal communication and the complete clinical and imaging assessment matter.
Does knowing the space identify a safe drainage route?
No. This lesson does not assess an individual's vessels, intervening organs or procedural risks. Spatial naming cannot authorise intervention.
2 · One aperture, four directional boundaries
Your task: Trace normal greater–lesser sac communication and separate the foramen's wall from structures within the adjacent ligament.
How do the two sacs normally communicate?
Through the epiploic or omental foramen, also called the foramen of Winslow. It lies behind the free edge of the lesser omentum—the hepatoduodenal ligament.
What assumption makes 'the natural communication' meaningful?
Conventional, unoperated anatomy without an acquired defect. An operation or pathological opening can create another route; that does not rename it the epiploic foramen.
What are its anterior and posterior boundaries?
Anterior: hepatoduodenal ligament. Posterior: peritoneum over the inferior vena cava. The portal vein lies within the anterior ligament, not in the posterior wall of the aperture.
Why can the word posterior produce two different answers?
Posterior within a ligament and posterior to an aperture use different reference objects. Always name the object whose boundary is being asked about.
What bounds the opening above and below?
The caudate lobe/process of the liver superiorly and the first part of the duodenum inferiorly in the conventional four-boundary model.
Can bowel pass into the lesser sac through this opening?
It can: this is the anatomical basis of a foramen-of-Winslow internal hernia. Location alone does not establish the cause, viability or treatment of an obstructed loop; no reduction or management instructions are provided.