## **Core Concept**
The question tests the knowledge of gastric anatomy and the potential spaces for perforated ulcers. A perforated ulcer in the pyloric antrum of the stomach can lead to leakage of gastric contents into the peritoneal cavity or localized areas.

## **Why the Correct Answer is Right**
The correct answer, , refers to the lesser sac (also known as the omental bursa). The pyloric antrum is located near the junction of the stomach and the duodenum and is part of the stomach that communicates with the lesser sac. When an ulcer in this region perforates posteriorly, the leakage of gastric contents is likely to be contained initially within the lesser sac. This can lead to localized peritonitis or abscess formation within this space before potentially spreading to the rest of the peritoneal cavity.

## **Why Each Wrong Option is Incorrect**
- **Option A:** The greater sac is the main compartment of the peritoneal cavity and is not the immediate space posterior to the pyloric antrum. While it's a potential site for spread, it's not the initial localized area for a posteriorly perforating ulcer in the pyloric antrum.
- **Option B:** The gastrohepatic ligament is not a space but rather a fold of peritoneum that connects the stomach to the liver. While it does contain the left gastric artery and vein, it's not directly relevant to the initial containment of a perforation.
- **Option C:** The infrahepatic space might be involved in cases of peritonitis or abscess formation but is not the immediate space posterior to the pyloric antrum.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the location of an ulcer's perforation significantly influences the clinical presentation. A posterior perforation of a pyloric antrum ulcer is likely to be contained within the lesser sac initially, potentially leading to a more contained and possibly less immediately severe presentation compared to a free perforation into the peritoneal cavity.

## **Correct Answer: .**