**Question:** A posteriorly perforating ulcer in the pyloric antrum of the stomach is likely to produce initial localized peritonitis or abscess formation in the

A. lesser sac
B. lesser omentum
C. greater sac
D. lesser omentum and peritoneum

**Correct Answer:** A. lesser sac

**Core Concept:**
Pyloric ulcers are a rare type of peptic ulcer disease that typically affect the posterior wall of the pyloric antrum in the stomach. These ulcers can perforate and lead to complications such as localized peritonitis or abscess formation due to the close proximity of the pyloric antrum to the lesser sac, a space between the stomach and the spleen.

**Why the Correct Answer is Right:**
A posteriorly perforating ulcer in the pyloric antrum will perforate into the lesser sac. When this occurs, the contents of the stomach, including bacteria and gastric juices, enter the lesser sac, leading to localized peritonitis and the formation of an abscess. This is due to the anatomical location of the lesser sac, which is adjacent to the posterior wall of the pyloric antrum.

**Why Each Wrong Option is Incorrect:**

A. C. Greater sac (These options are incorrect because the greater sac is located between the stomach and the liver, and does not directly connect to the pyloric antrum or stomach contents.)
B. Lesser omentum and peritoneum (This option is incorrect because the lesser omentum is a fold of peritoneum that connects the stomach to the spleen, not a space where peritonitis or abscess formation would occur.)

**Clinical Pearl:**
When evaluating patients with suspected peritonitis or abscess formation following a perforated ulcer, the presence of a perforation in the pyloric antrum should prompt consideration of the lesser sac as the site of abscess formation. Understanding the anatomy of the abdomen is crucial to accurately diagnose and treat these cases.