A 58-year-old man with a history of peptic ulcer disease presents to the emergency department with sudden-onset, severe, generalized abdominal pain that he recalls began while he was eating lunch. On examination, he has marked abdominal rigidity, guarding, and rebound tenderness. An erect chest X-ray is obtained. The structure marked **A** in the diagram shows a crescent-shaped lucency. Which of the following is the most likely diagnosis and primary pathophysiology?
A. Acute pancreatitis with retroperitoneal air tracking into the peritoneal cavity
B. Post-endoscopic perforation managed conservatively with observation and antibiotics alone
C. Pneumatosis intestinalis without perforation causing benign subdiaphragmatic air accumulation
D. Perforated duodenal ulcer with free air in the peritoneal cavity indicating hollow viscus perforation and generalized peritonitis
Explanation
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Why "Perforated duodenal ulcer with free air in the peritoneal cavity indicating hollow viscus perforation and generalized peritonitis" is right
The clinical presentation—sudden-onset severe abdominal pain with a recalled exact moment of onset, marked peritoneal signs (rigidity, guarding, rebound), and the radiographic finding of free air under the right hemidiaphragm (marked A)—is pathognomonic for hollow viscus perforation. Perforated peptic ulcer (duodenal > gastric) is the most common spontaneous cause of pneumoperitoneum. The right hemidiaphragm is the most reliable location for detecting free air on erect X-ray because the gastric air bubble can mimic free air on the left. The crescent-shaped lucency represents free air within the peritoneal cavity, a surgical emergency requiring immediate resuscitation, broad-spectrum antibiotics, and urgent exploratory laparotomy. (Harrison's 21e Ch 14; ACS Principles of Surgery)
Why each distractor is wrong
Acute pancreatitis with retroperitoneal air tracking into the peritoneal cavity: Acute pancreatitis does not produce free air in the peritoneal cavity. While pancreatitis can present with severe abdominal pain, the sudden-onset, recalled exact moment of pain onset, and the radiographic finding of free air under the hemidiaphragm are inconsistent with pancreatitis. Pancreatitis causes retroperitoneal inflammation, not pneumoperitoneum.
Pneumatosis intestinalis without perforation causing benign subdiaphragmatic air accumulation: Pneumatosis intestinalis is air within the bowel wall itself, not free air in the peritoneal cavity. It can occur without perforation and is often benign. The clinical presentation here—severe peritoneal signs and sudden-onset pain—indicates true pneumoperitoneum from perforation, not pneumatosis. Free air under the hemidiaphragm is not a feature of uncomplicated pneumatosis.
Post-endoscopic perforation managed conservatively with observation and antibiotics alone: While iatrogenic perforation from endoscopy is a recognized cause of pneumoperitoneum, the clinical presentation here—severe generalized peritonitis with rigidity and rebound tenderness—indicates a large perforation requiring urgent surgical intervention. Post-endoscopic perforations may be managed non-operatively only if they are small, contained, and the patient is stable and seen early (<24 hours); this patient has signs of generalized peritonitis and requires emergency laparotomy.
High-YieldNEET PG
Free air under the RIGHT hemidiaphragm on erect X-ray is the most reliable radiographic sign of pneumoperitoneum; perforated peptic ulcer is the most common spontaneous cause and is a surgical emergency.
