A 56-year-old man with untreated H. pylori infection and chronic NSAID use presents with sudden-onset severe epigastric pain that became generalized 3 hours ago. He lies motionless, unable to tolerate any movement. On examination, his abdomen is rigid with diffuse involuntary guarding, rebound tenderness, and absent bowel sounds. An erect PA chest radiograph is obtained. The structure marked **A** in the diagram represents a crescentic lucent collection beneath the right hemidiaphragm. What is the most likely diagnosis?
A. Spontaneous bacterial peritonitis with ascites
B. Perforated peptic ulcer with generalized peritonitis
C. Acute cholecystitis with biliary peritonitis
D. Acute pancreatitis with pleural effusion
Explanation
Why "Perforated peptic ulcer with generalized peritonitis" is right
The crescentic lucent air collection beneath the right hemidiaphragm (marked A) is the classic radiographic sign of free intraperitoneal air (pneumoperitoneum). In the clinical context of sudden severe epigastric pain that became generalized, rigid board-like abdomen with involuntary guarding, rebound tenderness, and absent bowel sounds in a patient with untreated H. pylori infection and chronic NSAID use, this finding is pathognomonic for a perforated hollow viscus—most commonly a perforated peptic ulcer. The erect chest X-ray is the single most specific radiographic sign of hollow viscus perforation, and the air rises to collect beneath the diaphragm where it is best visualized against the soft tissue contrast of the liver on the right side. Bailey & Love's Short Practice of Surgery emphasizes that free air under the diaphragm on erect imaging is the hallmark of peptic ulcer perforation.
Why each distractor is wrong
Acute pancreatitis with pleural effusion: Acute pancreatitis presents with epigastric pain and elevated lipase, but does not produce free intraperitoneal air. Pleural effusions are fluid collections, not air, and would not appear as lucent crescents under the diaphragm. The rigid abdomen with guarding and rebound is more consistent with perforation than uncomplicated pancreatitis.
Spontaneous bacterial peritonitis with ascites: SBP occurs in cirrhotic patients with ascites and presents with abdominal pain and peritoneal signs, but does not produce pneumoperitoneum. Ascites is fluid, not air, and would not create the characteristic lucent crescent sign. The acute presentation in a non-cirrhotic patient with NSAID/H. pylori history makes perforation far more likely.
Acute cholecystitis with biliary peritonitis: While acute cholecystitis can present with abdominal pain and peritoneal signs, it does not typically produce free intraperitoneal air unless the gallbladder has perforated (rare). The epigastric onset and history of dyspepsia responsive to antacids point to peptic ulcer disease, not biliary pathology. Pneumoperitoneum is not a feature of uncomplicated cholecystitis.
High-YieldNEET PG
Free air under the diaphragm on erect chest X-ray is the single most specific radiographic sign of hollow viscus perforation; the right hemidiaphragm is the most common site because the liver provides soft tissue contrast for visualization of the air.
Bailey & Love's Short Practice of Surgery, 28th Edition, Chapter 67: Peptic Ulcer Disease and its Complications
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