Correct Answer: C. Hollow viscus perforation
The clinical presentation of acute abdominal pain with fever for 3 days, combined with the chest X-ray finding of free gas under the diaphragm (pneumoperitoneum), is pathognomonic for hollow viscus perforation. The erect chest X-ray is the gold standard for detecting pneumoperitoneum as a thin crescent of air appears between the liver dome and the diaphragm. In India, peptic ulcer disease (PUD) remains the most common cause of perforation in the acute setting, followed by typhoid perforation (particularly in endemic areas), appendicitis, and trauma. The acute presentation with fever and peritoneal signs indicates bacterial translocation and peritonitis. Management requires urgent surgical exploration (laparotomy) for source control—either primary repair (for PUD) or resection (for typhoid perforations). The 3-day duration suggests the patient is in the early-to-intermediate phase of peritonitis before septic shock develops, making this a surgical emergency. Pneumoperitoneum on imaging is the discriminating finding that rules out other causes of acute abdomen without perforation.
Why the other options are wrong
A. Empyema thoracis — Empyema presents with pleural effusion and fever but does NOT produce free gas under the diaphragm on chest X-ray. While fever and systemic signs overlap, empyema is a loculated infection within the pleural space (post-pneumonia, post-surgery) and would show a blunted costophrenic angle or fluid level, not pneumoperitoneum. NBE may trap students who see 'fever + chest X-ray' and assume thoracic pathology without recognizing the specific finding of subdiaphragmatic air. B. Liver abscess — Liver abscess (amoebic or pyogenic) causes fever and right upper quadrant pain but does NOT cause pneumoperitoneum unless it ruptures into the peritoneal cavity—a rare complication. Imaging would show a localized hepatic lesion on ultrasound/CT, not free gas. The acute presentation with peritoneal signs and pneumoperitoneum is inconsistent with uncomplicated liver abscess. This is a common distractor because both present with fever and abdominal pain in Indian patients. D. Gastric volvulus — Gastric volvulus causes acute epigastric pain, vomiting, and inability to pass a nasogastric tube (Brinton's triad) but does NOT produce pneumoperitoneum unless perforation has occurred. Chest X-ray in volvulus shows a grossly dilated stomach with an air-fluid level, not subdiaphragmatic free air. While volvulus is a surgical emergency, the presence of pneumoperitoneum shifts the diagnosis toward perforation rather than simple obstruction or volvulus.
High-Yield Facts
- Pneumoperitoneum on erect chest X-ray (free gas under diaphragm) is pathognomonic for hollow viscus perforation until proven otherwise.
- Peptic ulcer perforation is the most common cause of pneumoperitoneum in India; typhoid perforation is the second most common in endemic areas.
- Rigler's triad for perforation: pneumoperitoneum, free fluid, and bowel wall thickening; pneumoperitoneum alone is sufficient for diagnosis.
- Urgent surgical exploration (laparotomy) is mandatory within 6–12 hours of perforation; delay increases mortality from peritonitis and sepsis.
- Primary repair is preferred for PUD perforation; resection is required for typhoid or gangrenous perforations.
Mnemonics
PERFORATION CAUSES (India-specific) PUD (Peptic Ulcer Disease) → Typhoid → Appendix → Trauma. PUD and Typhoid account for >80% of perforations in India. CXR SIGNS OF PERFORATION Free Air = Crescent of air under diaphragm on erect CXR. Remember: Erect CXR is BEST for detecting pneumoperitoneum (supine CXR may miss it).
NBE Trap
NBE pairs acute abdominal pain + fever + chest X-ray to lure students toward thoracic diagnoses (empyema, pneumonia) without recognizing that the specific finding of subdiaphragmatic free air is a surgical emergency, not a medical one. The presence of fever may also distract from the acute surgical nature of perforation.
Clinical Pearl
In Indian emergency departments, a young patient with acute abdominal pain + fever + pneumoperitoneum on CXR is peptic ulcer perforation until proven otherwise. Typhoid perforation should be suspected if there is a preceding history of enteric fever or if the patient is from an endemic region. Both require urgent surgical intervention—delay beyond 12 hours significantly increases mortality from peritonitis and septic shock.
_Reference: Bailey & Love Ch. 66 (Peritonitis & Perforation); Sabiston Textbook of Surgery Ch. 48 (Peptic Ulcer Disease)_