A 65-year-old male presents to the emergency department with sudden onset severe abdominal pain, guarding, and rigidity. An erect abdominal X-ray is performed. Which of the following findings would be most indicative of a perforated viscus?

Explanation

The clinical presentation of sudden onset severe abdominal pain with guarding and rigidity is highly suggestive of an acute abdomen, often due to a perforated viscus. On an erect abdominal X-ray, the most specific sign of pneumoperitoneum (free air in the peritoneal cavity due to perforation) is free air under the diaphragm. On a supine film, signs like Rigler's sign (visualization of both inner and outer bowel wall), the 'football sign' (large amount of free air outlining the abdominal cavity), or gas outlining ligaments such as the falciform ligament (as seen in option B) are indicative of pneumoperitoneum. Option A suggests small bowel obstruction. Option C is non-specific and could be gallstones or renal stones. Option D is a non-specific sign of retroperitoneal pathology.