All are causes of Pseudo Pneumo peritoneum except
**Core Concept**
Pseudo pneumoperitoneum refers to the appearance of free air under the diaphragm on radiographs, mimicking pneumoperitoneum, but without actual free gas in the abdominal cavity. This phenomenon can occur due to various causes that lead to the presence of air in the abdominal cavity or adjacent structures.
**Why the Correct Answer is Right**
Pseudo pneumoperitoneum can be caused by several conditions, including:
- **Option A:** Portal venous gas. This occurs when there is a mixture of air and blood in the portal venous system, often due to bowel infarction or ischemia, which can lead to the appearance of free air under the diaphragm on radiographs.
- **Option B:** Pneumobilia. This refers to the presence of air in the biliary tree, often due to a fistula between the biliary system and the intestine, which can mimic pneumoperitoneum.
- **Option C:** Pneumoretroperitoneum. This condition is characterized by the presence of air in the retroperitoneal space, often due to a fistula between the intestine and the retroperitoneal space, which can also lead to the appearance of free air under the diaphragm.
**Why Each Wrong Option is Incorrect**
- **Option D:** Actual pneumoperitoneum is not an exception to pseudo pneumoperitoneum, but rather a separate entity that requires a different diagnosis and management approach.
**Clinical Pearl / High-Yield Fact**
When interpreting radiographs, it's essential to consider the clinical context and look for other signs that may suggest pseudo pneumoperitoneum, such as the presence of abdominal tenderness or guarding, which can be indicative of an underlying condition.
**Correct Answer:** D.