CAMRT Radiography Practice Exam

What projection best demonstrates pneumoperitoneum in a standing patient?

1. AP supine abdomen

2. Left lateral decubitus

3. Dorsal decubitus

4. AP erect abdomen

The correct answer is: AP erect abdomen

The AP erect abdomen projection is the most effective for demonstrating pneumoperitoneum in a standing patient. This projection allows for the visualization of free air in the abdominal cavity, which is a critical sign of pneumoperitoneum, often resulting from perforation of a hollow organ. When a patient is upright, any free air will rise to the highest point of the abdominal cavity, which is typically under the diaphragm. The AP erect position effectively captures this area, making it possible for the radiologist to identify the presence of air pockets, particularly beneath the diaphragm on either side. In contrast, the other projections do not adequately demonstrate air-fluid levels or free air. The AP supine abdomen does not allow air to rise and can miss pneumoperitoneum, while the left lateral decubitus and dorsal decubitus positions are designed more to view fluid levels rather than free air in a non-upright situation. Thus, the AP erect abdomen is the optimal choice for identifying pneumoperitoneum in a standing individual.