CAMRT Radiography Practice Exam

Which projections may best demonstrate pneumoperitoneum in a patient unable to stand?

1. AP right lateral decubitus

2. AP left lateral decubitus

3. Lateral Dorsal decubitus

4. AP supine projection

The correct answer is: AP left lateral decubitus

The best projection to demonstrate pneumoperitoneum in a patient who is unable to stand is the AP left lateral decubitus position. This positioning allows air that may be present in the peritoneal cavity to rise to the anterior aspect of the abdomen, where it can be more easily visualized on the X-ray. In the left lateral decubitus position, the patient's left side is down, which enables any free air in the abdominal cavity to collect under the diaphragm on the right side. This is critical because pneumoperitoneum typically presents as an accumulation of air beneath the diaphragm, which is best seen in this specific orientation. The X-ray will show a crescent of radiolucency under the right hemidiaphragm, indicating the presence of free air. Other options, while related to abdominal imaging, do not provide the optimal visual access to detect free air in the same way. The AP supine projection may obscure the visualization of free air since it does not allow for the proper positioning of the air in relation to the diaphragm. Similarly, while the AP right lateral decubitus view does have its uses, positioning the right side down would not properly demonstrate air under the right diaphragm, limiting its effectiveness for detecting pneumoperitone