Certified Respiratory Therapist Practice Exam

If an anterior-posterior chest radiograph shows an elevated left hemidiaphragm, what is the most likely cause?

1. Pneumonia

2. Hepatomegaly

3. Right phrenic nerve paralysis

4. Subcutaneous emphysema

The correct answer is: Right phrenic nerve paralysis

An elevated left hemidiaphragm on a chest radiograph is most commonly associated with right phrenic nerve paralysis. The phrenic nerve is the primary nerve that controls the diaphragm, which is essential for proper breathing. When there is paralysis of the right phrenic nerve, the corresponding diaphragm on the left side may appear elevated due to the loss of downward movement during inspiration. This condition can result from various causes, including surgery, trauma, or a mass effect that impacts the phrenic nerve. When the diaphragm does not contract as it should, it leads to the appearance of elevation on imaging. Other conditions, such as pneumonia or hepatomegaly, might contribute to diaphragm elevation in certain scenarios but are less likely to result in a consistently elevated left hemidiaphragm compared to phrenic nerve paralysis. Similarly, subcutaneous emphysema is characterized by air accumulation in subcutaneous tissues and does not typically cause isolated diaphragm elevation.