Which of the following can cause a radioactive pulmonary perfusion scan to demonstrate an appearance similar to that of acute pulmonary embolism?

A. Atelectasis.

B. Pneumonitis.

C. Pleural fluid.

D. Emphysematous bullae.

DISCUSSION: It has been shown by routine radioactive pulmonary perfusion scans that atelectasis, pneumonia, pleural fluid, emphysematous bullae, and pulmonary embolism may reduce pulmonary arterial blood flow to the involved segment. For this reason, it is imperative simultaneously to obtain chest film to exclude any significant radiopacity, which is usually associated with any defect that causes diminished pulmonary vascular perfusion.