Intensive Care Medicine (ICM) Practice Exam

What distinguishes atypical pneumonia from community-acquired pneumonia on imaging?

1. Pleural effusion presence

2. Unilateral, discrete infiltrate

3. Patchy, diffuse infiltrate

4. Presence of a lobar consolidation

The correct answer is: Patchy, diffuse infiltrate

Atypical pneumonia is characterized by specific imaging findings that often differ from those seen in community-acquired pneumonia. The presence of a patchy, diffuse infiltrate is a hallmark of atypical pneumonia. This type of pneumonia typically results from atypical pathogens such as Mycoplasma pneumoniae or Chlamydia pneumoniae, which lead to an inflammatory process that causes a more widespread, less organized appearance on imaging compared to bacterial agents, which usually cause more localized findings. Community-acquired pneumonia, on the other hand, often presents with lobar consolidation or localized opacities that correspond to specific segments of the lung, reflecting the more typical pathogens like Streptococcus pneumoniae. Unlike atypical pneumonia, where the infiltrates are often patchy and dispersed, the more defined and localized patterns seen in community-acquired pneumonia are typically an indication of a distinct lobar or segmental involvement. While pleural effusions and bilateral or unilateral distributions can occur in both types of pneumonia, the defining imaging characteristic that sets atypical pneumonia apart is indeed the patchy, diffuse infiltrates.