Community Acquired Pneumonia

Pathophysiology:  The common community acquired pneumonias consist of  (1) streptococcal pneumonia  (2) staphylococcal pneumonia  (3) H. influenza  (4) mycoplasma pneumonia  (5) various viral and chlamydia agents  (6) tuberculosis  (7) Legionella pneumonia  (8) various Gram positive and negative bacteria such as Klebsiella and Friedlandler's pneumonias

CXR Findings:  With the exceptions of tuberculosis, Legionella, and some aggressive organisms like Klebsiella/Friendlander's, the CXR findings consist of non-specific findings:

1. subsegmental, segmental, or lobar airspace consolidation
2. para-pneumonic pleural effusions
3. atelectasis of involved areas

Specific Etiologic Clues:

1. primary tuberculosis - hilar or mediastinal adenopathy
2. staphylococcal pneumonia - cavitating nodular infiltrates
3. aggressive expansile pneumonias (eg. Klebsiella) - "bulging fissures"
4. reactivation tuberculosis - typical upper lobe cavitating, nodular infiltrates

“Aunt Sophies”:  Many

1. Almost any airspace CAP (community acquired pneumonia) can look the same on CXR
2. Other airspace infiltrates: eg.  COP, hemorrhage, aspiration, lung cancer eg. bronchoalveolar cell