Lung - nontumor
Pneumonia - general

Topic Completed: 1 August 2011

Revised: 29 January 2019, last major update August 2011

Copyright: (c) 2003-2018,, Inc.

PubMed search: Pneumonia [title] infection lungs general

Elliot Weisenberg, M.D.
Page views in 2019: 17,481
Page views in 2020 to date: 9,173
Cite this page: Weisenberg E. Pneumonia - General. website. Accessed May 28th, 2020.
Definition / general
  • Pneumonia is defined as any infection of lung parenchyma
  • Lung is #1 site for infections that cause lost workdays
  • Infection of lung is more frequent than any other visceral organ
  • Generally microorganisms are inhaled, but pneumonia may also occur through hematogenous spread or direct inoculation
  • Pneumonia is due to impairment of normal defense mechanisms or lowered host resistance
  • Normal defense mechanisms are nasal clearance (sneezing, blowing, swallowing), tracheobronchial clearance (mucociliary action) and alveolar clearance (alveolar macrophages)
  • Impairment is due to primary or acquired immunosuppression, suppression of cough reflex (drugs, virus, coma, anesthesia), injury to mucociliary apparatus (smoking, virus, Kartegeners syndrome), injury to macrophages (tobacco, alcohol, anoxia), pulmonary congestion / edema or accumulation of secretions (cystic fibrosis)
  • Note: viral pneumonia predisposes to bacterial pneumonia
Clinical features
  • Often divided into community acquired (Minerva Anestesiol 2011;77:196), hospital acquired (Clin Infect Dis 2010;51 Suppl 1:S42) and aspiration pneumonia
  • Common agents: Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, Legionella pneumophila, Pseudomonas aeruginosa, coliforms
  • Complications: abscess, empyema, organization, sepsis, meningitis
  • Consolidation: exudative solidification of lung
  • Signs and symptoms of pneumonia: shortness of breath, fever, productive cough, malaise, friction rub (if fibrinous pleuritis)
  • Bronchopneumonia: patchy consolidation of lung centered on bronchi; may progress to lobar pneumonia; patterns of bronco- and lobar pneumonia may overlap
  • Lobar pneumonia: affects entire lung but now rare due to antibiotics; associated with increased virulence of organism or increased host vulnerability (infants, elderly); may be due to extension of existing bronchiolitis or bronchitis
Gross images

Images hosted on other servers:

Bronchopneumonia - various images

Lobar pneumonia - various images

Microscopic (histologic) description
  • Bronchopneumonia: neutrophils in bronchi, bronchioles and adjacent alveolar spaces; lipid pneumonia, if marked, has lipid laden macrophages
  • Lobar pneumonia: initially congestion with bacteria and few neutrophils; then red hepatization (grossly resembles liver) with massive congestion, neutrophils, fibrin; then gray hepatization with fibrinopurulent exudate and organization; then resolution with resorption of exudate
Microscopic (histologic) images

Images hosted on PathOut server:

Contributed by Yuri Tachibana, M.D., Nagasaki University:

Alveolar exudate

Images hosted on other servers:

Bronchopneumonia - various images

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