Pneumonia

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Pneumonia is inflammation of the lung, which includes infectious and non-infectious etiologies.

It is a subset of the medical lung diseases. This article primarily deals with the infectious pneumonias. Idiopathic interstitial pneumonias are discussed very briefly; they are dealt with in detail in the diffuse lung diseases article.

Infectious pnemonia

Anatomical classification of pneumonia

  • Generally, not used by clinicians.
  • Use of the terms without qualification is discouraged... as they do not make explicit the etiology.

Bronchopneumonia

  • Multiple foci of (acute) inflammation involving the bronchi.
  • This is the most common form of (infectious) pneumonia.

Lobar pneumonia

  • Pneumonia that involves a whole lobe.
  • Rarely seen in areas where antibiotic treatments are widely available.

Acute infectious pneumonia

General

  • This is seen by pathologists, in autopsy, from time-to-time.

Most common cause:

  • Streptococcus pneumoniae.[1]

The top three community acquired (acute) pneumonia:[2]

  • Streptococcuc pneumonia.
  • Haemophilus influenzae.
  • Moraxella catarrhalis.

Other community acquired pneumonia:[1]

  • S. aureus.
  • Legionaella pneumophila.
  • Klebsiella pneumoniae.
  • Pseudomonas.

Hospital-acquired pneumonia:[1]

  • Gram-negative rods.
  • Staphylococcus aureus.

Radiologic correlate

  • Air space disease.

Gross pathology

  • Consolidation (the lung parenchyma is firm) - best appreciated by running a finger over the cut surface of the lung with a small-to-moderate amount of pressure.

Bronchopneumonia:

  • Classically yellow-white centered on the bronchi.[3]

Lobar pneumnia is classically described in four stages:[4][5]

  1. Congestion - day 1-2.
  2. Red hepatization - day 2-4.
  3. Gray hepatization - day 4-6.
  4. Resolution - day 6+.

Note:

  • The stages of lobar pneumonia is considered more-or-less historical. In the age of antibiotics, lobar pneumonia is uncommon.

Microscopic

Features:

  • Alveoli packed with PMNs.
  • +/-Clusters of bacteria - small dots or rods.
  • +/-Abscess formation.
    • Lung abscess = destruction of parenchyma + PMNs.[6]

Image:

Stains

  • Gram stain -- to type the bacteria.

Chronic infectious pneumonia

General

Common microorganisms:[1]

Note:

  • All of the later ones are granulomatous.

Microscopic

Features:

Aspiration pneumonia

General

  • Not associated with microorganisms - though empiric antibiotics are relatively common to cover infectious pneumonias that cannot be excluded easily on clinical grounds.[7]
  • Usually seen in the context of a toxin and/or pathology that affects the swallowing and cough reflexes.[8]

Common associations:[8]

Other risk factors:[7]

  • Traumatic brain injury.
  • Seizure disorder.
  • Bowel obstruction.
  • Drugs.
  • Obesity.
  • Labour.

Note:

  • A special type of aspiration pneumonia is lipoid pneumonia. It is dealt with in the lipoid pneumonia article.

Gross

  • More common in the right lung.
    • Right main stem bronchus is more vertical.

Microscopic

Features:

  • Neutrophils.
  • Foreign material, e.g. plant matter.
  • +/-Foreign body giant cells.
  • +/-Microorganisms.

DDx:

Images:

Cytomegalovirus pneumonia

Main article: Cytomegalovirus

General

  • Immunodeficiency.
  • Critical illness.[9]

Microscopic

Features:

  • CMV nuclear changes:
    • Large red nucleus with a pale halo.
  • Eosinophilic granular cytoplasmic inclusions.

Images:

IHC

  • CMV +ve -- cytoplasmic inclusions, large nucleus.

Diffuse lung diseases

Main article: Diffuse lung disease
  • AKA idiopathic interstitial pneumonia.

Histologic pattern:

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Kumar, Vinay; Abbas, Abul K.; Fausto, Nelson; Aster, Jon (2009). Robbins and Cotran pathologic basis of disease (8th ed.). Elsevier Saunders. pp. 711. ISBN 978-1416031215.
  2. ↑ Nicolau, D. (Sep 2002). "Clinical and economic implications of antimicrobial resistance for the management of community-acquired respiratory tract infections.". J Antimicrob Chemother 50 Suppl S1: 61-70. PMID 12239229.
  3. ↑ Rose, Alan G. (2008). Atlas of Gross Pathology with Histologic Correlation (1st ed.). Cambridge University Press. pp. 93. ISBN 978-0521868792.
  4. ↑ Rose, Alan G. (2008). Atlas of Gross Pathology with Histologic Correlation (1st ed.). Cambridge University Press. pp. 92. ISBN 978-0521868792.
  5. ↑ URL: http://www.histopathology-india.net/Lobar_Pneumonia.htm. Accessed on: 27 February 2012.
  6. ↑ Rose, Alan G. (2008). Atlas of Gross Pathology with Histologic Correlation (1st ed.). Cambridge University Press. pp. 95. ISBN 978-0521868792.
  7. ↑ 7.0 7.1 Raghavendran, K.; Nemzek, J.; Napolitano, LM.; Knight, PR. (Apr 2011). "Aspiration-induced lung injury.". Crit Care Med 39 (4): 818-26. doi:10.1097/CCM.0b013e31820a856b. PMID 21263315.
  8. ↑ 8.0 8.1 Ohrui, T. (Sep 2005). "Preventive strategies for aspiration pneumonia in elderly disabled persons.". Tohoku J Exp Med 207 (1): 3-12. PMID 16082150.
  9. ↑ Limaye, AP.; Boeckh, M. (Nov 2010). "CMV in critically ill patients: pathogen or bystander?". Rev Med Virol 20 (6): 372-9. doi:10.1002/rmv.664. PMID 20931610.
  10. ↑ URL: http://www.pathologyoutlines.com/topic/lungnontumorCMV.html. Accessed on: 23 January 2012.
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