infectious lung disease n.
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  2. Overview • ​Def: pneumonia is a cellular, exudative reactive condition within the lung ​Natural history ends in resolution (return to normal) or organization (fibrosis) ​Classification • ​Distribution: lobar pneumonia, bronchopneumonia, or interstitial • ​Etiology: infectious , aspiration, obstructive

  3. Bacterial pneumonia • ​Bronchopneumonia • ​Patchy distribution, ie multiple foci of inflammation at airspace-airway interfaces ​Caused by streptococci and staphylococci, pseudomonas, coliform bacteria ​Usually does not consolidate into lobar pneumonia

  4. Histology: peribronchial inflammation, infiltrate in bronchial lumen, ​Lobar pneumonia ​Entire lobe is uniformly affected ​Mostly caused by S. pneumoniae, as well as by Klebsiella • ​Histology: uniform intra-alveolar infiltrate

  5. Gram negative organisms: inhibits PMN influx causing congestion in blood vessels on histology • ​Legionella: Mf rich infiltrate, gram positive coccobacilli detectable by silver stain • ​Viral: eg CMV, adenovirus, herpes; hyaline membranes, inclusion bodies, lymphocytic infiltrate ​Pneumocystis carinii: affects immunocomp. esp. HIV, frothy/bubbly acellular exudates in alveoli

  6. Aspiration pneumonia, due to aspiration of: • ​Foreign bodies: can cause full or partial obstruction • ​Gastric contents: acid or food (granulomatous response) • ​Hydrocarbons: diffuse alveolar damage, bronchiolitis • Lipid materials • ​ Exogenous: eg mineral oil aspiration, granulomatous response • ​ Endogenous: obstructive pneumonia Mf exit route blocked congestion of Mf which degenerate and become fat-filled endogenous lipid pneumonia

  7. Airway infections • ​ Bronchiolitis: an inflammation of the small airways but airspaces mostly spared; viruses and bacteria are most common cause, but can be due to noninfectious causes • ​ Bronchiectasis: multiple inflammatory foci near large airways organization/scarring traction on bronchi permanent dilation of bronchi

  8. ​ Tuberculosis: typically upper lobe lesion, granulomatous inflammation w/ caseous necrosis, organisms are found in center of debris (not on edge!), acid fast stain can demonstrate organism • ​ Histoplasmosis: granulomatous w/ concentric rings, small budding yeast forms

  9. ​ Cryptococcus: mucoid capsule • ​Blastomyces: big organism, double wall • Coccidioides: small organisms found in big cysts (aka spherules

  10. ​Aspergillus: found in immunocompromised, Y-shaped septated hyphal forms, invasion of blood vessels causing occlusion and pulmonary infarct • Lung abscess • ​Defined as focal infection with necrosis and inflammation leading to cavitation and walling-off ​Causes “cross country” destruction, ie communication with multiple airways

  11. Pulmonary Infections – Pneumonia • Classification of pneumonia by distribution and outcome: • ​Bronchopneumonia (intra-alveolar, with patchy distribution through multiple lobes) • ​--Lobar pneumonia (intra-alveolar) • ​--Resolution • ​--Organizing (aberrant healing with fibrosis)

  12. Classification of pneumonia by etiology: • ​Infectious • Bacterial pneumonia is most often caused by Strep pneumo (Gram+ encapsulated diplococci, ​positive Quelung reaction). Bacterial pneumonia exudate has tons of PMNs. • Gram- rods (Pseudomonas, Klebsiella) may cause a necrotizing pneumonia with infarction.

  13. Viral and Mycoplasma pneumonia exudates have tons of lymphocytes, but few PMNs. • ​There may be hyaline membranes and intra-alveolar fibrin. • PCP causes an airway-filling pneumonia with a “frothy” acellular pink exudate. • Histoplasmosis creates a white granulomatous nodule that looks like a tree-trunk cross-section.

  14. • Aspiration • Usually from inhalation of vomit. In older patients, aspiration of mineral oil is very common, as ​it does not elicit a gag response when swallowed. • ​Obstructive • Usually from obstruction by a tumor or inhaled object. Macrophages accumulate in alveoli, and ​become fat-filled, giving obstructive pneumonia the name “golden pneumonia.”

  15. Other pathological features of pneumonia --Granulomas are part of a delayed hypersensitivity reaction with the accumulation of epithelioid ​macrophages and giant cells. There may be central necrosis. If the granuloma is white ​and looks like a tree-trunk cross-section, think Histoplasmosis. • Infarcts may be caused by vaso-invasive fungi or Pseudomonas that initiate pulmonary thrombosis.

  16. Lung abscess often leads to cavitation that communicates with multiple airways (“cross-country” ​cavitation). Lung abscesses are usually caused by aspiration of food or foreign bodies, along ​with poor dental hygiene (source of anaerobic bacteria). • Bronchiectasis is a condition characterized by permanent dilation of bronchi with scarring and ​retraction of lung parenchyma. The bronchi are permanently pulled open.