Pulmonary pathology

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The lung is a forgotten organ in pathology, 'cause radiologists can diagnose much with high resolution CT (HRCT) and a bit of history. This article introduces the lung, discusses an approach to the lung, and the tumours that afflicit it. Medical lung disease is dealt with in the medical lung disease article.

Basic approach

All lung pathology can be grouped into one of six categories (as per Leslie). The radiology directly correlates to the pathologic grouping, except that air space disease encompasses three pathologic categories (ALI, CCI, AFD).

Pathologic groups:

Lung pathology
Acute lung
Chronic cellular
infiltrates (ALI)
Alveolar filling
defect (AFD)
Near normal

Identification of the groups:

  • Acute lung injury: hyaline membranes (very pink on H&E).
  • Fibrosis = thick walls - pink on H&E.
  • Chronic cellular infiltrates = inflammation (blue on H&E).
  • Nodules = look at the history/radiology - should say mass or nodule.
  • Alveolar filling defect = crap in the alveoli.
  • Near normal = looks almost normal.

Radiologic groups:

Lung radiology
Air space
Near normal

Radiologic-pathologic correlation:

  • Air space disease (radiologic).
    • Acute lung injury.
    • Chronic cellular infiltrates.
    • Alveolar filling defects.
  • Interstitial disease (radiologic).
    • Fibrosis.
  • Mass/nodules (radiologic).
    • Nodules.
  • Near normal (radiologic).
    • Near normal histology.

Most of the things that come to pathology are in the mass/nodules category and lung tumours (discussed below). The other categories are dealt with in the medical lung disease article.

Normal histology


  • Type I pneumocyte - cover most of the alveolar surface.
  • Type II pneumocyte - stem cell, produce surfactant.
    • Typical location: "angle of alveolus".
  • Macrophages.

Lung lobule

Lung lobule:[1]

  • Arterial vessels travels with the bronchus.
  • Venules travel in the septae.
  • Arterial vessels in the lung should be approximately the same size as its accompanying airway.[2]

Memory device: arteries (which were once thought to contain air) are with the airway.

Small airways

The trip to the alveolus:[3]

  1. Membranous bronchiole.
  2. Terminal bronchiole - dilation distal to this = emphysema.
  3. Respiratory bronchiole.
  4. Alveolar duct - dilated in ARDS.
  5. Alveolus.

Anatomy - terms

  • Bronchus = has cartilage.
  • Bronchiole = non-cartilaginous airway.

Pathology terminology

  • Siderophages = mononuclear phagocyte with hemosiderin.[4]
  • Hyaline membrane = glassy layering of an alveolus/small airways with material that is eosinophilic on H&E.[5]
  • Smoker's macrophages = brown-pigmented macrophages - assoc. with smoking.[7]

Malignancy - lung cancer

This often comes to the pathologist.

Medical lung disease

Includes discussion of things like acute infectious pneumonia and idiopathic pulmonary fibrosis.

Bronchogenic cyst

  • Benign.
  • Usually in mediastinum.



  • Cyst lined by respiratory epithelium.


See also