Pulmonary pathology

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 and discusses an approach to the lung.

Medical lung disease is dealt with in the medical lung disease article. Tumours of the lung are dealt with in lung tumours article. Lung cytopathology is dealt with in the pulmonary cytopathology 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 injury

Fibrosis

Chronic cellular infiltrates (ALI)

Alveolar filling defect (AFD)

Nodules

Near normal histology

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 disease

Interstitial disease

Mass/nodules

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

Cells

Common:

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

Rare:

• Pulmonary neuroendocrine cells:
  • Histomorphology:
    • Single cells.
    • Small clusters ~ 6 cells ("neuroepithelial bodies").
  • Identified with immunostains:
    • Serotonin.
    • Bombesin.
    • Chromogranin A.
    • Synaptic vesicle 2.

Lung lobule

Lung lobule:

• 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.

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

Small airways

The trip to the alveolus:

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.

• Hyaline membrane = glassy layering of an alveolus/small airways with material that is eosinophilic on H&E.
  • Entomology of Hyaline: "... of glass" (Greek).
  • Image: Hyaline membrane (path.upmc.edu).

• Bronchiolization = ciliated (respiratory) epithelium or goblet cells in (distal) air space.
  • Image: Bronchiolization (ucsf.edu).

• Smoker's macrophages = brown-pigmented macrophages - assoc. with smoking.

Malignancy - lung cancer

Main article: Lung cancer

This often comes to the pathologist.

Medical lung disease

Main article: Medical lung disease

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

Pulmonary hypertension is dealt with in its own article pulmonary hypertension.

Lung transplant pathology

Main article: Lung transplant pathology

Bronchogenic cyst

• Benign.
• Usually in mediastinum.

Microscopy

Features:

• Cyst lined by respiratory epithelium.

Image:

• Bronchogenic cyst (wikimedia.org).

Malformations

Come in three flavours:

1. Congenital pulmonary airway malformation (CPAM).
2. Extralobar sequestration (ELS).
3. Intralobar sequestrations (ILS).

CPAM

General:

• Classified according to density:
  • Type I = mostly large cysts.
  • Type II = mostly small cysts.
  • Type III = solid mass.

Microscopic

Features:

• Irregular cystic spaces with bronchial epithelium.
  • Bronchial epithelium = cilia, pseudostratified.

ELS

General:

• Typically not connected to airway tree/trachea.
• Blood supply arises from aorta, not the pulmonary artery.
• Mass lesion.
• Intralobular sequestration can be considered a variant of ELS; it is like an ELS but surrounded by normal lung.

Microscopic

Features:

• Abnormal airways: dilated bronchi.
• +/-Infection.

See also

• Medical lung disease.
• Thyroid.
• Basics.
• Heart.