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Pathology of Pulmonary Infections Flashcards

1
Q

What is pneumonia?

A

Infection involving the distal airspaces usually with inflammatory exudation (“localised oedema”)

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2
Q

What do fluid-filled spaces caused by pneumonia result in?

A

Consolidation

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3
Q

What are classifications of pneumonia?

A
  • By clinical setting (e.g. community acquired pneumonia)
  • By organism (mycoplasma, pneumococcal etc)
  • By morphology (lobar pneumonia, bronchopneumonia)
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4
Q

What pathogens can cause pneumonia?

A
  • Viruses – influenza, parainfluenza, measles, varicella-zoster, respiratory syncytial virus (RSV).
  • Bacteria - Chlamydia, mycoplasma
  • Fungi
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5
Q

What is lobar pneumonia?

A

Confluent consolidation involving a complete lung lobe

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6
Q

What pathogen causes lobar pneumonia?

A
  • Most often due to Streptococcus pneumoniae (pneumococcus)

* Can also be caused by Klebsiella, Legionella

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7
Q

How are most cases of lobar pneumonia acquired?

A

Community acquired

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8
Q

What individuals are infected with lobar pneumonia?

A

Classically in otherwise healthy young adults

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9
Q

Describe the pathology of lobar pneumonia

A

A classical acute inflammatory response

  • Exudation of fibrin-rich fluid
  • Neutrophil infiltration
  • Macrophage infiltration
  • Resolution

Immune system plays a part - antibodies lead to opsonisation, phagocytosis of bacteria

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10
Q

Why is control of inflammation important in lobar pneumonia?

A

To prevent destruction of alveolar walls

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11
Q

What are histological characteristics of lobar pneumonia?

A
  • Congested capillaries due to increased blood flow
  • Alveolar lumens filled with neutrophils and macrophages
  • Thickened alveolar walls
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12
Q

What are complications of lobar pneumonia?

A
  • Organisation (fibrous scarring)
  • Abscess
  • Bronchiectasis
  • Empyema
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13
Q

Why is fibrous organisation dangerous?

A

Reduces capacity for gas exchange

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14
Q

What is bronchopneumonia?

A

Infection starting in airways and spreading to adjacent alveolar lung

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15
Q

What individuals are at risk of bronchopneumonia?

A

Most often seen in the context of pre-existing disease

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16
Q

What are risk factors for bronchopneumonia?

A
  • COPD (acute bronchitis due to exacerbation spreads pneumonia)
  • Cardiac failure (elderly)
  • Complication of viral infection (influenza)
  • Aspiration of gastric contents
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17
Q

What pathogens cause bronchopneumonia?

A

More varied – Strep. Pneumoniae, Haemophilus influenza, Staphylococcus, anaerobes, coliforms

(Staph/anaerobes/coliforms seen in aspiration)

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18
Q

What are the complications of bronchopneumonia?

A
  • Organisation
  • Abscess (v important)
  • Bronchiectasis
  • Empyema
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19
Q

What is an abscess?

A

Localised collection of pus (tumour-like)

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20
Q

What are symptoms of bronchopneumonia?

A

Chronic malaise and fever

21
Q

What is abscess formation associated with in bronchopneumonia?

A

Aspiration

22
Q

What is bronchiectasis?

A
  • Abnormal fixed dilatation of the bronchi

* Dilated airways accumulate purulent secretions

23
Q

What causes bronchiectasis?

A
  • Usually due to fibrous scarring following infection (pneumonia, tuberculosis, cystic fibrosis)
  • Also seen with chronic obstruction (tumour)
24
Q

What are histological characteristics of bronchiectasis?

A
  • Dilated bronchi

* Chronic suppuration

25
What is tuberculosis?
* Mycobacterial infection | * Chronic infection described in many body sites – lung, gut, kidneys, lymph nodes, skin
26
What is the pathology of TB?
Pathology characterised by delayed (type IV) hypersensitivity - granulomas with necrosis
27
What pathogens cause tuberculosis?
M. tuberculosis/M.bovis main pathogens in man
28
What is a type IV hypersensitivity reaction?
T cell mediated hypersensitivity - formation of granulomas
29
What is the pathogenicity of mycobacterium due to?
Due to ability: * to avoid phagocytosis * to stimulate a host T-cell response
30
Describe the processes (occur together in TB) of immunity and hypersensitivity (type IV)
* Immunity - T-cell response to organism enhances macrophage ability to kill mycobacteria * Hypersensitivity (type IV) - T-cell response causes granulomatous inflammation, tissue necrosis and scarring
31
What 2 immune processes occur together in TB?
* Immunity | * Hypersensitivity (type IV)
32
What is primary TB?
1st exposure and up to 5 years afterwards
33
Describe the process of a primary TB infection
* inhaled organism phagocytosed and carried to hilar lymph nodes * Immune activation (few weeks) leads to a granulomatous response in nodes (and also in lung) usually with killing of organism * in a few cases infection is overwhelming and spreads
34
What is secondary TB?
reinfection or reactivation of disease in a person with some immunity
35
Does secondary TB spread?
* disease tends initially to remain localised, often in apices of lung * however, can progress to spread by airways and/or bloodstream
36
What are tissue changes in primary TB?
* Small focus (Ghon focus) in periphery of mid zone of lung | * Large hilar nodes (granulomatous)
37
What are tissue changes in secondary TB?
Fibrosing and cavitating apical lesion (cancer an important differential diagnosis)
38
What is the characteristic pathology of tuberculosis?
* Granulomas (macrophages, lymphocytes, large cells) | * Caseous necrosis
39
How can secondary TB result in rapid death?
Can progress to miliary tuberculosis
40
What are histological characteristics of miliary TB?
White foci - due to blood spread of rapidly progressing disease
41
What does decreased immunity as a result of infection result in?
Many more organisms on acid fast stain
42
Why does disease reactivate?
* Decreased T-cell function (age, coincident disease (HIV), immunosuppressive therapy - steroids, cancer chemotherapy) * Reinfection at high dose or with more virulent organism
43
What factors lead to decreased T-cell function?
* age * coincident disease (HIV) * immunosuppressive therapy (steroids, cancer chemotherapy)
44
What factors lead to decreased T-cell function?
* age * coincident disease (HIV) * immunosuppressive therapy (steroids, cancer chemotherapy)
45
What can immunocompromisation result in?
Virulent infection with common organism (e.g. TB) Infection with opportunistic pathogen * virus (cytomegalovirus - CMV) * bacteria (Mycobacterium avium intracellulare) * fungi (aspergillus, candida, pneumocystis) * protozoa (cryptosporidia, toxoplasma)
46
How is a diagnosis of tuberculosis confirmed?
* Teamwork (physician, microbiologist, pathologist) * Broncho-alveolar lavage * Biopsy (ZN stain, etc)
47
What can aspergillum infection of the immunocompromised result in?
Fatal haemorrhage
48
Will immunocompromised individuals only be infected with one organism?
No, usually many organisms can be the cause of pulmonary infection
49
What are the histological characteristics of a HIV-positive patient with cytomegalovirus and pulmonary oedema?
* Big swollen cells

Respiratory: Pathology (4 decks)

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