Pathology of Lung Infection

Question 1

What is pneumonia?

Answer 1

Inflammation of the lung - mostly due to infection but not always

Question 2

What are the clinical features of pneumonia?

Answer 2

Fever and chills, unrelenting cough, sputum production (yellow or green), chest pain if pleura is inflamed, impaired gas exchange resulting in dyspnoea and tachypnoea

Question 3

What are the three groups of pneumonia according to clinical setting?

Answer 3

Community acquired, hospital acquired or compromised immune host

Question 4

What pathogen is most likely to cause community acquired pneumonia?

Answer 4

50% of cases are caused by streptococcus pneumoniae

Question 5

What pathogen is most likely to cause hospital acquired pneumonia?

Answer 5

A gram negative bacteria

Question 6

What pathogens are more likely in immune compromised hosts to cause pneumonia?

Answer 6

Fungi or protozoa (pneumocystis jirovecii)

Question 7

What are the four ways which pathogens can reach the lung?

Answer 7

Inhalation of pathogens in air droplets, aspiration of infected secretions from the URT, aspirating infected particles like gastric contents or food or drink, from the blood

Question 8

What are the three classes of pathogens causing pneumonia?

Answer 8

upper respiratory tract flora, enteric saprophytes, extraneous pathogens

Question 9

What are the upper respiratory tract flora which can cause pneumonia?

Answer 9

Streptococcus pneumoniae, haemophilus influenzae, staphlococcus aureus

Question 10

What are the enteric saprophytes which can cause pneumonia?

Answer 10

E. coli, pseudomonas

Question 11

What are the extraneous pathogens which can cause pneumonia?

Answer 11

Legionella pneumophila, tuberculosis

Question 12

What are the two patterns of infective pneumonia?

Answer 12

Alveolar inflammation or interstitial inflammation (atypical pneumonia)

Question 13

What cells are involved in alveolar inflammation?

Answer 13

Neutrophils in the alveolar spaces (consolidation)

Question 14

What pathogens cause alveolar inflammation?

Answer 14

bacterial pathogens such as streptococcus, staphylococcus, haemophilus, gram negatives

Question 15

What are the two kinds of alveolar inflammation?

Answer 15

Bronchopneumonia and lobar pneumonia

Question 16

What is the pattern of consolidation in bronchopneumonia?

Answer 16

Patchy and bilateral

Question 17

What is the pattern of consolidation in lobar pneumonia?

Answer 17

Entirety of a single lobe

Question 18

What does consolidation look like on a CXR?

Answer 18

White

Question 19

What does consolidation look like macroscopically?

Answer 19

White and solid

Question 20

What is the commonest cause of lobar pneumonia?

Answer 20

streptococcus pneumoniae

Question 21

What is the commonest way to get strep pneumoniae lobar pneumonia?

Answer 21

community acquired

Question 22

What are the symptoms of community acquired strep pneumoniae lobar pneumonia?

Answer 22

high fever with chills, raised white cell count, cough, pleuritic chest pain, blood stained sputum, gram positive diplococci present in sputum, often causes bacteraemia

Question 23

What are the 4 stages of lobar pneumonia?

Answer 23

congestion, red hepatisation, grey hepatisation, resolution

Question 24

What happens in congestion?

Answer 24

Protinaceous exudate full of diplococci in the alveoli

Question 25

What happens in red hepatisation?

Answer 25

Consolidation with haemorrhage into airspaces

Question 26

What happens in grey hepatisation?

Answer 26

mesh work of fibrin in alveolar spaces with neutrophils and macrophages

Question 27

Which patients most commonly get bronchopneumonia?

Answer 27

Young and old patients or patients with chronic disease e.g. COPD, cardiac failure, malignancies or cystic fibrosis - hospitalised patients

Question 28

What pathogens most commonly cause bronchopneumonia?

Answer 28

gram negative bacteria - pseudomonas or staphylococcus

Question 29

What are the complications of pneumonia?

Answer 29

Pleurisy, pyothorax, empyema, abscess, bronchiecstasis, fibrosis, cysts

Question 30

What is a lung abscess?

Answer 30

A cavity containing puss

Question 31

What pathogen almost always causes lung abscess?

Answer 31

Staphylococcus aureus

Question 32

What are other causes of lung abscess?

Answer 32

aspiration of infected contents from the URT such as gastric contents, distal to bronchial obstruction by a tumor, septic emboli to the lung

Question 33

What cells are involved in atypical pneumonia?

Answer 33

Lymphocytes and macrophages in intra alveolar septa

Question 34

What pathogens cause atypical pneumonia?

Answer 34

Viruses, bacteria (mycoplasma pneumonia, coxiella burnetti, legionella, chlamydia pneumoniae)

Question 35

What is seen in the lung macroscopically in atypical pneumonia?

Answer 35

lung looks dark, wet and heavy - there is no consolidation

Question 36

What is the clinical presentation of atypical pneumonia?

Answer 36

systemic symptoms more than respiratory systems - malaise, aches, pains, headache, diarrhoea, non productive cough - ‘walking pneumonia’

Question 37

What does the CXR of atypical pneumonia look like?

Answer 37

Dots and dashes in both lung fields

Question 38

What is tuberculosis?

Answer 38

a chronic granulomatous pneumonia due to infection with mycobacterium tuberculosis

Question 39

What are the unique features of tuberculosis compared to other bacterial pneumonias?

Answer 39

the human body cannot eradicate it, and it can lie dormant after the initial infection before causing a secondary infection

Question 40

What are the clinical features of primary TB?

Answer 40

mild often asymptomatic

Question 41

What are the histological features of primary TB?

Answer 41

Ghon’s complex

Question 42

What is a Ghon’s complex?

Answer 42

Ghon focus + involved hilar lymph node

Question 43

What is a Ghon’s focus?

Answer 43

Granuloma (aggregate of epithelioid macrophages + multinucleate macrophages) around caseous necrosis

Question 44

What causes the granuloma?

Answer 44

A type IV hypersensitivity response where monocytes under the influence of IGNgamma become epithelioid macrophages

Question 45

How does primary TB resolve?

Answer 45

The immune response controls the infection and the Gohn complex heals by fibrosis, often with some calcification

Question 46

What is secondary TB?

Answer 46

The reactivation of a dormant infection or a reinfection

Question 47

What area of the lung does secondary TB effect?

Answer 47

Lobar pneumonia involving the upper lobe

Question 48

What macroscopic features are seen in secondary TB?

Answer 48

casseous necrosis, fibrosis, calcification, cavitation (where caseation erodes into a bronchus)

Question 49

What are the complications of secondary TB?

Answer 49

Spread into surrounding lung, erosion of blood vessels, erosion into bronchial tree causing spread, pleural inflammation and fibrosis, lung scarring

Question 50

How is TB spread from person to person?

Answer 50

infected aerosolised droplets

Question 51

What are the clinical features of secondary TB?

Answer 51

weight loss, malaise, fevers, night sweats, haemoptysis, dyspnoea and chronic cough

Question 52

What are the features of mycobacterium tuberculosis?

Answer 52

aerobic rods with an acid fast wall - detected by ZN stain

Question 53

How does TB spread around the body?

Answer 53

Via lymphatics to pleura or to the opposite lung, via the bronchial tree - can be coughed up into larynx and swallowed and become intestinal - or can spread via the blood stream to other organs

Question 54

What is miliary TB?

Answer 54

progressive tuberculosis caused by spread through the blood stream where multiple organs are involved - macroscopically you see numerous small white granulomas in the organs

Question 55

What is single organ TB?

Answer 55

Where a single organ is infected in primary TB but lies dormant and then when becomes activated has effect on only one organ e.g. Potts disease in the spine