Infection in the Lung

Question 1

What is a basic explanation of Pneumonia?

Answer 1

Inflammation of the lung

Question 2

Describe Acute inflammation of the lung in terms of pneumonia?

Answer 2

• Classical pattern of acute inflammation in the lung is caused by infection with ‘traditional’ bacteria (c.f “atypical” bacteria such as mycoplasma and viruses)
• There are two patterns of acute bacterial pneumonia - acute bronchopneumonia and acute lobar pneumonia
• -> of these, acute bronchopneumonia is by far the most common form.

Question 3

What are some predisposing factors of bacterial pneumonia?

Answer 3

• Smoking
• Reduced cough
• Aspiration (reduced conscious state)
• Debility and Malnutrition
• Bronchial obstruction
• Immune suppresion
• Hospitalisation
• Surgery/anaesthesia
• Alcoholism

Question 4

What are some causes of Lung Abscesses?

Answer 4

• Aspiration -mixed infection with anaerobic bacteria (bacteroides)
• Obstruction of the bronchial tree
• Haematogenous seeding of the lung from an extra-pulmonary infection (ie. osteomyelitis)
• Certain types of bacterial pneumonia: Strep pyogenes, Staph aureus, Klebsiella
• Acute bronchopneumonia in debilitated hosts

Question 5

Describe the features of viral pneumonia?

Answer 5

• don’t produce consolidation
• Can cause bronchiolitis and inflammation of the alveolar septa (lymphocytic)
• Most are cytopathic (they cause death of epithelial cells within the upper and lower respiratory tract, predisposing to secondary bacterial infections and severe pulmonary oedema)
• Viral Pneumonias at autopsy (such as influenza pneumonia) are heavy, wet and red or ‘boggy’.

Question 6

What are two forms of chronic lung infection?

Answer 6

• Bronchiectasis

- Pulmonary Tuberculosis

Question 7

What is Bronchiectasis?

Answer 7

• dilation of large, cartilage containing airways
• permanent (irreversible)
• dilation is a consequence of scar tissue deposition around the bronchi and weakening of the bronchial wall by inflammation

Question 8

What are some complications of bronchiectasis?

Answer 8

• copious offensive sputum production
• poor drainage of secretions leads to recurrent bacterial pneumonia and abscesses.
• rupture of vessels in bronchial walls leads to heamoptysis
• pulmonary fibrosis leading to right ventricular failure (known as cor pulmonale)
• cerebral abscesses
• amyloidosis

Question 9

What are common features of pulmonary tuberculosis?

Answer 9

• Caused commonly by “acid fast bacilli” known as Mycobacteria tuberculosis.
• Because the body cannot clear the bacteria due to the acid fast quality of its cell wall, the body produces granulomas around the bacteria in an attempt to limit spread and damage.
• A tuberculous granuloma is known as a tubercle.

Question 10

What is the difference between primary and secondary TB?

Answer 10

Primary TB:

• Pattern of TB which occurs in individuals not previously exposed
• Clinically a mild, self limiting illness or subclinical
• Peripheral area of granulomatous inflammation and caseation = Ghon focus
• Drainage of bacteria to hilar lymph nodes which also caseate - Ghon focus + involved node = Ghon complex
• In most patients, immune response controls the infection and the Ghon complex heals by fibrosis, often with some calcification

Secondary TB:

• Apical areas of the upper lobes
• Tubercles and caseation
• Effective immune response or treatment: localization of infection and healing by fibrosis
• Dystrophic calcification

Question 11

What are some complications of secondary TB?

Answer 11

• Progressive spread of caseation into surrounding lung
• Erosion of blood vessels (haemoptysis)
• Erosion into bronchial tree leading to cavitation and spread of infection via airways
• Pleural inflammation and fibrosis
• Lung scarring

Question 12

What is Miliary TB?

Answer 12

• Numerous small granulomas in lungs or other organs

- Granulomas (tubercles) are about the size of Millet seeds (2-3mm)