PA25.1-2 | Pneumonia & Lung Abscess — Summary & Reflection

REFLECT

Take five minutes to think through the following before moving to the summary:

1. A 60-year-old patient with COPD and a recent influenza infection develops a rapid deterioration with multiple small cavitary lesions on CT scattered across both lungs. Which lung abscess mechanism fits best, and which organism would you most suspect?

1. A patient with right middle lobe bronchopneumonia is treated for three weeks but the lobe does not clear — it remains opaque and consolidated on CT with no cavitation. What complication has likely occurred, and what does the lung parenchyma look like on histology?

1. A chronic lung abscess patient develops proteinuria 6 months after the initial diagnosis. Name the complication and the type of protein deposited in the glomeruli.

Think through your answers before checking your notes. Discussing these cases with a colleague (or your tutor) will consolidate the pathological-clinical connections far better than re-reading the text.

KEY TAKEAWAYS

Core take-aways from this module:

Pneumonia classification
- Acquisition: CAP (S. pneumoniae), HAP (Gram-negatives + MRSA), aspiration (anaerobes), atypical (Mycoplasma, viruses).
- Anatomical: lobar (entire lobe, fibrin-rich, 4 stages) vs bronchopneumonia (patchy, peribronchial, bilateral lower lobes, mixed flora) vs interstitial (alveolar wall thickening, mononuclear, atypical agents).

Four stages of lobar pneumonia (PA25.1)
1. Congestion (serous exudate, engorged capillaries, abundant organisms).
2. Red hepatisation (fibrin + neutrophils + RBCs; firm, dark red, airless).
3. Grey hepatisation (RBCs lysed, macrophages arrive; grey-brown, still firm).
4. Resolution (fibrinolysis, macrophage clearance, re-aeration) — or organisation/carnification if it fails.

Complications of pneumonia: abscess, empyema, organisation (carnification), bacteraemia/sepsis, respiratory failure, pleuritis.

Lung abscess (PA25.2)
- Aetiology: aspiration (commonest, anaerobes, posterior segments), post-pneumonic (necrotising organisms), obstructive (tumour — exclude in >40), haematogenous (multiple bilateral, endocarditis/IV drug use).
- Gross: thick-walled cavity, liquefactive necrotic contents, air-fluid level on imaging.
- Micro: three concentric zones — central suppurative necrosis → granulation tissue → fibrous capsule.
- Complications: empyema/pyopneumothorax, massive haemoptysis, brain abscess, secondary amyloidosis, clubbing.
- Key clinical flag: foul sputum → anaerobic → aspiration mechanism.