Lobar pneumonia (also known as non-segmental pneumonia or focal non-segmental pneumonia 7) is a radiological pattern associated with homogenous, fibrinosuppurative consolidation of one or more lobes of a lung in response to bacterial pneumonia.
The radiological appearance of lobar pneumonia is not specific to any single causative organism, although there are organisms which classically have a radiological presentation of lobar pneumonia. Streptococcus pneumoniae (also known as pneumococcus) is the most common causative organism of lobar pneumonia.
Pneumonia is the most common cause of death due to infectious diseases in the United States, with an incidence 11.6 per 1000 persons/year reported in one study 4. Incidence is higher at the extremes of age.
The presentation of lobar pneumonia depends on the severity of the disease, host factors and the presence of complications. Lobar pneumonia may present with a productive cough, dyspnoea, pyrexia/fevers, rigors, malaise, pleuritic pain and occasionally haemoptysis.
Key features on physical examination are dullness to percussion in a lobar pattern, bronchial breathing and adventitious breath sounds. A pleural rub and reduced expansion on the affected side may be present 5.
Consolidation in lobar pneumonia mainly affect the alveolar air spaces. There is characteristic relative sparing of the bronchi, creating the appearance of air bronchograms. The lobar distribution of consolidation occurs because of the spread of infection across segmental boundaries - this is facilitated by the pores of Kohn and the canals of Lambert 3.
The most common cause of lobar pneumonia is Streptococcus pneumoniae. Other causative organisms that may cause a lobar pattern include 1:
- Klebsiella pneumoniae
- Legionella pneumophila
- Haemophilus influenzae
- Mycobacterium tuberculosis
Histology of infected lung can be broken down into four stages 2:
- congestion and dilation of blood vessels
- red hepatisation of the lung
- grey hepatisation of the lung
Red and grey hepatisation refer to the gross morphological appearance of a lung with inflammatory exudate in the alveolar spaces.
Characteristically, there is homogeneous opacification in a lobar pattern. The opacification can be sharply defined at the fissures, although more commonly there is segmental consolidation 3. The non-opacified bronchus within a consolidated lobe will result in the appearance of air bronchograms. Strictly speaking, consolidation is not associated with volume loss, however, atelectasis can occur with small airway obstruction.
Lobar pneumonia can have a pattern of focal ground-glass opacity in a lobar or segmental pattern. This is due to incomplete filling of alveoli and consolidation 1. At other times there can be dense opacification of the entire lobe.
Treatment and prognosis
Radiological follow-up of lobar pneumonia is often recommended - one study found ~5% of initially suspected community-acquired pneumonia were re-diagnosed with malignant or important benign pulmonary pathology on follow-up chest radiographs/CT (average follow-up at 11.5 weeks) 9.
For radiographic appearances of consolidation, consider other forms of lobar consolidation such as
- pulmonary malignancy
- lung adenocarcinoma affecting an entire lobe
- forms of pulmonary lymphoma 8 can affect an entire lobe
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