empyema - purulent fibrinous inflammatory reaction due to infectious spread into the pleural space.parapneumonic effusion - fibrinous inflammatory reaction to the adjacent pulmonary inflammation.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. However, there is overlap, and also factors such as pulmonary hemorrhage and underlying malignancy likely affect the lung density. For example, one small study used a threshold of 85 HU to distinguish between atelectasis versus pneumonia on CT PE protocol with a sensitivity of 90% and specificity of 92% 10. On contrast-enhanced CT, pneumonia often enhances less than atelectatic lung, although there is no clear Hounsfield unit threshold to distinguish the two. There may be additional associated areas of ground-glass opacity in a lobar or segmental pattern, likely representing areas of partial involvement or simply atelectasis 1. CTĬlassically, lobar pneumonia appears as a focal dense opacification of the majority of an entire lobe with relative sparing of the large airways. 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. The opacification can be sharply defined at the fissures, although more commonly there is segmental consolidation 3. Radiographic features Plain radiographĬharacteristically, there is homogeneous opacification in a lobar pattern. Red and grey hepatisation refers to the gross morphological appearance of a lung with inflammatory exudate in the alveolar spaces. resolution: final stage of processing the residual exudate.grey hepatisation: fibrinopurulent inflammatory alveolar exudate.red hepatisation: hemorrhagic inflammatory alveolar exudate.congestion: hyperemia, with alveolar edema and bacterial proliferation.The gross and histologic appearance of the infected lung can be broken down into four stages of inflammation 2: Other causative organisms that may cause a lobar pattern include 1: The most common cause of lobar pneumonia is Streptococcus pneumoniae. There is characteristic relative sparing of the bronchi, creating the appearance of air bronchograms. The distribution of consolidation is lobar because of the spread of infection across segmental boundaries - facilitated by the pores of Kohn and the canals of Lambert 3 - although limited by pleural boundaries. PathologyĬonsolidation in lobar pneumonia mainly affects the alveolar air spaces. A pleural rub and reduced expansion on the affected side may be present 5. Key features on physical examination are dullness to percussion in a lobar pattern, bronchial breathing, and adventitious breath sounds. 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, dyspnea, pyrexia/fevers, rigours, malaise, pleuritic pain, and occasionally hemoptysis. Incidence is higher at the extremes of age. Pneumonia is the most common cause of death due to infectious diseases in the United States, with an incidence of 11.
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