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. Red and grey hepatisation refers to the gross morphological appearance of a lung with inflammatory exudate in the alveolar spaces.Ĭharacteristically, there is homogeneous opacification in a lobar pattern.

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. Opaque aspirates are also well demonstrated on CT.Consolidation in lobar pneumonia mainly affects the alveolar air spaces. In an erect patient, aspiration is more likely to involve bilateral basal segments, middle lobe, and lingula 2.Īspirated low-density organic material such as mineral oil in the tracheobronchial tree or alveolar spaces cannot be diagnosed on plain radiographs but may be seen on CT. The posterior segment of the upper lobes and the superior segment of the lower lobes are the most commonly involved lung sites when aspiration occurs in a recumbent patient. The clinical and radiological manifestations are protean, varying from asymptomatic focal inflammatory reaction with few or no radiological abnormalities to severe life-threatening disease. Mixed anaerobic aerodigestive tract organisms are the underlying causative agent 4 The aspirated particles act as a foreign body and induce granuloma formation 5.ĭepending on the time course, patients may be classified as:Ĭhronic aspiration pneumonia: recurrent aspiration pneumonia Structural abnormalities of the pharynx and esophagusĪspiration may be clinically silent or present with dyspnea, cough, or fever. The clinical and radiographic features depend on the aspirated volume, pH, and chronicity 2.

Pneumonia cxr findings