Lobar pneumonia is often caused by Streptococcus pneumoniae infection. Inflammation often involves one or more complete lobes, or only lung segments.
Clinical presentation and pathology
This disease is common in young and middle-aged individuals, and is often characterized clinically by acute onset, rigors, high fever, thoracodynia, and rusty expectoration. If antibiotics are used in the early stage, the clinical course is often atypical. Blood routine test shows significant increase in the total count of white blood cells and neutrophils.
Pathologically, there are four stages. In the congestion stage, the capillaries in the alveolar wall are congested and dilated, small amounts of serous fluid exude from the alveoli, and air still exists in the alveolar cavity. In the red hepatization stage, the gross section of the lungs is red hepatized, because the alveoli are filled with massive exudation such as erythrocytes and fibrin. In the grey hepatization stage, erythrocytes in the alveoli are decreased and replaced by leukocytes, and the lung section is grey hepatized. In the remission stage, the fibrin exudates in the alveoli are dissolved and resorbed, and the alveoli are reinflated. After proper treatment, the lesion usually resolves in 1 week. The dynamic changes in pathology determine the different imaging manifestations in each stage.
Imaging manifestations
X-ray
In the congestion stage, there may be no positive findings, or only increased lung markings and decreased lung lucency. In the red and grey hepatization stages, there are homogeneous dense opacities; the morphology varies when different lobes or segments are involved, the involved pulmonary segment shows patchy or triangular dense opacity, the involved entire lobe shows massive dense opacities bounded by interlobar fissures; lucent bronchi can often be seen in the consolidation, which is air bronchogram sign. In the remission stage, the density of the consolidation gradually decreases, and the lesion shows variously sized, irregular, patchy opacities; the inflammation can eventually completely subside, or only few irregular linear opacities remain, and occasionally the disease can evolve into organizing pneumonia.
Figure 1 Lobar pneumonia in the upper left lung
Chest x-ray film shows large, poorly marginated, patchy, hyperdense opacity of consolidation in the upper left lung, and air bronchogram sign can be faintly seen.
CT
In the congestion stage, the lesion shows poorly marginated, ground-glass opacity, and the vascular opacities in the lesion is still faintly visible. In the red and grey hepatization stages, lobar or segmental, dense opacity of consolidation can be seen, and is air bronchogram sign. In the remission stage, with the resolution of the lesion, the density of the opacity of consolidation decreases; scattered, variously sized, patchy opacities can be seen; and the opacities can completely subside.
Figure 2 Lobar pneumonia in the upper right lung
Contrast-enhanced CT shows massive opacity of consolidation in the upper lobe of the right lung and air bronchogram sign.
Diagnosis and differential diagnosis
Lobar pneumonia often has typical clinical manifestations, and the diagnosis can be confirmed by combining clinical presentation with imaging manifestations. CT examination is conducive to early detection of lesion and differential diagnosis.
Atelectasis is characterized by reduced local lung volume and absence of air bronchogram sign.
Obstructive pneumonia often presents mass or nodule in the proximal end of the bronchus, or signs of bronchial stenosis or obstruction.
Lobar caseous pneumonia is often higher than lobar pneumonia in the density of pulmonary consolidation, and there are often mottled cavities. The tuberculosis history, clinical manifestations, and laboratory test are helpful to confirm the diagnosis.