Introduction
Pneumonia is the most common cause of death worldwide. The incidence of developing pneumonia is higher in younger and older populations. Pneumonia is categorized as broncho or lobar pneumonia, depending on the severity of the lung infection. Lobar pneumonia is a lung infection affecting one or more lung sections. Most bronchopneumonia progresses into lobar pneumonia. This article briefly discusses lobar pneumonia.
What Is Lobar Pneumonia?
Lobar Pneumonia is the acute exudative inflammation of the entire lung lobe. The condition is also termed non-segmental or focal non-segmental pneumonia. It is a radiologic feature with a uniform and fibro suppurative consolidation of one or more lung lobes due to bacterial pneumonia. Consolidation of complete or near complete lung lobes is noticed, but the lung volume is maintained.
Community-acquired Streptococcus pneumoniae is a common cause of developing lobar pneumonia. Other causes include Klebsiella pneumoniae, Haemophilus influenzae, Legionella pneumophila, and Mycobacterium tuberculosis. Lobar pneumonia is considered fatal as it affects an entire lobe.
What Is the Mechanism for Developing Lobar Pneumonia?
Inhaled microorganisms reach the subpleural space of the lung and induce alveolar wall injury along with severe hemorrhagic edema. Later, the invading organisms multiply and invade the infected edema fluid by polymorphonuclear leukocytes. The microorganisms rapidly spread from terminal airways and pores of Kohn, causing consolidation of the entire lobe or segment. Pleural boundaries limit the spread of the infection. The consolidation primarily affects the alveolar air spaces. The characteristic sign of lobar pneumonia is sparing the bronchi, which creates the appearance of air bronchograms. The process is inhibited by administering antibiotic therapy.
What Are the Stages of Lobar Pneumonia?
The histological and gross appearance can be classified into four stages of inflammation, which are:
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Congestion or Consolidation: This is the first stage of infection that develops after a lobe is infected. The lungs become heavy, red, and boggy in the first 24 hours of congestion or consolidation. Microscopic characteristics include intra-alveolar edema and vascular engorgement. Bacteria and a few neutrophils can be seen microscopically.
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Early Consolidation or Red Hepatization: This is the second stage of lobar pneumonia, which begins two to three days following consolidation and lasts two to four days. It is termed red hepatization due to its firm liver-like consistency. The affected lung appears red-pink, dry, granular, and airless. During this phase, fibrin strands take the place of the edema fluids. Microscopically, cellular exudate of neutrophils with ingested bacteria, erythrocyte extravasation, desquamated epithelial cells, and fibrin within alveoli are noticeable. The exudate makes the alveoli septa less prominent. As a result, the alveoli cannot transfer oxygen and other gasses efficiently to the bloodstream.
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Late Consolidation or Grey Hepatization: This stage begins two to three days after red hepatization. It lasts for four to eight days. The lung appears grey and has a liver-like consistency due to fibrinopurulent exudate. Additionally, there is progressive disintegration of red blood cells and hemosiderin. The macrophages become apparent.
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Resolution and Restoration: The pulmonary architecture resolution and restoration begins on the eighth day. The enzymatic action develops centrally and extends peripherally, liquefying previous solid fibrinous content and restoring aeration. Macrophages predominantly engulf neutrophils and debris.
What Are the Clinical Features of Lobar Pneumonia?
The clinical feature depends on the disease severity, host factors, and associated complications. Patients develop a productive cough, sputum, and purulent sputum. Other symptoms include dyspnea (shortness of breath), fever, malaise, and rigor. Pleuritic chest pain is typical in lobar pneumonia. Some even develop hemoptysis (blood in sputum). However, symptoms of lobar pneumonia are mild or absent in the older age group.
How Is Lobar Pneumonia Diagnosed?
On physical examination, dullness to percussion is sensed in the lobar pattern. One can detect accidental breath noises and bronchial breathing. A pleural rub and reduced expansion on the affected side are visible. Histologically, lobar pneumonia appears as alveolar spaces filled with exudate of edema fluid and neutrophils in later stages.
Radiographic characteristics are consolidation, which begins in the periphery of the lungs below the visceral pleura and spreads up to the interlobar fissure. The consolidation in lobar pneumonia crosses segmental boundaries and engulfs the entire lobe. The consolidation is homogeneous and involves an adjacent segment of lobes with progression. Severe cases of lobar pneumonia affect the entire lobe, and infection can spread to other remaining lungs. The bronchi remain patent, leading to air bronchograms with consolidation areas. Rarely do radiographic features of cavitation develop. It is apparent when the lungs are affected by Mycobacterium or Klebsiella pneumoniae. Small pleural effusions are expected, whereas large pleural effusions like empyema (pus collection in the lung cavity) and bronchopleural fistula can develop.
Plain radiographs reveal homogeneous opacification in the lobar pattern. The opacification becomes distinct at fissures even though there is segmental consolidation. The non-opacified bronchus appears as air bronchograms. Although lobar pneumonia does not cause volume loss, there is a possibility for developing atelectasis due to small airway obstruction.
CT (Computed Tomography) images demonstrate lobar pneumonia as focal dense opacification in most of the lobe but sparing large airways. Additional areas of ground-glass opacity in lobar or segmental patterns could indicate partial involvement or atelectasis. The primary role of imaging is to diagnose parenchymal abnormalities consistent with clinical features.
What Is the Differential Diagnosis for Lobar Pneumonia?
Differential diagnosis are:
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Lobar Atelectasis: It is associated with more volume loss and is more radiographically enhancing than lobar pneumonia.
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Obstructive Pneumonitis: Development of obstructive pneumonitis distal to lobar bronchus obstruction by a tumor or foreign body mimics lobar pneumonia. A differentiating feature in radiographs is the absence of bronchograms in obstructive pneumonitis.
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Pulmonary Malignancy: Malignant lung lesions such as adenocarcinoma or pulmonary lymphoma can mimic features of lobar pneumonia.
How Is Lobar Pneumonia Treated?
Treatment is mainly antimicrobial therapy. Radiological follow-up of lobar pneumonia is advised as there is a risk for pneumonia to recur as malignant or benign pulmonary pathology.
What Are the Complications of Lobar Pneumonia?
The complications associated with pulmonary pneumonia are:
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Pulmonary abscess.
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Pleural
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Parapneumonic effusion develops due to a fibrinous inflammatory reaction to adjacent pulmonary inflammation.
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Empyema is a purulent fibrinous inflammatory reaction due to the spread of infection into pleural space.
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Depending on the degree of fibroblastic organization, bland and pleural effusions progressively cause scarring and lung adhesions.
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3. Disseminated infection
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Bacteremia
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Multiorgan infection.
Conclusion
Lobar pneumonia is a severe form of lung infection. It develops when one or more of the five lung lobes become affected by infection. Therefore, it hampers the oxygen exchange mechanism of the lungs and results in unpleasant complications.
