Lung Abscess: Etiology, Gross and Microscopic Appearance, and Complications

Introduction

A lung abscess is a localized collection of pus within the lung parenchyma, typically caused by bacterial infection. It leads to significant tissue destruction and cavitation.

Etiology

The most common causes of lung abscess include:

• Aspiration pneumonia due to anaerobic bacteria (Peptostreptococcus, Bacteroides, Fusobacterium).
• Post-obstructive pneumonia in conditions like lung carcinoma.
• Hematogenous spread from a distant infection site.
• Immunocompromised states, including HIV and malignancies.

Gross Appearance

Macroscopic examination reveals a cavitary lesion filled with purulent material. The cavity is often surrounded by necrotic lung tissue.

Microscopic Appearance

Histological examination shows:

• Central necrosis and pus collection.
• Inflammatory infiltrates consisting of neutrophils.
• Granulation tissue and fibrosis in chronic cases.

Complications

Potential complications of lung abscess include:

• Bronchopleural fistula leading to empyema.
• Sepsis and systemic dissemination of infection.
• Chronic cavitary lung disease.

Differential Diagnosis

Lung abscess must be distinguished from other pulmonary conditions such as:

• Tuberculosis, which presents with caseating granulomas.
• Pulmonary infarction secondary to embolism.
• Necrotizing pneumonia.
• Bronchogenic carcinoma with cavitation.

Conclusion

Lung abscess is a serious condition that requires prompt diagnosis and management. Understanding its pathology aids in effective treatment strategies.