What is Pulmonary Infarction?
Pulmonary infarction refers to the death of lung tissue due to a lack of adequate blood supply. This typically occurs when a pulmonary artery is obstructed, often by a thrombus or embolus. The infarcted area becomes ischemic and subsequently necrotic, leading to various histological changes.
Histological Features of Pulmonary Infarction
In the acute phase, the infarcted lung tissue exhibits coagulative necrosis, where the basic cell outlines remain visible, but the cells are dead. Within the first 24-48 hours, there is an influx of neutrophils, followed by macrophages that begin to clear the dead cells.Chronic Phase Changes
As the infarction progresses to the chronic phase, granulation tissue forms, consisting of newly formed blood vessels, fibroblasts, and inflammatory cells. This granulation tissue gradually matures into a fibrous scar. This fibrotic area is devoid of normal lung architecture and function.Microscopic Examination
Under a microscope, pulmonary infarctions show a wedge-shaped area of coagulative necrosis. The necrotic zone is often hemorrhagic due to the rupture of blood vessels. The necrotic tissue is surrounded by a zone of inflammation and hyperemia. In chronic cases, the necrotic tissue is replaced by fibrous tissue.Role of Neutrophils and Macrophages
Neutrophils are the first responders to the site of infarction, arriving within hours. They play a crucial role in phagocytosing dead cells and releasing enzymes to degrade necrotic tissue. Macrophages arrive later and are key in clearing the debris and orchestrating tissue repair and fibrosis.Clinical Correlation
Histologically, pulmonary infarctions can help explain clinical symptoms such as pleuritic chest pain, hemoptysis, and dyspnea. The extent of infarction and the body's ability to repair the tissue determine the clinical outcome. In severe cases, large infarctions can lead to respiratory failure.Diagnosing Pulmonary Infarction
Histological examination of lung biopsy or autopsy specimens can confirm pulmonary infarction. The presence of coagulative necrosis, hemorrhage, and subsequent fibrosis are key histological findings. Special stains can highlight thrombosed vessels and the extent of tissue necrosis.Implications for Treatment
Histological understanding of pulmonary infarction aids in the development of therapeutic strategies. Treatment aims to restore blood flow, manage symptoms, and prevent further thromboembolic events. Anticoagulants, thrombolytics, and surgical interventions may be considered based on the extent of infarction.Conclusion
Pulmonary infarction is a significant pathological event with distinct histological features that evolve over time. Recognizing these changes under the microscope is essential for accurate diagnosis and effective management. Histology not only helps in understanding the disease process but also in guiding clinical treatment strategies.
