Monday 17 October 2005
In severe injuries resulting in great vascular permeability, larger molecules such as fibrinogen pass the vascular barrier, and fibrin is formed and deposited in the extracellular space.
A fibrinous exudate develops when the vascular leaks are large enough or there is a procoagulant stimulus in the interstitium (e.g., cancer cells).
A fibrinous exudate is characteristic of inflammation in the lining of body cavities, such as the meninges (fibrinous meningitis), pericardium (fibrinous pericarditis), and pleura (fibrinous pleuritis).
Histologically, fibrin appears as an eosinophilic meshwork of threads or sometimes as an amorphous coagulum.
Fibrinous exudates may be removed by fibrinolysis and clearing of other debris by macrophages. The process of resolution may restore normal tissue structure, but when the fibrin is not removed, it may stimulate the ingrowth of fibroblasts and blood vessels and thus lead to scarring.
Conversion of the fibrinous exudate to scar tissue (organization) within the pericardial sac leads either to opaque fibrous thickening of the pericardium and epicardium in the area of exudation or, more often, to the development of fibrous strands that reduce and may even obliterate the pericardial space (fibrinous pericarditis).