Pericarditis - Organizing - I

While serous transudates of pericardial fluid can be readily reabsorbed by the mesothelial cells of the serosal pericardium, the exudates cannot.
In contrast, the exudates contain large quantities of protein (namely fibrin) and variable amounts and types of inflammatory cells and, in infectious cases, microorganisms. Thus exudates are not readily reabsorbed, rather, these are organized. The organization process requires inflammatory cells that can remove the fibrin and other proteins. The formation of a network of vascular channels with a loose scaffold is defined as granulation tissue. As a function of time the granulation tissue organizes and matures through stages with more granulation tissue, replaced by connective tissue and fibroblasts (fibroplasia) to eventually form mature fibrous tissue. If the inflammatory process (pericarditis) relapses, this series of steps of organization are repeated, resulting in multiple strata of healed and healing events.

A. This photomicrograph shows acute fibrinous pericarditis in the early stages of organization. There is fibrinous exudate deposited over the fibrous pericardium. As it becomes organized it shows fibroblastic infiltration and neovascularization (granulation tissue formation). These areas of organization show a blue hue in the micrograph.

B. This Movat stains shows the fibrous pericardium in yellow (highlighted by the bracket) and the fibrin deposition in red. The blue-green aggregates of cells correspond to the areas of early organization of the fibrin deposits.
As the organization progresses, there is more inflammation, further neovascularization, collagen deposition and formation of dense fibrous tissue in the organized pericarditis.

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