Morphology of Acute Inflammation

Morphologic hallmark: dilation of small blood vessels and accumulation of leukocytes and fluid in extravascular tissue.

Robbins & Cotran Pathologic Basis of Diseases, South Asia edition, 9e, pg. no. 90

Marked by the exudation of cell-poor fluid into spaces created by cell injuries or into body cavities lined by peritoneum, pleura or pericardium.
Typically fluid is not infected by destructive organisms and doesn't contain large no. of leukocytes.
Effusion: accumulation of fluid in body cavities. Fluid may be derived from plasma or from secretions of mesothelial cells.
Eg: Skin blisters resulting from a burn or viral infection

Fibrinous exudate develops when the vascular leaks are large or there is local procoagulant stimulus.
Seen in inflammation of body cavities such as meninges, pericardium & pleura.
Histologically- fibrin seen as an eosinophilic meshwork of threads or as an amorphous coagulum.
Exudate may be dissolved by fibrinolysis (macrophages).
If fibrin not removed → scarring. Scarring within pericardial sac leads to opaque fibrous thickening. If it is extensive → obliteration of pericardial space.

Characterised by production of pus, an exudate consisting of neutrophils, the liquefied debris of necrotic cells and edema fluid.
Most frequent cause - infection with pyogenic bacteria (causes liquefactive necrosis)
Eg: Acute appendicitis
Abscess - localized collections of purulent inflammatory tissue caused by suppuration buried in tissue. Have a central region appearing as mass of necrotic leukocytes and tissue cells.

Local defect or excavation of an organ or tissue that is produced by sloughing (shedding) of inflamed necrotic tissue.
Can occur only when tissue necrosis and resultant inflammation exist on or near surface.
Mostly encountered in
- mucosa of mouth, stomach, intestine or genitourinary tract,
- skin & subcutaneous tissue of lower extremities (of older persons with circulatory disturbance)
Eg: Peptic ulcer of stomach and duodenum.