Local Reactions and Demarcation Inflammation
Any focus of tissue death inevitably triggers a reaction in the surrounding healthy structures. This process begins with the development of demarcation inflammation—an acute local reaction whose primary goal is to clearly isolate the dead masses from viable tissue.
The initiation of this inflammation is mediated by specific molecules released directly from disintegrating cells. First, lipid peroxidation of dying cell membranes actively generates leukotrienes. Second, when cells break down, mitochondrial components are released into the extracellular space, acting as potent triggers that activate the complement system.
However, demarcation inflammation also has a negative side—the phenomenon of secondary injury. An active inflammatory reaction at the border with healthy tissue (perifocal inflammation) can provoke additional death of neighboring cells. A classic example of this phenomenon is observed in myocardial infarction, where the initial necrosis zone can expand significantly precisely because of an aggressive inflammatory response.
Systemic Response and Autoimmunization
In addition to local changes, cell death triggers a generalized systemic reaction. The liver plays a key role here, stepping up its synthesis of acute-phase inflammatory proteins in response to injury.
- C-Reactive Protein (CRP): Its plasma concentration rises rapidly. CRP physically accumulates within necrotic masses, where it activates the complement system via the classical pathway, thereby initiating and maintaining demarcation inflammation.
- Serum Amyloid A (SAA): In cases of massive or prolonged tissue breakdown, SAA can serve as the precursor protein for AA amyloid synthesis, ultimately leading to a severe systemic complication—secondary systemic amyloidosis.
Another formidable systemic manifestation is linked to nuclear material entering the bloodstream. Chromatin released from breakdown sites undergoes opsonization, triggering pathological mechanisms of autoimmunization and prompting the immune system to attack its own tissues.
Adverse Outcomes
Adverse clinical courses often end in severe disability due to organ dysfunction or result in death. The most dangerous, life-threatening forms include myocardial infarction, ischemic cerebral infarction (stroke), acute pancreatitis, progressive hepatic necrosis, and necrosis of the adrenal glands and renal cortex.
An extremely hazardous scenario is purulent liquefaction. In this case, dead tissues are not simply walled off; instead, they undergo enzymatic lysis driven by purulent exudate. This creates a high risk of spreading purulent inflammation, allowing the infection to break beyond the primary focus and generalize into sepsis.
Favorable Outcomes and Repair
If the body succeeds in localizing the injury, repair processes are triggered from the zone of demarcation inflammation, aiming to isolate or replace the defect:
- Organization (Scarring): The most frequent outcome, in which dead masses are gradually resorbed and fully replaced by dense connective tissue.
- Encapsulation: If the focus is too large or dense for complete resorption, a secure connective tissue capsule forms around it, isolating the dead material.
- Petrification (Calcification): A process of dystrophic calcification in which calcium salts precipitate within necrotic tissues.
- Ossification: A relatively rare outcome representing the further progression of petrification, with true bone tissue forming within the former injury zone.
Separate mention should be made of the outcomes of liquefactive (colliquative) necrosis, which is typical of brain tissue. Due to the structural features of nervous tissue, classic scarring does not occur here. If the softening focus is small, glial cells proliferate at the site, forming a microglial scar. If the focus is large, the dead tissue is resorbed, leaving behind a fluid-filled cavity known as a cyst.