Type of necrosis occurring in brain-

Coagulative necrosis This is the most common type of necrosis. This type of necrosis is most frequently caused by sudden cessation of blood flow (ischemia) in organs such as the heart (MI), Kidney (ATN), adrenal gland, and spleen. Note: Brain is the only exception, i.e., It is the only solid organ in which ischemia leads to liquefaction necrosis, not coagulative necrosis. It is also seen with other types of injury e.g., liver necrosis in viral hepatitis, Coagulative necrosis of skin after burns (Thermal injury). Why there are predominant protein denaturation and no enzymatic digestion? Hypoxia causes intracellular acidosis (has been explained earlier) → 4 pH results in denaturation of proteins which includes not only structural proteins but also enzymes → So, there is no enzymatic digestion Liquefactive necrosis It is the necrotic degradation of tissue that rapidly undergoes softening and liquefaction because of the action of hydrolytic enzymes. It occurs after 1. Infection Le., suppurative inflammation (most common). 2. Ischemic necrosis in the brain. Note: Brain lacks any substantial supportive stroma, so ischemic necrosis in the brain is liquefactive, unlike other organs where it is coagulative. Mechanism of liquefactive necrosis → Microbes stimulates accumulation of inflammatory cells and these cells to release lysosomal enzymes. Caseous necrosis It is a variant of coagulative necrosis. It is most commonly encountered when cell death is attributable to certain organisms e.g., Mycobacterium tuberculosis (TB) and fungi (Histoplasma, Coccidioidomycosis). Why is it called caseous necrosis, not coagulative necrosis? In contrast to coagulative necrosis where tissue architecture is maintained, in caseous necrosis, the tissue architecture is completely obliterated. So, it has been called caseous because of its cheesy white appearance of the area of necrosis.