Necrosis Lecture Notes PDF

Necrosis Definition: Local death of cells inside the living body.  Cellular characteristics of necrosis: a) Nuclear changes: 1. Pyknosis, the condensation of nuclear chromatin into a dark, round homogenous mass smaller than in a normal nucleus. 2. Karyorrhexis, the splitting...

Necrosis Definition: Local death of cells inside the living body.  Cellular characteristics of necrosis: a) Nuclear changes: 1. Pyknosis, the condensation of nuclear chromatin into a dark, round homogenous mass smaller than in a normal nucleus. 2. Karyorrhexis, the splitting of the nucleus into numerous pieces. 3. Karyolysis, dissolution of nuclear chromatin, leaving a hallow, large, round, ghost form of the nucleus b) Cytoplasmic changes 1. Increased acidophilia, which is most common. 2. Lysis of the cytoplasm, giving a pale vacuolated appearance. C) Changes in the cell as whole 1. The cells as whole loses its outline. 2. Reduced differential staining of nucleus and cytoplasm. 3. Complete loss of cells. Normal Pyknosis Karyorrhexis Karyolysis Kidney showing coagulative necrosis represented by pyknosis, karyolysis and karyorrhexis. H&E.  Gross characteristics of necrosis The gross indications of necrosis are loss of color or paleness of the tissue, loss of strength of the tissue as it softness, a defined zone of demarcation between necrotic and viable tissue Types of necrosis: 1- Coagulative 2- Caseous 3- Liquefactive 4- Fat 5- Fibrinoid  1- Coagulative necrosis: - Definition: Coagulative necrosis is characterized by a maintained organ architecture and loss of cellular details. It occurs in tissues rich with proteins as the parenchymatous organs, skeletal muscles. Causes: - This type of necrosis is frequently caused by viral infection, toxins or lack of blood supply (ischemia). Macroscopic picture: The necrosed area is dry, firm and pale (grayish white or yellow).  - Microscopic picture: Organ architecture is maintained and cellular details are lost. The cytoplasm appears highly eosinophilic, granular or homogenous, structurless mass. Pyknosis and karyolysis are present in the center of the necrotic area and karyorrhexis at the borders. Coagulative necrosis. A, A wedge-shaped kidney infarct (yellow)  Liver showing coagulative necrosis represented by nuclear changes and cytoplasmic changes. Moreover, numerous eosinophils separate the necrotic tissue from normal one, H&E. Kidney showing coagulative necrosis of the epithelium lining of renal tubules, H&E.  Zenker’s necrosis : Definition: - It is a coagulative necrosis of striated muscles where the protein of the sarcoplasm coagulates. Etiology: - Vitamin E. deficiency. -Toxins of pathogenic microorganisms as Cholestridia. -Ischemia -Viral infection Macroscopic picture: The affected muscles appear white, gray or yellow foci and streaks parallel with the muscle fibers Microscopic picture: The affected muscle fibers appear swollen, homogenous and eosinophilic. Loss of both longitudinal and cross striations in longitudinal sections. The cross section doesn’t show the fields of Cohenheim. The nuclei of muscle fibers are pyknotic.  Muscle showing Coagulative necrosis (Zenker's necrosis) infiltrated with inflammatory cells, H&E.  1- Caseous necrosis: - Definition: Caseous necrosis is characterized by the disappearance of both tissue architecture and cellular details and the tissue is replaced by granular cheesy like material or granular eosinophilic and basophilic debris. It is seen in tuberculosis, and other granulomas. Causes: - Granuloma as T.B. -Antigen-antibody reaction (allergic necrosis). The area of necrosis is soft, granular, and friable with a cream- cheesy appearance.  Lymph node infected with tuberculosis showing caseous necrosis characterized by replacement of the lymphoid tissue with eosinophilic and basophilic debris H&E. Organ: Lung Lesion: Caseous necrosis. Gross appearance: A tuberculous lung with a large area of caseous necrosis containing yellow-white and cheesy debris.  3- Liquefactive necrosis Definition: Liquefactive necrosis is characterized by disappearance of both tissue architecture and cellular details with replacement of the necrotic tissue with fluid. The later may disappear leaving a cavity. or replaced by pus. Tissue affected: - The central nervous system: the nervous tissue is rich in non- coagulable lipoidal substances and poor in coagulable albumin. In suppurative inflammation: there are numerous neutrophils which die and liberate proteolytic enzyme. These enzymes in addition to the lytic toxins (lysin) produced by the pathogenic bacteria digest the dead tissue into fluid.  Macroscopic picture: Cyst like cavities of variable size in nervous tissue with or without fluid. Microscopic picture: Pinkish or empty cavities are seen in the nervous tissue. Evidence of necrosis is seen in the cell lining the cavities. Pus (intact and fragmented neutrophils, with necrotic cellular debris and fibrin) in suppurative inflammation. Inflammatory reaction (vascular and exudative) surrounds the necrotic areas.  Lung showing liquefactive necrosis represented by replacement of the pulmonary tissue with structure less basophilic materials. H&E  4- Fat necrosis Definition: Fat necrosis is the death of the adipose tissue. is characterized by the disappearance of both tissue architecture and cellular details and the tissue is replaced by soap. Types: a) Internal or abdominal or pancreatic fat necrosis. b) External or subcutaneous or traumatic fat necrosis. - Causes of internal fat necrosis: Acute pancreatitis, neoplasms of pancreas - Pathogenesis: The enzyme lipase which escape from the ruptured pancreatic duct act on the fat of the omentum, mesentery and abdominal organs. Lipase split fat into glycerol and fatty acid. Glycerol is absorbed in the blood. Fatty acids combine with sodium, potassium, or calcium to form soap. Causes and pathogenesis of external fat necrosis: Trauma in the adipose tissue of the breast and subcutaneous fat. The fat cell rupture and self digestion takes place. Macroscopic picture: The necrotic area appear small dull opaque chalky white or yellowish-white and well circumscribed. Microscopic picture: The affected fat cells appear cloudy. It contain acicular crystal which stain blue (sodium soap), pinkish (potassium soap) or purple (calcium soap). Fat cells have pyknotic nuclei. The necrotic area is surrounded by inflammatory reaction and contains foreign body, giant cells and macrophage.  Adipose tissue showing fat necrosis represented by foci of shadow outline of necrotic fat cells containing pink crescentic crystals. Moreover, the nuclei are pyknotic and the necrotic area surrounded by inflammatory reaction. H&E  Sequelae of necrosis Removed by the macrophage. Liquefied and absorbed by lymphatics or veins. Desquamation and sloughing especially in skin and mucous membrane. Healing by regeneration or granulation tissue formation followed by fibrosis. Invasion of the necrotic area by pyogenic bacteria with formation of pus. Get surrounded by fibrous capsule and may show dystrophic calcification later on. Gangrene occurred when invasion of the necrotic tissue by saprophytic bacteria. Fatal: necrosis of the vital organs as brain, heart may be fatal.  Fat Liquefactive Caseous Coagulative Criterion - - - + Tissue - - - - architecture + + + + Cellular details Acicular crystals of Structurless basophilic Granular eosinophilic Coagulated eosinophilic mass Line of defense Na soap blue substance (pus), fluid or and basophilic debri replacement K soap pink cavity Ca soap purple a- nuclear changes Criteria of - - - pyknosis, karyorrhexis,( necrosis )karyolysis b- cytoplasmic (more eosinophilic) c- cellular changes Indistinct borders followed by disappearance Firm Liquid Friable Firm Consistency Chalky-white Grayish , whitish, bluish Grayish white Grayish Color or reddish Proteolytic enzymes of Death of macrophages Toxin Cause pus or eosinophils Viral Cells.Vit. E def CNS( rich in non coagulable lipoidal material and poor in coagulable albumin) Adipose tissue Any tissue Any tissue Any tissue Tissue involved zenker’s necrosis affect