Basic Histopathologic Neuronal Reaction to Injury PDF

Basic histopathologic neuronal reaction to injury Prof. Dr. Süheyla Uyar Bozkurt Components of CNS  brain, spinal cord, olfactory tract and bulb, optic nerve and retina  1. Gray matter  contain large numbers of nerve cell bodies; give gross color  Neuropil - de...

Basic histopathologic neuronal reaction to injury Prof. Dr. Süheyla Uyar Bozkurt Components of CNS  brain, spinal cord, olfactory tract and bulb, optic nerve and retina  1. Gray matter  contain large numbers of nerve cell bodies; give gross color  Neuropil - dendrites and terminals of axons forming network around neuronal cell bodies  2.White matter  Regions composed mainly of myelinated fibers;so designated because of gross color cerebellum (Nerve cell) - specialized, long-lived (life-long and does not replicate), multibranched cell electrically-excitable membrane for reception, integration, and communication of information Shape varies form stellate to pyramidal (triangular or flask-shaped) size varies from about 4-125 m diameter Perikaryon (nerve cell body; soma; sometimes referred to simply as “neuron”) Nucleus - contains prominent nucleolus, Neuron  Nissl substance  Basophilic granules in nerve cell perikaryon  Fills cytoplasm of nerve cell perikaryon and extends into dendrites,  Composed of concentrated collections of ribosomes and endoplasmic reticulum for protein synthesis 7 CNS Structure and Function Neuron  Axon  Slender, cylindrical,  arise from perikaryon at axon hillock  only one from each neuron  Ensheathed by supporting cells  Schwann cells in peripheral nervous system  oligodendrocytes in central nervous system  make myelin (myelinated axons) or do not make myelin (unmyelinated axons) 8 CNS Structure and Function Neuroglia  include  macroglia  astrocytes,  oligodendrocytes,  ependymal cells  microglia 9 CNS Structure and Function Neuroglia Astrocyte  branched stellate cell  oval nucleus , little perinuclear cytoplasm,  numerous cell processes Neuroglia Oligodendrocyte (oligodendroglia)  1. Cell with small, darkly-staining, round nucleus, minimal perinuclear cytoplasm, few processes, and no cytoplasmic filaments  2. Myelin sheath  Ependymal cell  Ciliated cells that form cuboidal epithelial lining of ventricular cavities 12 CNS Structure and Function Microglial cell Microglia have thin, elongated, and hyperchromatic nuclei. Microglia are most readily identified in their reactive state, “rod cells.” Reactions of cells to injury  Neuronal rxn  Glial rxn Reactions of Neurons to Injury Neurons share pathways for response to injury, including necrosis and apoptosis Neurons are not capable of cell division; so if there is a neuronal cell loss; neurological deficit Stem cells may represent a potential for repair after injury Principles patterns of neuronal injury  1-Acute neuronal injury  2-Subacute and chronic neuronal injury  3-Axonal reaction  4-Subsellular alterations  5-Neuronal intracytoplasmic inclusions 1-Acute neuronal injury  ("red neurons") a spectrum of changes that seen in acute CNS hypoxia/ischemia or other acute insults and reflects cell death  "Red neurons" are evident in(H&E) preparations at about 12 to 24 hours after an irreversible hypoxic/ischemic insult. Necrotic "dead red" neurons can be identified in the infarcted area Acute neuronal injury  The morphologic features consist of;  shrinkage of the cell body  pyknosis of the nucleus  disappearance of the nucleolus  loss of Nissl substance  intense eosinophilia of the cytoplasm. 2-Subacute and chronic neuronal injury ("degeneration")  refers to neuronal death occurring as a result of a progressive disease process of some duration, as is seen in certain slowly evolving neurologic diseases  amyotrophic lateral sclerosis (ALS).  2-Subacute and chronic neuronal injury ("degeneration")  The characteristic histologic feature is cell loss, often selectively involving functionally related groups of neurons, and reactive gliosis.  early stage; the cell loss is difficult to detect; the associated reactive glial changes are often the best indicator of the pathologic process.  normal pronounced reactive gliosis 3-Axonal reaction  refers to the reaction within the neuronal cell body that attends regeneration of the axon;  it is best seen in anterior horn cells of the spinal cord when motor axons are cut or seriously damaged.  There is increased protein synthesis associated with axonal sprouting. Axonal reaction  Morphology;  enlargement and rounding up of the cell body, peripheral displacement of the nucleus,  enlargement of the nucleolus,  dispersion of Nissl substance from the center to the periphery of the cell (central chromatolysis). 4-subcellular alterations  Neuronal damage may be associated with a wide range of subcellular alterations in the neuronal organelles and cytoskeleton.  Neuronal inclusions may occur as a manifestation of aging ; intracytoplasmic accumulations of complex lipids (lipofuscin), proteins, or carbohydrates.  Abnormal cytoplasmic deposition of complex lipids and other substances also occurs in genetically disorders of metabolism. 4-Subcellular alterations  Viral infection can lead to abnormal  intranuclear inclusions, herpetic infection (Cowdry body),  cytoplasmic inclusions, rabies (Negri body),  both nucleus and cytoplasm as in cytomegalovirus (CMV) infection. B-Reactions of Astrocytes to Injury Gliosis (or astrogliosis)  is the most important histopathologic indicator of CNS injury, regardless of etiology, and is characterized by both hypertrophy and hyperplasia.  Gliosis is proliferation of astrocytes at sites of injury, the counterpart of "scarring" elsewhere in the body.  İnjury to astrocytes;  When directly injured, astrocytes can react with cytoplasmic swelling.  This is seen in acute insults that cause the cell's ATP-dependent ion channels to fail, as occurs in hypoxia, hypoglycemia, and toxic injuries.  Gemistocytic astrocytes  are astrocytes seen in reactive processes. They are large, pink cells. The Alzheimer type II astrocyte  is a gray-matter cell with a large nucleus, pale- staining central chromatin, an intranuclear glycogen droplet, and a prominent nuclear membrane and nucleolus.  Its name is a misnomer, as it is mainly seen not in Alzheimer disease but in  long-standing hyperammonemia due to;  chronic liver disease  Wilson disease or  hereditary metabolic disorders of the urea cycle. Piloid gliosis-Rosenthal fibers  are thick, elongated, brightly eosinophilic, irregular structures that occur within astrocytic processes, and contain proteins  Rosenthal fibers are typically found in regions of long-standing gliosis; around tumors, vascular abnormalities corpora amylacea, or polyglucosan bodies;  round, faintly basophilic concentrically lamellated structures located wherever there are astrocytic end processes, especially in the subpial and perivascular zones. occur in increasing numbers with advancing age are thought to represent a degenerative change in the astrocyte. Reactions of Other Glial Cells to Injury  oligodendrocytes and ependyma do not participate in the active response to CNS injury  show a more limited features of reactions.  Oligodendroglial cytoplasmic processes wrap around axons and form myelin.  Injury or apoptosis of oligodendroglial cells is a feature of acquired demyelinating disorders and leukodystrophies. Ependymal cells,  do not have specific patterns of reaction.  When there is inflammation or marked dilation of the ventricular system;  disruption of the ependymal lining is & proliferation of subependymal astrocytes produce small irregularities on the ventricular surfaces (ependymal granulations). Reactions of Microglia to Injury  Microglia are tissue macrophage system in the CNS.  They respond to injury by  (1) proliferating  (2) developing elongated nuclei (rod cells)  (3) forming aggregates about small foci of tissue necrosis (microglial nodules)  (4) concentrating around cell bodies of dying neurons (neuronophagia). Characteristic findings of viral encephalitis include microglial nodules This is an example of neuronophagia in which a dying neuron is surrounded by microglial cells.