features of CNS pathology

Transcription

1 سالي ابو رمان Characteristic features of CNS pathology

2 Important notes : - In this sheet I arranged slides within what the doctor said plus what is written in the book, hopefully it will be helpful and understood. - please notice that I couldn t put the figures from the slides in the sheet, so be sure to go back to them, I wrote what the doctor said about them in the last page. - sorry in advance for any unintentionally mistakes, good luck CNS as any organ in the body can be affected by different pathogenic processes either neoplastic or nonneoplastic Normal brain The brain is covered and protected by three layers of tissue called meninges. From the outermost layer inward they are: the dura mater, arachnoid mater, and pia mater. Normally the brain is composed of the gray matter which is in the surface and the white matter which is inside of the brain

3 - The neocortex (gray matter): it is termed neocortex due to presence of cell bodies, the neurons are arranged in 6 layers horizontally, in some diseases this distribution of neurons is disrupted which leads to absence of normal layers. those layers are : outer plexiform, outer granular, outer pyramidal, inner granular, inner pyramidal, polymorphous. the layers differ in the shape of neurons they contain. - White matter : it is made up of myelinated axons of the neurons from the neocortex and glial cells (oligodendrocytes, astrocytes, ependymal cells and microglia) mainly oligodendrocytes and astrocytes. Astrocytes present in gray and white matter and are distributed between the neurons forming a network that aid in the blood brain barrier. Oligodendeocytes coat the axons of CNS with myelin, Schwann cells do that in PNS. Ependymal cells line the ventricles and are responsible for CSF secretion. Microglial are CNS macrophages. Features of Neuronal Injury Acute neuronal injury can be on the cell body or the axon of the neuron, acute means within 12 hours of ischemia or hypoxia in the CNS ( as example : Stroke ). the changes after neuronal injury appear like necrosis. 1-shrinkage of the cell body 2-pyknosis of the nucleus : condensation of chromatin 3- disappearance of the nucleolus 4- loss of Nissl substance : large granular bodies found in the neurons, they are the site for protein synthesis. 5-intense eosinophilia of the cytoplasm ( red neurons ) Features of axons injury : notice that axon injury leads to reactive injury to the cell body. 1- Axonal swellings (spheroids) : whenever you see axon swelling it means there is injury to the axon. 2- cell body enlargement and rounding 3- peripheral displacement of the nucleus 4- enlargement of the nucleolus 5- peripheral dispersion of Nissl substance (central chromatolysis) Intracellular inclusions Many neurodegenerative diseases are associated with specific intracellular inclusions. Pathogenic viruses may form inclusions in infected neurons, just as in other cells, and such inclusions aid in the diagnosis. Inclusions may be seen due to deposition of lipofuscin ( by

4 aging ) in different parts of the body but most importantly in the brain, lipofuscin is lipid material. dystrophic neuritis : neuronal processes become thickened and tortuous in some neurodegenerative diseases. Astrocytes in Injury and Repair Scar formation in the peripheral tissue is done by the fibroblasts and is termed Fibrosis, but in the brain the scar formation differs in that it is done by Astrocyetes and in a process termed Gliosis. Astrocytes have 2 types : fibrous astrocytes (thin and long dendrites, present in white matter ) and protoplasmic astrocytes (thick and branched dendrites, present in gray matter ). In response to injury, astrocytes undergo both hypertrophy and hyperplasia.the nucleus enlarges and becomes vesicular ( this indicates a reactive process ), and the nucleolus becomes prominent. gemistocytic astrocyte : The cytoplasm expands and become esinophilic, and the cell extends multiple stout,ramifying processes. fibrillary astrocytes : In long-standing gliosis,the cytoplasm of reactive astrocytes shrinks in size, and the cellular processes become more tightly interwoven. Rosenthal fibers : are thick, elongated, brightly eosinophilic protein aggregates found in astrocytic processes in chronic gliosis and in some low-grade gliomas. Presence of gemistocytic astrocytes and Rosenthal fibers indicates : reactive astrocytic process or neoplastic astrocytic process. Oligodendrocytes : are vulnerable to viral inclusions, most commonly polioma virus ( PMLE). Microglial cells: When activated by tissue injury, infection, or trauma, they proliferate and become more prominent histologically. Microglial cells take on the appearance of activated macrophages in areas of demyelination, organizing infarct, or hemorrhage. Rod cells :microglial cells that developed elongated nuclei in infection Aggregates of elongated microglial cells at sites of tissue injury are termed microglial nodules, Similar collections can be found congregating around and phagocytosing injured neurons(dead neurons) (neuronophagia). Ependymal cells line the ventricular system and the central canal of the spinal cord. Certain pathogens, particularly cytomegalovirus (CMV), can produce extensive ependymal injury, with typical viral inclusions Cerebral edema It is the accumulation of excess fluid within the brain parenchyma. It can be extracellular (vasogenic edema) or intracellular (cytotoxic edema), these two types differ in the pathologic process and causes but often occur together particularly after generalized injury Vasogenic edema occurs when the integrity of the normal blood-brain barrier is disrupted, allowing fluid to shift from the vascular compartment into the extracellular spaces of the

5 brain. Vasogenic edema can be localized (e.g., the result of increased vascular permeability due to inflammation or in tumors) or generalized. Cytotoxic edema is an increase in intracellular fluid secondary to neuronal and glial cell injury, as might follow generalized hypoxic or ischemic insult or exposure to certain toxins The edematous brain is: softer than normal. often appears to over fill the cranial vault. In generalized edema the gyri are flattened, the intervening sulci are narrowed, the ventricular cavities are compressed. Hydrocephalus Normally the CSF is formed in the lateral ventricles, circulates through the interventricular foramens(foramen of monro) into the third ventricle, and then via the cerebral aqueduct into the fourth ventricle. Here the fluid escapes via the lateral apertures of the fourth ventricle and the medial foramen of the fourth ventricle into the subaracnoid spaces, where it diffuses over the brain and spinal cord. The hydrocephalus is : an increase in the volume of the CSF within the ventricular system. This disorder most often is a consequence of impaired flow or decreased resorption of CSF or over production of CSF. Most common cause for impaired flow of CSF is inflammation such as meningitis, but most common cause for overproduction of CSF is tumor of choroid plexus ( which is rare condition). Types of hydrocephalus are : 1- Noncommunicating hydrocephalus ( obstruction ) : occurs when a localized obstacle to CSF flow within the ventricular system, then a portion of the ventricles enlarges while the remainder does not.this condition most commonly is caused by masses obstructing the foramen of Monro or compressing the cerebral aqueduct. 2- Communicating hydrocephalus (nonobstruction) : the entire ventricular system is enlarged; it is usually caused by reduced CSF resorption (ex : meningitis) The main manifestation of hydrocephalus is increased intracranial pressure which leads to headache, nausea, vomiting, decreased level of consciousness, coma and neurological defect If hydrocephalus develops in infancy before closure of the cranial sutures, the head enlarges. Once the sutures fuse, hydrocephalus causes ventricular expansion and increased intracranial pressure, but no change in head circumference. In contrast to these disorders, in which increased CSF volume is the primary process, a compensatory increase in CSF volume (hydrocephalus ex vacuo) may occur secondary to a loss of brain volume from any underlying cause (e.g., infarction, neurodegenerative disease). In such settings, the hydrocephalus merely reflects the primary disorder and is of no clinical significance. Herniation

6 Before discussing herniation lets recap normal brain anatomy, the brain is coverd by meninges, the outer layer of them is the dura matter which has extensions in the brain : Falx cerebri that divides the two cerebral hemispheres and Falx cerebelli which divides the cerebral hemisphere from the cerebellum. when the intracranial pressure increase the brain gyri squeeze through these folds and depending on the location the name of herniation is determined. So Herniation is the displacement of brain tissue from one compartment to another in response to increased intracranial pressure. This herniation often leads to compromise of the blood supply to compressed tissue, producing infarction, additional swelling, and further herniation. Types of herniation : 1-Subfalcine (cingulate) herniation :the most common type of herniation, occurs when unilateral or asymmetric expansion of a cerebral hemisphere displaces the cingulate gyrus ( in frontal lobe and that s why its named cingluate herniation ) under the edge of the falx. This may compress the anterior cerebral artery. the patient of this condition comes with vague symptoms such as decreased level of consciousness or coma. 2-Transtentorial (uncinate) herniation: occurs when the medial aspect of the temporal lobe is compressed against the free margin of the tentorium. As the temporal lobe is displaced, the third cranial nerve is compromised, resulting in pupillary dilation and impaired ocular movements on the side of the lesion ( blown pupil ). The posterior cerebral artery may also be compressed, resulting in ischemic injury to tissue supplied by that vessel, including the primary visual cortex. With further displacement of the temporal lobe, pressure on the midbrain may compress the contralateral cerebral peduncle against the tentorium, resulting in hemiparesis ipsilateral to the side of the herniation. The compression of the peduncle creates a deformation known as Kernohan s notch. Progression of transtentorial herniation is often accompanied by linear or flame-shaped hemorrhages in the midbrain and pons, termed Duret hemorrhages These lesions usually occur in the midline and paramedian regions and are believed to be the result of tearing of penetrating veins and arteries supplying the upper brain stem 3- Tonsillar herniation refers to displacement of the cerebellar tonsils through the foramen magnum. This type of herniation causes brain stem compression and compromises vital respiratory and cardiac centers in the medulla, and is often fatal Figures in the slides : Slide 6 : fig A : acute neuronal injury, notice the shrinkage of cell bodies, red neurons also can be seen Fig B : here you can clearly see the swelling of axons due to injury.

7 Fig C : as we mentioned before, axonal injury leads to reactive process in the cell body as can be seen by the swelling of the cell body Slide 8 : this is immunohistochemical stain to GFAP in astrocytes which help to highlight them, the blue cells can be glial cells or neurons. Slide 9 : here you can see gemistotic astrocyes, notice the nucleus in the periphery and abundant cytoplasm, those cells can be seen in a reactive process or some tumors Slide 17 : in this slide the doctor explained the normal CSF secretion, which is written in the sheet Slide 26 : the doctor named the types of herniation )) إهما إلعلم علمان : علم إلدين وعلم إلدهيا. فالعلم إلذي للدين هو إلفقه وإلعلم إلذي للدهيا هو إلطب (( " إلشافعي"