Characteristic features of CNS pathology By: Shifaa AlQa qa
Normal brain: - The neocortex (gray matter): six layers: outer plexiform, outer granular, outer pyramidal, inner granular, inner pyramidal, polymorphous - The white matter - Glial cells: oligodendrocytes, astrocytes, ependymal cells and microglia,
Features of Neuronal Injury: acute neuronal injury: - Within 12 hours of an irreversible hypoxic-ischemic insult - Neurons: shrinkage of the cell body pyknosis of the nucleus disappearance of the nucleolus loss of Nissl substance intense eosinophilia of the cytoplasm ( red neurons )
- axons : Axonal swellings (spheroids) cell body enlargement and rounding, peripheral displacement of the nucleus, enlargement of the nucleolus, peripheral dispersion of Nissl substance (central chromatolysis)
- intracellular inclusions: neurodegenerative diseases Pathogenic viruses With age (lipofuscin) - dystrophic neurites (neuronal processes become thickened and tortuous): Neurodegenerative diseases
Astrocytes in Injury and Repair: Gliosis ( scar formation) hypertrophy and hyperplasia The nucleus enlarges and becomes vesicular the nucleolus becomes prominent gemistocytic astrocyte (cytoplasm expands) fibrillary astrocytes (cytoplasm shrinks) Rosenthal fibers
Oligodendrocytes: viral inclusions (PMLE)
Microglial cells: - activated macrophages in areas of demyelination, organizing infarct, hemorrhage, or trauma - rod cells (elongated nuclei)---- infection?? - microglial nodules/neuronophagia
Ependymal cells: Injury with viral inclusions???
Cerebral Edema Accumulation of excess fluid within the brain parenchyma Extracellular ----- Vasogenic edema Intracellular ------ Cytotoxic edema Often occur together particularly after generalized injury
Vasogenic edema: - blood-brain barrier is disrupted/ increased vascular permeability---- trauma, tumors, focal inflammation - Localized - Generalized Cytotoxic edema: - cell membrane injury (neurons, glial cells)/ hypoxicischemic insult or after exposure to some 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 accumulation of excessive CSF within the ventricular system
impaired flow or resorption; Overproduction of CSF
Noncommunicating hydrocephalus/: - localized obstacle to CSF flow - portion of the ventricles enlarges - Eg: masses obstructing the foramen of Monro or compressing the cerebral aqueduct Communicating hydrocephalus: - The entire ventricular system is enlarged - Caused by reduced CSF resorption - Eg: meningitis
The head enlarges----- Infants Increased intracranial pressure
Hydrocephalus ex vacuo????
Herniation When the volume of tissue and fluid inside the skull increases beyond the limit permitted by compression of veins and displacement of CSF, intracranial pressure rises---- trauma, intracranial hemorrhage, brain tumors The cranial vault is subdivided by rigid dural folds (falx and tentorium), and a focal expansion of the brain displaces it in relation to these partitions. If the expansion is sufficiently large, herniation occurs-------- displacing tissue across dural partitions inside the skull or through openings in the skull
Subfalcine (cingulate) herniation: - Unilateral or asymmetric expansion of a cerebral hemisphere displaces the cingulate gyrus (frontal lobe) under the edge of falx. - compression of the anterior cerebral artery
Transtentorial (uncinate) herniation: - medial aspect of the temporal lobe is compressed against the free margin of the tentorium - posterior cerebral artery may also be compressed (primary visual cortex) - the third cranial nerve is compromised (pupillary dilation and impaired ocular movements on the side of the lesion) - Hemiparesis ipsilateral to the side of the herniation (false localizing sign)---- compression of the contralateral cerebral peduncle against the tentorium---kernohan s notch - Duret hemorrhages---- midbrain and pons
Tonsillar herniation: - displacement of the cerebellar tonsils through the foramen magnum - life-threatening, because it causes brain stem compression and compromises vital respiratory and cardiac centers in the medulla