CNS :( Flashcards
c. One of the most common changes in neurons is associated with
hypoxic/ischemic injury of the brain. This is characterized by loss of ribonucleoproteins and denaturation of cytoskeletal proteins, resulting in cytoplasmic eosinophilia (red neurons), observed in hematoxylin and eosin stained sections.
Neuron morphology
d. Morphology: 5-100 µm in size
• Prominent nucleolus
• Nissl substance: granular basophilic cytoplasmic material (RER)
• Radiating axons and dendrites
b. in response to brain injury, the astrocytes react by producing a
dense network of cytoplasmic processes surrounding the area of injury. This is somewhat analogous to a fibrous scar occurring elsewhere in the body, and is known as reactive gliosis.
Ependymal cells
a. cells that line the ventricles.
b. Vary from ciliated columnar to flattened cuboidal cells
Microglia (phagocytes, macrophages)
a. Microglia derived from
circulating monocytes
microglia:
b. serve as
antigen presenting cells in inflammatory conditions
Microglia: c. act as scavengers during
tissue necrosis (cells with large, foamy cytoplasm called gitter cells) d. In some infections, appear as rod cells
a. Acute “red neurons” see
12-24 h after irreversible hypoxic/ischemic insult. See shrinkage of the cell body, pyknosis of the nucleus, loss of nucleolus, loss Nissl substance, red cytoplasm, break down in bloodbrain barrier with acute injuries.
a. Subacute and chronic “degeneration”. More
slowly progressive injury e.g. AML amyotrophic lateral sclerosis-often see selective cell loss and reactive gliosis.
a. Axonal reaction-see with
regeneration of axon-Nissl substance from center to periphery e.g. anterior horn cells spinal cord when motor axons seriously damaged.
a. Neuronal damage and subcellular changes e.g.
lipofuscin, viral inclusions e.g. Herpes-Cowdry body.
a. Intracytoplasmic inclusions-
Lewy bodies-Parkinson’s, neurofibrillary tangles-Alzheimer Disease.
a. Astrocytes and injury: Often show
astrogliosis (repair and/or scar formation). Increased bright pink cytoplasm, cytoplasmic swelling, formation Rosenthal fibers (thick eosinophilic protein aggregates seen in chronic gliosis)
a. Oligodendrocytes: Function to form
myelin around axons. Injury apoptosis seen in demyelinating or leukodystrophic diseases. Limited changes, may see viral inclusions “leukoencephalopathy”
a. Ependymal cells: Line the ventricles. No
injury specific response. Inflammation note disruption ependymal lining and proliferation of subependymal astrocytes “ependymal granuloma”. Certain pathogens (e.g. CMV) cause extensive ependymal injury with viral inclusions.
a. Microglia: Fixed macrophages in CNS are
CD68 and CR3 positive.
microglia: Can also note
blood borne macrophages with inflammation. Proliferation, elongated nuclei (rod cells), foci microglial nodules, neuronophagia.
- Focally expanding mass lesions-regardless of etiology-can ALL
increase intracranial pressure
- Cerebral Edema
a. Increased fluid content within
brain parenchyma (trauma, hypoxia, tumor, infection)
cerebral edema: b. Common form of
secondary brain damage, occurs in 75% of patients with brain injury
c. Major cause of elevated intracranial pressure.
cerebral edema: d. Clinical Classic indications of raised intracranial pressure are
headache, vomiting and papilledema (swelling of optic disc)
Cerebral edema: e. Presents as
swollen gyri, narrowed sulci, compressed ventricles, brain shifting
Cerebral edema: f. Vasogenic edema-
blood brain barrier disruption and increased vascular permeability-note fluid shift from vascular component to the brain.
Cerebral edema: g. Cytotoxic edema-
increased intracellular fluid secondary to neuronal glial or endothelial cell membrane injury e.g. hypoxic or metabolic damage.
h. Often note elements of both types of edema
b. Hydrocephalus=
accumulation of excessive CSF within ventricular system
a. Choroid plexus produces
CSF. In continuity with ependyma, intraventricular fibrovascular cores lined by epithelial cells.
Hydrocephalus: b. Causes:
- Decreased CSF resorption (CSF flow obstructed by: tumor, hemorrhage or inflammation i.e. meningitis)
- Increased CSF production (tumors of the choroid plexus; rare)
- Increased intracranial pressure and herniation.
a. Can cause
displacement of brain tissue from one intracranial compartment to another
- Increased intracranial pressure and herniation.
a. Most cases associated with a
mass effect either diffuse-generalized (brain edema) or focal (tumors, abscesses, hemorrhage).
- Increased intracranial pressure and herniation.
a. Cranial vault is divided by
rigid dural folds-localized expansion may cause displacement relative to partitions-if severe-note herniation syndrome.
- Increased intracranial pressure and herniation.
a. 3 main types
subfalcine
uncinate
tonsillar herniation
• Subfalcine (cingulated):
Unilateral or asymmetric expansion of the cerebral hemisphere displaces cingulated gyrus under falx cerebri-may compress anterior cerebral artery.
• Uncinate (transtentorial):
Medial aspect temporal lobe compressed-CN III compromised-pupils dilate and impairment ocular movements-may also compress posterior cerebral artery-affecting visual cortex-Duret Hemorrhage-midbrain bleeds.
• Tonsillar herniation:
Displacement cerebellar tonsils through foramen magnum-life threatening as the brain stem becomes compromised as the breathing and cardiac regulatory centers are located in the medulla oblongata.
B. CNS trauma:
. Effects of the trauma depend on the
site affected e.g. frontal lobe of the brain in the parenchyma-may be silent with no obvious effects while trauma at the spinal cord can be severely disabling or fatal if the brainstem is affected. 25% of accidental deaths.
B. CNS trauma:
2. Physical forces responsible for CNS trauma can include:
skull fractures, parenchymal injury, vascular injury (subdural, epidural hematoma) can co-exist.
B. CNS trauma:
3. Magnitude and distribution of the damage dependent on:
object shape, force of impact, whether or not the head is in motion.
B. CNS trauma:
4. May be a
penetrating or a blunt blow. May note open injury or closed.
B. CNS trauma:
5. Skull fractures-skull bone displaced into cranial cavity, greater thickness bone-displaced skull fracture. Pattern of falls affect the site- if the patient is conscious and falls off a ladder
-occipital generally affected, if patient is unconscious-frontal damaged site.
. Parenchymal Injuries-concussion.
a. Concussion: Altered consciousness brought about by sudden change in momentum of head-e.g. moving head hits a rigid surface.
b. Neurologic changes-
note transient neurologic dysfunction, loss of consciousness, respiratory arrest, loss of reflexes-develop amnesia for the event-neurologic recovery complete.
Direct parenchymal injuries:
Contusion and laceration:
Direct parenchymal injury (disruption and hemorrhage of superficial brain) via either kinetic energy transfer e.g. similar to bruising in soft tissue or penetration and tearing of brain parenchyma in a laceration. Increased contusions with areas of brain in contact with irregular inner skull surface e.g. frontal lobes over orbital ridges and temporal lobes.
Direct parenchymal injuries:
b. Coup injury:
Damage occurs at the point of contact.
Direct parenchymal injuries:
c. Contrecoup:
Note damage at site diametrically opposed. If head stable-coup injury, if head is mobile-may see both.
Direct parenchymal injuries:
d. Violent posterior or lateral hyperextension neck-may avulse
pons from medulla or medulla from cervical cord resulting in death.
Traumatic vascular injury: Frequent component of CNS trauma-dependent upon
vascular location. May note hemorrhage at: epidural (arterial-meningeal artery-usually skull fracture (dura peeled off skull), subdural (damage to bridging veins-dura still attached), subarachnoid, intraparenchymal compartments (or combination thereof).
- Epidural hematomadural arteries most frequently the
mid-meningeal artery
• Usually associated with a skull fracture
• Dura separates from blood accumulation. Rupture of a meningeal artery- arterial bleeding
• “Lucid interval”, then progressive loss of consciousness
• Neurosurgical emergency Need PROMPT DRAINAGE as this is a life-threatening condition.
- Subdural hematoma
• Brain can
move but venous sinuses are fixed
• Blood between dura and arachnoid membrane
•
Subdural hematoma: See this in the
elderly (chronic) with brain atrophy (bridging veins are stretched out) and infants (acute – Whiplash injury, Shaken baby syndrome) (bridging veins are thin-walled)
Subdural hematoma: • Usually note slowly progressive
neurologic dysfunction-remove blood and organizing granulation tissue.
Cerebrovascular Disease; 3 categories:
1) thrombosis (formation of blood clot)
2) embolism (blood clot now mobile in blood stream)
3) hemorrhage (rupture of blood vessel)
Working definition of stroke:
acute onset, non-epileptic, neurological deficit that lasts > 24 hours.
Strokes can arise from two processes:
hypoxia (Ischemia, Infarction) and hemorrhage.
Hypoxia, ischemia and infarction-
due to impaired blood supply and decreased oxygenation of CNS tissues.
Hemorrhage-rupture of CNS vessels. Most common disorders:
global ischemia, embolism, hypertensive, intraparenchymal hemorrhage, subarachnoid hemorrhage, vascular malformations and ruptured aneurysm.
d. Focal cerebral ischemia-major source of collateral blood flow is the
circle of Willis which is supplemented by the External Carotid.
Majority vascular occlusions are due to atherosclerotic plaques resulting in thrombosis or embolism and most frequently affecting the
middle cerebral artery (MCA). Can also involve fat or air.