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Systems Pathology: week 2
Pathologies of the CNS
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Monday
brain herniation - Movement and injury to the brain as a result of an increase in ICP.
Subfalcine Herniation - Displacement of cingulate gyrus under falx cerebri. Caused by anterior cerebral artery compression.
Clinical manifestation of this is usually hemiparesis - a weakness or paralysis of one side of the body.
Transtentorial Herniation - Displacement of medial portion of temporal lobe (uncus) through tentorium cerebelli.
Posterior cerebral artery compression is a complication.
Clinical manifestations include:
- hemiparesis
- mydriasis - dilation of the pupil (miosis means dilated pupil)
- blindness
- Duret’s hemorrhage - small, linear hemorrhages in the midline of the brainstem and upper pons caused by traumatic downward displacement of the brainstem.
Tonsillar Herniation - Displacement of the cerebellar tonsils through the foramen magnum
Basilar artery compression and respiratory arrest is are complications.
Coma can come about from only two ways. focal damage to the brainstem or diffuse damage bilateral cerebral damage.
Hydrocephalus - excessive CSF in the brain.
There are three ways this can be caused.
- 1. Over production of CSF. This can come about from tumors called papillomas. Papillomas are tumors of the epithelium; in this case the choroid plexus, which is the CSF production tissue of the brain.
- 2. Poor drainage. Usually from inflamation of the arachnoid matter. Example - tubercular meningitis - meningitis (inflamation of the meninges) from tuberculitis.
- 3. Obstruction. the four areas of obstruction are:
- foramina of Monroe
- aqueduct of sylvius (remember, blockage is most common here)
- foramina of megendie and Lushka
- subarachnoid space - found in middle aged and older people. the arachnoid villi become inadequete in draining the CSF. The pressure in the brain increases and the ventricles increase, but the pressure is not outside normal. The pressure is at the upper limit of normal however.
Some random fun facts:
- first described by Hippocrates
- This occurs in 3/1000 live births
- 88% - 90% are NTD's (Neural Tube Defects)
- 100,000 shunts are implanted a year.
- 20 to 40% shunt failure in the first 2 years.
- the obstruction is often due to infection
Craniosynostosis - premature suture fusion of some sutures and not others. This leads to vast cranial distortions and sometimes brain damage. This can sometimes be fixed through reconstructive surgery depending on the type of craniosynostosis.
Approximate dates for fontanelle closure:
- 3 months - posterior fontanelle closure
- 6 months - interlocking cranial sutures with fibrous union
- 20 to 24 months - anterior fontanelle closure
- 8 years - complete cranial bone ossification
- 12 to 30 years - cranial suture fusion
Types of hydrocephalus
- noncommunicating - Obstruction of flow within system. Brain damage is direct.
- communicating - Obstruction of flow outside the ventricular system, subarachnoid space. Direct brain damage.
- ex vacuo - Expansion of the ventricular system as a result of brain atrophy (think aging). Ex, Alzheimer's, chronic alcoholism. The damage to the brain here is indirect. Pik's disease is related to Alzheimer's. Note: Alzheimer's and piks disease will be covered in more detail later.
- normal pessure - First recognized in 1965. Was confused with Alzheimer's except that the patient got worse a lot quicker. It is characterized as cycles of high pressure followed by ventricle enlargement with normalized pressure. It is thought to come about because of diminished CSF absorption by arachnoid villi.
Tuesday and Wednesday
Pseudotumor cerebri - benign tumor hypertension. There is an increase in ICP without evidence of cause. It is believed to be caused by venous sinus blockage. It is often seen in obese females aged 20 - 50 for unknown reasons.
Stroke
1. Global Ischemia - Global Ischemia - Reduction of blood flow or O2 to entire CNS. Things that would cause this are cardiac arrest or carbon monoxide poisoning.
2. Infarcts - Localized vascular obstruction. Thrombus in situ.
Cerebral Blood Flow (CBF)
- 50 - 60 ml/100g/min - normal
- 20 - 30ml/100g/min cessation of electrical activity
- 10ml/100g/min - neurological death
Some facts about strokes
- third leading cause of death in the US (heart attack and cancer are #1)
- 500,000 - 600,000 per year
- 600,000 are fatal
- 85%ischemic
<15%>hemorrhagic
- 10% preceded by TIA about 50,000
of the survivors
- 10%are disabled - with permanent institutional care
- 40% require special care
- 40% persistent neurological deficits
- 10% Normal
- 300,000,000 are present in the US that have survived a stroke. long term survivors >6 months
- 48% hemiparesis - paralysis affecting one side of the body.
- 22% can't walk
- 33% clinically depressed
- 18% Aphasic
TIA - a neurological deficit that lasts less than 24 hours folloowed by complete recovery.
completed stroke - persistent neurological deficit
two major sites for occlusion are the middle cerebral artery and the basilar artery.
The course of a stroke
- 1 to 3 - minutes - occlusion
- 8 to 12 hours = gross brain normal
- 36 to 48 hours - gross edema and liquefaction
- 1 month - gross cavitation
- 6 months - complete cavitation
There are two types of infarction. Pale Infarction - infarction occuring in dense tissue that does not lead to hemorrhage. Hemorrhagic infarction that occurs in less dense tissue like the lung. The brain is motly inbetween these two densities.
Cyst - liquid filled lesion surrounded by scar tissue or astrocytes the brain's scar forming tissue.
cavitation - happens when you have a stroke on the surface of the brain. This tissue is then liquefied leading to a cavity on the brain.
parenchyma - the functional elements of an organ.
Intraparenchymal hemorrhage - major risk factor in hypertension. The major site is the basal ganglia with charcot bouchard aneurysms (dilation of the small arteries and arterioles resulting from long standing hypertension).
clinical notes:
- Peak age is 60
- there are acute focal deficits
- increased intracranial pressure
subarachnoid hemorrhage
- is seen in 1% of the population with Berry/Saccular aneurysms. The major site is the circle of Willis.
- average age is 20 - 50
- sudden severe headache
- vomiting
- loss of consciousness
- nuchal rigidity
complications include infarction, hydrocephalus, and herniation.
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