L2 Flashcards
There are three main pathogenic mechanisms for Cerebrovascular diseases ?
• Thrombotic occlusion
• Embolic occlusion
• Vascular rupture
brain may be deprived of oxygen by two general mechanisms:
A. Functional hypoxia
B. Ischemia
causes of functional hypoxia are
- Low partial pressure of oxygen at high altitude
- Severe anemia
- Carbon monoxide poisoning
- Cyanide poisoning
Ischemia of brain occur due to:
tissue hypoperfusion, which can be caused by hypotension, vascular obstruction, or both
It’s can be ( transient or permanent)
Global Cerebral Ischemia:
ischemic-hypoxic injury severe systemic hypotension (systolic pressures below 50 mm Hg)
as in cardiac arrest and shock.
most susceptible neurons in global cerebral ischemia are ?
pyramidal cells of the hippocampus
neocortex and Purkinje cells of the cerebellum.
1-swollen with wide gyri and narrowed sulci.
2- The cut surface shows poor demarcation between gray and white matter.
Global Cerebral Ischemia
Microscopic Appearance in global cerebral haemorrhage
• Early changes
(12 to 24 hours after the injury)
acute neuronal cell change (red neurons)
• Subacute changes
(24 hours to 2 weeks)
Necrosis of tissue, Influx of macrophages
Vascular proliferation, Reactive gliosis
• Repair
(after 2 weeks)
Removal of all necrotic tissue.
Gliosis
Morphology in Global Cerebral Ischemia
1-Border zone (“watershed”) infarcts occur in regions of the brain and spinal cord most distal portions of arterial territories
2- seen after hypotensive episodes.
3- In the cerebral hemispheres, the border zone between the anterior and the middle cerebral artery distributions is at greatest risk.
4-Damage produces a wedge-shaped band of necrosis lateral to the interhemispheric fissure.
Focal Cerebral Ischemia
Cerebral arterial occlusion leads first to:
focal ischemia and then to infarction in the distribution of the compromised vessel
Little or no any collateral flow to structures such as :
- thalamus,
- basal ganglia
- deep white matter (which are supplied by deep penetrating vessels)
so they are more susceptible to Focal Cerebral Ischemia
are a frequent source of emboli in brain ?
Cardiac mural thrombi
is most frequently affected by embolic infarction?
In FCI
The territory of the (((middle cerebral artery))))
a direct extension of the internal carotid artery,
• Emboli tend to lodge where vessels (branch )or in areas
of (stenosis) usually caused by :
atherosclerosis.
Emboli of venous origin may cross over to the
arterial circulation through ?
FCI
a patent foramen ovale
and lodge in the brain (paradoxical embolism)
which include thromboemboli from deep leg veins and fat emboli (usually following bone trauma).
Thrombotic occlusions causing cerebral
infarctions usually are superimposed on?
atherosclerotic plaques.
• Common sites of Thrombotic Occlusions are ?
carotid bifurcation
origin of the middle cerebral artery
either end of the basilar artery
1- results from acute vascular occlusions
2- macroscopic appearance of a evolves over time
3-During the first 6 hours, the tissue is unchanged in appearance,
but by 48 hours, the tissue becomes pale, soft, and swollen
4-From days 2 to 10, the injured brain turns gelatinous and friable.
5-From day 10 to week 3, the tissue -liquefies- eventually leaving a fluid-filled cavity.
Non-Hemorrhagic infarct
1-occurs due to reperfusion of ischemic tissue, either through collaterals or after dissolution of emboli.
2- manifest as multiple, sometimes confluent, petechial hemorrhages
Hemorrhagic infarct