Pathogenesis, Classification, and Epidemiology of Cerebrovascular Disease
Definition and Nosology
Stroke: sudden loss of neurologic function (global or focal) due to vascular disruption (infarction or hemorrhage) in CNS.
Transient Ischemic Attack (TIA): clinically identical to stroke but shorter duration (<24 hrs, most <1 hr) and no MRI evidence of infarction.
Stroke types: infarct (ischemic stroke, sometimes with hemorrhagic transformation), hemorrhage (subarachnoid, intracerebral). “Silent” stroke: no clinical manifestations but found on CT, MRI, or autopsy.
Prior TIA in <20% of stroke patients. Focal premonitory symptoms: more frequent with infarct than hemorrhage. Headache, vomiting, seizures, coma more frequent with hemorrhage than infarct.
Vascular Anatomy
Anterior Circulation (Carotid Artery and Its Branches)
Common carotid origin: innominate artery on left, aortic arch on right.
Internal carotid branches: ophthalmic, superior hypophyseal, posterior communicating, anterior choroidal. Final bifurcation to anterior cerebral artery (ACA), middle cerebral artery (MCA). Posterior cerebral artery directly from internal carotid in 15% of individuals.
Carotid system territory: optic nerves, retina, anterior portion of cerebral hemisphere (frontal, parietal, anterior temporal lobes).
MCA branches and territories: (a) lenticulostriate penetrators (extreme capsule, claustrum, putamen, most of globus pallidus, part of head and entire body of caudate, superior portions of anterior and posterior limbs of internal capsule; (b) two or three branches (upper, lower, and sometimes middle divisions) reaching most cerebral cortex (including insula, operculum, and cortex of frontal, parietal, temporal, occipital lobes).
ACA: frontal pole, medial and orbital surface of frontal lobe. Largest branch: recurrent artery of Heubner.
Posterior Circulation (Vertebrobasilar System)
Vertebral artery: arises from subclavian. Branches: anterior and posterior spinal arteries (spinal cord), posterior inferior cerebellar artery (PICA; inferior surface of cerebellum). Lateral medulla: supplied by PICA branches or direct vertebral branches.
Basilar artery: merger of right and left vertebral arteries. Branches: paramedian and circumferential penetrators (brainstem); anterior inferior cerebellar, superior cerebellar arteries (ventrolateral aspect of cerebellar cortex); internal auditory (labyrinthine) artery (direct branch from basilar or from anterior cerebellar artery; cochlea, labyrinth, part of facial nerve). Final bifurcation: left and right posterior cerebral arteries (PCA).
PCA branches: penetrators (posteromedial, thalamoperforates, thalamogeniculate, tuberothalamic; supply hypothalamus, dorsolateral midbrain, lateral geniculate, thalamus). PCA itself supplies inferior surface of temporal lobe and medial and inferior surfaces of occipital lobe, including lingual and fusiform gyri.
Other Features
Anastomoses: potential alternate blood routes in case of blockage.
Penetrators: usually end arteries, without anastomoses.
Physiology
Normal total cerebral blood flow: 50 mL/min per 100 g of brain tissue. Adult brain weighs 1500 g.
Cerebral autoregulation: cerebral blood flow maintained constant over range of mean arterial pressure between 60 and 140 mm Hg. Constant flow maintained by cerebral arterioles, which dilate/constrict in response to reduction/increase of partial pressure of carbon dioxide (PaCO2). Changes of partial pressure of oxygen (PaO2) have the opposite effect.
Pathogenesis and Classification
Brain Infarction
Sudden interruption of cerebral blood supply: (a) alteration of brain metabolism (after 30 seconds); (b) cessation of neuronal function (1 minute); (c) chain of events leads to infarct (5 minutes; usually irreversible); (d) tissue necrosis and softening (days), then replacement by fluid and gliosis (weeks to months).
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
