N E U ROLOGY ` N E U ROLOGYANATOMY AN D P HYS IOLOGY SECTION III 459

Cerebral arteriescortical distribution

Anterior cerebral artery (supplies anteromedial surface)Middle cerebral artery (supplies lateral surface)Posterior cerebral artery (supplies posterior and inferior surfaces)

Watershed zones Between anterior cerebral/middle cerebral, posterior cerebral/middle cerebral arteries. Damage in

severe hypotension p upper leg/upper arm weakness, defects in higher-order visual processing.

Regulation of cerebral

perfusion

Brain perfusion relies on tight autoregulation.

Cerebral perfusion is primarily driven by

PCO2 (PO2 also modulates perfusion in severe

hypoxia).

Therapeutic hyperventilation (r PCO2) helps r intracranial pressure in cases of acute cerebral edema (stroke, trauma) via r cerebral perfusion by vasoconstriction.

Cerebral blood flow

Hypoxemia increases cerebral perfusion pressureonly when PO2 < 50 mmHg

Cerebral perfusion pressure PCO2 untilPCO2 > 90 mmHg

Arterial gaspressure (mmHg)50 100 150

Arterial gaspressure (mmHg)40 80 120

Normal

Cerebral blood flow

Normal

normal PO2

normal PCO2

O2

CO2

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N E U ROLOGY ` N E U ROLOGYANATOMY AN D P HYS IOLOGYSECTION III460

Effects of strokes

ARTERY AREA OF LESION SYMPTOMS NOTES

Anterior circulation

MCA Motor cortexupper limb and face.

Sensory cortexupper limb and face.

Temporal lobe (Wernicke area); frontal lobe (Broca area).

Contralateral paralysisupper limb and face.

Contralateral loss of sensationupper and lower limbs, and face.

Aphasia if in dominant (usually left) hemisphere. Hemineglect if lesion affects nondominant (usually right) side.

ACA Motor cortexlower limb.

Sensory cortexlower limb.

Contralateral paralysislower limb.

Contralateral loss of sensationlower limb.

Lenticulo-

striate

artery

Striatum, internal capsule. Contralateral hemiparesis/hemiplegia.

Common location of lacunar infarcts, 2 to unmanaged hypertension.

Posterior circulation

ASA Lateral corticospinal tract.

Medial lemniscus. Caudal medullahypoglossal nerve.

Contralateral hemiparesisupper and lower limbs.

r contralateral proprioception. Ipsilateral hypoglossal dysfunction

(tongue deviates ipsilaterally).

Stroke commonly bilateral.Medial medullary syndrome

caused by infarct of paramedian branches of ASA and vertebral arteries.

PICA Lateral medullavestibular nuclei, lateral spinothalamic tract, spinal trigeminal nucleus, nucleus ambiguus, sympathetic fibers, inferior cerebellar peduncle.

Vomiting, vertigo, nystagmus; r pain and temperature sensation from ipsilateral face and contralateral body; dysphagia, hoarseness, r gag reflex; ipsilateral Horner syndrome; ataxia, dysmetria.

Lateral medullary (Wallenberg)

syndrome. Nucleus ambiguus effects are

specific to PICA lesions. Dont pick a (PICA) horse

(hoarseness) that cant eat (dysphagia).

AICA Lateral ponscranial nerve nuclei; vestibular nuclei, facial nucleus, spinal trigeminal nucleus, cochlear nuclei, sympathetic fibers.

Middle and inferior cerebellar peduncles.

Vomiting, vertigo, nystagmus. Paralysis of face, r lacrimation, salivation, r taste from anterior 23 of tongue, r corneal reflex. Facer pain and temperature sensation. Ipsilateral r hearing. Ipsilateral Horner syndrome.

Ataxia, dysmetria.

Lateral pontine syndrome. Facial nucleus effects are specific to AICA lesions.

Facial droop means AICAs pooped.

PCA Occipital cortex, visual cortex. Contralateral hemianopia with macular sparing.

Basilar artery Pons, medulla, lower midbrain,

corticospinal and corticobulbar

tracts, ocular cranial nerve nuclei,

paramedian pontine reticular

formation.

Preserved consciousness and

blinking, quadriplegia, loss of

voluntary facial, mouth, and

tongue movements.

Locked-in syndrome.

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N E U ROLOGY ` N E U ROLOGYANATOMY AN D P HYS IOLOGY SECTION III 461

Effects of strokes (continued)

ARTERY AREA OF LESION SYMPTOMS NOTES

Communicating arteries

ACom Most common lesion is aneurysm. Can lead to stroke. Saccular (berry) aneurysm can impinge cranial nerves.

Visual field defects. Lesions are typically aneurysms, not strokes.

PCom Common site of saccular aneurysm. CN III palsyeye is down and out with ptosis and pupil dilation.

Lesions are typically aneurysms, not strokes.

Aneurysms In general, an abnormal dilation of artery due to weakening of vessel wall.

Berry aneurysm Occurs at the bifurcations in the circle of

Willis A . Most common site is junction

of the anterior communicating artery and

anterior cerebral artery. Rupture (most

common complication) leads to subarachnoid

hemorrhage (worst headache of life) or

hemorrhagic stroke. Can also cause bitemporal

hemianopia via compression of optic chiasm.

Associated with ADPKD, Ehlers-Danlos

syndrome, and Marfan syndrome. Other risk

factors: advanced age, hypertension, smoking,

race (q risk in blacks). A Berry aneurysm. Coronal (left) and sagittal (right) contrast CT shows berry aneurysm (arrows). Charcot-Bouchard

microaneurysm

Associated with chronic hypertension; affects

small vessels (e.g., in basal ganglia, thalamus).

Central post-stroke

pain syndrome

Neuropathic pain due to thalamic lesions. Initial sensation of numbness and tingling followed in

weeks to months by allodynia (ordinarily painless stimuli cause pain) and dysaesthesia. Occurs in

10% of stroke patients.

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