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Vasculature
77
Left middle meningeal artery
Right and Ieft middle cerebral arteries
Right and Ieft posterior
cerebral arteries
Right and Ieft anterior cerebral arteries
Anterior communicating artery
Right and Ieft superior
cerebellar arteries
Right ophthalmic artery
Right posterior
communicating artery
Basilar artery
Cavernous sinus
Mastoid branch of
Ieft occipital artery
Left interior auditory
(labyrinthine) artery
Right deep temporal artery
Posterior meningeal branch
of Ieft ascending
pharyngeal artery
Right maxillary artery
Right middle meningeal artery
Right and Ieft anterior
inferior cerebellar arteries
Right superficial temporal artery
Right and Ieft posterior
inferior cerebellar arteries
Right exterior carotid artery
Posterior meningeal branches
of right and Ieft vertebral arteries
Anterior meningeal branch
of right vertebral artery
Right posterior auricular artery
Right occipital artery
Right interior carotid artery
Right ascending pharyngeal artery
Right carotid sinus
Right facial artery
Right lingual artery
Carotid body
Right superior laryngeal artery
Right superior thyroid artery
Thyroid cartilage
Right common carotid artery
Right vertebral artery
Right inferior thyroid artery
Transverse process of C6
Right interior thoracic artery
Right deep cervical artery
Right thyrocervical trunk
Brachiocephalic trunk
Right costocervical trunk
Right subclavian artery
7.2 ARTERIAL SUPPLY TO THE BRAIN
AND �MENINGES
The internal carotid artery )>>ICA) and the vertebral artery ascend through the neck and enter the skull to supply the brain
with blood. The tortuous bends and sites of branching )>>such
as the bifurcation of the common carotid artery into the internal and external carotids) produce turbulence of blood flow
and are sites where atherosclerosis can occur. The bifurcation
of the common carotid is particularly vulnerable to plaque
formation and occlusion, threatening the major anterior part
of the brain with ischemia, which would result in a stroke. The
ICA passes through the cavernous sinus, a site where carotidcavernous fistulae can occur, resulting in damage to the extraocular and trigeminal cranial nerves, which also pass through
this sinus. Studies of blood flow through these arteries are important diagnostic tools. Magnetic resonance arteriography
and Doppler flow studies have, for most purposes, replaced
the older dye studies for performing cerebral angiography.
CLINICAL POINT
The paired carotid arteries and vertebral arteries supply the brain and
part of the spinal cord with blood. The carotids supply the anterior
circulation, including most of the forebrain except for the occipital
lobe and inferior surface of the temporal lobe. The bifurcation of
the common carotid artery is a common site of plaque formation in
atherosclerosis, leading to gradual occlusion of blood flow to the forebrain on the ipsilateral side. Early warnings can be seen in the form of
transient ischemic attacks, forerunners of a full-blown stroke. The best
treatment is prevention, with exercise, proper diet and weight control,
careful regulation of lipid levels and other contributing factors such as
inflammatory mediators. In cases in which severe and symptomatic
occlusion has occurred as the result of atherosclerotic plaque, carotid
endarterectomy can be performed to remove the plaque and attempt
to open up more robust flow to the anterior circulation. Carefully
performed controlled studies have established criteria that determine
which patients can best benefit from this surgical procedure as opposed to more conservative medical treatment. Current studies are
investigating the use of carotid stents to enhance blood flow to the
brain.
78
Overview of the Nervous System
Vidian nerve
Lateral View
Carotid plexus
Cavernous sinus
Ophthalmic artery
Internal carotid artery
Maxillary nerve
Great superficial petrosal nerve
Nervus intermedius
Facial nerve
Internal carotid artery
Carotid nerve
Superior cervical ganglion
Spheno-palatine
ganglion
7.3 INTERNAL CAROTID AND OPHTHALMIC
�ARTERY COURSE
The ophthalmic artery is the first major branch of the ICA. It
supplies the eyeball, ocular muscles, and adjacent structures.
This artery is commonly involved in the first phases of clinical
recognition of cerebrovascular disease. Because of its position
as the first branch of the ICA, emboli from atherosclerotic
arteries that are found at sites such as the bifurcation of the
common carotid artery travel through the ophthalmic artery,
resulting in a transient ischemic attack with the symptom of
fleeting blindness in the affected eye.
Vasculature
79
Anterior communicating artery
Anterior cerebral artery
Circle of Willis
Recurrent artery (of Heubner)
Internal carotid artery
Medial and lateral lenticulostriate arteries
Middle cerebral artery
Lateral orbitofrontal artery
Ascending frontal (candelabra) branch
Anterior choroidal artery
Posterior communicating artery
Posterior cerebral artery
Superior cerebellar artery
Basilar artery and pontine branches
Internal auditory (labyrinthine) artery
Anterior inferior cerebellar artery
Vertebral artery
Anterior spinal artery
Posterior inferior cerebellar artery
Posterior spinal artery
7.4 ARTERIAL DISTRIBUTION TO THE BRAIN:
BASAL VIEW
The anterior circulation )>>middle and anterior cerebral �arteries;
MCAs, ACAs) and the posterior circulation )>>the vertebrobasilar system and its end branch, the posterior cerebral artery;
PCA) and their major branches are shown. The right temporal
pole is removed to show the course of the MCA through the
lateral fissure. The circle of Willis )>>the paired ACAs, MCAs,
and PCAs and the anterior and two posterior communicating
arteries) surrounds the basal hypothalamic area. The circle of
Willis appears to allow free flow of blood around the anterior
and posterior circulation of both sides, but usually it is not
sufficiently patent to allow bypass of an occluded zone.
CLINICAL POINT
The vertebrobasilar system supplies the posterior circulation of the
brain, including most of the brain stem, part of the diencephalons,
and the occipital and inferior temporal lobes of the forebrain. The
paired PCAs are the end arteries of the vertebrobasilar system. An infarct in the PCAs )>>top of the basilar infarct) results in damage to the
ipsilateral occipital lobe, including both the upper and lower banks of
the calcarine fissure. Functionally, this infarct results in contralateral
blindness, called contralateral homonymous hemianopia. There may
be macular sparing if the MCA has some anastomoses with the posterior cerebral circulation.
80
Overview of the Nervous System
Anterior communicating artery
Recurrent artery (of Heubner)
Anterior cerebral artery
Middle cerebral artery
Posterior communicating artery
Anterior choroidal artery
Optic tract
Cerebral peduncle
Lateral geniculate body
Posterior medial choroidal artery
Posterior lateral choroidal artery
Choroid plexus of lateral ventricle
Medial geniculate body
Pulvinar
Lateral ventricle
7.5 ARTERIAL DISTRIBUTION TO THE BRAIN:
CUTAWAY BASAL VIEW SHOWING THE
CIRCLE OF WILLIS
The circle of Willis and the course of the choroidal arteries
are shown. The arteries supplying the brain are end arteries
and do not have sufficient anastomotic channels with other
arteries to sustain blood flow in the face of disruption. The occlusion of an artery supplying a specific territory of the brain
results in functional damage that affects the performance of
structures deprived of adequate blood flow.
CLINICAL POINT
Obstruction of the MCA near its origin is relatively unusual compared
with obstruction or infarcts in selected branches, but it demonstrates
the full range of blood supply of this critical artery. Obstruction near
the origin usually results from embolization, not from atherosclerotic
or thrombotic lesions. It causes contralateral hemiplegia )>>resolving to
spastic), contralateral central facial palsy )>>lower face), contralateral
hemianesthesia, contralateral homonymous hemianopia, and global
aphasia if the left hemisphere is involved. Additional problems with
anosognosia )>>inability to recognize a physical disability), contralateral
neglect, and spatial disorientation may occur.
Vasculature
81
Frontal View with Hemispheres Retracted, Tilted for a View of the Ventral Brain Stem
Paracentral artery
Corpus callosum
Medial and lateral
lenticulostriate arteries
Frontal branches
Lateral orbitofrontal artery
Pericallosal artery
Callosomarginal artery
Ascending frontal
(candelabra) branch
Frontopolar artery
Anterior and posterior
parietal branches
Anterior cerebral
arteries
Precentral
(prerolandic)
and central
(rolandic)
branches
Medial orbitofrontal artery
Recurrent artery
(of Heubner)
Angular branch
Temporal branches
(posterior, middle,
anterior)
Interior carotid
artery
I
Middle cerebral
artery and branches,
deep in lateral
cerebral (sylvian) fissure
Anterior choroidal
artery
II
III
Anterior communicating artery
IV
Posterior cerebral
artery
V
VII
VIII
Posterior communicating artery
XII
Superior cerebellar artery
Basilar artery
Interior auditory
(labyrinthine) artery
IX
X
Anterior inferior cerebellar artery
Posterior spinal artery
VI
Vertebral artery
Posterior inferior cerebellar artery
XI
7.6 ARTERIAL DISTRIBUTION TO THE BRAIN:
FRONTAL VIEW WITH HEMISPHERES
�RETRACTED
With the hemispheres retracted, the course of the ACAs and their
distribution along the midline are visible. This artery supplies
blood to the medial zones of the sensory and motor cortex, which
are associated with the contralateral lower extremity; an ACA
stroke thus affects the contralateral lower limb. With the lateral
fissure opened up, the MCA is seen to course laterally and to give
branches to the entire convexity of the hemisphere. End-branch
infarcts of the MCA affect the contralateral upper extremity and,
if on the left, also affect language function. More proximal MCA
infarcts affecting the MCA distribution to the internal capsule
can cause full contralateral hemiplegia with drooping of the contralateral lower face; this results from damage to corticospinal
and other corticomotor fibers traveling in the posterior limb of
Anterior spinal artery
the internal capsule and damage to corticobulbar fibers traveling
in the genu of the internal capsule.
CLINICAL POINT
The ACA branches from the internal carotid as it splits from the middle cerebral artery. It supplies a medial strip of the forebrain with
blood. ACA occlusion is usually caused by embolization, although an
anterior communicating artery aneurysm, vasospasm resulting from
a subarachnoid hemorrhage, or subfalcial herniation can occlude this
artery. If the ACA is occluded distal to the recurrent artery of Heubner, it results in contralateral spastic paresis and sensory loss in the
lower extremity. A more proximal lesion involving the recurrent artery of Heubner may involve the upper body and limb as well. In addition, there may be internal sphincter weakness of the urinary bladder,
frontal release signs, and conjugate deviation of the eyes toward the
side of the lesion )>>damage to frontal eye fields with unopposed deviation from the intact side).