Blood Supply of the Brain

1- Internal carotid arteries -They arises from the common carotid arteries

and enter the middle fossa of the cranial cavity through the carotid canal which opens into the side of the foramen lacerum above the closed inferior opening.

- It turns upward to reach the side of the body of sphenoid bone. It then turns forward in the cavernous sinus to reach the medial aspect of the anterior clinoid process and lies lateral to the optic chiasma.

- Its course follows a series of bends ( carotid syphon ).

Branches ( internal carotid system ):

1- Hypophyseal arteries -They arise from the intracavernous section of

the internal carotid to supply the neurohypophysis.

-They also form the pituitary portal system of vessels by which releasing factors are carried from the hypothalamus to adenohypophysis.

2- Ophthalmic artery: - It passes into the orbit through the optic foramen. - It supplies the structures of the orbit, frontal and

ethmoidal sinuses, frontal part of the scalp and dorsum of the nose.

3- Anterior choroidal artery: - It supplies the optic tract, choroid plexus of the lateral

ventricle, hippocampus and some of the deep structures of the hemisphere, including the internal capsule and globus pallidus.

4- Anterior cerebral artery: - It passes medially above the optic nerve and then

passes into the great longitudinal fissure between the frontal lobes where it joins the corresponding vessels of the opposite side by anterior communicating artery.

- It follows the curvature of corpus callosum within the great longitudinal fissure. It ramifying over the medial surface of the frontal and parietal lobes and supplies them. Also, branches extend out of the great longitudinal fissure to supply a narrow lateral band of frontal and parietal cortices.

-The territory supplied by it includes the motor and

sensory cortices for the lower limb.

5- Posterior communicating artery: - It passes backwards to join the posterior cerebral artery.

6- Middle cerebral artery: - It is the largest branch of the 3

cerebral arteries and its cortical territory is the largest. It passes laterally to enter the lateral fissure within which it subdivides.

- Its branches supply the whole of the lateral surface of the frontal, parietal and temporal lobes except those areas which are supplied by the anterior cerebral artery.

- It supplies the primary motor and sensory cortices for the whole body excluding the lower limb. The auditory cortex and the insula in the depth of the lateral fissure.

Vertebral Artery

- It arises from the 1st part of subclavian artery and ascends through the foramina transversaria of the upper 6 cervical vertebrae and enters the cranial cavity through foramen magnum along side the ventrolateral aspect of the medulla.

- Along its course, it gives rise to a number of branches including the anterior and posterior spinal arteries which supply the medulla and spinal cord.

- Its largest branch is the posterior inferior cerebellar artery which supplies the inferior aspect of the cerebellum.

-The 2 vertebral arteries unite at the junction between medulla and pons to form the basilar artery which runs the length of the pons and supplies it by pontine branches. At the junction of pons and midbrain it divides into 2 pairs of vessels, the superior cerebellar arteries and the posterior cerebral arteries.

N.B. The brain stem, cerebellum and occipital lobe are supplied by the vertebrobasilar system.

Branches of Basilar Artery:

1. Pontine arteries

2. Anterior inferior cerebellar artery It supplies the anterior and inferior

portion of the cerebellum.

3. Labyrinthine artery It passes into the internal acoustic

meatus to supply the inner ear.

4. Superior cerebellar artery It supplies the superior aspect of the

cerebellum.

5. Posterior cerebral artery: It curves around the midbrain to supply

the visual cortex of the occipital lobe and the infero medial aspect of the temporal lobe.

The internal carotid and vertebrobasilar systems are joined by 2 thin vessels which are the posterior communicating arteries. They pass rostrocaudally between the ends of the posterior cerebral and the internal carotid arteries.

Circle of Willis

- It is an arterial anastomosis in the interpeduncular fossa at the base of the brain. This fossa is formed anteriorly by optic chiasma. Posteriorly by the upper border of the pons. Anterolaterally by the 2 optic tracts. Posterolaterally by the 2 cerebral peduncles.

- It is formed of:

Anterior cerebral; anterior communicating; internal carotid; posterior communicating and posterior cerebral arteries.

From the arteries of circle of Willis numeroussmall vessels penetrate the surface of the brain. These are perforating arteries ( central or ganglionic ).

1- Anterior perforating arteries:

They arise from the anterior cerebral artery. Anterior communicating artery

and the region of origin of the middle

cerebral artery. They enter the brain in the region between the optic chiasma and termination of the olfactory tract ( anterior perforated substance ). They supply basal ganglia, optic chiasma, internal capsule and hypothalamus.

2- Posterior perforating arteries:

They arise from the posterior cerebral and posterior communicating arteries. They enter the brain ( posterior perforating substance ) to supply the ventral portion of the midbrain and parts of the subthalamus and hypothalamus.

Venous Drainage of the Brain

1- Superficial veins: They lie within the subarachnoid space.

a. Superior cerebral veins They drain the lateral surface of the cerebral

hemispheres and empty into the superior sagittal sinus.

b. The superficial middle cerebral vein

It runs along the line of the lateral fissure and empties into the cavernous sinus.

c. Superior ( great ) anastomotic vein It drains into the superior sagittal sinus.

d. Inferior anastomotic vein It drains into the transverse sinus.

N.B. The circular sinus is a venous circle around the hypophysis.

B

C

D

A

2- Deep cerebral veins: -They drain the internal structures of

the forebrain -They are the thalamostriate vein and the choroidal vein. They drain the basal ganglia, thalamus, internal capsule, choroid plexus and hippocampus.

-These vessels merge to form the 2 internal cerebral veins. -These 2 internal cerebral veins unite

in the midline to form the great cerebral vein which lies beneath the splenium of the corpus callosum

- Thus the great cerebral vein drains the deep structures of the forebrain and the inferior sagittal sinus.

- It continuous with the straight sinus

which lies in the midline of the tentorium cerebelli.

3- Dural venous sinuses

- The dural venous sinuses are connected to extracranial veins via emissary veins.

- Cerebral damage caused by venous infarction manifests as epileptic attacks and focal paralysis of the limbs.

Disorders of Blood Supply of the Brain

- The sudden occlusion of the cerebral artery leads to death of brain tissue (infarction ). Rupture of a blood vessel causes cerebral haemorrhage.

- Strokes related to the carotid artery and its cerebral branches are associated with focal epilepsy ; a contralateral sensory & motor deficit and a psychological deficit ( aphasia ).

- Strokes involving the vertebrobasillar circulation lead to a focal brain stem syndrome. Recovery of function can occur but take up to 2 years and can be incomplete.

- An aneurysm is an abnormal, balloon-like, swelling of an artery. Rupture of this artery may cause subarachnoid haemorrhage or intracerebral haemorrhage. A sudden severe headache and neck stiffness are followed by coma and neurological deficits.

- An angioma or arteriovenous malformation is a congenital collection of swollen, blood vessels that can rupture causing cerebral haemorrhage or steal blood from adjacent brain regions leading to epilepsy and a focal cerebral syndrome.