Central Nervous System(CNS) -Blood Supply

Arterial Supply
        - Spinal Arteries
                       Anterior (1) & Posterior (2) Spinal Artery
                       From Vertebral artery
          - Radicular Arteries ----- Segmental arteries
                       From Vertebral, Ascending Cervical, Intercostal and Lumbar Artery
     Venous Drainage
           - Longitudinal & Radicular Veins
                  to Intervertebral veins ---- to Internal Vertebral Venous Plexus
                  to external vertebral venous plexus ---- to segmental veins

Anterior spinal artery 
                           
Segmental arteries

Adamkiwicz artery

Blood Supply to the Spinal Cord and Brain Stem

The brain is one of the most metabolically active organs  in the body, receiving 17% of the total cardiac output and about 20% of the oxygen available  in the body.
The brain receives it’s blood from  two pairs of arteries, the carotid and vertebral. About 80% of the brain’s  blood supply comes from the carotid, and the remaining 20% from the vertebral.


The Vertebrobasilar System 

The vertebral arteries originate from the subclavian artery,and ascend through the transverse foramen of the upper six cervical vertebra. At the upper margin of the Axis (C2) it moves outward and upward to the transverse foramen of the Atlas (C1). It then moves backwards along the articular process of atlas into a deep groove, passes beneath the atlanto-occipital ligament and enters the foramen magnum. The arteries then run forward and unite at the caudal border of the pons to form the basilar artery.

The  Spinal Cord receives its blood supply from two major sources;
1. Branches of the vertebral arteries, the major source of blood supply, via the anterior spinal and posterior spinal arteries.
2. Multiple radicular arteries, derives sporadically from segmental arteries  The Medulla, Pons and Midbrain areas receive their major sources of blood  supply from several important branches of the Basilar artery

Branches of the Vertebral Artery
 
1. Posterior Inferior Cerebellar Artery (PICA),  the largest branch of the vertebral, arises at the caudal end of the medulla on each side.
Runs a course winding between the
medulla and cerebellum
Distribution:
   a. posterior part of cerebellar hemisphere
   b. inferior vermis
   c. central nuclei of cerebellum
   d. choroid plexus of 4th ventricle
   e. medullary branches to dorsolateral medulla

2. Anterior Spinal Artery, formed from a Y-shaped union of a branch from each vertebral artery.  Runs down the ventral median fissure the length of the cord.
Distribution:
 a. supplies the ventral 2/3 of the spinal cord.
3. Posterior Spinal Arteries (2), originate from each vertebral artery or Posterior Inferior Cerebellar on each side of the Medulla.  Descends along the dorsolateral sulcus.
Distribution:   supplies the dorsal 1/3 of the cord of each side.
4. Posterior meningeal, one or two branches that originate  from the vertebral opposite the foramen magnum. This branch moves into the dura matter of the cranium
5. Bulbar branches, composed of several smaller arteries which originate from the vertebral and it’s branches. These branches head for the pons, medulla and cerebellum

Branches of the Vertebral Artery

Spinal Cord Blood Supply

                                                    Ventral                                Dorsal

Anterior Spinal Artery, provides sulcal branches which penetrate the ventral median fissure and supply the ventral 2/3 of the spinal cord.
Posterior Spinal Arteries, each descends along the dorsolateral surface of the spinal cord and supplies the dorsal 1/3.
Radicular arteries, originating from segmental arteries at  various levels, which divide into anterior and posterior radicular arteries as they move along ventral and dorsal roots to reach the spinal cord. Here they reinforce spinal arteries and anastomose with their branches.
From these varied sources of blood supply, a series of circumferential anastomotic channels are formed around the spinal cord, called the arterial vasocorona, from which short branches penetrate and supply the lateral parts of the cord

The radicular arteries provide the main blood supply to the cord at the thorasic, lumbar and sacral segments. There are a greater number on the posterior (10-23) than anterior (6-10 only) side of the cord.
One radicular artery, noticeably larger than the others, is called the artery of Adamkiewicz, or the artery of the lumbar enlargement. Usually located with the lower thorasic or upper lumbar spinal segment on the left side of the spinal cord
The spinal cord lacks adequate collateral supply in some areas, making  these regions prone to ischemia after vascular occlusions. The upper
Thorasic (T1-T4) and first lumbar segments are the most vulnerable regions of the cord.
There are several arteries that reinforce the spinal cord blood supply and are termed segmental arteries
1. The Vertebral arteries, spinal branches which are present in the upper cervical (~C3-C5) levels
2. Ascending Cervical arteries, present in the lower cervical areas
3. Posterior Intercostal, present in the  mid-thorasic region
4. First Lumbar arteries, present in the  mid-lumbar regions
The spinal veins arranged in an irregular pattern.
The anterior spinal veins run along the midline and the ventral roots. The posterior spinal veins run along the midline and the dorsal roots. These are drained by the anterior and posterior radicular veins. These in turn empty into an epidural venous plexus which connects into an external vertebral venous plexus, the vertebral, intercostal and lumbar veins.
Occlusion of the anterior spinal artery may lead to the anterior  cord syndrome, characterized by;
1. Loss of ipsilateral motor function, due to damage to ventral gray matter and the ventral corticospinal tract.
2. Loss of contralateral pain and temperature sensation, due to damage to the spinothalamic pathway

Occlusion of the posterior spinal arteries may lead to the rare posterior cord syndrome, characterized by;
1. Ipsilateral motor deficits, due to damage to corticospinal tract
2. Ipsilateral loss of tactile discrimination, position sense, vibratory sense, due to damage to the dorsal columns

Blood Supply to the brain stem

The brain stem (medulla, pons midbrain) receives the bulk of its blood supply from the  vertebrobasilar system. Except for the labyrynthine branch, all other branches supply the brain stem and cerebellum
The posterior cerebral has only a small contribution, its main target being the posterior cerebral hemispheres

Branches of the Basilar Artery

1. Anterior Inferior Cerebellar Arteries  (AICA), originates near the lower border of the Pons just past the union of the vertebral arteries.
Distribution:
 a. supplies anterior inferior surface and underlying white matter of cerebellum
 b. contributes to supply of central cerebellar nuclei
 c. also contributes to upper medulla and lower pontine areas

2. Pontine arteries, numerous smaller branches that can be subdivided into Paramedian and Circumferential pontine arteries. The Circumferential can be  further subdivided into Long and Short  pontine arteries.
Distribution:
 a. paramedian pontine - basal pons
 b. circumferential pontine - lateral pons and middle cerebellar peduncle, floor of fourth ventricle and pontine tegmentum

3. Superior Cerebellar arteries, originates near the end of the Basilar artery,  close to the Pons-Midbrain junction. Runs along dorsal surface of cerebellum
Distribution:
 a. cerebellar cortex, white matter and central nuclei
 b. Additional contribution to rostral pontine tegmentum, superior cerebellar peduncle and inferior colliculus

4. Posterior cerebral arteries, the terminal branches of the Basilar artery. They appear as a bifurcation of the Basilar,  just past the Superior Cerebellar arteries and the oculomotor nerve.  Curves around the midbrain and reaches the medial surface of the cerebral hemisphere beneath the splenium of the corpus callosum
Distribution:
a. mainly neocortex and diencephalon
b. some contribution to interpeduncular plexus

5. Labyrynthine arteries, may branch from the basilar, but variable in its  origin. Supplies the region of the inner ear

Blood Supply to the Medulla 
The Medulla is supplied by the;
1. Anterior spinal artery, sends blood to the paramedian region of the caudal medulla.
2. Posterior spinal artery, supplies rostral areas, including the gracile and cuneate fasiculi and nuclei, along with dorsal areas of the inferior cerebellar peduncle.
3. Vertebral artery, bulbar branches supply areas of both the caudal and rostral medulla.
4. Posterior inferior cerebellar artery, supplies lateral medullary areas.
Occlusion of branches of the anterior spinal artery will produce
a inferior alternating hemiplegia (aka medial medullary syndrome), characterized by;
1. A contralateral hemiplegia of the limbs, due to damage to the pyramids or the corticospinal fibers
2. A contralateral loss of position sense, vibratory sense and discriminative touch, due to damage to the medial leminiscus
3. An ipsilateral deviation and paralysis of the tongue, due to damage to the hypoglossal nucleus or nerve
Occasionally, these symptoms will develop after occlusion of the vertebral artery before gives off its branches to the anterior spinal  artery

The posterior spinal arteries supply the  gracile and cuneate fasiculi and nuclei,  spinal trigeminal tract and nucleus,  portions of the inferior cerebellar peduncle

The vertebral arteries supply  the pyramids at the level of the Pons,  the inferior olive complex,  the medullary reticular formation,  solitary motor nucleus  dorsal motor nucleus of the Vagus  (cranial nerve X),  hypoglossal nucleus  (cranial nerve XII).  spinal trigeminal tract, spinothalamic tract  spinocerebellar tract
The posterior inferior cerebellar arteries (PICA) supply  spinothalamic tract,  spinal trigeminal nucleus and tract, fibers from the nucleus ambiguous,  dorsal motor nucleus of the Vagus (cranial nerve X)  inferior cerebellar peduncle
Occlusion of the posterior inferior cerebellar artery (or contributing vertebral) will produce a lateral medullary syndrome or Wallenberg’s syndrome, characterized by;
1. A contralateral loss of pain and temperature sense, due to damage to the anterolateral system (spinothalamic tract)
2. An ipsilateral loss of pain and temperature sense on the face, due to damage to the spinal trigeminal nucleus and tract
3. Vertigo, nausea and vomiting, due to damage to the vestibular nuclei
4. Hornor’s syndrome, (miosis [contraction of the pupil],  ptosis [sinking of the eyelid], decreased sweating), due to  damage to the descending hypothalamolspinal tract

Blood Supply to the Pons
The Pons is supplied by the;
1. The Basilar artery, contributions of this main artery can be further
subdivided;
                a. paramedian branches, to medial pontine region
                b. short circumferential branches, supply anterolateral pons
                c. long circumferential branches, run laterally over the anterior  surface of the Pons to anastomose with branches of the anterior inferior cerebellar artery (AICA).
2. Some reinforcing contributions by the anterior inferior cerebellar and superior cerebellar arteries
Additional branches of the Basilar artery can be found branching off within the  region of the Pons;
1. Anterior Inferior Cerebellar Arteries (AICA), originates near the lower border of the Pons just past the union of the vertebral arteries.
Distribution:
 a. supplies anterior inferior surface and underlying white matter of cerebellum
 b. contributes to supply of central cerebellar nuclei
 c. also contributes to upper medulla and lower pontine areas
2. Superior Cerebellar arteries, originates near the end of the Basilar artery, close to the  Pons-Midbrain junction. Runs along dorsal surface of cerebellum
Distribution:
 a. cerebellar cortex, white matter and central nuclei
 b. Additional contribution to rostral pontine tegmentum, superior cerebellar peduncle and inferior colliculus
2. Labyrynthine arteries, may branch from the basilar, but variable in its origin. Supplies the region of the inner ear.
Divides into two branches;
  a. anterior vestibular
  b. common cochlear
The labyrinthine has a variable origin, according to a study done by Wende et. al., 1975, (sample size of 238) the artery originated from;
1. Basilar (16%)
2. AICA (45%)
3. Superior cerebellar (25%)
4. PICA (5%)
5. Remaining 9% were of duplicate origin


The paramedian branches of the Basilar artery supplies the paramedian regions of the Pons, this includes corticospinal fibers (basis pedunculi),  the medial leminiscus, abducens nerve and nucleus (cranial nerve VI) ,  pontine reticular area, and periaquaductal gray areas
The paramedian branches of the Basilar artery supply  corticospinal fibers,  the medial leminiscus, abducens nerve and nucleus (cranial nerve VI) ,  pontine reticular area, periaquaductal gray areas
Obstruction of the paramedian pontine arteries will produce a  middle alternating hemiplegia  (also termed medial pontine syndrome)  which is characterized by;
1. Hemiplegia of the contralateral arm and leg, due to damage to the corticospinal tracts
2. Contralateral loss of tactile discrimination, vibratory and position sense, due to damage to the medial leminiscus
3. Ipsilateral lateral rectus muscle paralysis, due to damage to the  abducens nerve or tract (can cause diplopia “double vision”)

The short circumferential branches supply, pontine nuclei,  pontocerebellar fibers,  medial leminiscus  the anterolateral system (spinothalamic fibers)
The long circumferential branches supply, along with the anterior inferior cerebellar (caudally),  and superior cerebellar artery (rostrally). middle and superior cerebellar peduncles,  vestibular and cochlear nerves and nuclei,  facial motor nucleus (cranial nerve VII) trigeminal nucleus (cranial nerve V)  spinal trigeminal nucleus and tract (cranial nerve V),  hypothalamospinal fibers,  the anterolateral system (spinothalamic) pontine reticular nuclei.
Occlusions of long branches circumferential branches of the basilar artery produce a lateral pontine syndrome, characterized by;
1. Ataxia, due to damage to the cerebral peduncles (middle and superior)
2. Vertigo, nausea, nystagmus, deafness, tinitus, vomiting, due to damage to vestibular and cochlear nuclei and nerves
3. Ipsilateral pain and temperature deficits from face, due to damage to the spinal trigeminal nucleus and tract
4. Contralateral loss of pain and temperature sense from the body, due to damage to the anterolateral system (spinothalamic)
5. Ipsilateral paralysis of facial muscles and masticatory muscles, due to damage to the facial and trigeminal motor nuclei (cranial nerves VII and V)


Blood Supply to the Midbrain
The major blood supply to the midbrain is derived from branches of the basilar artery;
1. Posterior cerebral artery, forms a plexus with the posterior communicating arteries in the interpeduncular fossa, branches from this plexus supply a wide area if the midbrain
2. Superior cerebellar artery, supplies dorsal areas around the central gray and inferior colliculus with support from branches of the posterior cerebral artery.
3. Quadrigeminal, (some posterior choroidal) a branch of the posterior cerebral, provides support for the tectum (superior and inferior colliculi)
4. Posterior communicating artery, derived from the internal carotid, joins the posterior cerebral to form portions of the circle of Willis  (arterial circle). Contributes to the interpeduncular plexus
5. Branches of these arteries are best understood when grouped into paramedian, short circumferential and long circumferential

The paramedian arteries, derived from the posterior communicating and posterior cerebral, form a plexus in the interpeduncular fossa, enter the  through the posterior perforated substance, this system supplies
  • raphe region,
  • oculomotor complex,
  • medial longitudinal fasiculus,
  • red nucleus
  • substantia nigra
  • crus cerebri
Occlusion of midbrain paramedian branches produces a medial midbrain or superior alternating hemiplegia (or Weber’s syndrome) characterized by;
1. Contralateral hemiplegia of the limbs, and contralateral face and tongue due to damage to the descending motor tracts
(crus cerebri).
2. Ipsilateral deficits in eye motor activity, caused by damage to the oculomotor nerve

The short circumferential arteries originate from the interpeduncular plexus and portions of the posterior cerebral and superior cerebellar arteries, this system supplies
  • crus cerebri,
  • substantia nigra
  • midbrain tegmentum
The long circumferential branches originate mainly from the posterior  cerebral artery, one important branch, the quadrigeminal (collicular artery) supplies the superior and inferior colliculi.

The posterior choroidal arteries originate near the basilar  bifurcation into the posterior  cerebral arteries. In addition to providing reinforement to the midbrain short and long circumferential arteries they move forward to supply portions of the diencephalon and the choroid plexus of the third  and lateral ventricles

Other Clinical Points
Substantial infarcts within the Pons are generally rapidly fatal, due to failure of central control of respiration Infarcts within the ventral portion of the Pons can produce paralysis of all movements except the eyes. Patient is conscious but can communicate only with eyes. LOCKED-IN-SYNDROME



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