Central Nervous System(CNS) -Blood Supply

Arterial Supply

        - Spinal Arteries

                       Anterior (1) & Posterior (2) SpinalArtery

                       From Vertebral artery

          - RadicularArteries ----- Segmental arteries

                       From Vertebral, Ascending Cervical, Intercostaland Lumbar Artery

     Venous Drainage

           - Longitudinal & Radicular Veins

                  to Intervertebralveins ---- to Internal Vertebral Venous Plexus

                  to external vertebral venous plexus ---- to segmental veins

Anterior spinalartery 

                           

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 thetotal 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 supplycomes from the carotid, and the remaining 20% from the vertebral.

The Vertebrobasilar System 

The vertebral arteries originate from the subclavian artery,and ascendthrough the transverse foramen of the upper six cervical vertebra. At the uppermargin of the Axis (C2) it moves outward and upward to the transverse foramenof the Atlas (C1). It then moves backwards along the articular process of atlasinto a deep groove, passes beneath the atlanto-occipital ligament and entersthe foramen magnum. The arteries then run forward and unite at the caudalborder of the pons to form the basilar artery.

The  Spinal Cord receives itsblood supply from two major sources;

1. Branches of the vertebral arteries, the major source of bloodsupply, via the anterior spinal and posterior spinalarteries.

2. Multiple radicular arteries, derives sporadically from segmental arteries  The Medulla, Pons and Midbrain areas receivetheir major sources of blood  supply from several important branches of the Basilarartery

Branches of the Vertebral Artery

 

1. Posterior Inferior Cerebellar Artery (PICA),  the largest branch of the vertebral, arisesat the caudal end of the medulla on each side.

Runs a course winding between the

medulla and cerebellum

Distribution:

   a. posterior part ofcerebellar hemisphere

   b. inferior vermis

   c. central nuclei ofcerebellum

   d. choroid plexus of 4thventricle

   e. medullary branches to dorsolateral medulla

2. Anterior Spinal Artery, formed from a Y-shaped union of a branch fromeach vertebral artery.  Runs down the ventral median fissure the lengthof the cord.

Distribution:

 a. supplies the ventral 2/3 ofthe spinal cord.

3. Posterior Spinal Arteries (2), originate from each vertebral artery orPosterior Inferior Cerebellar on eachside 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 thevertebral opposite the foramen magnum. This branch moves into the dura matter of the cranium

5. Bulbar branches, composed of several smaller arteries which originatefrom 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 theventral median fissure and supply the ventral 2/3 of the spinal cord.

Posterior Spinal Arteries, each descends along the dorsolateral surfaceof the spinal cord and supplies the dorsal 1/3.

Radicular arteries, originating from segmental arteries at  variouslevels, which divide into anterior and posterior radicular arteries as theymove along ventral and dorsal roots to reach the spinal cord. Here theyreinforce spinal arteries and anastomose with their branches.

From these varied sources of blood supply, a series of circumferentialanastomotic channels are formed around the spinal cord,called the arterial vasocorona, from whichshort branches penetrate and supply the lateral parts of the cord

The radicular arteries provide the main blood supply to the cord at thethorasic, lumbar and sacral segments. There are a greater number on theposterior (10-23) than anterior (6-10 only) side of the cord.

One radicular artery, noticeably larger than the others, is called the arteryof Adamkiewicz, or the artery of the lumbar enlargement. Usually located with the lower thorasic or upper lumbarspinal segment on the left side ofthe spinal cord

The spinal cord lacks adequate collateral supply in some areas, making  theseregions prone to ischemia after vascular occlusions. The upper

Thorasic (T1-T4) and first lumbar segments are the most vulnerableregions of the cord.

There are several arteries that reinforce the spinalcord blood supply and are termed segmentalarteries

1. The Vertebral arteries, spinal branches whichare present in the upper cervical (~C3-C5)levels

2. Ascending Cervical arteries, present in the lowercervical 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. Theseare drained by the anterior and posterior radicular veins. These in turn emptyinto an epidural venous plexus which connects into an external vertebral venousplexus, 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 graymatter and the ventral corticospinal tract.

2. Loss of contralateral pain and temperature sensation, due to damageto thespinothalamic 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 bulkof its blood supply from the  vertebrobasilarsystem. Except for the labyrynthinebranch, all other branches supplythe brain stem and cerebellum

The posterior cerebral has only a small contribution, itsmain target being the posteriorcerebral 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 inferiorsurface and underlying white matter of cerebellum

 b. contributes to supply ofcentral cerebellar nuclei

 c. also contributes to upper medulla and lowerpontine areas

2. Pontine arteries, numerous smaller branches that can besubdivided into Paramedian and Circumferentialpontine arteries. TheCircumferential can be  further subdivided into Long and Short  pontinearteries.

Distribution:

 a. paramedian pontine - basalpons

 b. circumferential pontine -lateral pons and middle cerebellar peduncle, floor of fourth ventricle and pontine tegmentum

3. Superior Cerebellar arteries, originates nearthe end of the Basilar artery,  close to the Pons-Midbrain junction. Runs along dorsal surface of cerebellum

Distribution:

 a. cerebellar cortex, whitematter and central nuclei

 b. Additional contribution to rostral pontinetegmentum, superior cerebellar peduncle and inferior colliculus

4. Posterior cerebral arteries, the terminal branchesof the Basilar artery. They appearas a bifurcation of the Basilar,  just past the Superior Cerebellar arteriesand the oculomotor nerve.  Curvesaround the midbrain and reaches themedial surface of the cerebral hemispherebeneath the splenium of the corpuscallosum

Distribution:

a. mainly neocortex anddiencephalon

b. some contribution to interpeduncular plexus

5. Labyrynthine arteries, may branch from the basilar, butvariable in its  origin. Supplies the region of the innerear

Blood Supply to the Medulla 

The Medulla is supplied by the;

1. Anterior spinal artery, sends blood to the paramedian region of thecaudal medulla.

2. Posterior spinal artery, supplies rostral areas, including thegracile and cuneate fasiculi and nuclei, along with dorsal areas of theinferior cerebellar peduncle.

3. Vertebral artery, bulbar branches supply areas of both the caudaland rostral medulla.

4. Posterior inferior cerebellar artery, supplies lateral medullaryareas.

Occlusion of branches of the anterior spinal artery will produce

a inferior alternating hemiplegia (aka medial medullary syndrome), characterizedby;

1. A contralateral hemiplegia of the limbs, due to damage to the pyramidsor the corticospinal fibers

2. A contralateral loss of position sense, vibratory sense and discriminativetouch, due to damage to the medial leminiscus

3. An ipsilateral deviation and paralysis of the tongue, due to damageto the hypoglossal nucleus or nerve

Occasionally, these symptoms will develop after occlusion of the vertebralartery before gives off its branches to the anterior spinal  artery

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

The vertebral arteries supply  the pyramids at the level of the Pons,  theinferior olive complex,  the medullary reticular formation,  solitarymotor nucleus  dorsal motor nucleus of the Vagus  (cranialnerve X),  hypoglossal nucleus  (cranial nerve XII).  spinaltrigeminal tract, spinothalamictract  spinocerebellar tract

The posterior inferior cerebellar arteries (PICA) supply  spinothalamictract,  spinal trigeminal nucleus and tract, fibers from the nucleus ambiguous,  dorsalmotor nucleus of the Vagus(cranial nerve X)  inferior cerebellar peduncle

Occlusion of the posterior inferior cerebellar artery (or contributing vertebral)will produce a lateral medullarysyndrome or Wallenberg’ssyndrome, characterized by;

1. A contralateral loss of pain and temperature sense, due to damageto the anterolateral system (spinothalamic tract)

2. An ipsilateral loss of pain and temperature sense on the face, due todamage 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  damageto 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. paramedianbranches, to medial pontine region

                b. shortcircumferential branches, supply anterolateral pons

                c. longcircumferential branches, run laterally over the anterior  surfaceof the Pons to anastomose with branches of the anterior inferior cerebellar artery (AICA).

2. Some reinforcing contributions by the anterior inferior cerebellarand superiorcerebellar arteries

Additional branches of the Basilar artery can be foundbranching off within the  regionof the Pons;

1. Anterior Inferior Cerebellar Arteries (AICA), originates near thelower border of the Pons just past the union of thevertebral arteries.

Distribution:

 a. supplies anterior inferiorsurface and underlying white matter of cerebellum

 b. contributes to supply ofcentral cerebellar nuclei

 c. also contributes to upper medulla and lower pontine areas

2. Superior Cerebellar arteries, originates near the end of the Basilarartery, close to the  Pons-Midbrainjunction. Runs along dorsalsurface of cerebellum

Distribution:

 a. cerebellar cortex, whitematter and central nuclei

 b. Additional contribution to rostral pontine tegmentum, superior cerebellarpeduncle and inferior colliculus

2. Labyrynthine arteries, may branch from the basilar, but variable inits 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 byWende et. al., 1975, (sample sizeof 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 regionsof the Pons, this includes corticospinal fibers (basis pedunculi),  themedial leminiscus, abducens nerve and nucleus (cranial nerve VI) ,  pontinereticular area, and periaquaductal gray areas

The paramedian branches of the Basilar artery supply  corticospinalfibers,  the medial leminiscus, abducens nerve and nucleus (cranial nerve VI) ,  pontinereticular area, periaquaductalgray areas

Obstruction of the paramedian pontine arteries will produce a  middlealternating hemiplegia  (alsotermed medial pontine syndrome)  which is characterized by;

1. Hemiplegia of the contralateral arm and leg, due to damage to the corticospinaltracts

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  abducensnerve or tract (can cause diplopia “double vision”)

The short circumferential branches supply, pontinenuclei,  pontocerebellar fibers,  medial leminiscus  theanterolateral system (spinothalamic fibers)

The long circumferential branches supply, along with the anteriorinferior cerebellar (caudally),  and superior cerebellar artery (rostrally).middle and superior cerebellar peduncles, vestibular and cochlear nerves and nuclei,  facialmotor nucleus (cranial nerve VII) trigeminalnucleus (cranial nerve V)  spinal trigeminal nucleus and tract (cranialnerve V),  hypothalamospinal fibers,  theanterolateral system (spinothalamic) pontinereticular nuclei.

Occlusions of long branches circumferential branches of the basilar arteryproduce a lateral pontine syndrome, characterized by;

1. Ataxia, due to damage to the cerebral peduncles (middle andsuperior)

2. Vertigo, nausea, nystagmus, deafness, tinitus, vomiting, due to damageto vestibular and cochlear nuclei and nerves

3. Ipsilateral pain and temperature deficits from face, due to damageto thespinal trigeminal nucleus and tract

4. Contralateral loss of pain and temperature sense from the body, dueto damage to the anterolateral system (spinothalamic)

5. Ipsilateral paralysis of facial muscles and masticatory muscles, due todamage 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 ofthe basilar artery;

1. Posterior cerebral artery, forms a plexus with the posterior communicatingarteries in the interpeduncular fossa, branches from this plexus supply a wide area if the midbrain

2. Superior cerebellar artery, supplies dorsal areas around the centralgray 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, joinsthe posterior cerebral to form portions of the circle of Willis  (arterialcircle). 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 posteriorcerebral, form a plexus in the interpeduncular fossa, enter the  throughthe 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 midbrainor superior alternating hemiplegia (or Weber’s syndrome) characterized by;

1. Contralateral hemiplegia of the limbs, and contralateral face andtongue due to damage to the descending motor tracts

(crus cerebri).

2. Ipsilateral deficits in eye motor activity, caused by damage to the oculomotornerve

The short circumferential arteries originate from the interpeduncular plexusand 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  cerebralartery, one important branch, the quadrigeminal (collicular artery) supplies the superior and inferiorcolliculi.

The posterior choroidal arteries originate near the basilar  bifurcationinto 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  andlateral ventricles

Other Clinical Points

Substantial infarcts within the Pons are generally rapidly fatal, dueto 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 cancommunicate only with eyes. LOCKED-IN-SYNDROME