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 . Blood Supply to the Spinal Cord and Brain Stem
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 .
Blood Supply to the Spinal Cord and Brainstem 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
Branches of the Vertebral Artery 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.
Branches of the Vertebral Artery 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 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. Spinal Cord Blood Supply 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
Spinal Cord Blood Supply 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
Spinal Cord Blood Supply 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.
Spinal Cord Blood Supply 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. Spinal Cord Blood Supply
Spinal Cord Blood Supply 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
Spinal Cord Blood Supply 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
Branches of the Basilar Artery 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
Branches of the Basilar Artery 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
Branches of the Basilar Artery 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
Branches of the Basilar Artery 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.
Blood Supply to the Medulla 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
Blood Supply to the Medulla The posterior spinal arteries supply the gracile and cuneate fasiculi and nuclei, spinal trigeminal tract and nucleus, portions of the inferior cerebellar peduncle
Blood Supply to the Medulla 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
Blood Supply to the Medulla 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
Blood Supply to the Medulla 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
Blood Supply to the Pons 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
Blood Supply to the Pons 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
Blood Supply to the Pons 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
Blood Supply to the Pons 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
Blood Supply to the Pons 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
Blood Supply to the Pons 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”)
Blood Supply to the Pons The short circumferential branches supply, pontine nuclei, pontocerebellar fibers, medial leminiscus the anterolateral system (spinothalamic fibers)
Blood Supply to the Pons 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.
Blood Supply to the Pons 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
Blood Supply to the Midbrain 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
Blood Supply to the Midbrain 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
Blood Supply to the Midbrain 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
Blood Supply to the Midbrain The long circumferential branches originate mainly from the posterior cerebral artery, one important branch, the quadrigeminal (collicular artery) supplies the superior and inferior colliculi.
Blood Supply to the Midbrain 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