Blood supply and cerebrospinal fluid

Vascular Supply of the Central Nervous System (CNS)

  • Arterial Trunks Supplying the Brain

    • Internal Carotid Artery

    • Supplies rostral 2/3 of brain, including most of basal ganglia and internal capsule.

    • Vertebral Artery

    • Major contributor to the posterior circulation of the brain.

  • Major Branches of the Vertebral-Basilar System

    • Supplies:

    • Posterior parts of cerebral hemisphere

    • Cerebellum

    • Brainstem

    • Most of the thalamus

    • Spinal cord

  • Major Branches of Internal Carotid

    • Supplies cerebrum.

  • Blood Barriers of the Brain

    • Blood-Brain Barrier (BBB): Protects the brain from harmful substances while allowing essential nutrients to pass.

    • Blood-CSF Barrier: Regulates the exchange between blood and cerebrospinal fluid (CSF).

Ventricles and Cerebrospinal Fluid (CSF)

  • Ventricular System of the Brain

    • Components

    • Paired lateral ventricles

      • Consist of anterior, inferior, and posterior horns and body.

    • Third ventricle

      • Located in the diencephalon.

    • Cerebral aqueduct

      • Located in the midbrain.

    • Fourth ventricle

      • Located between the pons and medulla, with a roof covered by the cerebellum.

    • Attachments

    • Communicates with the subarachnoid space via lateral and median apertures.

  • Production, Pathways, and Reabsorption of CSF

    • CSF is produced by the choroid plexus and flows through the ventricles into the subarachnoid space.

    • Total volume of CSF is approximately 150 ml, with only about 23 ml located in the ventricles.

    • CSF characteristics:

    • Low glucose, protein, and immunoglobulin compared to blood plasma.

    • Typically contains 1-5 cells (mainly leukocytes) per microlitre; no red blood cells.

  • Consequences of Hydrocephalus

    • Can be congenital or acquired.

    • Symptoms include increased CSF pressure, dilatation of ventricles, head enlargement in infants, and may lead to papilledema.

    • Two types:

    • Communicating Hydrocephalus: Interference with CSF absorption or increased production.

    • Non-communicating Hydrocephalus: Obstruction of CSF circulation.

Posterior Circulation of the CNS

  • Vertebral Arteries

    • Originate as branches of the subclavian arteries and progress through the cervical vertebrae's transverse foramina.

    • They join at the caudal border of the pons to form the basilar artery.

  • Basilar Artery

    • Runs through the pontocerebellar cistern and bifurcates into two posterior cerebral arteries.

  • Branches

    • Anterior spinal artery, posterior inferior cerebellar artery (PICA), and anterior inferior cerebellar artery (AICA).

  • Cerebellar Blood Supply

    • PICA: Supplies the inferior portion of the cerebellum.

    • AICA: Supplies the anterior and lateral portions of the cerebellum, among other regions.

    • Superior cerebellar arteries maintain the supply of superior cerebellar peduncles and the upper cerebellar hemispheres.

Brainstem Vascular Syndromes

  • Medial Medullary Syndrome

    • Result of damage to the medial lemniscus, pyramidal tract, and hypoglossal nerve root on one side.

    • Symptoms:

    • Paralysis of the contralateral arm and leg (medial lemniscus).

    • Weakness of limbs (medullary pyramid).

    • Tongue deviation to the affected side (hypoglossal nerve).

  • Pathology

    • Infarction due to occlusion of paramedian branches of the anterior spinal artery and/or vertebral artery.

    • Treatment for ischaemic stroke may include oxygen therapy, thrombolysis, and long-term anticoagulant therapy.

Anterior Circulation of the CNS

  • Internal Carotid Artery Segmentation

    • Cervical segment: Ascends to the carotid canal.

    • Petrous part: Turns horizontally and enters cranial cavity.

    • Cavernous part: Traverses cavernous sinuses.

    • Cerebral segment: Joins the cerebral arterial circle.

  • Circle of Willis

    • Connects the anterior and posterior blood supply systems of the brain and is notable for its variations and asymmetries.

    • Cerebral arteries emerge from this structure.

Venous Drainage of the Brain

  • Cerebral Veins

    • Superficial cerebral veins drain the cortex and subcortical white matter, primarily into the superior sagittal sinus.

    • Deep cerebral veins drain structures like the choroid plexus and basal ganglia into the internal cerebral veins and great cerebral vein of Galen.

    • Anatomical significance of the dural sinuses for managing drainage.

  • Clinical Significance

    • Dural sinus thrombosis and subdural bleeding can occur due to various pathological conditions.

CSF Circulation and Arachnoid Structures

  • Arachnoid Granulations

    • Main exit points for CSF from the subarachnoid space; active in the absorption of CSF back into the venous system.

  • Arachnoid Cisterns

    • Cerebellomedullary cistern is the largest and plays a crucial role in CSF circulation.

    • Other significant cisterns include:

    • Pontine cistern

    • Interpeduncular cistern

    • Chiasmatic cistern

    • Superior cistern (largest in area near corpus callosum).

Hydrocephalus Cases and Mechanisms

  • Examples of Hydrocephalus

    • Example cases showcase the underlying mechanisms driving symptoms like headache, poor coordination, and changes in behavior due to CSF dynamics and pressures.

    • Important differential diagnostic considerations (e.g. obstruction of aqueduct leading to cyst formation).

    • Neuroimaging techniques (like CT and MRI) are pivotal in diagnosing and managing hydrocephalus.

  • Common Causes of CSF Accumulation

    • Increased production, circulation interference, and absorption issues leading to significant clinical consequences.