Chapter 27: Disorders of Circulation within the CNS

1,

Central Nervous System (CNS)

• Brain and spinal cord are mejor components

  • Detect, transmit, analyze sensory information

  • Generate signals to autonomic and motor pathways that orchestrate visceral and endocrine functions, coordination, and movement

• Tissue of CNS rely heavily on receiving constant perfusion

  • Cerebral autoregulation

  • Blood-brain barrier

Major disorders of circulation

• Transient ischemic attacks (TIA)

  • Brief appearance of symptoms resembling stroke

  • Generally resolve within 24 hours

• Stroke

  • Brain attack

  • Enduring disruption of speech, motor, communication accompanied by cognitive deficits

• Subdural and spinal cord hemorrhage 

• Disorders of circulation within brain revolve around lack of oxygen and increased pressure within skull

Ischemia

• Obstructed blood vessels

• Drop in blood flow to brain

Increased pressure within skull (increased intracranial preassure) 

• Hematoma

• Excessive production of cerebral spinal fluid

• Blockage of duct system conveying cerebral spinal fluid 

Vascular Supply of Central Nervous System 

• Brain: 2.5% of total body mass; receives 15% of cardiac output; large portion of blood is sent to the brain because it always needs O2

  • White matter: 60% of brain mass; used 6% of cerebral oxygen

  • Gray matter uses 94% of cerebral oxygen; where most neuro activities happen

• Maintenance of cerebral circulation

  • Right and left internal carotid arteries

  • Right and left vertebral arteries 

Production and Circulation of Cerebrospinal Fluid (CSF)

• Produced in choroid plexi of ventricles

  • Flows through ventricular system of brain; keeps the brain floating

  • Flows through subarachnoid space surrounding brain and spinal cord

• Reabsorbed into venous dural sinuses via arachnoid villi

• Hydrocephalus

  • Blockage in flow of CSF though ventricles of brain or when cannot be resorbed by arachnoid villi 

• Cerebral perfusion pressure (CCP)

  • Cerebral blood flow (CBF)= CPP/Cerebral vascular resistance (CVR)

Blood-Brain Barrier

• Specialized endothelium in brain capillaries

• Permits selective entry of substances

  • Tight junctions between endothelial cells

  • Few pinocytotic vesicles

  • No fenestra- no force in the capillaries

  • Active transport

• Substances that cross barrier

  • Highly lipophilic substances cross directly 

  • Most nutrients cross barrier by facilitated diffusion 

• Regions of brain lacking blood-brain barrier

  • Subfornical organ and area postrema of brainstem 

  • Infundibulum of hypothalamus and pituitary gland 

Cerebral autoregulation

• Autoregulation mechanisms fail

  • Loss of match between oxygen supply and demand of tissues

Intracranial pressure

• Help to keep resistance and control mechanism

• Pressure exerted by contents of cranium

• Monro-Kellie hypothesis

  • Compensatory relationship maintaining cerebral compliance in response to changes in volume

Injured brain tissue

• Cytotoxic edema- any increasing pressure that damages cells in the brain

• Vasogenic edema- blood-brain barrier breaks, blood gets into the brain

• Clearance of brain tissue swelling

Hydrocephalus

• Excessive accumulation of CSF in cranial vault

• Compresses surrounding structures

• Causes 

  • Lesions that obstruct flow of CSF 

  • Problems with resorption 

Concurrent ischemia and hypoxia

• Mitochondrial dysfunction 

  • Leads to infarction and tissue death

  • Anaerobic glycolytic pathways initiated

• Energy deprivation and loss of ion homeostasis

  • Cells unable to maintain negative membrane potential 

  • Excitatory amino acids in extracellular space

  • Glutamate and influx of calcium ions

  • Apoptosis- programmed cell death

• Cerebral hemorrhage in sepsis

  • Immune cells activated

  • leukocytes enter brain 

  • Inflammatory agents contribute to brain inflammation

  • Nitric oxide/nitric oxide synthetase pathway 

  • Mitochondrial dysfunction and apoptosis

Transient Ischemic Attack (TIA)

• Temporary episode of neurologic dysfunction

• Caused by focal brain, spinal cord, or retinal ischemia without acture infarction

• Etiology and pathogenesis

  • Same as ischemic stroke

  • Clot blocking blood supply to region of brain 

  • Atherosclerosis 

Transient Ischemic Attack- Risk Factors 

• Nonmodifiable 

  • Age, Family history, Prior TIA or stroke, Race, Sex, Sickle cell disease

• Modifiable 

  • Cardiovascular disease, Carotid artery disease, Diabetes, Excess weight, High blood pressure, High cholesterol, Cigarette smoking, Heavy drinking, Physical inactivity, Poor nutrition, Use of birth control pills

Transient Ischemic Attack- Clinical manifestations 

• Facial drooping

• Arm or leg weakness on one side of body

• Speech difficulty 

• Sudden trouble seeing in one or both eyes

• Difficulty walking with dizziness 

• Lack of balance or coordination

• Severe headache 

Transient Ischemic Attack- Diagnosis and treatment

• Exclusion of conditions that mimic TIA

• Blood glucose and other blood tests 

• Electrocardiography 

• Noncontrast CT 

• MRI with diffusion-weighted imaging

• CT angiography or magnetic resonance angiography

• Carotid doppler 

Stroke

• Interruption in blood supply to region of brain or bleeding vessel resulting in brain tissue damage or infarction

• Ischemic: 87%

• Hemorrhagic: 13%

Ischemic Stroke

• Etiology and Pathogenesis

  • Partial or complete occlusion of cerebral blood flow

  • Atherosclerosis

  • Cardiac disorders 

  • Thrombotic strokes: Internal carotid artery, Middle cerebral artery, Basilar artery 

• Treatment

  • Restoration of blood flow and reducing area of infarction

    • Penumbra: tissue surrounding infarction

    • Supplemental oxygen

    • Glycemic control

    • Fibrinolytic therapy

    • Antihypertensive therapy

    • Aspirin 325mg

    • Hypothermia- decreases blood flow to certain areas

Hemorrhagic stroke

• Etiology and pathogenesis

  • Bleeding into brain from burst blood vessel: Intracerebral, Intraventricular, Extracerebral

  • Subarachnoid hemorrhage

  • Cerebral aneurysm 

  • Atriovenous malformation (AVMs)

• Treatment

  • Osmotic diuretics

  • Surgical evacuation

  • Craniotomy with aneurysm clipping

  • Endovascular therapy with coil embolization 

  • Delayed cerebral ischemia (DCI)

Ischemic and Hemorrhagic stroke- Clinical manifestations

• Sudden onset of focal neurologic deficit persisting for at least 24 hours due to reduction or occlusion of cerebral circulation or rupture of blood vessel 

• Other signs and symptoms depending on area of brain or spinal cord affected 

Subdural hematoma

• Bleeding from bridging veins between dura mater and arachnoid membrane 

• Etiology and pathogenesis

  • Trauma from high-speed impact to skull

  • Acute subdural hematoma

    • Bleeding identified immediately after injury

  • Chronic subdural hematoma

    • brain atrophy- shrinks 

Subdural Hematoma- Manifestations and treatment

• Manifestations

  • Headache

  • Confusion, changes in behavior

  • Dizziness

  • Nausea, vomiting

  • Lethargy or excessive drowsiness, weakness

  • Apathy- lack of motivation

  • Seizures

• Treatment

  • Surgery- to control bleeding

Spinal Cord Hemorrhage

• Rare

• Etiology and pathogenesis

  • Trauma, vascular malformation, bleeding disorders

  • Epidural, subdural, subarachnoid, or intramedullary 

    • Intramedullary hemorrhage (hematomyelia)

    • Epidural and subdural spinal cord hemorrhage 

Spinal Cord Hemorrhage- Manifestations and treatment

• Manifestations

  • Sudden, severe back pain with or without radioculopathy- compression on the nerves

  • Headache, neck stiffness

  • Phtotsensitivity

  • Irreversible sensory loss below level of bleed

• Treatment

  • Spinal subdural hemorrhage

    • Surgical decompression

  • Spinal subarachnoid hemorrhage

    • Surgical resection

    • Catheter-based interventional techniques

    • Focal radiation therapy with gamma knife, cold photon knife