Pathophysiology of Stroke

• Cerebrovascular disease


  any disease that affects the blood vessels of the brain
• Stroke


  Leading cause of disability

  Occur in the cerebrum, brainstem, cerebellum, or spinal cord

  Hallmark sign is its rapid onset compared with other diseases of the brain
• Men have a greater age-adjusted stroke occurrence compared with women which reverses in women greater than 85 years old
• African Americans have twice the risk of stroke compared to Caucasian Americans
• Prevalence rates are also higher in Mexican Americans, American Indians, and Alaskan Natives
• Atherosclerosis


  Plaque formation accumulates on the arterial walls leading to progressive narrowing of blood vessels
• The most common sites for lesions to occur

  Origin of the common carotid artery or at its transition into the middle cerebral artery

  The main bifurcation of the middle cerebral artery

  The junction of the vertebral arteries with the basilar artery
• Ischemic stroke


  Inadequate blood flow resulting in tissue death

  Lack of oxygen due to mechanical obstruction of one or more arteries that prevents adequate blood supply to the vessels and brain tissue distal to the site of blockage
• Hemorrhagic stroke


  Bleeding into the nervous system tissues and potentially into the ventricles
• Transient ischemic attack

  When people have a complete resolution of the deficit within minutes after the onset of the event
• There is a 10 percent chance that a person who had a single TIA will have another TIA within a week and a 2 percent risk that he or she could have a complete stroke within that week
• Typically, a complete loss of blood flow can be tolerated only for a maximum of five or six minutes before there is death of the neurons and the supporting glial cells and the cells of the circulation causing infarction and necrosis
• Thrombus


  Blockage of an artery that develops from the build-up of plaques within the wall of the vessel that slows blood flow substantially or blocks it all together
• Embolus


  A clot that forms elsewhere and travels to the brain lodging into one of the cerebral vessels
• Lacunar stroke


  An ischemic stroke in small vessels which can go undiagnosed until many such strokes have occurred, and larger areas of damage has developed
• Embolic stroke


  Composed of bits of matter (blood clot, plaque) formed elsewhere and released into the bloodstream, traveling to the cerebral arteries where they lodge in a vessel, producing occlusion and infarction
• Thrombotic stroke


  The formation or development of a blood clot within the cerebral arteries or their branches
• Lacunar infarcts


  Obstructions of blood flow in small, deep arteries
• Primary intracerebral hemorrhage


  Direct leakage of blood from an artery into brain tissue
• Subarachnoid hemorrhage


  Bleeding into the subarachnoid space surrounding the brain and spinal cord, usually associated with the rupture of saccular or berry aneurysms
• Subdural hemorrhage


  Venous bleeding into the potential space beneath the dura mater covering the brain
• Epidural hemorrhage


  Arterial bleeding from a torn meningeal artery with the blood accumulating outside the dura mater
• Major risk factors for stroke

  • Hypertension
  • Diabetes mellitus
  • Atrial fibrillation
  • Hyperlipidemia
  • Tobacco use
  • Cardiovascular disease
• Excessive alcohol consumption is associated with increased clotting which can case stroke
• Sleep apnea is an independent risk factor for stroke, almost doubling the risk of stroke or death
• Other symptoms of stroke

  Sudden numbness or weakness of the face, arm, or leg especially on one side of the body

  confusion

  Trouble speaking or understanding speech

  Trouble seeing in one or both eyes

  Trouble walking, dizziness, loss of balance or coordination

  Severe headache with no known cause
• Early warning signs of stroke

  • Face drooping
  • Arm weakness
  • Speech difficulty
  • Time to call 911
• Vascular syndromes


  Categorization of the pathology and clinical consequences of ischemic strokes based on the territory of the cerebrum supplied by a vessel
• Anterior cerebral artery stroke


  • Affects the most anterior-medial portions on the cerebrum
  • Causes personality changes and cognitive changes due to frontal lobe damage

  
• Deficits from anterior cerebral artery stroke

  • Contralateral hemiplegia
  • Loss of fine touch sensation, more severe in lower limb
  • Gait apraxia
  • Flat affect
  • Impulsiveness
  • Motor perseveration
  • Confusion
  • Motor inactivity
  • Difficulty with divergent thinking
  • Urinary incontinence
• Middle cerebral artery stroke

  • Deprives the optic radiation and the lateral parts of the sensorimotor cortex and adjacent white matter of blood
  • Causes contralateral homonymous hemianopia combined with contralateral hemiplegia and hemisensory loss
  • Upper limb and face more affected than lower limb
  • Causes aphasia if in language-specialized hemisphere
  • Causes difficulty understanding spatial relationships, neglect, and impairment of nonverbal communication if in hemisphere specialized for understanding spatial relationships and nonverbal communication

  
• Deficits from middle cerebral artery stroke

  • Hemisensory loss affecting face and upper limb more than lower limb
  • Face and upper limb more impaired than lower limb
  • Homonymous hemianopia
  • If right hemisphere (left hemiplegia): easily distracted, poor judgment, impulsiveness
  • If left hemisphere (right hemiplegia): apraxia, compulsiveness, overly cautious
  • Aphasia if left hemisphere
  • Difficulty understanding spatial relationships, neglect, impairment of nonverbal communication, dressing apraxia, constructional apraxia if right hemisphere
• Posterior cerebral artery stroke

  • Causes eye movement paresis or paralysis
  • Causes cortical blindness affecting information from the contralateral visual field
  • Causes visual agnosia, the inability to recognize objects by sight despite intact vision
  • Lack of blood flow to the thalamus can cause thalamic syndrome, characterized by severe pain, contralateral hemisensory loss, and flaccid hemiparesis
  • Vascular compromise of the hippocampus interferes with declarative memory
• Deficits from posterior cerebral artery stroke

  • Hemisensory loss
  • Slow nociception loss
  • Eye movement problems: vertical gaze palsy, oculomotor nerve palsy, loss of medial deviation of the eyes with preserved convergence, vertical skew deviation
  • Rarely hemiparesis
  • Homonymous hemianopia
  • Cortical blindness
  • Hallucinations
  • Lack of depth perception
  • Visual agnosia
  • Limbs may show vasomotor and/or trophic abnormalities
  • Difficulty reading
  • Memory loss
• Vertebral and basilar artery strokes

  • Occlusions of the vertebrobasilar system can produce a wide variety of symptoms with both ipsilateral and contralateral signs
  • Most common signs are gait and limb ataxia, limb weakness, oculomotor palsies, and oropharyngeal dysfunction
  • Other common signs and symptoms are loss of vision, double vision, numbness, dizziness, headache, and vomiting
  • Emboli in the vertebral arteries within the skull usually cause cerebellar infarction
  • Complete occlusion of the basilar artery causes death due to ischemia of brainstem nuclei and tracts that control vital functions
  • Partial occlusions of the basilar artery can cause tetraplegia, loss of sensation, coma, and cranial nerve signs
• Four Ds of brainstem region dysfunction

  Dysphagia, dysarthria, diplopia, dysmetria
• Anterior inferior cerebellar artery stroke


  • Causes lateral inferior pontine syndrome with ipsilateral horizontal and vertical nystagmus, vertigo, nausea, vomiting, facial paralysis, paralysis of conjugate gaze, deafness, tinnitus, ataxia, loss of discriminative touch and proprioception in face, contralateral loss of pain and temperature sense
• Posterior inferior cerebellar artery stroke

  • Causes lateral medullary (Wallenberg's) syndrome with ipsilateral decreased pain and temperature sensation in face, ipsilateral cerebellar ataxia, ipsilateral vertigo, nausea, vomiting, nystagmus, Horner's syndrome, dysphagia and dysarthria, ipsilateral loss of discriminative touch and proprioception upper and lower extremity and trunk, contralateral loss of pain and temperature body
• Superior cerebellar artery stroke

  • Causes lateral superior pontine syndrome with ipsilateral cerebellar ataxia of limbs and gait, ipsilateral horizontal nystagmus, ipsilateral loss of optokinetic nystagmus, ipsilateral Horner's syndrome, vertigo, dizziness, nausea, vomiting, contralateral loss of pain and temperature face, limbs, trunk, contralateral loss of discriminative touch, vibration and position sense body
• Altered Consciousness


  Altered level of consciousness (coma or decreased arousal levels) may occur with extensive brain damage such as a large proximal MCA occlusion; Levels of Consciousness: normal, lethargy, obtundation, stupor, and coma