ISCHEMIC STROKE

• posterior circulation strokes account for 20-25% (range 17-40%) of ischemic strokes
• posterior (vertebrobasilar) circulation includes the vertebral (extra- and intracranial), basilar, and posterior cerebral arteries, as well as their branches
• it supplies the posterior regions of the brain (brainstem, thalamus, cerebellum, and the occipital and temporal lobes)
• in general, the term vertebrobasilar insufficiency (VBI) describes inadequate blood flow through the posterior circulation
  • it can be either transient (transient ischemic attack (TIA), drop attack, Bow Hunter’s syndrome) or permanent (infarct)
  • several mechanisms leading to hypoperfusion may be involved and even combined (embolism, atherothrombosis, external mechanical compression, steal syndrome)
  • the term has been overused (often referring to various nonvascular vertiginous conditions in the geriatric population), and its use is currently discouraged
• certain occlusions cause characteristic clinical patterns and syndromes
• however, vertebrobasilar stroke shares features with other conditions (stroke mimics); differential diagnosis in the acute setting can be challenging
  • DDx of vertigo (labyrinthitis, vestibular neuritis, benign paroxysmal positional vertigo, etc.)
  • DDx of impaired consciousness (metabolic coma, nonconvulsive seizure, etc.)
• the outcome depends on the location and extent of the stenosis/occlusion, the quality of the collateral circulation, and adequate and timely therapy
  • if extensive basilar artery occlusion (BAO) is left untreated, the mortality rate is over 90%
• strokes in the posterior territory have a higher risk of recurrence compared to those in the carotid territory  (Werring, 2014)
  • the risk of recurrence after a previous stroke/TIA with VA/BA stenosis ≥ 50% is ~ 22% within 90 days   (Gulli, 2013)  [Marquardt, 2009]

→ arterial territories

→ anatomy of cerebral arteries

• the symptoms of a vertebrobasilar stroke can differ significantly among patients, depending on the type of occluded artery, the extent of occlusion, and the quality of the collateral circulation
• a combination of symptoms is common → see Topical diagnosis of stroke
• while traditional brainstem syndromes have been described, some symptoms may not be specific (DDx of vertigo)

• vestibular syndrome (vertigo, nystagmus, tonic deviations)
  • isolated vertigo is usually of nonvascular origin
  • nonspecific balance disorders must be distinguished (see below)
  • vertigo due to stroke is usually associated with other brainstem and cerebellar symptoms.
• nausea and vomiting
• eye movement disorder (nuclear/supranuclear) +/- diplopia
• visual field disturbances
• signs of sympathetic lesions
  • Horner’s syndrome (ptosis and miosis, sometimes anhidrosis on the affected side) 
  • Harlequin sign 
• ataxia and/or dysmetria
• dysarthria/dysphonia
• dysphagia
• paresthesia/hypesthesia in the face and/or extremities and trunk
• combination of paresis or sensory deficit in the extremities
  • hemiparesis or quadriparesis
• isolated hearing loss is typically not caused by stroke (except for occlusion of the labyrinthine artery)
• alternating syndromes are typical for localized brainstem lesions with an ipsilateral nuclear lesion of a cranial nerve, Horner’s syndrome or cerebellar syndrome, and contralateral fascicular disorder (hemiparesis or hemihypesthesia)
• larger occlusions lead to impaired consciousness (coma may be the initial manifestation) → Examination of the patient with impaired consciousness
• transient circulatory disturbances may also cause drop attacks

→ Etiologic classification of ischemic stroke

→ Diagnosis of a vertebrobasilar steno-occlusive disease

• the most frequent causes of vertebrobasilar stroke are atherosclerosis (AS) and arteriolopathy; cardioembolism is less common
  • AS lesions are most commonly located in the V0 and V4 segments of the vertebral arteries, in the proximal and middle segments of the basilar artery, and in the P1 segment of the posterior cerebral artery (PCA)    
    
  • occlusion of a perforator results in lacunar stroke  
• arterial dissection most commonly affects the V3 segment 
  • typical presentations include neck or occipital pain +/- TIA or infarction
• stenosis can cause:
  • atherothrombotic occlusion
  • perforator occlusion
  • thromboembolism
  • hypoperfusion in distal segments
  • steal phenomenon
    • occurs with stenosis/occlusion of the proximal segments of the subclavian artery or brachiocephalic trunk
    • usually causes only transient symptoms (dizziness), not stroke
  • Bow-Hunter’s syndrome (also known as rotational vertebral artery syndrome) – transient ischemic symptoms caused by external mechanical compression of the vertebral artery (usually at the C1-2 level) during lateral flexion or rotation of the head, often in combination with contralateral stenosis
• a less common cause of stroke is dolichoectasia and its complications 
  • flow stasis increases the likelihood of thrombus formation
  • arterial wall stress predisposes to dissection
    
  • enlarged artery may cause a mass effect on adjacent neural structures

• diagnosis is based on a careful history with a detailed clinical examination and the correct indication and interpretation of imaging studies
• all cases of suspected stroke require urgent brain imaging to exclude haemorrhage, vessel imaging is essential to identify artery occlusion. It should be performed without delay, as minimizing the time between stroke onset and initiation of thrombolysis is associated with a good outcome

• ischemia or hemorrhage in the brain stem and cerebellum does not usually cause diagnostic difficulties due to typical symptoms
• nonvascular etiologies (external brainstem compression, brainstem tumor) must be excluded
• isolated vertigo and altered consciousness are challenging because of the wide range of potential etiologies

• not every vertigo is of vascular origin (especially in the elderly)
• dizziness should always be specified and accurately described – distinguish vestibular vertigo from various nonvestibular conditions, ataxia, or other balance disorders and psychogenic conditions
  • the term vertigo should be reserved for the dizziness of vestibular origin
  • distinguish other nonspecific conditions (weakness, fainting, blurred vision, or unsteady gait)
• to determine whether the dizziness is vestibular, nonvestibular, or caused by another balance disorder, the following should be obtained and evaluated:
  • an accurate description of the current condition, including associated symptoms (hearing loss, lesions of other cranial nerves, brainstem, and cerebellar symptoms)
  • onset (sudden x gradual), duration, and provoking factors (e.g.,  head or body movement or position)
  • course (constant x fluctuating, spontaneous worsening x improvement)
• consider the patient´s age

• these possibilities must be distinguished based on the patient’s history:
  • true vertigo (usually rotational) is caused by vestibular pathway dysfunction (central or peripheral)
  • impaired balance without rotatory vertigo
    • instability manifesting particularly when walking or standing; symptoms typically alleviate when sitting or in a supine position
    • the absence of rotational vertigo suggests a nonvestibular etiology
  • presyncope (fainting) and other nonspecific symptoms
    • a feeling of impending fainting but without actual loss of consciousness, lightheadedness, or general malaise
    • e.g., due to hypoglycemia, hyperventilation, anemia, side effects of medication, etc.
• exclude vascular etiology, especially in elderly patients with vascular risk factors, and look for subtle lesions on neuroimaging (perform DWI if possible)