Posterior Circulation Ischemic Strokes

Last week we had the opportunity to learn about posterior circulation ischemic strokes from vascular neurologist, Dr. Osteraas.

Diagnosing posterior circulation ischemic strokes can be challenging in the emergency department, largely because posterior circulation ischemic strokes frequently lack “traditional” stroke signs and symptoms and the symptoms that you do see are often non-specific and can be slow onset. Despite this, it is important to do our best to diagnose these as about 20% of ischemic events involve the posterior circulation and posterior circulation ischemic strokes can lead to some of the most devastating neurologic outcomes, including massive cerebellar infarcts with subsequent herniation and locked in syndrome.

 

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A posterior circulation ischemic stroke is defined as an infarct occurring in the vascular territory supplied by the vertebrobasilar system. Before discussing posterior circulation stroke syndromes, it is important to first understand the anatomy. Two vertebral arteries arise from the subclavian arteries and converge to form the basilar artery. The basilar artery eventually branches into the two posterior cerebral arteries at the ponto-mesencephalic junction. These main arteries and their branches (including anterior and posterior inferior cerebellar arteries, superior cerebellar artery and multiple pontine arteries) supply the occipital lobe, cerebellum and brainstem. It is important to note that posterior circulation anatomy can be quite variable and incidental findings such as a dominant vertebral artery are common.

In addition to embolic and atherosclerotic etiologies of posterior circulation ischemic strokes, vertebral artery dissection is a common cause of posterior circulation ischemia, especially in young patients. Presence of headache, neck pain, trauma (even minor) or neck manipulation should raise your suspicion for vertebral artery dissection.

While there are a number of posterior circulation stroke syndromes (see table below), “classic” symptoms are often incomplete or absent. More commonly, patients present with non-specific symptoms, most frequently dizziness, unilateral limb weakness, ataxia, dysarthria, nausea and vomiting.

PCIS 1

PCIS 2

As emergency physicians, we are not expected to have all of these syndromes memorized. Dr. Osteraas recommended some easier ways to help us keep posterior circulation ischemic strokes in our differentials:

  • Dreaded D’s: dysarthria, dysphagia, diplopia, dizziness, drowsiness and drop attacks (sudden falls without loss of consciousness or precipitating factors, followed by a rapid return to baseline)
  • M’s for medial syndromes
    • (M)otor pathway (corticospinal tract): contralateral weakness of the arm and leg
    • (M)otor nuclei of CN: 3, 6, 12
    • (M)edial lemniscus: contralateral loss of vibration and proprioception in the arm and leg
  • S’s for side (lateral) deficits
    • (S)pinocerebellar pathway: ipsilateral ataxia of the arm and leg
    • (S)pinothalamic pathway: contralateral alteration of pain and temperature affecting the arm, leg and rarely the trunk
    • (S)ensory nucleus of the 5th cranial nerve: ipsilateral alteration of pain and temperature on the face in the distribution of the 5th cranial nerve
    • (S)ympathetic pathway: ipsilateral Homer’s syndrome (ptosis, miosis)

 

Other interesting findings in posterior circulation ischemic strokes:

  • Patients may present with pinpoint pupils in pontine infarct, which can be easily mistaken for intoxication when presenting with acute coma or altered mental status
  • Patients with acute cortical blindness may be unaware of this and may deny any visual deficits, often associated with confabulation (Anton’s syndrome)
  • Lateral medullary infarcts can be associated with persistent hiccups

 

Vertigo is a common presenting symptom of posterior circulation ischemic stroke. While the HINTS exam is a useful way to differentiate between central and peripheral causes of vertigo, diagnosis truly relies on imaging. While head CTs can underestimate or entirely miss ischemic changes in the posterior circulation, CTA head and neck is an easy test to rapidly assess for vessel patency or dissection. Of course, MRI and MRA are the most sensitive studies. Treatment is the same for any ischemic stroke, including thrombolysis and endovascular therapy.

In summary, you should always keep in mind posterior circulation ischemia when patients present with non-specific or unusual neurologic symptoms. Have a high index of suspicion and remember the dreaded D’s.

 

References:

  • Dr. Nicholas Osteraas
  • Schulz UG, Fischer U. Posterior circulation cerebrovascular syndromes: diagnosis and management. J Neurol Neurosurg Psychiatry2017;88:45-53.
  • Nouh A, Remke J, Ruland S. Ischemic posterior circulation stroke: a review of anatomy, clinical presentations, diagnosis, and current management. Front Neurol. 2014;5:30. Published 2014 Apr 7. doi:10.3389/fneur.2014.00030

 

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