Posterior Circulation Stroke
Zachary Tillett, MD, Resident Physician Emergency Medicine, Maine Medical Center
Jane Morris, MD, Stroke and TeleStroke Program Medical Director, Maine Medical Center
Deborah Gregoire, MSN RN SCRN CCRN-K, Maine Medical Center Stroke Program Coordinator
Brian Chipman, BSN RN CCRN, Maine Medical Center TeleStroke Program Manager
Discuss the incidence and unique diagnostic challenges of posterior circulation strokes.
Identify the two primary circulatory components of the brain and what areas they supply.
Identify common signs and symptoms of posterior circulation stroke using the "5 D's"
Describes signs and symptoms of a vertebral artery dissection.
Describe the performance and utility of the BEFAST stroke assessment tool.
Discuss the diagnostic assessment and treatment modalities of posterior circulation stroke.
Posterior Circulation Stroke: Incidence and Challenges
Posterior circulation stroke (PCS) accounts for about 20% of all acute ischemic strokes . This subset of stroke is relatively common, yet is often missed by clinicians on initial presentation. A study from 2016 revealed an initial missed diagnosis rate for stroke involving the posterior circulation to be 37% compared to just 16% for the anterior circulation . This is an uncomfortably high number when one considers there are nearly 800,000 strokes in the U.S annually .
There are a multitude of factors that make identifying these strokes challenging. PCS often presents with a wide array of vague symptoms. Additionally, there are a litany of common conditions that present with similar clinical manifestations, such as vestibulopathy, migraine and intoxication. Further complicating the assessment and diagnosis and that widely used stroke scales are not designed or validated to assess for infarcts involving the posterior circulation. Delayed or missed diagnosis of PCS can have devastating clinical sequelae for patients and may represent potential litigious ramifications for the providers involved in the care.
So, what is the posterior circulation and how do these strokes occur? Why are we missing PCS? How can we better evaluate for PCS in our patients? How will these patients be treated? Read on to learn about PCS, how to formulate a diagnosis, and finally the best treatment practices for PCS.
The circulation in the brain is divided into two main components. The anterior circulation supplies the frontal lobes, parietal lobes, the anterior temporal lobes and basal ganglia with blood from the internal carotid arteries. The posterior circulation, also called the vertebrobasilar system, perfuses the upper cervical spinal cord, brain stem, cerebellum, occipital lobes and the inferomedial temporal lobes. This represents the most common anatomical formation, but it is important to recognize that there are many variants and each person’s vascular anatomy must be analyzed with vascular imaging (typically CT angiogram or MR angiogram) to know how an individual’s brain gets its blood supply.
Posterior circulation strokes are caused by the same mechanisms as anterior circulation strokes. The most prevalent causes being cardiac embolism, large artery atherosclerosis of the aorta or vertebrobasilar system, and small vessel disease involving the small deep perforating arteries. Dissection of the arteries themselves (both traumatic and spontaneous) need to be considered given their propensity to present in younger patients without known vascular risk factors and are often accompanied by pain (cervical or cranial) which can serve as a clue to the diagnosis but paradoxically mislead the clinician by focusing more on the pain than the neurological deficits. Rare causes of stroke include fibromuscular dysplasia, migrainous infarction, coagulopathies and other vascular disorders .
Patients experiencing PCS often present quite differently from “classic” or anterior circulation strokes. Signs and symptoms are frequently vague in nature and often lack the prominent sensory and motor deficits that may herald an anterior circulation event. This makes the diagnosis of PCS particularly challenging.
Emergency Department and Prehospital Challenges
A study from 2012 of 407 patients that had suffered a PCS, gives some insight into the signs and symptoms of PCS .
Likewise, a systematic review of 21 studies evaluating common symptoms in strokes not identified in the Pre-hospital environment, found posterior circulation type symptoms to be the most commonly missed . Similar to the ED realm, the confluence of symptomology is reflective of a wide range of clinical conditions making identifying PCS difficult.
As discussed earlier, common stroke scales such as the Prehospital Cincinnati Stroke Scale rely heavily on mechanism for identification of anterior circulation stroke . Maine EMS currently utilizes the FAST-ED Score  as a way to help rapidly identify large vessel occlusions, however, this score was designed to detect occlusions in the anterior circulation. MaineHealth hospitals currently encourage the use of the BEFAST  tool for ED triage evaluation of patient’s with symptoms concerning for stroke and specifically was designed to increase the recognition of posterior circulation symptoms of changes in balance and vision. More research is needed before BEFAST can be validated for use in the prehospital realm.
Given the constellation of generic symptoms, combined with a lack of validated testing tools, how can we better assess patients for potential posterior circulation involvement?
Assessment of PCS
Pertinent Medical History
When assessing any patient for stroke, it is important to consider predisposing risk factors. Known risk factors for stroke includes age, history of prior stroke, atrial fibrillation, hypertension, atherosclerotic disease, diabetes, congestive heart failure and many others. An important take away here is, any patient with underlying risk factors, should raise clinical suspicion for a posterior circulation stroke if they have symptoms described above.
When assessing for posterior circulation stroke, one method is to ask a patient about the 5 Ds. Having any of these should raise suspicion for PCS.
1. Dizziness – Does the patient have dizziness, with no triggering event, that is not relieved with rest? Asking the patient to subjectively describe the dizziness is less useful in determining potential stroke. Rather, the sudden onset of dizziness in conjunction with stroke risk factors or signs and symptoms, including the HINTS exam (below) are more useful predictors.
2. Dysarthria – The slurred speech with PCS can have a more guttural quality that may be more difficult to detect to the untrained ear. Asking relatives/care givers about a change in the quality of the speech can be helpful.
3. Dysphagia – Does the patient have any change in ability to swallow? Are they choking on food or having fluid regurgitate though the nose?
4. Diplopia – Has the patient had the abrupt onset of double vision or a loss of vision in one eye or one part of vision?
5. Dystaxia – Does the patient have difficulty grasping objects or walking? Was this an abrupt change?
Patients who report the above symptoms require a careful assessment for clinical manifestations of PCS. Common abnormal exam findings involving the structures supplied by the posterior circulation are listed below.
Ocular movements: Have the patient follow your finger in an ‘H’ pattern to assess for any malalignment. The patient should be asked if they notice diplopia in any particular direction of gaze.
Nystagmus: Nystagmus is involuntary rhythmic jerking movements of the eyes and is present in up to 25% of posterior circulation strokes. Specific types of nystagmus are more concerning than others, in particular, direction changing nystagmus and vertical nystagmus. These can be quite challenging to differentiate on exam. There are many helpful YouTube videos that are available for learners.
Visual field testing: This is a critical part of the examination that is often omitted by physicians other than neurologists. The patient should be instructed to look at the examiner’s nose (and not at the examiner’s hands) while the examiner holds up fingers to be counted in each of the 4 visual quadrants, preferably with each eye tested separately. A visual field defect in the same area of each eye suggests an occipital lobe infarction may have occurred.
HINTS Exam (Head Impulse, Nystagmus, Test of Skew) : These bedside exams are highly sensitive for differentiating between central and peripheral nystagmus in patients who remain symptomatic with dizziness at the time of the evaluation. This exam is quiet comprehensive and beyond the scope of this article. There are many resources in print and online detailing the use of HINTS.
Finger-to-nose: Instruct the patient touch their nose with their index finger and then your finger with their arm fully outstretched (their elbow should extend completely). This should be repeated back and forth several times while the examiner looks for erratic movements or an inability to accurately hit the target.
Heel-to-Shin: Ask the patient to rub the heel of one foot up and down the shin of the opposing leg. Repeat for both sides. The patient should be able to do this smoothly. Heel-to-Shin is a measure of coordination of the legs.
Truncal Ataxia: Have the patient sit on the edge of the bed. Can they do this without assistance? Patient with cerebellar strokes will tend to fall to one side repeatedly.
Gait Ataxia: If a patient is vertiginous for any reason their gait will be unsteady. However, if a patient is no longer symptomatic with dizziness but still cannot walk in a straight line, this can be a sign of midline cerebellar dysfunction.
Vertebral Artery Dissection
Vertebral artery dissection (VAD) deserves special consideration. While VAD only accounts for about 2% of all strokes, it represents as much as 25% of strokes in young and middle aged patients . A missed VAD diagnosis can be devastating. Vertebral artery dissection can occur spontaneously, provoked, or with trauma. Traumatic dissection often involves a whiplash type mechanism. Provoking factors may include chiropractic manipulation, inverted yoga postures and other activities that involve prolonged extension of the neck (i.e. painting a ceiling) .
Patients with VAD can present with any of the previously described symptoms of posterior circulation strokes. They may also present with neck pain which radiates into the posterior head, or a primary complaint of headache . However, it is important to note that pain is not required to suspect this diagnosis as vertebral artery dissections may be painless. CT angiogram is an excellent study to quickly evaluate for dissection, as well as other vascular abnormalities that can cause stroke.
Common Mimics of Posterior Circulation Stroke
Benign Paroxysmal Positional Vertigo (BPPV): This common syndrome presents with recurrent, brief, severe vertigo provoked by head turning or rolling over in bed. It may be accompanied by nausea and vomiting. Of note is that a patient’s symptoms will resolve completely with rest but may return rapidly with head movement. Clarifying that the spinning sensation does not persist beyond a minute when the patient stays completely still is key to the diagnosis. A Dix-Hallpike maneuver can confirm the diagnosis and be transitioned into an Epley maneuver for a low cost and effective bedside treatment.
Acute Vestibular Neuritis (AVN): This is thought to be due to a viral infection involving the nerve from the inner ear to the balance centers of the brain. Occurs in all age groups, including children (though less common than in adults). Patients may describe dizziness or vertigo, disequilibrium or imbalance, and nausea and/or vomiting. The dizziness is constant and can last days. Any sudden movement will exacerbate symptoms and should not be confused with BPPV.
The HINTS exam is recommended in patients who remain symptomatic at the time of
presentation and is the best way to discriminate from PCS.
Migrainous vertigo: 25-50% of pts with migraine will experience episodes of vertigo and about 1/3 of these are during headache-free periods. Onset usually in the 40-50s. The vertigo is moderate or severe in intensity, may be accompanied by nausea and vomiting, is not associated with hearing loss or tinnitus, and can last from minutes to days. Symptoms are exacerbated by motion, loud noises and bright lights. As opposed to AVN, there is usually minimal or no spontaneous nystagmus. However, when nystagmus is present, it is often directed vertically (e.g. up beating or down beating) as it is a central source.
Meniere’s disease: Peak onset in 60s, but can occur anywhere from the 20s-80s. Incident in males is greater than or equal to females. Affects ~ 0.05% of the US population. Typical episode is preceded by a feeling of fullness in the ear. Fluctuating hearing loss and tinnitus may also be present. Acute attack: Vertigo tends to be severe and associated with nausea, vomiting and imbalance with an acute reduction in hearing lasting hours followed by a feeling of exhaustion and needing to sleep. Patients tend to be highly sensitive to visual stimuli during the attacks (i.e. the ride in was awful). Attacks are usually separated by weeks-months or even years and usually last days.
Patients presenting with the discussed signs and symptoms, especially those with vascular risk factors, should engender a high index of suspicion for PCS. Neither blood tests nor brain imaging are cost-effective when applied to patients without discrimination.
A thorough history focusing on the onset and duration of symptoms, presence of any triggers and associated symptoms, and risk factors should direct further diagnostic testing. Labs to consider when evaluating for conditions that can mimic a posterior circulation stroke include point of care glucose, comprehensive metabolic panel, complete blood count, drug levels (especially for patients on anticonvulsants), thyroid function tests, troponin, carbon monoxide level, drug toxicology screen, blood alcohol level and an electrocardiogram.
For patients suspected of having a stroke, urgent imaging and assessment for candidacy for thrombolysis is essential. A non-contrast head CT has a low sensitivity for acute ischemic stroke but is necessary for ruling out acute hemorrhagic stroke and can identify other pathologies such as a brain tumor. CT angiography of the head and neck should be obtained with the initial non-contrast head CT to evaluate for large vessel occlusion, high-grade stenosis and atherosclerotic or other vascular disease, including arterial dissection. Magnetic Resonance Imaging (MRI) is an excellent imaging option with a much higher sensitivity for stroke than CT and CTA; However, when obtained within the first 24 hours of symptom onset, MRI has been associated with a 15-20% false negative rate in patients with small posterior circulation infarctions . MRI is resource intensive, expensive, time consuming and not all patients can undergo MRI due to metal implants or clinical severity. Its use should be reserved for patients who have vascular risk factors or risk factors or symptoms of dissection with sudden onset unprovoked symptoms of more than one of the 5D’s (dizziness, diplopia, dysphagia, dysarthria, dystaxia).
Treatment can be quite variable depending on the type and underlying cause of the stroke. In the acute setting, treatment may include fibrinolysis and/or mechanical thrombectomy. Systemic anticoagulation is occasionally still utilized in the acute setting of arterial dissection and in the sub-acute stage for patients with atrial fibrillation or other high-risk cardiac sources of embolism. Dual antiplatelet therapy is recommended for patients with TIA, minor stroke or significant atherosclerotic disease regardless of anterior vs. posterior site of ischemia. Single antiplatelet therapy is appropriate for others.
There is a significant focus on preventing future strokes by optimizing modifiable risk factors. This is accomplished by medications to control hypertension, hyperlipidemia and diabetes and lifestyle modification around obesity, smoking cessation and sedentary lifestyle. Ultimately, the most important part of treatment for a posterior circulation stroke is early recognition and correct diagnosis.
Take Home Points
Prehospital Clinicians/EMS - Consider evaluating a patient with stroke like signs and symptoms for the 5Ds – Dizziness, Dysarthria, Dysphagia, Diplopia, and Dystaxia. If any of these are present and you are concerned for stroke, target transport to the most appropriate facility with pre-notification of possible stroke patient. Utilize strong communication with medical control to help guide treatment and transport decisions. Do not forget about the possibility of arterial dissection in young patients who present with severe neck pain and stroke like symptoms, especially if they report preceding trauma or provocation.
Triage Nursing – For walk-in patients, or patients arriving via EMS without pre-notification but with neurological symptoms, completing a BEFAST screen to help identify potential stroke patients early. If any one item on the BEFAST screen is positive, this should prompt an immediate Emergency Medicine provider evaluation for stroke.
Emergency Medicine Physicians and APPs - Ask these patients about the 5Ds – Dizziness, Dysarthria, Dysphagia, Diplopia, and Dystaxia. Be skilled in how to perform an appropriate neurological examination, including the HINTS exam, on patients who present with symptoms concerning for posterior circulation stroke. Patients with suspected stroke require expedient labs and imaging including head CT and CTA head and neck. Eligibility for thrombolysis should be assessed and expert consultation involved early for any potential treatment-eligible stroke.
In summary, PCS occurs less frequently than stroke in the anterior circulation and are more commonly missed given their unique features, challenging presentation and symptoms that mimic other common problems.
BEFAST screening questions can help identify potential stroke patients for rapid provider assessment. Presence of one or more of the 5 D’s raises concern for PCS. Emergency medicine providers must have the skills to perform an appropriate examination to quickly identify possible stroke patients, especially if patients are candidates for thrombolysis. Urgent imaging including a CT and CT angiogram should be performed in any patient suspected of having an acute stroke to give patients the best chances for correct diagnosis and management.
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