Introduction
Posterior circulation infarction accounts for 20% or more of all acute ischemic stroke cases [
5,
11,
14]. Posterior circulation acute ischemic stroke is characterized by mild symptoms of transient neurological attacks of nausea, vomiting, dizziness, and vertigo and moderate to severe symptoms of headache, altered consciousness, bulbar signs of slurred speech and dysphagia, weakness, sensory dysesthesia, and ataxia [
16,
22]. However, patients with posterior circulation stroke may exhibit a delayed time to presentation, compared with patients with anterior circulation stroke [
4]. Until now, no reliable method has been established for predicting the functional outcome of posterior circulation ischemic stroke.
Routine examinations for patients with stroke include clinical assessment using the National Institutes of Health Stroke Scale (NIHSS) and brain imaging. In regional community hospitals and large medical center hospitals, noncontrast brain computed tomography (CT) remains the most widely performed brain-imaging technique because it rapidly detects hemorrhage, is readily available, and saves time, which are crucial for tissue plasminogen activator administration [
9]. Despite being widely used, noncontrast CT is not the optimal method of comprehensively assessing posterior circulation infarction [
9].
Brain magnetic resonance imaging (MRI) has advantages of visualization of the posterior fossa, detection of hyperacute infarct lesions within 3–6 h by using a diffusion-weighted imaging (DWI) sequence [
7,
9,
17], and a high rate of agreement among physicians for use in the detection of early ischemic lesions [
6]. Over the past decade, the posterior circulation Alberta stroke program early computed tomography score (PC-ASPECTS)—a 10-point scoring tool similar to the anterior circulation ASPECTS [
3] and having advantages of simplicity and easy application—has been used to evaluate posterior circulation infarction [
18,
19,
23]. The extent of early infarction may help physicians predict a patient’s functional outcome.
Although proven to accurately predict the outcome of stroke [
1], the NIHSS is weighted for anterior circulation symptoms [
10]. Our main goal was to investigate whether the PC-ASPECTS with DWI sequences within 36 h of stroke onset as well as the baseline NIHSS corresponds to the functional outcomes of our Chinese patients.
Discussion
The PC-ASPECTS and baseline NIHSS help physicians predict an unfavorable outcome, both individually and in combination. In addition to the effect of aging, a PC-ASPECTS of ≤ 7 was the strongest predictor of unfavorable outcomes in our univariate and multivariate models.
A large percentage of patients with a PC-ASPECTS of ≤ 7 had unfavorable outcomes, and this finding is compatible with that of a previous study revealing that a PC-ASPECTS of < 8 was very unlikely to predict favorable outcomes in basilar artery occlusion [
19]. The age stratification analysis results reveal that in patients younger than 70 years, the PC-ASPECTS was not a significant predictor of unfavorable outcomes. This result can be attributed to the few young patients with unfavorable outcomes and numerous young patients with acute medullary infarction. The patients with acute medullary infarction were later confirmed as having vertebral artery dissection. In fact, vertebral artery dissection has been recognized as a frequent cause of posterior circulation stroke among young adults [
13,
24]. The PC-ASPECTS cannot be accurately assessed in medullary infarction.
On the ROC curve, the AUC determined for the PC-ASPECTS was slightly larger than that for the baseline NIHSS for patients with low NIHSS scores. These patients had a clinical presentation that included symptoms of dizziness, vertigo, neck pain, headache, and signs of Horner syndrome. Although these symptoms and signs are necessary for an acute stroke diagnosis, the NIHSS scoring system does not provide a score for them. Because the NIHSS is weighted more toward anterior circulation symptoms and signs [
10], the PC-ASPECTS or MRI is more suitable for the diagnosis and assessment of posterior circulation ischemic stroke [
23], particularly in older patients who may not be able to adequately describe their symptoms. Therefore, a combination model of the PC-ASPECTS and baseline NIHSS had an additive effect because the PC-ASPECTS is more powerful in detecting unfavorable outcomes with posterior circulation acute ischemic stroke with an NIHSS score of 0–1 (Supplemental Tables II and III).
For imaging of posterior circulation acute ischemic stroke, MRI with DWI sequences is considered the gold standard for diagnosis [
6,
7,
9,
12]. However, in some community hospitals, only CT is available for acute stroke imaging. Nevertheless, non-contrast CT is not recommended for PC-ASPECTS scoring for predicting functional outcomes due to its low sensitivity (0.46, 95% CI 0.37–0.55) to posterior circulation ischemic change [
19]. Alternatively, perfusion CT [
15] or CT angiography source imaging (CTASI) [
18,
19] improved the outcome prediction and facilitated the delineation of the ischemic core when applied to the PC-ASPECTS. For patients with basilar artery occlusion, a PC-ASPECTS of < 8 on perfusion CT [
15] and CTASI [
18,
19] has been reported to more likely have unfavorable functional outcomes, which is compatible with our result obtained using MRI as an imaging modality. According to our review of the relevant literature, for patients with small artery occlusion in the posterior circulation, no study has investigated whether the PC-ASPECTS is suitable for functional outcome prediction with CT as an imaging modality.
The present study has limitations. Our hospital is located among an aging community; thus, more than half of our patients were older than 70 years. Because these elders had a favorable clinical condition, they were promptly transferred to long-term care facilities under the post-acute care policy in Taiwan [
8]. Moreover, because of the retrospective study design involving the review of our own hospital’s stroke registry database, the study was prone to sampling older patients, and data on longitudinal records of functional outcomes after 3 months were unavailable. Nevertheless, our hospital is the only large-scale hospital in the southernmost district of Taipei, Taiwan. Most patients with acute stroke living in southern Taipei usually present to our hospital for admission. With approximately 11.7‰ of the total population in Taiwan, the estimated incidence of acute ischemic stroke is 454 person-years in our district. Because our registry comprised a total of 549 patients from 2015 to 2016, we assumed that more than half of the patients with acute ischemic stroke in this district were admitted to our hospital. We thus consider our enrolled patients as a fairly representative sample of the whole population.
In conclusion, both the PC-ASPECTS and NIHSS help clinicians predict functional outcomes. The PC-ASPECTS is more reliable than the NIHSS in minor stroke prediction. We determined that the combination of the PC-ASPECTS and NIHSS (AUC 0.7685, p < 0.0001) has an addictive effect in predicting the functional outcomes of patients with posterior circulation stroke.