Early ischaemic changes in the middle cerebral artery
Measured Factor Disease
- Symptomatic intracerebral hermorrhage
- Poor functional outcome
Measured Factor Detail
The Alberta Stroke Program Early CT Score (ASPECTS) determines a patient’s likelihood of poor functional outcomes after a stroke that appears to have clinically affected the middle cerebral artery. This test consists of looking at 10 different factors or regions available from a computed tomography (CT) scan. To compute the score, 1 point is subtracted from 10 for any evidence of early ischemic change for each of the defined factors or regions. This test depends on subtle CT findings; therefore, an experience radiologist should be consulted. ASPECT scores ≥ 8 indicate a greater chance for functional outcomes, whiles scores < 8 indicate a greater chance of poor outcomes.
Measured Factor Low Impact
- An ASPECT ≤7 suggests a higher risk of symptomatic intracerebral hemorrhage and greater likelihood of poor functional outcomes.
Measured Factor High Impact
- An ASPECT > 7 suggests a lower risk of symptomatic intracerebral hemorrhage and lower likelihood of poor functional outcomes.
- Critical Low: Score of 7 and below
- Normal: Score of 10
- Normal Adult Male: Score of 10
- Normal Adult Female: Score of 10
- Normal Geriatric Male: Score of 10
- Normal Geriatric Female: Score of 10
The presence of an old infarction is a limitation when using a narrowed window width setting in the CT scan because it interferes with the interpretation.
Study Validation 1
Article illustrating the method used in the ASPECTS test and how clinicians from varying levels of experience can use it to assess acute ischemic CT changes. ASPECTS is a 10-point quantitative topographic CT scan score that avoids having physicians estimate volumes from two-dimensional images. An ASPECTS score of 7 or less shows a higher risk of dependence and death, while a score greater than 7 demonstrates a lower risk. In this article patients from two different cities had CT individual scans performed for better definition and these scans were then interpreted using the ASPECTS method. The scores were determined from two standardized axial CT cuts. A score of 10 was considered normal, while a score of zero indicated diffuse ischemic involvement in the middle cerebral artery (MCA). A total of 6 clinicians, 3 neurologists and 3 neuroradiologists, were asked to interpret the CT using the ASPECTS score and were interviewed about their individual methods of interpretation. The interpretations were compared with one another and with other standards in literature, the inter-observer reliability for ASPECTS was also assessed vs the one-third rule for acute middle cerebral artery stroke (1/3 MCA rule) using k statistics. The interobserver agreement between the neurologists (k = 0.61 for 1/3 MCA rule and 0.85 for ASPECTS), neuroradiologists ( k= 0.52 and 0.89), and radiology residents (k = 0.64 and 0.71) were as reported. Overall the interobserver agreement across specialties was superior for ASPECTS (k = 0.56 – 0.83) than the 1/3 MCA rule (k = 0.20-0.51).
Study Validation 2
Retrospective study comparing different ASPECTS thresholds for CT perfusion (CTP) parameters versus noncontrast CT (NCCT) parameters to determine superiority. Patient population consisted of patients treated with consecutive tissue plasminogen activator (tPA) that presented with suspected acute stroke within 3 hours of onset and who underwent a CT stroke protocol. A total of 36 baseline acute stroke NCCT and CTP studies were reviewed by 3 neuroradiologists and ASPECTS scores were assigned. Follow-up NCCT ASPECTS and 90-day modified Rankin score (mRS) were radiologic and clinical reference standards; an mRS of 2 was a good outcome and 3 was a bad outcome. For all analyses, the statistical significance was determined by P < 0.05. NCCT ASPECTS scores of 7 and a cerebral blood volume threshold of 8 discriminated patients patients with poor follow-up scans (P<0.0002 and P=0.0001) and mRS < or = 2 (P=0.001 and P<0.001). Interobserver agreement had an intraclass correlation coefficient of 0.69. Cerebral blood volume ASPECTS sensitivity was 60%, specificity was 100%, positive predictive value was 100% and negative predictive value was 45%. Patients with an ASPECTS score <8 did not achieve good clinical outcomes. Overall, the cerebral blood volume ASPECTS was equivalent to NCCT at predicting outcomes.
Study Validation 3
A two-part retrospective cohort study evaluating the use of posterior circulation Acute Stroke Prognosis Early CT score (pc-ASPECTS) in predicting functional outcome in patients with basilar artery occlusion (BAO). Study consisted of two parts; part 1 tested the diagnostic and prognostic value of CT angiography source images (CTASI) in patients with clinically suspected vertebrobasilar ischemia, part 2 tested the prognostic value of CTASI in patients with acute BAO. Data was reported using standard descriptive statistics and the sensitivity, specificity, positive and negative predictive values were calculated for noncontrast CT (NCCT) and CTASI. The primary clinical outcome for patients with suspected vertebrobasilar ischemia (part 1) was independent functional outcome (mRS ≤2); and for patients with basilar artery occlusion (part 2) it was favorable functional outcome (mRS ≤3). Secondary outcome was death. The pc-ASPECTS values for discriminating favorable functional outcomes versus unfavorable were 8 and <8 respectively. Results for part 1 (functional outcomes) at 3 months indicated 71% (n=92) of patients were functionally independent with mRS ≤2, 18% (n=24) were functionally dependent with mRS 3 to 5, and 11% were deceased. Additionally, sensitivity for ischemic changes was better with CTASI compared to NCCT (65% [95% CI 57-73%] versus 46% [95% CI 37-55%], respectively). Pc-ASPECTS score on CTASI was shown to predict functional independence while NCCT did not (OR 1.58; P=0.005 versus 1.22; P=0.42, respectively). Results for part 2 demonstrated that for patients with BAO, 52% (12/23) of patients with a CTASI pc-ASPECTS score ≥8 and 4% (1/23) of patients with a CTASI pc-ASPECTS score <8 had a favorable functional outcome (RR 12.1; 95% CI 1.7-84.9). Moreover, at 3 months, 28% (n=13) of BAO patients had a favorable functional outcome (mRS ≤3), 26% (n=12) had an unfavorable functional outcome (mRS 4 to 5), and 46% (n=21) were deceased.
Study Additional 1
Review article focusing on summarizing the Alberta Stroke Program Early CT Score (ASPECTS) methodology. The article explains the rationale for the development of ASPECTS; the controversies regarding early ischemic changes (EIC) importance and the difficulties with the reliability of the 1/3 Middle Coronary Artery (MCA) rule. ASPECTS allot the MCA territory a total of 10 regions of interest and weights each region a set amount of points depending on their functional importance. Smaller structures (internal capsule, basal ganglia, and caudate regions) are given the same weight, while larger regions are given the same greater weight. To determine ASPECTS all axial cuts of the brain CT scan and early ischemic changes is defined as parenchymal hypo attenuation and focal swelling or mass effect. Once the data is available, to compute the ASPECTS a single point is subtracted from 10 for evidence of EIC in each of the 10 regions. A score of 10 reflects a normal CT scan, while a score of 0 reflects diffused ischemic involvement. Reliability of the 1/3 rule with ASPECTS dichotomized at >7 vs. ≤7 showed higher agreement (k=0.71-0.89) when compared to the 1/3 rule (k=0.52-0.64) among stroke neurologists, radiology trainees and experienced neuroradiologists. This review concludes that ASPECTS has not been proved to have higher reliability than the 1/3 rule. This review also summarized the utility of ASPECTS when applied to thrombolysis trials in which it successfully proved to be a strong predictor of functional outcomes.
Study Additional 2
A retrospective data review article describes the differences and similarities involved in the calculation of ASPECTS between an on-call radiology resident and expert raters. Study also sought to ascertain the appropriate window setting for early detection of acute ischemic stroke and interobserver agreement between interpreters. Data was collected from patients that presented with suspected acute ischemic stroke and underwent a non-contract CT (NCCT) scan and a computed tomography angiography (CTA) of the brain. Patients who had images with intracranial hemorrhage were excluded from the review. Descriptive statistical analysis was performed, categorical data expressed as percentages with continuous data expressed as mean or median, standard deviation and range. For interobserver agreement an ASPECTS >7 showed better clinical outcomes to intra-arterial treatment and an ASPECTS ≤7 showed worse clinical outcomes. Agreement among interpreters was assessed using Cohen’s kappa (k) coefficient (slight agreement was 0.00 – 0.2, fair was 0.21-0.40, moderate was 0.41-0.6, substantial was 0.61-0.8, almost perfect was 0.81-1.0) and Intraclass Correlation Coefficient (ICC). Results were based on a total of 43 patients that were included in the study. Using the Cohen’s k coefficient, the interobserver agreements for ASPECTS varied from 0.486 to 0.678 between two neuroradiologists and a neuroradiology fellow, and from 0.198 to 0.491 between two neuroradiologists and a senior radiology resident. The ICC among raters was very good when 8HU window width and 32 HU center level setting were used.
Study Additional 3
An international, multicenter, quasi-factorial, prospective, randomized, open-label trial evaluated the utility of the electronic Alberta Stroke Program Early CT Score (e-ASPECTS), an automated system for quantifying signs of infarction, in patients with acute ischemic stroke who received thrombolysis treatment. Outcomes were assessed by a blinded observer and the primary outcome was death or any disability defined by scores of 2-6 on the modified Rankin Scale (mRS). Secondary outcomes included death or major disability (mRS scores, 3-6) and death alone. All continuous variables were presented as mean ± SD or median and interquartile range. Categorical data was presented as frequencies in percent (%). Correlation between the e-ASPECTS and baseline neurological severity (National Institutes of Health Stroke Scale [NIHSS] score) was estimated using spearman correlation and statistical significance included two-sided P values (P<0.05). A total of 1480 images were included in the study for analyses of e-ASPECTS scores (median 9 [interquartile range, 8-10], 77% with good scores [range 8-10]). Lower e-ASPECTS scores were associated with increasing baseline NIHSS (r, -0.31, P<0.0001) and 90-day poor outcomes (modified Rankin Scale scores, 2-6; r, -0.27; P<0.001). In conclusion, the e-ASPECTS scores from thin CT slices (≤6mm) correlated with baseline neurological severity and independently predicted functional recovery and adverse outcomes.