Acute ischemic stroke is a time-sensitive medical emergency requiring immediate assessment. When a major blood vessel is blocked, brain tissue begins to die, necessitating rapid evaluation of the damage. Medical professionals use computed tomography (CT) scans to quickly visualize the brain and estimate the injury’s extent. This rapid imaging is crucial for determining if a patient can safely receive reperfusion therapies, which aim to restore blood flow. A standardized, quick method to assess the brain’s condition led to the development of a specific scoring system.
Defining the Alberta Stroke Program Early CT Score
The standardized method used to evaluate initial stroke damage in the anterior circulation is the Alberta Stroke Program Early CT Score (ASPECTS). This 10-point system quantifies the severity and location of early ischemic changes—signs of oxygen deprivation—within the territory supplied by the middle cerebral artery (MCA). ASPECTS is applied to non-contrast computed tomography (NCCT) scans, which are the fastest imaging studies available upon a patient’s arrival. Early ischemic changes can appear as subtle signs, such as a loss of distinction between gray and white matter or focal swelling.
ASPECTS provides a simple, reproducible method for healthcare providers to quickly and consistently assess the amount of brain tissue affected by the stroke. The score was originally developed to standardize the evaluation of early damage before administering intravenous thrombolysis (clot-busting drugs). By translating complex visual information from the CT scan into a single number, ASPECTS allows for a standardized way to compare patient severity across different medical centers and clinical trials. This quantitative approach is more reliable than earlier methods that attempted to estimate the volume of damaged tissue.
The Anatomical Regions Used in Scoring
The ASPECTS scoring system divides the MCA territory into 10 specific anatomical regions that are particularly vulnerable to stroke damage. These 10 regions are assessed across two standard axial CT slices: one at the level of the basal ganglia and one immediately superior to it. Scoring begins with a maximum of 10 points, representing a completely normal brain scan with no signs of early ischemia.
The 10 regions include four deep subcortical structures and six cortical areas. The deep structures are:
- Caudate nucleus
- Lentiform nucleus
- Internal capsule
- Insular cortex
The six cortical areas (M1 through M6) cover the frontal, temporal, and parietal lobes supplied by the MCA. For every region showing evidence of early ischemic change (e.g., hypo-attenuation or swelling), one point is subtracted from the initial score of 10. This subtractive process means the final score reflects the number of unaffected areas, showing an inverse relationship with the extent of damage.
Interpreting the Numerical Score
The final ASPECTS score provides direct information about the extent of potentially damaged brain tissue. A high score, such as 9 or 10, suggests minimal or no early ischemic changes are visible on the scan. This generally correlates with a smaller area of initial damage and a better predicted functional outcome for the patient. A perfect score of 10 means the CT scan appears completely normal in all 10 assessed regions.
Conversely, a lower score signifies a more extensive area of the MCA territory is already showing signs of injury. A score of 0 indicates that ischemic changes are visible in all 10 regions, representing a large and severe stroke with a poor prognosis. Scores of 7 or less are often associated with a significantly worse functional outcome at three months, even following treatment. A key concern with lower scores is the increased risk of symptomatic intracranial hemorrhage (bleeding into the brain tissue) if the patient receives certain reperfusion therapies.
Guiding Acute Stroke Treatment
The ASPECTS score plays a significant role in decision-making for acute stroke interventions. For patients with a large vessel occlusion, the score helps determine eligibility for treatments like intravenous thrombolysis and mechanical endovascular thrombectomy. Intravenous thrombolysis is considered less effective and carries a higher risk of symptomatic bleeding when the ASPECTS score is low, particularly below 8. Patients scoring 7 or less face a considerably higher risk of complications and poor functional results following thrombolysis.
For mechanical thrombectomy (physical clot removal), a high ASPECTS score is generally preferred to ensure the best chance of a favorable outcome. Many treatment guidelines recommend that patients considered for thrombectomy within the first six hours of symptom onset should have an ASPECTS of 6 or higher, though this threshold can vary. A low score, particularly 5 or less, suggests that a large amount of brain tissue is already infarcted. This reduces the potential benefit of clot removal and increases the likelihood of a high mortality rate. However, ASPECTS is not the sole determinant; it is considered alongside other factors, including the patient’s clinical presentation, the time since stroke onset, and the results of other advanced imaging studies.