Use of the Alberta Stroke Program Early CT Score (ASPECTS) for assessing CT scans in patients with acute stroke

Abstract

Background and purpose: Clinicians are insecure reading CT scans by using the one-third rule for acute middle cerebral artery stroke (1/3 MCA rule) before treating patients with recombinant tissue plasminogen activator. The 1/3 MCA rule is a poorly defined volumetric estimate of the size of cerebral infarction of the MCA. A 10-point quantitative topographic CT scan score, the Alberta Stroke Program Early CT Score (ASPECTS), is described and illustrated. A sharp increase in dependence and death occurs with an ASPECTS of 7 or less. We describe how to use ASPECTS and why it works with CT scans obtained on all commonly used axial baselines. We also describe interobserver reliability among clinicians from different specialties and with different experience in reading CT scans in the context of acute stroke.

Methods: The six physicians who developed ASPECTS answered a questionnaire on precisely how they interpret and use ASPECTS. The ASPECTS areas as interpreted by these physicians were compared with one another and with standards in the literature. kappa statistics were used to assess the interobserver reliability of ASPECTS versus the 1/3 MCA rule.

Results: The exact methods of interpretation varied among the six individual observers, with either a 3:3 or 4:2 split on the specific questions. The overall interobserver agreement was good compared with that of the 1/3 MCA rule. Normal anatomic vascular and interobserver variations explain why ASPECTS can be applied with different CT axial baselines.

Conclusion: ASPECTS is a systematic, robust, and practical method that can be applied to different axial baselines. Clinician agreement is superior to that of the 1/3 MCA rule.

fig 1.

ASPECTS study form and MCA variants. A and B, Right hemisphere, observer variations: lower and upper ASPECTS slices show as shaded areas the minimal and maximal variations in size of the cortical areas of the MCA (M1–M6) chosen by six expert observers. Left hemisphere, ASPECTS study form: A = anterior circulation; P = posterior circulation; C = caudate head; L = lentiform nucleus; IC = internal capsule; I = insular ribbon; MCA = middle cerebral artery; M1 = anterior MCA cortex; M2 = MCA cortex lateral to insular ribbon; M3 = posterior MCA cortex; M4, M5, and M6 are anterior, lateral, and posterior MCA territories, respectively, approximately 2 cm superior to M1, M2, and M3, respectively, rostral to basal ganglia. C and D, Cortical MCA area variations with change of baseline. In the right hemisphere, the baseline is parallel to the inferior OML; in the left hemisphere, the baseline is the superior OML. E and F, Normal vascular variations in MCA size on the two ASPECTS slices. The right hemisphere shows the larger normal variations described by van der Zwan (light shading). The left hemisphere of each shows the smaller, textbook , variations (dark shading).

fig 2.

CT scans in a 65-year-old woman with left-sided hemiplegia, hemianopia, and neglect less than 3 hours after symptom onset. A and B, Baseline CT scans show hypoattenuation with swelling and effacement in regions M1, M2, insula (I), M4, and M5 (ASPECTS = 5). Intravenous thrombolysis was administered. C and D, Follow-up CT scans show a large area of hypoattenuation involving much of the MCA territory. The patient was dependent at 3 months.

fig 3.

CT scans in a 68-year-old man with global aphasia and an NIHSS score of 7. A and B, Baseline scans show a region of hypoattenuation involving the anterior insula (I) and hypoattenuation and swelling in the M2 region (ASPECTS = 8). C and D, Follow-up scans confirm the area of infarction. The patient made a full neurologic recovery.

fig 4.

CT scans in a 79-year-old woman with left-sided weakness and NIHSS score of 15, 2 hours after symptom onset. A and B, Baseline CT scans show hypoattenuation of the right lentiform nucleus (L) and caudate nucleus (C) on two axial cuts (ASPECTS = 8). C and D, Follow-up scans at 24 hours confirm the area of infarction. The patient made a full neurologic recovery after thrombolysis.

fig 5.

Maximal variation of ASPECTS sections with baseline alteration. The two ASPECTS sections with two different baselines: superior OML (solid line) and parallel two slices, and inferior OML (dashed line) and parallel two slices. The respective upper and lower slices are divided into thirds. Cuts are through the basal ganglia and roof of the lateral ventricle to show that disagreement is not more than 2 cm