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ASPECT Scoring to Estimate >1/3 Middle Cerebral Artery Territory Infarction

  • Bart M. Demaerschalk (a1), Brian Silver (a2), Edward Wong (a3), Jose G. Merino (a4), Arturo Tamayo (a5) and Vladimir Hachinski (a6)...

Abstract:

Purpose:

To compare the inter-observer reliability of Alberta Stroke Programme Early CT Scoring (ASPECTS) with the ICE (Idealize-Close-Estimate) method of estimating > 1/3 middle cerebral artery territory (MCAT) infarction amongst stroke neurologists and to determine how well ASPECT Scoring predicts > 1/3 MCAT infarctions in acute ischemic stroke (AIS).

Background:

The European Cooperative Acute Stroke Study suggested that > 1/3 involvement of the MCAT on early CT scan was a risk factor for symptomatic intracerebral hemorrhage (SICH) following treatment with tissue plasminogen activator (tPA) for AIS but, in the absence of a systematic method of estimation had poor interobserver reliability (Kappa 0.49). The ICE method was developed to standardize the approach to estimating early MCAT infarct size and has very good interobserver reliability (Kappa 0.72). ASPECTS has comparable interobserver reliability and is reported to predict both neurological outcome and SICH.

Methods:

Five stroke neurologists were tested with 40 AIS CT scans. Each performed blinded independent assessments of early ischemic changes with both ASPECTS and ICE. The reference standard was majority opinion of 1/3 MCAT determination of five neuroradiologists. A receiver operator curve (ROC) was constructed and likelihood ratios (LR) were calculated. Chance corrected agreement (kappa) and chance independent agreement (phi) were calculated for both methods, and analysis of variance was used to calculate reliability by intraclass correlation coefficient (ICC) for ASPECTS.

Results:

The LR for a positive test (> 1/3 MCAT) were extremely large and conclusive (approaching infinity) for ASPECTS of 0-3; were large and conclusive (30, 20, and 10) for ASPECTS of 4, 5, and 6 respectively; was an unhelpful 1 for ASPECTS of 7, and were again extremely large and conclusive (approaching zero) for ASPECTS of 8-10. A ROC plot supported an ASPECTS cutoff of < 7 as best for 1/3 MCAT estimation (94% sensitivity and 98% specificity). Kappa and Phi statistics were moderately good for both ASPECTS and ICE (0.7). ICC for ASPECTS was 0.8.

Conclusion:

When experienced stroke neurologists utilize a formalized method of quantifying early ischemic changes on CT, either ASPECTS or ICE, the interobserver agreement and reliability are satisfactory. ASPECTS allows for a strong and conclusive estimation of the presence of 1/3 MCAT involvement and a cutoff point of < 7 results in best test performance.

RÉSUMÉ: Objectif:

Comparer la fiabilité interobservateur, chez des neurologues spécialisés dans l’accident vasculaire cérébral (AVC), pour le score ASPECT et la méthode ICE (idealize-closeestimate) d’estimation de l’infarctus >1/3 du territoire de l’artère cérébrale moyenne (TACM) et déterminer si le score ASPECT prédit bien l’infarctus >>1/3 du TACM dans l’AVC ischémique aigu.

Contexte:

Selon les données du European Cooperative Acute Stroke Study, l’atteinte >1/3 du TACM à la tomodensitométrie réalisée tôt après l’événement serait un facteur de risque de l’hémorragie intracérébrale symptomatique (HICS) suite au traitement par l’activateur du plasminogène tissulaire (t-PA) dans l’AVC ischémique aigu, mais sa fiabilité interobservateur serait médiocre (kappa 0,49) en l’absence d’une méthode systématique d’estimation. La méthode ICE a été développée pour standardiser la démarche d’estimation de la taille de l’infarctus du TACM en phase précoce et elle a une très bonne fiabilité interobservateur (kappa 0,72). ASPECTS possède une fiabilité interobservateur comparable et on considère qu’il peut prédire tant l’issue neurologique que l’HICS.

Méthodes:

Cinq neurologues spécialistes de l’AVC ont participé à l’étude de 40 tomodensitométries d’AVC ischémique aigu. Chaque neurologue a fait une évaluation indépendante des changements ischémiques précoces, à l’aveugle, au moyen du score ASPECT et de la méthode ICE. Le standard de référence était l’opinion majoritaire de 1/3 TACM determine par cinq neuroradiologistes. Une courbe ROC a été établie et des rapports de vraisemblances ont été calculés. La concordance aléatoire corrigée (kappa) et la concordance aléatoire indépendante (phi) ont été calculées pour les deux méthodes et une analyse de variance a été utilisée pour estimer la fiabilité au moyen du coefficient de corrélation intraclasse pour ASPECTS.

Résultats:

Les rapports de vraisemblances pour un test positif (>1/3 TACM) étaient extrêmement élevés et concluants (près de l’infini) pour des scores ASPECT de 0 à 3; ils étaient élevés et concluants (30, 20 et 10) pour des scores ASPECT de 4, 5 et 6 respectivement; ils étaient de 1 et inutiles pour un score ASPECT de 7 et de nouveau extrêmement élevés et concluants (près de zéro) pour des scores ASPECT de 8 à 10. La courbe ROC suggérait qu’un point de coupe ASPECTS de moins de sept était optimal pour estimer 1/3 TACM (sensibilité de 94% et spécificité de 98%). Les statistiques kappa et phi étaient assez bonnes pour ASPECTS et ICE (0,7). Le coefficient de corrélation intraclasse était de 0,8.

Conclusions:

Quand des neurologues possédant une vaste expérience de l’AVC utilisent une méthode standard reconnue, soit ASPECTS ou ICE, pour l’évaluation quantitative des changements précoces observés à la tomodensitométrie de l’AVC ischémique aigu, la concordance interobservateur et la fiabilité en sont améliorées et sont satisfaisantes. ASPECTS permet un estimé robuste et concluant de la presence de l’atteinte de 1/3 TACM et un point de coupe < 7 donne la meilleure performance.

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Copyright

Corresponding author

Mayo Clinic College of Medicine, Department of Neurology, Mayo Clinic Arizona, 13400 East Shea Boulevard, Scottsdale, AZ, 85259, USA

References

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