Stellenwert der CT-Perfusion für die Therapie des Schlaganfalls

Zusammenfassung

Moderne Mehrzeilen-CT-Scanner bieten die Möglichkeit einer multimodalen CT-Bildgebung mit einer nativen CT, einer CT-Angiografie und einer CT-Perfusion. Ein 64-Zeilen-CT ermöglicht eine Scanstrecke von 4 cm, zur Darstellung des gesamten zerebralen Parenchyms ist ein 128- bis 256-Zeilen-CT-Scanner erforderlich. Der routinemäßige Einsatz der Perfusions-CT erfordert eine Optimierung des Scan-Protokolls zur Reduktion der Strahlendosis. Bei optimiertem Protokoll sind von einer CT-Perfusion keine deterministischen Strahlenschäden zu befürchten. Die CT-Perfusionsbildgebung erhöht die Detektionsrate von ischämischen Schlaganfällen im Vergleich zur Nativ-CT +/– CT-Angiografie. Dies betrifft insbesondere die Detektion kortikaler, peripherer Ischämien. Die Aussagekraft bezüglich lakunärer und infratentorieller Infarkte bleibt eingeschränkt. Die Perfusions-CT erlaubt eine Abschätzung der Kollateralsituation bei akutem Gefäßverschluss. Verlässliche Schwellenwerte der Perfusionsparameter zur Bestimmung des bereits irreversibel geschädigten Kerns der Ischämie und der Penumbra liegen für die CT-Perfusion nicht vor, zumal die Berechnung der Perfusionskarten von der Gerätetechnik und dem Postprocessing-Algorithmus abhängt. Eine Vielzahl von Studien sprechen aber dafür, dass eine Minderung des zerebralen Blutvolumes (CBV) von unter 2 ml/100 g mit großer Wahrscheinlichkeit den Kern der Ischämie darstellt. Eine ausgedehnte CBV-Läsion wird als ungünstiger Prädiktor für das Stroke-Outcome angesehen auch bei erfolgreicher Rekanalisation. Wesentlicher Faktor aus der CT-Bildgebung zur Indikationsstellung einer Reperfusionstherapie bleibt das Ausmaß der Frühhypodensitäten in der Nativ-CT. Das Perfusions-CT erhöht aber die diagnostische und therapeutische Sicherheit in der Akutsituation und erlaubt ähnlich wie das Schlaganfall-MRT die Definition von Risikogewebe nach dem Mismatch-Konzept. Weitere Erkenntnisse über die Validität der Perfusionsparameter werden im Rahmen der aktuellen Thrombektomiestudien zu erwarten sein.

Abstract

Modern multislice CT scanners enable multimodal protocols including non-enhanced CT, CT angiography, and CT perfusion. A 64-slice CT scanner provides 4-cm coverage. To cover the whole brain, a 128 – 256-slice scanner is needed. The use of perfusion CT requires an optimized scan protocol in order to reduce exposure to radiation. As compared to non-enhanced CT and CT angiography, the use of CT perfusion increases detection rates of cerebral ischemia, especially small cortical ischemic lesions, while the detection of lacunar and infratentorial stroke lesions remains limited. Perfusion CT enables estimation of collateral flow in acute occlusion of large intra- or extracranial arteries. Currently, no established reliable thresholds are available for determining infarct core and penumbral tissue by CT perfusion. Moreover, perfusion parameters depend on the processing algorithms and the software used for calculation. However, a number of studies point towards a reduction of cerebral blood volume (CBV) below 2 ml/100 g as a critical threshold that identifies infarct core. Large CBV lesions are associated with poor outcome even in the context of recanalization. The extent of early ischemic signs on non-enhanced CT remains the main parameter from CT imaging to guide acute reperfusion treatment. Nevertheless, perfusion CT increases diagnostic and therapeutic certainty in the acute setting. Similar to stroke MRI, perfusion CT enables the identification of tissue at risk of infarction by the mismatch between infarct core and the larger area of critical hypoperfusion. Further insights into the validity of perfusion parameters are expected from ongoing trials of mechanical thrombectomy in stroke.

Schlüsselwörter

Computertomografie - Perfusion - akuter Schlaganfall

Keywords

computed tomography (CT) - perfusion - acute stroke

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