CT Perfusion In Acute Ischemic Stroke
Abstract
CT perfusion (CTP) has been applied increasingly in research of ischemic stroke. However, in clinical practice, it is still a relatively new technology. For neurologists and radiologists, the challenge is to interpret CTP results properly in the context of the clinical presentation. In this article, we will illustrate common CTP patterns in acute ischemic stroke using a case-based approach. The aim is to get clinicians more familiar with the information provided by CTP with a view towards inspiring them to incorporate CTP in their routine imaging workup of acute stroke patients.
Favorable Pattern
This pattern on CT perfusion (CTP) is characterized by a small infarct core and a large penumbra. It is typically observed in patients with a proximal (M1 or M2) segment occlusion of the middle cerebral artery (MCA). Patients with this pattern have a higher potential to benefit from thrombolytic treatment if reperfusion is achieved in a timely manner. Successful early reperfusion can lead to the salvage of the penumbra, resulting in a smaller final infarct and good clinical recovery
Unfavorable Pattern
This pattern shows a large infarct core and a small penumbra on CTP. It is also commonly seen in MCA occlusion. Patients with this pattern have a limited room for clinical improvement, and treatment is likely to be futile and potentially harmful even if reperfusion is achieved. This pattern can be observed early after stroke onset and challenges the current time-based treatment guidelines
Intermediate CTP Pattern
This refers to patients who present with a moderate-sized infarct core and a moderate-sized penumbra on CTP. For these patients, the extent of benefit from reperfusion treatment is less clear, and further studies are needed to define cut-off points for potential benefit.
Malignant CTP Pattern
This pattern indicates an extensive severely ischemic lesion, particularly in the anterior circulation, and is associated with poor outcome regardless of treatment. While most information about malignant patterns comes from MR research (large DWI lesion or large perfusion lesion with severe delay), a large core on CTP (>53 mL in one study) has been associated with a higher risk of intracranial hemorrhage. Reperfusion in such cases may even lead to worse outcomes
Lacunar Stroke
Caused by the occlusion of small penetrating arteries, lacunar lesions are typically small. While DWI is superior to CTP for detecting acute lacunar stroke due to its high spatial resolution, newer 320-slice CTP with whole brain coverage and thin slices has increased sensitivity. However, specificity remains lower due to noise, particularly in white matter. Delay Time (DT) maps may perform better in identifying these lesions. CTP might also be useful in predicting the progression of lacunar stroke based on the severity of hypoperfusion.
Posterior Circulation Stroke
These strokes can be clinically difficult to diagnose. With the advent of whole-brain-coverage CTP (like 320-slice scanners), CTP can now play a useful role in identifying posterior circulation ischemia and potentially the presence of a favorable penumbral pattern. However, the criteria for a favorable pattern may differ from anterior circulation strokes.
Reperfusion Prior to CTP
In cases where reperfusion occurs before or during CTP scanning (either spontaneously or after thrombolysis), the hemodynamic parameters on CTP may return to normal or even show hyperperfusion in the infarct area, leading to a "false normal" CTP. However, CTP source images (CTPSI) may still show early hypodensity. Recognizing this pattern is crucial to avoid misinterpreting CTP results and potentially withholding unnecessary thrombolytic treatment.
