Hemorrhagic transformation is due to the permeability disruption of the blood-brain barrier by matrix metalloproteinases and free radical pathway during ischemia and reperfusion.

According to the imaging, European Cooperative Acute Stroke Study trialists classified hemorrhagic transformation into four categories ¹:

• hemorrhagic infarction type 1 (HT-1): small petechiae along the margin of infarct
• hemorrhagic infarction type 2 (HT-2): confluent petechiae within infarct without space occupying effect
• parenchymal hematoma type 1 (PH-1): hematoma 30% or less with some space occupying effect
• parenchymal hematoma type 2 (PH-2): dense hematoma >30% with space occupying effect or any hemorrhagic lesion outside the infarcted area