Haemorrhagic transformation in acute ischaemic stroke following thrombolysis therapy: classification, pathogenesis and risk factors.

Haemorrhagic transformation of cerebral infarction is a common and potentially serious occurrence following acute ischaemic stroke. Though often a "natural" evolution, particularly in acute embolic stroke, haemorrhagic transformation is a prime concern with the use of thrombolytic therapy for acute ischaemic stroke. The severity of haemorrhage may range from a few petechiae to a large haematoma with space occupying effect. The pathogenesis of haemorrhagic transformation is not well established, though ischaemia and reperfusion have been proposed to cause disruption of the blood-brain barrier leading to extravasation of blood. At the molecular level, free radicals and proteolotic enzymes (metalloproteinases) may cause tissue injury. Studies have identified a number of clinical, radiological, and biochemical parameters that may serve as potential predictors of increased risk for haemorrhagic transformation. The knowledge of these factors may help in improving patient selection for thrombolytic therapy.