Hematological abnormalities in stroke

It has been estimated that only about 4% of all ischemic strokes are directly caused by an underlying, well-defined hematological abnormality [1], but this represents but a fraction of the important pathological interactions between blood and blood vessels that result in both hemorrhagic and thrombotic stroke. Hematological aspects of neurology are evolving to include disorders of hemostatis and thrombosis, also encompassing neurological symptoms produced as a result of malignancy or by compromise of the immune system. The diseases and conditions affecting hemostasis and thrombosis with respect to stroke can be divided into abnormalities that produce bleeding and those that cause thrombosis, although this distinction is not always clear-cut. It is also useful to evaluate abnormalities in plasma factors separately from the cellular or organelle elements of blood, such as platelets that are associated with a risk of stroke. These hemorheological considerations are particularly important with respect to the cerebral microcirculation or during episodes of cerebral hypoperfusion or ischemia when there is coexisting impaired collateral circulation or severe large vessel stenosis. The following discussion focuses on the common bleeding, thrombotic and hemorheological conditions that contribute to an increased risk of stroke. Within this framework, certain specific hematological disorders and syndromes are described in some detail.