Editing Thrombosis (section)

==== Natural history ====
[[Fibrinolysis]] is the physiological breakdown of blood clots by enzymes such as [[plasmin]].{{cn|date=February 2025}}

Organisation: following the thrombotic event, residual vascular thrombus will be re-organised histologically with several possible outcomes. For an occlusive thrombus (defined as thrombosis within a small vessel that leads to complete occlusion), [[wound healing]] will reorganise the occlusive thrombus into collagenous [[scar]] tissue, where the scar tissue will either permanently obstruct the vessel, or contract down with [[myofibroblast]]ic activity to unblock the [[lumen (anatomy)|lumen]]. For a mural thrombus (defined as a thrombus in a large vessel that restricts the blood flow but does not occlude completely), histological reorganisation of the thrombus does not occur via the classic [[wound healing]] mechanism. Instead, the [[platelet-derived growth factor]] degranulated by the clotted [[platelet]]s will attract a layer of [[smooth muscle]] cells to cover the clot, and this layer of mural smooth muscle will be vascularised by the blood inside the vessel lumen rather than by the [[vasa vasorum]].{{citation needed|date=November 2021}}

Ischemia/infarction: if an arterial thrombus cannot be lysed by the body and it does not embolise, and if the thrombus is large enough to impair or occlude blood flow in the involved artery, then local [[ischemia]] or [[infarction]] will result. A [[venous thrombosis|venous thrombus]] may or may not be ischemic, since veins distribute deoxygenated blood that is less vital for cellular metabolism. Nevertheless, non-ischemic venous thrombosis may still be problematic, due to the swelling caused by blockage to venous drainage. In [[deep vein thrombosis]] this manifests as pain, redness, and swelling; in [[retinal vein occlusion]] this may result in [[macular oedema]] and [[visual acuity]] impairment, which if severe enough can lead to blindness.{{cn|date=February 2025}}