Temporal Profile of Transient Ischemic Attack (TIA) and Completed Infarction (CI)

Subarachnoid hemorrhages are usually caused by rupture of an aneurysm that breaks, spilling blood instantly into the spinal fluid. The sudden release of blood under arterial pressure increases intracranial pressure, causing severe sudden-onset headache, often with vomiting and often a lapse in brain function so that the patients may stare, drop to their knees, or become confused and unable to remember. The symptoms in patients with subarachnoid hemorrhage relate to diffuse abnormalities of brain function because usually there is no bleeding into one part of the brain. In contrast, in patients with intracerebral hemorrhages, the hematoma is localized and causes loss of function related to the area damaged by the local blood collection.

Subdural and epidural hemorrhages are most often caused by head injuries that tear blood vessels. In subdural hemorrhages, the bleeding is usually from veins located between the arachnoid and the dura mater. In epidural hemorrhages, the bleeding most often results in tearing of meningeal arteries. The tear is often caused by a skull fracture. Arterial bleeding develops faster than venous bleeding so that symptoms develop sooner after head injury in patients with epidural hemorrhages. In subdural hemorrhages, the bleeding can be slow so that symptoms may be delayed for weeks after head injury.

Brain Ischemia

Insufficient blood supply to the brain is called ischemia. When ischemia is prolonged, it leads to death of tissue—infarction.

There are three different major categories of brain ischemia—thrombosis, embolism, and systemic hypoperfusion; each indicates a different mechanism of blood vessel injury or reason for decreased blood flow. The difference between these mechanisms is easiest to understand by using an analogy to house plumbing. Suppose, turning on the faucet in the second floor bathroom results in no flow, or instead, water dribbles out. The malfunctioning could be due to a local problem, such as rust buildup in the pipe supplying that sink. This is analogous to thrombosis, a term used to describe a local problem that involves an artery supplying the brain. Atherosclerosis or another condition often narrows the arterial lumen. When the lumen becomes very narrow, blood flow is severely reduced, causing localized stagnation of the blood column. This change in flow causes blood to clot, resulting in total arterial occlusion. This is a local problem in one pipe; a plumber would try to fix the damaged blocked pipe. Similarly, treating physicians could try to open or bypass a stenotic or occluded artery.

Alternatively, blockage of that second floor sink pipe could be due to debris in the water system that came to rest in that pipe rather than a local problem that began within the pipe. A neck or cranial artery supplying the brain can become blocked by thrombi or other particulate matter that breaks loose from a downstream site. The source could be from the heart, the aorta, or from a major artery in the neck or head located before the blocked artery along the same circulatory pathway. The process of particles breaking loose and blocking a distant artery is known as embolism. The source of the material is called the donor site, and the receiving vessel is called the recipient site. The material is called an embolus, and the process is called embolism. Treatment of embolism could involve unblocking the recipient artery but also trying to prevent further embolization.

Another reason for poor flow in the second floor sink might be a general problem with the water tank, water pump, or water pressure. In that case, flow through all pipes in the house should be affected. Turning on the faucets elsewhere in the house will reveal the nature of the problem. In the body, this type of problem is called systemic hypoperfusion. Abnormal cardiac performance could lead to low pressure in the system. Abnormally slow or fast heart rhythms, cardiac arrest, and failure of the heart to pump blood adequately can all lead to diminished brain perfusion. Hypotension and hypoperfusion due to an inadequate amount of fluid in the vascular compartment of the body are other causes. Bleeding, dehydration, and shock all lead to inadequate brain perfusion. This would be akin to having a very low water tank.

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