Anatomy And Physiology

Anatomy Physiology



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The term "brain hemorrhage" implies the rupture of a cerebral blood vessel (usually an artery), leakage of blood into the surrounding brain tissue, and the resulting damage, including the sensory and motor deficits characteristic of stroke as well as seizures.

A useful way of classifying brain hemorrhages would be distinguishing between traumatic and non-traumatic causes. Traumatic injury can be subdivided into blunt and penetrating head trauma. Blunt trauma tends to occur during motor vehicle accidents and includes closed head injuries. Penetrating trauma includes gunshot wounds or stab wounds from knives or other sharp objects.

The results of head trauma may include one or more of the following:

1) Epidural hematoma - when the middle meningeal artery is torn, blood collects between the skull and dura mater (outer layer of the meninges that surround the brain). These can occur over the course of a few hours and may be fatal without surgical intervention.

2) Subdural hematoma - occurs when bridging veins under the dura mater are torn, leading to the slow pooling of blood between the dura and pia mater (a thin film that lines the surface of the brain and spinal cord).

3) Hemorrhagic stroke - as we shall see, this usually results from non-traumatic causes.  

Non-traumatic causes of brain hemorrhage can be broken down into acute (sudden onset) causes vs. chronic processes whose endpoint is a brain hemorrhage.

Acute causes:  

1) Aneurysmal rupture - aneurysms are weakened areas of arterial walls prone to rupture. Contrary to popular belief, most people with cerebral aneurysms are entirely asymptomatic. Berry aneurysms occur most often in the Circle of Willis, located on the ventral surface of the brain's frontal lobes. Although the cause of berry aneurysms remains unknown, they occur most often in people with APKD (Adult Polycystic Kidney Disease). The rupture of a berry aneurysm results in a subarachnoid hemorrhage, characterized by intense headache ("worst headache of my life"), coma, and often death.

2) Hypertensive crisis - a sudden surge in blood pressure (to levels of 300/200 mmHg) may be triggered by certain drugs (cocaine, amphetamines) or rarely, the sudden release of catecholamines from a pheochromocytoma tumor. In the past, patients taking antidepressants called MAOIs (monoamine oxidase inhibitors) were prone to hypertensive crises if they ate foods containing the chemical tyramine, e.g. aged cheese or Chianti wine. Since virtually no one in the U.S. is prescribed MAOIs anymore, tyramine induced hypertensive crises have dropped off the radar screen.

Chronic causes:

1) Atherosclerosis - untreated or poorly managed high blood pressure is far and away the most common cause of hemorrhagic stroke.

2) Lacunar infarcts - occur following the rupture of small blood vessels deep in the brain, associated with uncontrolled hypertension as well as diabetes.

3) Diseases with vasculitis as a prominent component - these tend to be autoimmune diseases like lupus (SLE), polyarteritis nodosa (PAN), and Takayasu's arteritis.            

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