What is a subarachnoid hemorrhage?
Subarachnoid hemorrhaging is hemorrhaging of the cerebral vessels primarily vessels of the Circle of Willis into the subarachnoid space. These vessels can also rupture in the ventricles causing interventricular hemorrhage. Causes of subarachnoid hemorrhage include traumatic and nontraumatic. Traumatic causes are suffering blunt force trauma or being hit in the head with a bat. Traumatic causes can also include penetrating trauma or being jabbed in the head with a knife. Nontraumatic causes include aneurysms. An asymmetrical outpouching on one side of a vessel wall and a bigger aneurysm on the other wall is called a saccular or berry aneurysm. The bigger aneurysm is termed a Giant berry aneurysm. Symmetrical outpouching of a vessel is termed a fusiform aneurysm. A dissection of a vessel causing it to look like an aneurysm is termed a pseudoaneurysm. There is a hole in the vessel wall. Infected material in the vessel wall with the look of an aneurysm is called mycotic or infectious.
What causes these aneurysms to pop? Increased stress on the vessel wall weakens it. I. In conditions such as, hypertension, sympathomimetic abuse (cocaine or methamphetamines) things that increase the sympathetics, smoking, ethanol, oral contraceptives and/or pregnancy. These causes can turn the vasa vasorum of the vessel wall into hyaline arteriosclerosis. II. Connective tissue defect weakens the vessel wall. Marfan's syndrome because of an absence of fibrillin. Elher's Danlos because of a deficiency of collagen. Polycystic kidney disease because of a defect in polycystin protein. III. Dyplasia of smooth muscle causes weakness of vessel wall. Fibromuscular dysplasia or alternating instances of thick and larger smooth muscle connected to thin layers of smooth muscle. IV. Infective endocarditis forms vegetations on valves. If these vegatations break off then infective material may get stuck in vessel walls. If the pressure increases, then the walls will pop. V. Arteriovenous malformation which are common in children. The problem is that there are no true capillaries. Leads to a nidus of ball of blood vessels.
Where can these aneurysms form? The most common location is the anterior communicating artery 30%. Second the posterior communicating artery is at 25%. Followed by the middle communicating artery is 20%. Fourth is the internal carotid artery terminus 7.5%. Fifth is the basilar tip at 7%. Sixth is the anterior cerebral artery at 4%. Seventh is the PICA at 3.5%
What is the trigger for rupture? An acute rise in blood pressure, pain, or an anger fit.
Where is the subarachnoid space? The tissue that clings to the brain is called the pia mater. The next structure superior to that is the arachnoid mater. The structure superior to that is the intermarginal layer of the dura mater. The outermost layer is the outer periosteal layer of the dura mater. Blood accumulates in the subarachnoid space.
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