Diseases And Conditions
Subarachnoid hemorrhage
Subarachnoid hemmorhage, or SAH, refers to bleeding around the brain, usually at its base. This form of bleeding occurs in a space in the brain called the subarachnoid space. SAH is a subtype of hemorrhagic stroke, which refers to the 15% of stroke cases caused by bleeding in the brain. The incidence of primary SAH, meaning SAH caused by a brain derangement other than trauma, is about 30,000 cases annually in the U.S.
In 90% of cases SAH is caused by bleeding from a brain aneurysm. A brain aneurysm is a blister or bubble that develops in a brain artery. Cerebral aneurysms are found in an estimated 0.5% to 6% of people. There is some controversy regarding the risk of rupture in a cerebral aneurysm. This is the subject of ongoing clinical trials. When a brain aneurysm has caused an SAH there is a high likelihood that the aneurysm will rebleed. Studies have shown a 4% risk of rebleeding in the first 24 hours after the initial hemorrhage. This risk declines to 1.5% in the second 24 hours and continues to decline thereafter. The risk of rebleeding is 20% within the first two weeks and is 60% by 6 months after an initial SAH. Brain aneurysms tend to occur on the medium sized arteries of the brain as they travel through the subarachnoid space, hence the subarachnoid location of aneurismal hemorrhages. In 10% of cases the cause of a primary SAH is never identified. In those cases, repeat evaluations are critical because in a minority of cases an aneurysm may be eventually identified. If repeat evaluations are negative, the risk of a repeat hemorrhage is low, but not zero.
SAH is one of the most complex and dangerous conditions in medicine. Up to 15% of patients with SAH will die before reaching the hospital. Within the first 30 days after a SAH, up to 50% of victims will die. Of the survivors, about half suffer some form of neurological disability. The management of SAH focuses on identifying and managing the variables that result in this extremely high rate of death and disability. At experienced centers, the 30 day death rate can be reduced to about 30%, which is still significantly higher than most diseases. Rebleeding of a ruptured aneurysm is one factor that leads to such a high death rate. Rebleeding has been associated with a nearly 70% risk of death. The risk of rebleeding can be reduced by operating on ruptured aneurysms early, within the first 24 to 48 hours.
Aneurysm surgery is very complex, demanding and carries significant risks itself. Therefore, while the goal of surgery is to repair the aneurysm early, it is widely accepted to defer surgery until the next day in order for the surgical team to be fully prepared. Aneurysm treatment options involve either a craniotomy or embolization. In a craniotomy, the skull is opened and a clip is placed across the aneurysm, closing it. In embolization, the surgeon navigates a small tube from the leg artery to the brain. A device is the inserted into the aneurysm, blocking it from the inside. Whether craniotomy or embolization, the surgeon will recommend the best method of treating the aneurysm. Some SAH patients will develop a condition called hydrocephalus. Hydrocephalus occurs when there is a blockage of the normal brain fluid production-reabsorbtion cycle. The brain produces 20 cc’s of cerebrospinofluid each hour. This fluid circulates in the brain and around the spine. This fluid is reabsorbed by the body by outpunchings of the arachnoid space. In SAH, the arachnoid space is covered in blood. Thus, the outpunching of the arachnoid space cannot reabsorb the fluid. As a result, fluid accumulates, building up pressure in the brain. To relieve this pressure, a surgeon drills a small hole through the skull. Through this hole, a small catheter is inserted in the brain, draining the built up cerebrospinofluid. This procedure is called a ventriculostomy and is a life saving procedure.
In some patients with SAH, the blood in the subarachnoid space will cause a significant irritation in the arteries traveling through the subarachnoid space. This irritation causes the arteries to spasm and narrow, impeding blood flow. This condition is called vasospasm. Vasospasm is seen in up to a third of SAH patients. The presence of vasospasm is directly related to the degree of bleeding. This spasm of the brain arteries results in stroke. Vasospasm results in disability in up to 40% of SAH survivors. Vasospasm does not occur immediately. It begins about 4 days after an SAH and can persist for up to 14 days or higher. When vasospasm does exist, the first line of therapy is artificially raising blood pressure and giving intravenous fluids. This serves to increase the total amount of blood to the brain. At the same time, surgeons may attempt to open the spastic arteries, directly increasing cerebral blood flow. This is achieved either by navigating a small balloon from the groin artery to the brain artery, or by navigating a catheter to the spastic artery and infusing medications directly into the brain artery. Whether using a small balloon or infusing medications, this therapy open the spastic arteries, increasing blood flow to the brain. SAH is a serious medical condition.
By treating aneurysms early, treating hydrocephalus and treating vasospasm, significant reductions in patient disability can be made. However, SAH continues to have a high rate of death and disability. Physicians will continue to seek new ways to improve outcomes in this disease and this will continue to be a focus for research in the field of neurovascular surgery.
