A subarachnoid hemorrhage (SAH) is an abnormal and very dangerous condition in which blood collects beneath the arachnoid mater, a membrane that covers the brain. This area, called the subarachnoid space, normally contains cerebrospinal fluid. The accumulation of blood in the subarachnoid space can lead to stroke, seizures, and other complications. Additionally, subarachnoid hemorrhages may cause permanent brain damage and a number of harmful biochemical events in the brain. A subarachnoid hemorrhage and the related problems are frequently fatal.

Subarachnoid hemorrhages are classified into two general categories: traumatic and spontaneous. Traumatic refers to brain injury that might be sustained in an accident or a fall. Spontaneous subarachnoid hemorrhages occur with little or no warning and are frequently caused by ruptured aneurysms or blood vessel abnormalities in the brain.

Traumatic brain injury is a critical problem in the United States. According to annual figures compiled by the Brain Injury Association, approximately 373,000 people are hospitalized, more than 56,000 people die, and 99,000 survive with permanent disabilities due to traumatic brain injuries. The leading causes of injury are bicycle, motorcycle, and automobile accidents, with a significant minority due to accidental falls, and sports and recreation mishaps.

Exact statistics are not available on traumatic subarachnoid hemorrhages, but several large clinical studies have found an incidence of 23%～39% in relation to severe head injury. Furthermore, subarachnoid hemorrhages have been described in the medical literature as the most common brain injury found during autopsy investigations of head trauma.

Spontaneous subarachnoid hemorrhages are often due to an aneurysm (a bulge or sac-like projection from a blood vessel) which bursts. Arteriovenous malformations (AVMs), which are abnormal interfaces between arteries andveins, may also rupture and release blood into the subarachnoid space. Both aneurysms and AVMs are associated with weak spots in the walls of blood vessels and account for approximately 60% of all spontaneous subarachnoid hemorrhages. The rest may be attributed to other causes, such as cancer or infection, or are of unknown origin.

In industrialized countries, it is estimated that there are 6.5-26.4 cases of spontaneous subarachnoid hemorrhage per 100,000 people annually. Certain factors raise the risk of suffering a hemorrhage. Aneurysms are acquired over a person's lifetime and are rarely a factor in subarachnoid hemorrhage before age 20. Conversely, arteriovenous malformation (AVM) are present at birth. In some cases, there may be a genetic predisposition for aneurysms or AVMs. Other factors that have been implicated, but not definitively linked to spontaneous subarachnoid hemorrhages, include atherosclerosis, cigarette use, extreme alcohol consumption, and the use of illegal drugs, such as cocaine. The exact role of high blood pressure is somewhat unclear, but since it does seem linked to the formation of aneurysms, it may be considered an indirect risk factor.

In 85% of cases of spontaneous SAH, the cause is rupture of a cerebral aneurysm—a weakness in the wall of one of the arteries in the brain that becomes enlarged. They tend to be located in the circle of Willis and its branches. While most cases of SAH are due to bleeding from small aneurysms, larger aneurysms (which are less common) are more likely to rupture.

In 15%～20% of cases of spontaneous SAH, no aneurysm is detected on the first angiogram. About half of these are attributed to non-aneurysmal perimesencephalic hemorrhage, in which the blood is limited to the subarachnoid spaces around the midbrain (i.e. mesencephalon). In these, the origin of the blood is uncertain. The remainder are due to other disorders affecting the blood vessels (such as arteriovenous malformations), disorders of the blood vessels in the spinal cord, and bleeding into various tumors. Cocaine abuse and sickle cell anemia (usually in children) and, rarely, anticoagulant therapy, problems with blood clotting and pituitary apoplexy can also result in SAH.

Subarachnoid blood can be detected on CT scanning in as many as 60% of people with traumatic brain injury. Traumatic SAH (tSAH) usually occurs near the site of a skull fracture or intracerebral contusion. It usually happens in the setting of other forms of traumatic brain injury and has been linked with a poorer prognosis. It is unclear, however, if this is a direct result of the SAH or whether the presence of subarachnoid blood is simply an indicator of severity of the head injury and the prognosis is determined by other associated mechanisms.

Risk factors for a subarachnoid hemorrhage include:

Aneurysm in a vessel outside the brain.

●Aneurysm in the chest

●Aneurysm in the abdomen

●Cerebral aneurysm

●Cerebral arteriovenous malformation

●Diabetes

●Family history of subarachnoid hemorrhage

An arterial disease of unknown cause that affects the arteries of young to middleaged women. Commonly affected arteries include the carotid arteries in the neck and the renal arteries in the kidneys.

●Heart disease

●Ehlers Danlos syndrome type 4

●Neurofibromatosis type 1

●High cholesterol

●Hypertension

●Obesity

●Polycystic kidney disease

●Smoking

Headache is usually severe, peaking within seconds. Loss of consciousness may follow, usually immediately but sometimes not for several hours. Severe neurologic deficits may develop and become irreversible within minutes or a few hours. Sensorium may be impaired, and patients may become restless. Seizures are possible. Usually, the neck is not stiff initially unless the cerebellar tonsils herniate. However, within 24h, chemical meningitis causes moderate to marked meningismus, vomiting, and sometimes bilateral extensor plantar responses. Heart or respiratory rate is often abnormal. Fever, continued headaches, and confusion are common during the first 5 to 10 days. Secondary hydrocephalus may cause headache, obtundation, and motor deficits that persist for weeks. Rebleeding may cause recurrent or new symptoms.

When a patient is brought to the emergency room with an SAH, doctors will learn as much as possible about his or her symptoms, current and previous medical problems, medications, and family history. A physical exam will be performed. Diagnostic tests will help determine the source of the bleeding.

Computed Tomography (CT) is a noninvasive X-ray that provides detailed images of anatomical structures within the brain. It is especially useful to detect blood in or around the brain. A newer technology called CT angiography (CTA) involves the injection of contrast into the blood stream to view the arteries of the brain. CTA provides the best pictures of blood vessels (through angiography) and soft tissues (through CT).

Lumbar puncture is an invasive procedure in which a hollow needle is inserted into the subarachnoid space of the spinal canal to detect blood in the cerebrospinal fluid (CSF). The doctor will collect 2 to 4 tubes of CSF. If the CT scan does not show evidence of bleeding but the patient symptoms are typical for SAH, a lumbar puncture may be performed.

Angiogram is an invasive procedure in which a catheter is inserted into an artery and passed through the blood vessels to the brain. Once the catheter is in place, contrast dye is injected into the bloodstream and X-ray images are taken.

Magnetic resonance imaging (MRI) scan is a noninvasive test that uses a magnetic field and radio-frequency waves to give a detailed view of the soft tissues of the brain. An MRA (Magnetic Resonance Angiogram) is the same non-invasive study, except that it is also an angiogram, which means it examines the blood vessels in addition to structures of the brain.

Treatment for SAH varies, depending on the underlying cause of the bleeding and the extent of damage to the brain. Treatment may include lifesaving measures, symptom relief, repair of the bleeding vessel, and complication prevention.

For 10 to 14 days following SAH, the patient will remain in the neuroscience intensive care unit (NSICU), where doctors and nurses can watch closely for signs of renewed bleeding, vasospasm, hydrocephalus, and other potential complications.

Pain medication will be given to alleviate headache, and anticonvulsant medication may be given to prevent or treat seizures.

If the SAH is from a ruptured aneurysm, surgery may be performed to stop the bleeding. Options include:

●Surgical clipping: an opening in the skull (craniotomy) is made to locate the aneurysm. A small titanium clip is placed across the neck of the aneurysm to stop blood flow from entering.

●Endovascular coiling: a catheter is inserted into an artery in the groin during an angiogram. The catheter is advanced through the blood stream to the aneurysm. Platinum coils or liquid glue (Onyx) are packed into the aneurysm to stop blood flow from entering.

Clotted blood and fluid buildup in the subarachnoid space may cause hydrocephalus and increase intracranial pressure. Blood pressure is lowered to reduce further bleeding and to control intracranial pressure. Excess cerebrospinal fluid (CSF) and blood can be removed with 1) a lumbar drain, which is inserted into the subarachnoid space of the spinal canal in the lower back, or 2) a ventricular drain, which is inserted into the ventricles of the brain.

Five to 10 days after an SAH, the patient may develop vasospasm. Vasospasm narrows the artery and reduces blood flow to the region of the brain that the artery feeds. Vasospasm occurs in 70% of patients after SAH. Of these, 30% have symptoms that require treatment.

A patient in the NSICU will be monitored for signs of vasospasm, which include weakness in an arm or leg, confusion, sleepiness, or restlessness. Transcranial doppler (TCD) ultrasounds are preformed routinely to monitor for vasospasm. TCDs are used to measure the blood flow through the arteries. This test can show which arteries are in spasm as well as the severity. To prevent vasospasm, patients are given the drug nimodipine while in the hospital. Additionally, these following therapy are used:

●Hypertension: involves increasing the blood pressure to force blood through the narrowed arteries.

●Hypervolemia: involves increasing IV fluids to make more blood volume.

●Hemodilution: involves making the blood thin and watery so that it flows more easily through narrowed arteries.

If vasospasm is severe, patients may require an injection of medication directly into the artery to relax and stop the spasm. This is done through a catheter during an angiogram. Sometimes balloon angioplasty is used to stretch open the artery.

abdomen ['æbdəmən,æb'domən] n.下腹； 腹腔

aneurysm ['ænjə,rizəm] n.动脉瘤

arachnoid [ə'ræknɔid] n.蛛网膜；adj.蛛网状的，蛛网膜的

atherosclerosis [,æθərosklə'rosis] n.动脉粥样硬化

catheter ['kæθitɚ] n.导尿管，尿液管，导管

hemodilution [,hiːməudai'ljuʃən] n.血液稀释

intracranial [,intrə'kreniəl] n.头颅内的，颅骨内的

ischemia [i'skimiə] n.缺血

meningitis [,mɛnin'dʒaitis] n.脑膜炎

obesity [o'bisiti] n.肥胖； 肥胖症

sensorium [sɛn'sɔriəm, -'sor-] n.感觉中枢，感觉器官

traumatic [traʊ'mætik] adj.外伤的； 创伤的； 治外伤的

vasospasm ['vezo,spæzəm] n.血管痉挛

anticonvulsant medication 抗惊厥药

arteriovenous malformation (AVM) 动静脉畸形

cerebrospinal fluid (CSF) 脑脊髓液

Ehlers Danlos Syndrome 埃勒斯-当洛综合征

fibromuscular dysplasia 纤维肌性发育不良

high cholesterol 高胆固醇

polycystic kidney disease 多囊性肾病

plantar responses 跖反射

subarachnoid hemorrhage (SAH) 蛛网膜下出血

spinal cord 脊髓

tonsils herniate 扁桃体疝

surgical clipping 手术夹闭

transcranial doppler 经颅多普勒