<?xml version="1.0" encoding="UTF-8"?>
<document>
<title>Subarachnoid hemorrhage</title>
<authors>Wikipedia</authors>
<publisher>wikipedia.org</publisher>
<publishedplace>network</publishedplace>
<publishedyear>2010</publishedyear>
<edition></edition>
<category>Neurosurgery</category>
<section id="25249" fatherid="0" title="" lv="" priority="-1" level="1">
A subarachnoid hemorrhage (SAH, , or subarachnoid haemorrhage in British English) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. This may occur spontaneously, usually from a ruptured cerebral aneurysm, or may result from head injury.
Symptoms of SAH include a severe headache with a rapid onset ("thunderclap headache"), vomiting, confusion or a lowered level of consciousness, and sometimes seizures. The diagnosis is generally confirmed with a CT scan of the head, or occasionally by lumbar puncture.  Treatment is by prompt neurosurgery or radiologically guided interventions with medications and other treatments to help prevent recurrence of the bleeding and complications. Surgery for aneurysms was introduced in the 1930s, but since the 1990s many aneurysms are treated by a less invasive procedure called "coiling", which is carried out by instrumentation through large blood vessels.
SAH is a form of stroke and comprises 1–7% of all strokes. It is a medical emergency and can lead to death or severe disability—even when recognized and treated at an early stage. Up to half of all cases of SAH are fatal and 10–15% die before reaching a hospital, and those who survive often have neurological or cognitive impairment.

</section>
<section id="25250" fatherid="0" title="Signs and symptoms" lv="" priority="2" level="1">
The classic symptom of subarachnoid hemorrhage is thunderclap headache (a headache described as  "like being kicked in the head", or the "worst ever", developing over seconds to minutes). This headache often pulsates towards the occiput (the back of the head). About one-third of sufferers have no symptoms apart from the characteristic headache, and about one in ten people who seek medical care with this symptom are later diagnosed with a subarachnoid hemorrhage. Vomiting may be present, and 1 in 14 have seizures. Confusion, decreased level of consciousness or coma may be present, as may neck stiffness and other signs of meningism. Neck stiffness usually presents six hours after initial onset of SAH. Isolated dilation of a pupil and loss of the pupillary light reflex may reflect brain herniation as a result of rising intracranial pressure (pressure inside the skull). Intraocular hemorrhage (bleeding into the eyeball) may occur in response to the raised pressure: subhyaloid hemorrhage (bleeding under the hyaloid membrane, which envelops the vitreous body of the eye) and vitreous hemorrhage may be visible on fundoscopy. This is known as Terson syndrome (occurring in 3–13% of cases) and is more common in more severe SAH.
Oculomotor nerve abnormalities (affected eye looking downward and outward and inability to lift the eyelid on the same side) or palsy (loss of feeling) may indicate bleeding from the posterior communicating artery. Seizures are more common if the hemorrhage is from an aneurysm; it is otherwise difficult to predict the site and origin of the hemorrhage from the symptoms. SAH in a person known to have fits is often diagnostic of an arteriovenous malformation.
As a result of the bleeding, the body releases large amounts of adrenaline and similar hormones. This leads to a sharp increase in the blood pressure; the heart comes under substantial strain, and neurogenic pulmonary edema (accumulation of fluid in the lungs), cardiac arrhythmias (irregularities in the heart rate and rhythm), electrocardiographic changes (in 27% of cases) and cardiac arrest (in 3% of cases) may occur rapidly after the onset of hemorrhage.
Subarachnoid hemorrhage may also occur in people who have suffered a head injury. Symptoms may include headache, decreased level of consciousness and hemiparesis (weakness of one side of the body). SAH is a frequent occurrence in traumatic brain injury, and carries a poor prognosis if it is associated with deterioration in the level of consciousness.

</section>
<section id="25251" fatherid="0" title="Diagnosis" lv="" priority="3" level="1">
The initial steps for evaluating a person with a suspected subarachnoid hemorrhage are obtaining a medical history and performing a physical examination; these are aimed at determining whether the symptoms are due to SAH or to another cause. The diagnosis cannot, however, be made on clinical grounds alone; therefore medical imaging is generally required to confirm or exclude bleeding. The modality of choice is computed tomography (CT scan) of the brain. This has a high sensitivity and will correctly identify over 95% of cases—especially on the first day after the onset of bleeding. Magnetic resonance imaging (MRI) may be more sensitive than CT after several days.
Lumbar puncture, in which cerebrospinal fluid (CSF) is removed with a needle from the lumbar sac, will show evidence of hemorrhage in 3% of people in whom CT was found normal; lumbar puncture is therefore regarded as mandatory in people with suspected SAH if imaging is negative. At least three tubes of CSF are collected. If an elevated number of red blood cells is present equally in all bottles, this indicates a subarachnoid hemorrhage. If the number of cells decreases per bottle, it is more likely that it is due to damage to a small blood vessel during the procedure (known as a "traumatic tap"). The CSF sample is also examined for xanthochromia—the yellow appearance of centrifugated fluid. More sensitive is spectrophotometry (measuring the absorption of particular wavelengths of light) for detection of bilirubin, a breakdown product of hemoglobin from red blood cells. Xanthochromia and spectrophotometry remain reliable ways to detect SAH several days after the onset of headache. An interval of at least 12 hours between the onset of the headache and lumbar puncture is required, as it takes several hours for the hemoglobin from the red blood cells to be metabolized into bilirubin.
As only 10% of people admitted to the emergency department with a thunderclap headache are suffering from an SAH, other possible causes are usually considered simultaneously, such as meningitis, migraine, and cerebral venous sinus thrombosis. Intracerebral hemorrhage, in which bleeding occurs within the brain itself, is twice as common as SAH and is often misdiagnosed as the latter. It is not unusual for SAH to be initially misdiagnosed as a migraine or tension headache, which can lead to a delay in obtaining a CT scan. In a 2004 study, this occurred in 12% of all cases and was more likely in people who had smaller hemorrhages and no impairment in their mental status. The delay in diagnosis led to a worse outcome. In some people, the headache resolves by itself, and no other symptoms are present. This type of headache is referred to as "sentinel headache", because it is presumed to result from a small leak (a "warning leak") from an aneurysm. A sentinel headache still warrants investigations with CT scan and lumbar puncture, as further bleeding may occur in the subsequent three weeks.
After a subarachnoid hemorrhage is confirmed, its origin needs to be determined. If the bleeding is likely to have originated from an aneurysm (as determined by the CT scan appearance), the choice is between cerebral angiography (injecting radiocontrast through a catheter to the brain arteries) and CT angiography (visualizing blood vessels with radiocontrast on a CT scan) to identify aneurysms. Catheter angiography also offers the possibility of coiling an aneurysm (see below).

</section>
<section id="25252" fatherid="0" title="Causes" lv="" priority="-4" level="1">
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.

</section>
<section id="25253" fatherid="0" title="Classification" lv="" priority="5" level="1">
There are several grading scales available for SAH.  The Glasgow Coma Scale is ubiquitously used for assessing consciousness. Three specialized scores are used to evaluate SAH; in each, a higher number is associated with a worse outcome. These scales have been derived by retrospectively matching characteristics of patients with their outcomes.
The first scale of severity was described by Hunt and Hess in 1968:
The Fisher Grade classifies the appearance of subarachnoid hemorrhage on CT scan. This scale has been modified by Claassen and coworkers, reflecting the additive risk from SAH size and accompanying intraventricular hemorrhage.
The World Federation of Neurosurgeons classification uses Glasgow coma score (GCS) and focal neurological deficit to gauge severity of symptoms.

</section>
</document>
