subarachnoid hemorrhage subarachnoid hemorrhage subarachnoid hemorrhage (sah) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. symptoms may include a severe headache of rapid onset, vomiting, decreased level of consciousness, fever, weakness, numbness, and sometimes seizures. neck stiffness or neck pain are also relatively common. in about a quarter of people a small bleed with resolving symptoms occurs within a month of a larger bleed. subarachnoid hemorrhageother namessubarachnoid haemorrhagect scan of the brain showing subarachnoid hemorrhage as a white area in the center (marked by the arrow) and stretching into the sulci to either sidepronunciation/ˌsʌbəˈræknɔɪd ˈhɛmərɪdʒ/ specialtyneurosurgery, neurologysymptomssevere headache of rapid onset, vomiting, decreased level of consciousnesscomplicationsdelayed cerebral ischemia, cerebral vasospasm, seizurestypestraumatic, spontaneous (aneurysmal, nonaneurysmal, perimesencephalic)causeshead injury, cerebral aneurysmrisk factorshigh blood pressure, smoking, alcoholism, cocainediagnostic methodct scan, lumbar puncturedifferential diagnosismeningitis, migraine, cerebral venous sinus thrombosistreatmentneurosurgery or radiologically guided interventionsmedicationlabetalol, nimodipineprognosis45% risk of death at 30 days (aneurysmal)frequency1 per 10,000 per year sah may occur as a result of a head injury or spontaneously, usually from a ruptured cerebral aneurysm. risk factors for spontaneous cases include high blood pressure, smoking, family history, alcoholism, and cocaine use. generally, the diagnosis can be determined by a ct scan of the head if done within six hours of symptom onset. occasionally, a lumbar puncture is also required. after confirmation further tests are usually performed to determine the underlying cause. treatment is by prompt neurosurgery or endovascular coiling. medications such as labetalol may be required to lower the blood pressure until repair can occur. efforts to treat fevers are also recommended. nimodipine, a calcium channel blocker, is frequently used to prevent vasospasm. the routine use of medications to prevent further seizures is of unclear benefit. nearly half of people with a sah due to an underlying aneurysm die within 30 days and about a third who survive have ongoing problems. between ten and fifteen percent die before reaching a hospital. spontaneous sah occurs in about one per 10,000 people per year. females are more commonly affected than males. while it becomes more common with age, about 50% of people present under 55 years old. it is a form of stroke and comprises about 5 percent of all strokes. surgery for aneurysms was introduced in the 1930s. since the 1990s many aneurysms are treated by a less invasive procedure called endovascular coiling, which is carried out through a large blood vessel. signs and symptoms 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 people 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 percent 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 movement) 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 seizures is often diagnostic of a cerebral arteriovenous malformation. the combination of intracerebral hemorrhage and raised intracranial pressure (if present) leads to a "sympathetic surge", i.e. over-activation of the sympathetic system. this is thought to occur through two mechanisms, a direct effect on the medulla that leads to activation of the descending sympathetic nervous system and a local release of inflammatory mediators that circulate to the peripheral circulation where they activate the sympathetic system. as a consequence of the sympathetic surge there is a sudden increase in blood pressure; mediated by increased contractility of the ventricle and increased vasoconstriction leading to increased systemic vascular resistance. the consequences of this sympathetic surge can be sudden, severe, and are frequently life-threatening. the high plasma concentrations of adrenaline also may cause cardiac arrhythmias (irregularities in the heart rate and rhythm), electrocardiographic changes (in 27 percent of cases) and cardiac arrest (in 3 percent of cases) may occur rapidly after the onset of hemorrhage. a further consequence of this process is neurogenic pulmonary edema where a process of increased pressure within the pulmonary circulation causes leaking of fluid from the pulmonary capillaries into the air spaces, the alveoli, of the lung. subarachnoid hemorrhage may also occur in people who have had 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. while thunderclap headache is the characteristic symptom of subarachnoid hemorrhage, less than 10% of those with concerning symptoms have sah on investigations. a number of other causes may need to be considered. causes circle of willis with the most common locations of ruptured aneurysms marked most cases of sah are due to trauma such as a blow to the head. traumatic sah usually occurs near the site of a skull fracture or intracerebral contusion. it often happens in the setting of other forms of traumatic brain injury. in these cases prognosis is poorer; however, it is unclear if this is a direct result of the sah or whether the presence of subarachnoid blood is simply an indicator of a more severe head injury. in 85 percent of spontaneous cases the cause is 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 are due to bleeding from small aneurysms, larger aneurysms (which are less common) are more likely to rupture. aspirin also appears to increase the risk. in 15–20 percent 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 cerebral 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. dissection of the vertebral artery, usually caused by trauma, can lead to subarachnoid hemorrhage if the dissection involves the part of the vessel inside the skull. pathophysiology cerebral vasospasm is one of the complications caused by subarachnoid hemorrhage. it usually happens from the third day after the aneurysm event, and reaches its peak on 5th to 7th day. there are several mechanisms proposed for this complication. blood products released from subarachnoid hemorrhage stimulates the tyrosine kinase pathway causing the release of calcium ions from intracellular storage, resulting in smooth muscle contraction of cerebral arteries. oxyhaemoglobin in cerebrospinal fluid (csf) causes vasoconstriction by increasing free radicals, endothelin-1, prostaglandin and reducing the level of nitric oxide and prostacyclin. besides, the disturbances of autonomic nervous system innervating cerebral arteries is also thought to cause vasospasm. diagnosis a lumbar puncture in progress. a large area on the back has been washed with an iodine-based disinfectant, leaving brown coloration. as only 10 percent of people admitted to the emergency department with a thunderclap headache are having 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 percent 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. the initial steps for evaluating a person with a suspected subarachnoid hemorrhage are obtaining a medical history and performing a physical examination. the diagnosis cannot be made on clinical grounds alone and in general medical imaging and possibly a lumbar puncture is required to confirm or exclude bleeding. imaging the modality of choice is computed tomography (ct scan), without contrast, of the brain. this has a high sensitivity and will correctly identify 98.7% of cases within six hours of the onset of symptoms. a ct scan can rule out the diagnosis in someone with a normal neurological exam if done within six hours. its efficacy declines thereafter, and magnetic resonance imaging (mri) is more sensitive than ct after several days. angiography 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). in emergency department patients complaining of acute-onset headache without significant risk factors for sah, evidence suggests that ct scanning of the head followed by ct angiography can reliably exclude sah without the need for a lumbar puncture. the risk of missing an aneurysmal bleed as the cause of sah with this approach is less than 1%. lumbar puncture xanthochromia versus normal csf lumbar puncture, in which cerebrospinal fluid (csf) is removed from the subarachnoid space of the spinal canal using a hypodermic needle, shows evidence of bleeding in three percent of people in whom a non-contrast ct was found normal. a lumbar puncture or ct scan with contrast is therefore regarded as mandatory in people with suspected sah when imaging is delayed to after six hours from the onset of symptoms and 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"). while there is no official cutoff for red blood cells in the csf no documented cases have occurred at less than "a few hundred cells" per high-powered field. the csf sample is also examined for xanthochromia—the yellow appearance of centrifugated fluid. this can be determined by spectrophotometry (measuring the absorption of particular wavelengths of light) or visual examination. it is unclear which method is superior. xanthochromia remains a 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