Subarachnoid Haemorrhage

oPatientPlus articles are written by UK doctors and are based on research evidence, UK and European Guidelines. They are designed for health professionals to use, so you may find the language more technical than the condition leaflets.

Subarachnoid haemorrhage (SAH) is usually the result of bleeding from an aneurysm in the Circle of Willis, most often from a berry aneurysm.[1] They are called berry aneurysms because of their shape. They were once thought to be mostly congenital but the theory now is that the aetiology may vary from genetic malformations of the elastic lamina to stressors such as hypertension and atherosclerosis. The incidence increases with age.[2]

  • Subarachnoid haemorrhage (SAH) affects 6-12 people per 100,000 of the population per year and constitutes about 6% of first strokes.
  • Approximately 85% of patients bleed from intracranial arterial aneurysms, 10% from a non-aneurysmal peri-mesencephalic haemorrhage and 5% from other vascular abnormalities including arteriovenous malformation.[3]
  • SAH represents a mere 5% of cases of stroke but it is relatively far more important, as it tends to affect younger people, of whom about half die in that episode.
  • The mean age is 50 years.
  • 10-15% fail to reach hospital.

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Risk factors[1]

  • The bigger the aneurysm, the more likely it is to bleed. However, as about 90% of aneurysms are small, the majority that bleed are less than 1 cm in diameter.[4]
  • Most small berry aneurysms (under 7 mm in diameter) do not rupture.[5]
  • Hypertension.
  • Smoking.
  • Excessive alcohol intake.

The last 3 each roughly double the risk and these modifiable risk factors account for around two thirds of SAH.[6] One study found that a combination of cigarette smoking and hypertension increases the risk of a bleed from smaller aneurysms.[7]

  • Although no single gene has been isolated, genetic factors also play a part and account for around 10%.[8]
  • Patients with a positive family history tend to have their first SAH at a younger age.
  • They are also more likely to have large and multiple aneurysms.

However, as this group accounts for only 10%, most patients with large or multiple aneurysms are sporadic rather than familial.

Berry aneurysms are found in 10% of patients with autosomal dominant adult polycystic kidney disease but they represent only 1% of cases of SAH.

The most characteristic feature is a sudden headache. This may last a few seconds or even a fraction of a second. The patient may even look round and accuse someone of hitting him on the back of the head. In general practice, it may be the only symptom in a third of patients.[9] Of patients who present in general practice with a sudden headache, around 10% have subarachnoid haemorrhage (SAH).[10]

SAH should be considered in any patient presenting with sudden-onset, severe and unusual headache with or without any associated alteration in consciousness.[11]
  • The headache is often diffuse.
  • The dominant feature is the severity, rather than the suddenness, of the headache, often being described as the most severe ever experienced.
  • It usually lasts a week or two.

Other features include:

  • Vomiting, which may occur; however, this does not distinguish it from other causes of headache including thunderclap headache without haemorrhage.
  • Seizures, which occur in only about 7% but, when they do, are highly suggestive of a haemorrhage.
There may be symptoms that represent small leaks called sentinel bleeds or expansion of the aneurysm.
  • They are estimated to occur in 10-15% of patients.
  • The most common symptoms are headache (48%), dizziness (10%), orbital pain (7%), diplopia (4%) and visual loss (4%).
  • Signs may accompany these sentinel bleeds: sensory or motor disturbance (6%), seizures (4%), ptosis (3%), bruits (3%) and dysphasia (2%).
  • If a sentinel bleed is suspected, patients should be admitted urgently for investigations (treat as if an SAH has occurred).


  • On admission to hospital two thirds have a depressed level of consciousness, of whom half are in coma; however, beware - SAH patients have been known to walk into the surgery, complaining of sudden onset of headache.
  • Neck stiffness may occur due to meningeal irritation by the blood but it is not invariable.
  • Ophthalmoscopy will show intraocular haemorrhages in around 15% and especially in those with a depressed level of consciousness.
  • There may be focal neurological signs, suggestive of a stroke. Complete or partial palsy of the oculomotor nerve is well recognised, especially with rupture of aneurysms of the internal carotid artery at the origin of the posterior communicating artery.
  • Hypertension is a risk factor for the condition but a marked rise in blood pressure may occur as a reflex following haemorrhage.

Thunderclap headache is an idiopathic condition. Headache is intense but benign; however, it can resemble the headache of subarachnoid haemorrhage (SAH). Onset is acute, possibly within 30 seconds, and CT scan or even angiography may be required to rule out SAH. The angiogram may be normal or show focal cerebral vasoconstriction. Most patients with thunderclap headache never have a second episode, and are not at higher risk for haemorrhage. However, the term thunderclap headache is often used to describe the headache that is associated with SAH.

  • Arterial blood gases to exclude hypoxia.
  • An ECG may show changes. If these are wrongly interpreted as acute myocardial infarction and thrombolysis is given, the result is disastrous.
  • Every patient should have a CT scan at the earliest opportunity if subarachnoid haemorrhage (SAH) is suspected. This should be done immediately if the patient presents with sudden severe headache and as soon as possible in all other cases.
  • CT angiography should follow immediately if acute SAH is confirmed.
  • If the CT scan is negative, lumbar puncture should be undertaken, providing the scan shows no contra-indications. A small number of patients with a negative CT scan will prove, on lumbar puncture, to have had an SAH.
  • Spectrophotometry should be used to permit detection of small amounts of xanthochromia (yellow discolouration of the spinal fluid).

Early management

Initial management of subarachnoid haemorrhage (SAH) aims to prevent further bleeding and to reduce the rate of secondary complications, such as cerebral ischaemia or hydrocephalus.

  • Every patient should be started on nimodipine 60 mg four-hourly. A Cochrane review confirms that calcium antagonists help to reduce spasm and cerebral ischaemia.[13]
  • Phenytoin is sometimes used to prevent the spread of seizure activity.
  • Nitroprusside (a potent vasodilator) and labetolol may be employed to treat hypertension; the level should be low enough to prevent rebleeding whilst high enough to maintain cerebral perfusion.
  • The evidence base supporting the use of statins in combating vasospasm and cerebral ischaemia is controversial and is being investigated. Other novel treatments being tried include magnesium sulphate infusion and endothelial antagonists.[14]
  • Patients should not be given an antifibrinolytic agent or steroids.
  • Every patient should be referred to a specialist unit, usually neurosurgical, for investigation and, if appropriate, definitive treatment. This transfer should take place within 24 hours if appropriate.
  • All necessary supportive care should be provided.
  • If the patient has not already had a CT angiogram they should have imaging of all cerebral arteries.
  • Any aneurysm associated with the haemorrhage should be treated by surgical clipping or endovascular embolisation as appropriate.[15]
  • Insertion of an endovascular coil is increasingly being used for posterior circulation aneurysms, as this has less associated mortality than clipping.
  • The use of stents to facilitate coil insertion is also being explored.
  • The evidence base supports the use of early rather than late surgery.
  • Surgical intervention may be contra-indicated in patients who fail to respond to medically stabilising measures, those over the age of 80, those with other medical problems or where the aneurysm is large or complicated.
  • All patients should be monitored for the development of treatable complications, especially hydrocephalus, cerebral ischaemia, electrolyte imbalance and hypotension.

Further management

  • All surviving patients should be advised on secondary prevention, especially on treatment for hypertension and the need to stop smoking.
  • Any patient with residual impairment after investigation and treatment should be referred to an appropriate specialist rehabilitation service.
  • Patients with a strong family history (one other affected first-degree relative and/or with a history of polycystic kidney disease) should be advised that their family may be at greater risk of SAH and a referral made to a neurovascular specialist for up-to-date information and advice.
  • In about 3%, cardiac arrest occurs at the onset but, of those successfully resuscitated, about half can leave hospital for an independent existence.
  • A delayed complication is cerebral ischaemia. The risk is reduced with oral nimodipine and probably by maintaining circulatory volume. The peak time for occurence is 5-14 days after the haemorrhage.
  • Hydrocephalus might cause gradual obtundation in the first few hours or days. It can be treated by lumbar puncture or ventricular drainage, depending on the site of obstruction.
  • Abnormalities of biochemistry are common and need appropriate management in intensive care.
  • 5% or more of patients develop epilepsy after discharge.
  • After occlusion of the anterior communicating artery in particular, around 30% develop anosmia.

A sudden deterioration in level of consciousness within the first few hours suggests further bleeding. This carries a mortality rate of 51-80%.

Improvement tends to occur between 4 and 18 months after the event but even those who have independent living often have some cognitive defect. Younger patients do better.

Up to 60% of patients die in the first 30 days. 10% die immediately without any warning symptoms and an additional 25% die or become disabled.

Hospitalised patients have an average mortality rate of 40% in the first month. Rebleeding, a major complication, carries a mortality rate of 51-80%.

Delayed cerebral ischaemia due to vasospasm, the most deadly of all complications, affects 20% of angiographically visualised cases of vasospasm.

In a survey of 610 patients who were interviewed a mean of 8.9 years after subarachnoid haemorrhage (SAH), there was marked morbidity.[16]

  • Of the employed patients, 26% stopped working and 24% worked shorter hours or had a position with less responsibility.
  • On average, patients returned to work 9.4 months after discharge (range 0-96 months).
  • Related problems caused divorce in 7%.
  • There were changes in personality in 59%, with the most common being increased irritability (37%) or emotionality (29%).
  • Patients with SAH had a statistically significant higher mean depression score than the control population. Approximately 10% of the patients had a Hospital Anxiety and Depression Scale score in the range of a probable depressive or anxious state.
  • Only 25% reported a complete recovery without psychosocial or neurological problems.

As hypertension, smoking and excessive alcohol consumption are risk factors, individuals need to address such issues.

The question of management of aneurysms falls into 3 groups:

  • Patients may be found to have incidental aneurysms.
  • Patients with subarachnoid haemorrhage (SAH) might have one or more unruptured aneurysms.
  • There is the question of screening for aneurysms in patients who survive an episode of SAH and in first-degree relatives of patients with SAH.

The management of incidental findings will depend upon many aspects. The risk of rupture increases with age but so does morbidity of the procedure and younger people stand to gain more years. It is a difficult decision and family history and patient wishes must be considered.

Those who have already had an SAH are usually offered treatment, although if it is small or difficult to reach, it may be left alone.

One study found that predictive factors for rupture of an aneurysm were width:height ratio, maximum diameter of neck (≤3 mm) and family history of cerebrovascular disease.[17]

The results of screening first-degree relatives of patients for aneurysms are not promising and few apparently dangerous lesions are found. Even routine screening of people with adult polycystic kidney disease is not recommended.

Further reading & references

  1. Becske T et al; Subarachnoid hemorrhage, eMedicine, Dec 2010
  2. Liebeskind D; Cerebral Aneurysms, eMedicine, Oct 2010
  3. van Gijn J, Rinkel GJ; Subarachnoid haemorrhage: diagnosis, causes and management. Brain. 2001 Feb;124(Pt 2):249-78.
  4. van Gijn J, Kerr RS, Rinkel GJ; Subarachnoid haemorrhage. Lancet. 2007 Jan 27;369(9558):306-18.
  5. Cerebral Aneurysm Fact Sheet, National Institute of Neurological Disorders and Stroke
  6. Feigin VL, Rinkel GJ, Lawes CM, et al; Risk factors for subarachnoid hemorrhage: an updated systematic review of epidemiological studies. Stroke. 2005 Dec;36(12):2773-80. Epub 2005 Nov 10.
  7. Etminan N, Beseoglu K, Steiger HJ, et al; The impact of hypertension and nicotine on the size of ruptured intracranial J Neurol Neurosurg Psychiatry. 2011 Jan;82(1):4-7. Epub 2010 Jul 28.
  8. Ruigrok YM, Buskens E, Rinkel GJ; Attributable risk of common and rare determinants of subarachnoid hemorrhage. Stroke. 2001 May;32(5):1173-5.
  9. Carolei A, Sacco S; Headache attributed to stroke, TIA, intracerebral haemorrhage, or vascular Handb Clin Neurol. 2010;97:517-28.
  10. Linn FH, Wijdicks EF, van der Graaf Y, et al; Prospective study of sentinel headache in aneurysmal subarachnoid haemorrhage. Lancet. 1994 Aug 27;344(8922):590-3.
  11. Stroke: The diagnosis and acute management of stroke and transient ischaemic attack (TIA); NICE Clinical Guideline (July 2008)
  12. Management of patients with stroke or TIA: assessment, investigation, immediate management and secondary prevention; Scottish Intercollegiate Guidelines Network - SIGN (December 2008)
  13. Rinkel GJ, Feigin VL, Algra A, et al; Calcium antagonists for aneurysmal subarachnoid haemorrhage. Cochrane Database Syst Rev. 2002;(4):CD000277.
  14. Rabinstein AA, Lanzino G, Wijdicks EF; Multidisciplinary management and emerging therapeutic strategies in aneurysmal Lancet Neurol. 2010 May;9(5):504-19.
  15. Coil embolisation of ruptured intracranial aneurysms, NICE Interventional Procedure Guideline (2005)
  16. Wermer MJ, Kool H, Albrecht KW, et al; Subarachnoid hemorrhage treated with clipping: long-term effects on employment, relationships, personality, and mood. Neurosurgery. 2007 Jan;60(1):91-7; discussion 97-8.
  17. You SH, Kong DS, Kim JS, et al; Characteristic features of unruptured intracranial aneurysms: predictive risk J Neurol Neurosurg Psychiatry. 2010 May;81(5):479-84. Epub 2009 Sep 2.

Disclaimer: This article is for information only and should not be used for the diagnosis or treatment of medical conditions. EMIS has used all reasonable care in compiling the information but make no warranty as to its accuracy. Consult a doctor or other health care professional for diagnosis and treatment of medical conditions. For details see our conditions.

Original Author:
Dr Laurence Knott
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