Contents
Introduction
A subarachnoid haemorrhage (SAH) describes bleeding in the brain into the subarachnoid space. A subarachnoid haemorrhage is considered a type of hemorrhagic stroke. The bleeding occurs as the result of rupture of aneurysm (80%) and AV malformations (15%). In the remainder of cases, no cause can be identified.
- Cerebral aneurysms are present in about 2% of the population
- Previously thought to be congenital, now they are believed to be acquired, but their cause is unknown
- Trauma is also a major cause, but is not considered true SAH.
The classical sign of a subarachnoid haemorrhage is a sudden onset (“thunderclap”) intense headache (“feels like I’ve been hit on the back of the head”). Most patients are aged under 60 years, with a mean age of onset at 50.
Early diagnosis and management reduces long term disability and death – the diagnosis is time critical.
Diagnosis is usually made with a plain CT of the brain, but in patients whose symptoms started more than 6 hours ago the blood cannot always be seen, and if the CT is negative – lumbar puncture should be performed. The presence of blood confirms the diagnosis.
Epidemiology and Aetiology
- Incidence is about 8 per 100 000
- About 5% of all strokes
- Risk factors
- These are very similar to the risk factors for all causes of stroke, and include:
- ↑BP
- Smoking
- Known aneurysm – Or disease that causes aneurysm – e.g. polycystic kidney disease, co-arctation of the aorta, Ehlers-Danlos Syndrome
- Family history – increases risk by 3-5x
- Increased alcohol intake – increases risk by 2x
- Female gender has slightly increased risk (1.6x)
- Afro-Caribbean ethnicity increases risk (2x)
- Also higher incidence in Finland and Japan
- Incidence is declining in the last 40 years
- Probably due to declining rates of smoking and better control of hypertension
- Mean age of onset is 50
- 85% cases of SAH are due to arterial aneurysms
- 10% from non-aneurysms
- 5% from other vascular malformations
The role of cerebral aneurysms
- About 2% of the population have a cerebral aneurysm – most of these are completely asymptomatic
- 90% of aneurysms are <1cm – these have a low risk of bleeding and are unlikely to cause localised effects
- Some larger aneurysms (about 5% of all aneurysms) can cause mass effects by pressing on local brain structures with can lead to focal neurological symptoms, or seizures
- The bigger the aneurysm the bigger the risk of bleeding
- Up to 90% of aneurysms are located in the anterior circulation (internal carotid, middle cerebral arteries)
Signs and Symptoms
You should have a low threshold of suspicion for SAH in patients with sudden onset headache. Early treatment prevents rebelled and is associated with lower risk of long-term disability and death. Making the diagnosis is time critical. Patients seen outside of the emergency department should be referred to hospital immediately for assessment.
- Sudden onset severe headache, often at the back of the head
- Known as thunderclap headache
- The headache reaches its maximum severity within 1-5 minutes of onset
- Most patients with thunderclap headache do not have SAH. Other causes include migraine, cough, coitus headache
- Neck stiffness – Kernig’s sign may be present after 6 hours (due to chemical meningitis), or in massive bleeds it may occur sooner due to herniation of the cerebellar tonsils (due to raised ICP).
- Sometimes the chemical meningitis can cause vomiting and extensor plantar responses after 24hrs
- Photophobia
- Nausea and vomiting
- Impaired consciousness (drowsiness / coma) – usually occurs very shortly after the onset of symptoms, but can occur several hours later.
- Cranial nerve signs
- Hemiplegia
- CNS deficits can become permanent within minutes. If it lasts more than several hours it is highly unlikely to ever resolve.
- Sentinel headache – is experienced by about 6% of patients, and is a prodromal headache thought to be the result of a small leak before rupture of an aneurysm or malformation.
Classification
|
Grade
|
Signs
|
Mortality (%)
|
|
I
|
None
|
0
|
|
II
|
Neck stiffness, cranial nerve lesions
|
11
|
|
III
|
± Drowsiness
|
37
|
|
IV
|
± Hemiplegia
|
71
|
|
V
|
Prolonged coma
|
100
|
Prognosis
- Overall mortality is 35-50%
- About 30% die within a few days, and another 10-15% within a few weeks.
- Most patients die within 1 month
- After 1 month, 90% of patients will survive >1 year
- Prognosis is worse with aneurysm, better with AMV, and best when no lesion is detected (presumably the lesion was small, and has healed in these instances).
Pathology
- The period of haemorrhage is actually very short – and it normally stops bleeding by itself.
- After the initial haemorrhage, patients are at risk from vasospasm. This can causes ischaemia, which can result in secondary brain damage and further neurological signs.
- 25% of patients will have signs of TIA / stroke after SAH as a result of vasospasm
- Brain oedema and risk of vasospasm is greater between 72hrs and 10 days
- Secondary acute hydrocephalus often occurs
- Re-bleeding is VERY COMMON and usually occurs within 7 days. The risk thereafter is about 3% / year
Investigations
Diagnosis is by CT, or if this is normal with a high sense of suspicion, CSF.
CT – is able to detect >90% of lesions within 48 hours of onset of symptoms.
- Often star shaped lesion on CT – or the blood fills in giral patterns around the brain the ventricles
- If CT is negative, but SAH is highly suspected, consider lumbar puncture, or CT angiogram of the brain.
Lumbar puncture – contraindicated in raised ICP – so be careful! – Several features:
- Blood – detected via the presence of bilirubin. Previously, people would use the level of RBCs as an indicator, however, it is unreliable to use the rule: if blood remains constant in 3 separate samples = SAH, if blood declines = tap trauma.
- Xanthochromia – yellow appearance of CSF if it is left to stand for a few hours
Treatment
- Get specialist help! – call the Medical Registrar, the Neurosurgeon on call, and depending on GCS, call the anaesthetist. (Patients are unable to maintain a competant airway at GCS <8)
- Stablise the patient haemodynamically
- Many patients require ICU treatment
- Neurosurgical interventions are limited, but in severe cases, a drain may be placed.
- After the acute presentation, the patient may have their aneurysm clipped or coiled to prevent further bleeds
References
- Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
- Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
- Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy
- 2023 Guideline for the Management of Patients With Aneurysmal Subarachnoid Hemorrhage: A Guideline From the American Heart Association/American Stroke Association – Stroke. 2023 Jul;54(7):e314-e370
- Subarachnoid Haemorrhage – patient.info