Subarachnoid haemorrhage (SAH)

SAH describes spontaneous, rather than traumatic, arterial bleeding into the subarachnoid space and is usually clearly recognisable by its dramatic onset. SAH accounts for 10% of cerebrovascular disease and has an annual incidence of 6 per 100,000.

Causes:

Common causes:

• Saccular (‘berry’) aneurysms ~70%
• Arteriovenous malformations ~10%
• No lesion found ~20%

Rare associations:

• Bleeding disorders
• Mycotic aneurysms
• Acute bacterial meningitis
• Brain tumours (e.g. metastatic melanoma)
• Marfan’s syndrome

Saccular (‘berry’) aneurysms:

Saccular aneurysms form on the circle of Willis and its adjacent branches. The common sites of aneurysms are:

• Posterior communicating artery aneurysm (junction of the posterior communicating artery and the internal carotid artery)
• Anterior communicating artery aneurysm (junction of the anterior communicating artery and the anterior cerebral artery)
• Middle cerebral artery aneurysm (the bifurcation of the middle cerebral artery)

Aneurysms cause symptoms either by:

• Spontaneous rupture
• Direct pressure on surrounding structures (e.g. a posterior communicating artery aneurysm is a cause of a painful third-nerve palsy)

Arteriovenous malformations (AVM):

• This is a lesion of developmental origin, usually within the hemisphere
• An AVM may also cause epilepsy (which is often focal)
• Once an AVM has ruptured to cause SAH, there is a tendency to rebleed at a rate of 10% per year

Clinical features of SAH:

• Sudden onset of a devastating headache, often occipital
• Vomiting
• Loss of consciousness
• The patient remain comatose or drowsy for several hours to several days
• Less severe headaches cause diagnostic difficulties (SAH is possible diagnosis in any sudden headache)

On examination:

• Neck stiffness
• Positive Kernig’s sign:
• Pain and resistance on passive knee extension with hips fully flexed

• Papilloedema is occasionally present

Investigations:

CT imaging:

• Is the initial investigation of choice
• Subarachnoid or intraventricular blood is usually seen

LP:

• Only necessary after CT if the diagnosis is in doubt
• The CSF becomes yellow (xanthochromic) several hours after SAH

Carotid and vertebral angiography:

• Usually performed in all patients who are potentially fit for surgery (i.e. <65 years and not in a coma) to establish the cause and site of bleeding

Differential diagnosis:

• Severe migraine
• Acute bacterial meningitis (caused by the rupture of a meningeal microabscess)

Complications:

Hydrocephalus:

• Caused by blood clots in the subarachnoid space obstructing the flow of CSF
• Is a cause of deteriorating consciousness level a few days or weeks after the initial bleed
• Shunting may be required

Severe spasm of the intracranial arteries

• Is an occasional complication
• Is a poor prognostic sign

Management:

• Where angiography demonstrates aneurysm, a direct neurosurgical approach to clip the neck of the aneurysm is carried out
• In selected cases, the results of surgery are excellent

Immediate treatment:

• Bedrest
• Supportive measures
• Control HT
• Dexamethasone is often prescribed to reduce cerebral oedema

All cases of SAH should be referred to a specialist centre for a decision about angiography and possible surgery

Prognosis:

• 50% of cases are dead or moribund before they reach hospital
• of the remainder, a further 10-20% die in the early weeks in hospital from further bleeding