SUBARACHNOID HAEMORRHAGE

Epidemiology:• 3/4 are < 65 years.• Women are more frequently affected than men. • It typically presents with a sudden, severe 'thunderclap' headache

(often occipital) which lasts for hours or even days, often accompanied by vomiting.

• Physical exertion, straining, sexual excitement are common antecedents.

• There may be loss of consciousness at the onset, so it should be considered if a patient is found comatose.

• Since it is rare (incidence 6/100 000)& only 1/8 with a sudden severe headache has had a SAH, clinical vigilance is necessary to avoid a missed diagnosis.

• All patients with a sudden severe headache require investigation to exclude a SAH.

EXAM:• The patient is usually distressed & irritable, with photophobia. • There may be neck stiffness due to subarachnoid blood but this

may take some hours to develop. • Focal hemisphere signs (hemiparesis, aphasia etc.) may be present

at onset if there is an associated intracerebral haematoma. • A 3rd nerve palsy may be present due to local pressure from an

aneurysm of the posterior communicating artery, though this is rare.

• Fundoscopy may reveal a subhyaloid haemorrhage, which represents blood tracking along the subarachnoid space around the optic nerve.

Pathology:• 85% are caused by saccular ('berry') aneurysms bulging out from

the bifurcations of the cerebral arteries, particularly in the region of the circle of Willis.

• These rarely present before the age of 20 years. • There is an increased risk in first-degree relatives of those with

saccular aneurysms& with polycystic kidney disease & congenital collagen defects, e.g. Ehlers-Danlos syndrome.

• Of the remainder, 10% are non-aneurysmal haemorrhages (so called peri-mesencephalic haemorrhages), which have a very characteristic appearance on CT& a benign outcome in terms of mortality&recurrence.

• Some 5% of SAHs are due to rarities including arteriovenous malformations & vertebral artery dissection.

Management & prognosis:• The immediate mortality of aneurysmal SAH is about 30%. • Survivors have a recurrence, or re-bleed, of 40% in the first 4

weeks & 3% annually thereafter. • Insertion of platinum coils into an aneurysm (via an endovascular

procedure) or surgical clipping of the aneurysm neck reduces the risk of both early & late recurrence.

• Coiling may be associated with fewer perioperative complications &better outcomes.

• A re-bleed is not the only cause of early deterioration. • The clinician should also consider obstructive hydrocephalus,

delayed cerebral ischaemia due to vasospasm, hyponatraemia & systemic complications associated with immobility, e.g. chest infection or pulmonary embolism.

• Nimodipine (60 mg) is given to prevent vasospasm in the acute phase.