Subarachnoid haemorrhage of unknown aetiology: what next?

Subarachnoid haemorrhage (SAH) is often associated with negative cerebral angiography. Following the exclusion of other causes, a patient may be suspected of harbouring an occult intracranial aneurysm, with risk of recurrent bleeding and death. These patients are often identified on the basis of clinical presentation and computed tomography (CT) findings, and require expeditious further investigation if morbidity and mortality are to be minimized. Currently available options include repeated cerebral angiography, surgical exploration, and the newer technologies of computed tomography angiography (CTA) and magnetic resonance angiography (MRA). We review these options, based on current literature, with particular emphasis on the expanding roles of CTA and MRA. A multimodality management protocol is proposed, with decisions based on clinical urgency, patient progress and the natural history of aneurysmal SAH, particularly vasospasm and aneurysm thrombosis.