CT use in subarachnoid haemorrhage

Abstract

Subarachnoid haemorrhages (SAH's) are the fourth most frequent type of acute cerebrovascular event and account for approximately 8% of the total. In most cases (at least 75%), SAH's are caused by the rupture of aneurysms of the circle of Willis, with the aneurysm itself lying within the subarachnoid space. SAH's affect approximately 11 of every 100,000 inhabitants in the general population. The most critical period is during the first few days after the haemorrhage: 25% of deaths occur on the first day and 50% in the first five days. Remedying this situation calls for rapid and specific diagnosis, which is not possible using clinical data alone. In recent years SAH survival rates have increased, due in part to progress in intensive care and surgical techniques, but above all thanks to the more precise diagnostic methods that are now available (6). Computerized Tomography (CT) plays a fundamental role (19). From the outset its non-invasive nature and sensitivity have made it an examination technique capable of achieving early diagnosis. More specifically, its sensitivity is given as ranging between 93-100% if performed within the first 12 hours of the onset of symptoms (24, 26). In addition to the observation of subarachnoid bleeding (with the typical hyperdensity of the basal subarachnoid cisterns and within the cortical sulci), CT is also able to document collateral phenomena and complications such as intraparenchymal, intraventricular and subdural haemorrhages, any mass effect upon the cerebrum, hydrocephalus and cerebral infarcts associated with vasospasm. In some cases, it is possible to establish the more or less precise origin of the haemorrhage from the distribution pattern of blood collection, which is particularly useful in directing subsequent selective angiographic examinations. In the case of multiple aneurysms, the pattern of the blood collection on CT is important in indicating which of them has bled (4). CT allows approximative prognosis assessment (e.g., widespread and massive forms of SAH have a more severe prognosis than smaller ones). Lastly, CT is useful in selecting which patients are to undergo angiography and in determining when it should be performed (28). © 2006 Springer Berlin Heidelberg.