Aneurysmal subarachnoid haemorrhage: guidance in making the correct diagnosis.

BACKGROUND The natural history of untreated aneurysmal subarachnoid haemorrhage carries a dismal prognosis. Case fatalities range between 32% and 67%. Treatment with either surgical clipping or endovascular coiling is highly successful at preventing re-bleeding and yet the diagnosis is still missed. METHODS Based on the national guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage and a review of other available literature this study has compiled guidance in making the diagnosis. CONCLUSION In patients presenting with a suspected non-traumatic subarachnoid haemorrhage, computed tomography within 12 hours will reliably show 98% of subarachnoid haemorrhage. In patients who present after 12 hours with a negative computed tomogram, formal cerebrospinal fluid spectophotometry will detect subarachnoid haemorrhage for the next two weeks with a reliability of 96%. Between the early diagnosis with the aid of computed tomography and the later diagnosis with the added benefit of spectophotometry in the period where computed tomograms become less reliable, it should be possible to diagnose most cases of subarachnoid haemorrhage correctly.