Diagnosis of subarachnoid hemorrhage.

The ideal therapy and neurocritical care for patients with aneurysmal subarachnoid hemorrhage (SAH) follows from an early and accurate diagnosis. However, approximately 30% of patients with SAH are misdiagnosed at their initial visit to a physician. This article explores the reasons for this alarming error rate: failure to understand the full spectrum of presentation of SAH and failure to know the limitations of the major diagnostic tests (computed tomography of the brain and lumbar puncture [LP]). I suggest a strategy for selecting which patients with headache require evaluation beyond history and physical examination and how that evaluation should proceed. Other diagnostic issues are also discussed, such as use of magnetic resonance scanning and angiography for diagnosis, distinguishing the traumatic LP from true SAH, the concept of warning bleeds, and the LP-first diagnostic strategy.