title: A retrospective review of sudden onset severe headache and subarachnoid haemorrhage on the clinical decision unit: looking for a needle in a haystack?
abstract: BACKGROUND
  Patients commonly present to the Emergency Department with sudden onset acute severe headache, but exclusion of significant secondary causes, particularly subarachnoid haemorrhage (SAH), is vital. The misdiagnosis of SAH is most likely in patients with a normal neurological examination, and the consequences can be disastrous. A noncontrast computed tomography (CT) brain scan is the initial investigation of choice, and most would recommend that, if negative, this be followed by a lumbar puncture (LP) and cerebrospinal fluid (CSF) analysis. Many hospitals in the UK have developed Clinical Decision Unit (CDU) pathways to provide a standardized approach to the investigation and management of neurologically normal patients with headache suggestive of SAH.
  
  
  OBJECTIVE
  The aims of this study were to describe the prevalence of SAH and to evaluate the performance of CT and LP in a CDU population with sudden onset acute severe headache.
  
  
  METHODS
  A retrospective review of neurologically pristine patients admitted to a CDU pathway for exclusion of SAH was conducted. Structured case notes were reviewed; patient demographics, investigation results and clinical outcomes were recorded in each case.
  
  
  RESULTS
  The overall prevalence of SAH in this population was 14/517 (2.7%). A noncontrast CT of the brain had a negative predictive value of 99.8%, reducing the post-test probability of having an angiogram-positive SAH detected by LP and CSF analysis to 0.21% (95% confidence interval 0.04-0.36%).
  
  
  CONCLUSIONS
  The management of neurologically pristine patients with sudden onset severe headache on a CDU pathway is feasible. In light of the low prevalence of SAH in this population, the decision to follow a negative CT with an LP in all cases needs careful consideration, as CSF results may only rarely confer therapeutic benefit to patients suspected of SAH.
authors: aEmergency Department, Aberdeen Royal Infirmary, Aberdeen bEmergency Department, Leeds General Infirmary, Leeds, UK.
authors: Jamie G
authors: JG
authors: Cooper
authors: Benedict
authors: B
authors: Smith
authors: Tajek B
authors: TB
authors: Hassan
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging; D003661:Decision Support Techniques; D005260:Female; D006261:Headache / Q000134:cerebrospinal fluid / Q000175:diagnosis* / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging; D017410:Practice Guidelines as Topic; D012189:Retrospective Studies; D013129:Spinal Puncture; D013345:Subarachnoid Hemorrhage / Q000134:cerebrospinal fluid / Q000175:diagnosis* / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed; D055815:Young Adult