Objectives: The objective was to determine the incidence of subarachnoid hemorrhage (SAH) diagnosed by lumbar puncture (LP) when the head computed tomography (CT) was reported as demonstrating no subarachnoid blood.Methods: Data were obtained on patients who received LP to diagnose or exclude SAH attending six hospitals over 5 years. Subsequent investigations and outcomes were reviewed in all patients with LPs that did not exclude SAH.Results: A total of 2,248 patients were included. A total of 1,898 LPs were suitable for biochemical analysis, of which 92 (4.8%) were positive for blood, suggesting SAH; 1,507 (79.4%) were negative; and 299 (15.6%) were inconclusive. Of the 92 patients with positive cerebrospinal fluid analysis, eight patients (0.4%) had aneurysms on further imaging, and one had a carotid cavernous fistula.
Conclusions:In patients presenting to the emergency department with acute severe headache, LP to diagnose or exclude SAH after negative head CT has a very low diagnostic yield, due to low prevalence of the disease and uninterpretable or inconclusive samples. A clinical decision rule may improve diagnostic yield by selecting patients requiring further evaluation with LP following nondiagnostic or normal noncontrast CT brain imaging.ACADEMIC EMERGENCY MEDICINE 2015;22:1267-1273© 2015 by the Society for Academic Emergency Medicine A cute headache is a common presentation to the emergency department (ED), accounting for around 1% to 2% of all encounters.1,2 The differential diagnosis is wide and includes potentially life-threatening conditions, such as aneurysmal subarachnoid hemorrhage (SAH). Aneurysmal SAH has an incidence of approximately six to eight per 100,000 per person-years, and prevalence of 0.4% to 6%, estimated overall to be around 2%. 3,4 There is an overall risk of rupture of 1.9%.4 SAH has a 1-month mortality of around 40% to 45%, and of those surviving the hemorrhage, around 30% will have severe disabilities. 5,6 Following the initial presentation, the risk of rebleeding is approximately 1.5% per day and 15% to 20% in the first