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An Observational Study of 2,248 Patients Presenting with Headache, Suggestive of Subarachnoid Hemorr

The Article: Sayer, David et al. An observational study of 2,248 patients presenting with headache, suggestive of subarachnoid hemorrhage, who received lumbar punctures following normal computed tomography of the head. Academic Emergency medicine. 2015;22:1267-1273.

The Goal: To determine the incidence of subarachnoid hemorrhage (and secondarily, aneurysmal subarachnoid hemorrhage) in patients undergoing lumbar puncture for evaluation of subarachnoid hemorrhage (SAH) after a negative CT scan.

The Study: The study was a retrospective chart review of adult patients in 6 urban teaching hospital EDs in the UK over 5 years presenting with acute headache concerning for subarachnoid hemorrhage that had negative initial CT with subsequent LP performed. Patients were excluded for positive CT results and LPs that were being performed primarily to evaluate for meningitis. Multislice CT scanners of varying slice thickness were used at each hospital, and CT scans were read either by general radiologists or neuroradiologists. CSF was evaluated for bilirubin by spectrophotometry.

Findings: Of 2248 lumbar punctures, 92 (4.1%) were suggestive of SAH.  Of these, all had follow-up neuroimaging with CTA or MRA. 9 (0.45%) were found to have a vascular abnormality: 8 (0.4%) had an aneurysm on angiography, while one had a carotid cavernous fistula. 350 of the LPs were uninterpretable and 299 were inconclusive. Overall, 204 LPs were performed in order to diagnose one vascular abnormality. A majority of patients with negative CTs and positive LPs presented with about one week of symptoms; only one received a CT scan within 6 hours of headache onset.

Takeaway: Lumbar puncture is a risky procedure that has low diagnostic yield in the evaluation of SAH after a negative CT secondary to low prevalence of the disease and high number of uninterpretable or inconclusive samples. This is particularly true of patients who presented soon after headache onset. Further studies are needed to develop a clinical decision rule to determine which patients are truly in need of lumbar puncture and which patient may safely forego LP after negative CT.

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