Introduction: Acute severe headache is a common presentation: subarachnoid hemorrhage (SAH) is the cause in a minority of patients and has a high rate of morbidity and mortality. With advancement in imaging technology, emerging evidence now suggests that LP is no longer required for a subset of patients as CT has 100% sensitivity in detecting SAH [1-2], calling into question the requirement of LP as a secondary test in the event of a negative CT scan.
The West of Scotland has a high proportion of deprived areas in relation to the rest of the United Kingdom, and resources are a premium as part of a socialized healthcare model. To that end, we aim to assess the proportion of patients with conclusive LP results following a negative CT scan in suspected SAH to determine the diagnostic efficacy of LP in order to re-validate this as a useful, cheap test.
Methods: CSF spectrophotometric absorbance data from all centres in a regional health board were identified for consecutive patients over a 6-month period. Results were stratified as conclusive (positive/negative), or inconclusive according to national guidelines.
Results: were positive (12 of 255), revealing 4 cerebral aneurysms requiring treatment. 16 out of 255 (6.3%) samples were inconclusive, yielding 1 aneurysm requiring treatment. In the same period, we estimate that over 2,000 CTA and 50 incidental aneurysms have been saved in a single neurosurgical centre.
Conclusions: LP has a high diagnostic yield, eliminating the need for neurosurgical opinion or investigation in almost 90% of cases. The test is both cost and time efficient and subjects only a small number of patients to the radiation and contrast risks of angiography. This has important implications for socialized healthcare systems, and in areas that can ill afford the increased cost of angiography becoming the “gold standard” in SAH exclusion following a negative CT scan.
Patient Care: We feel that this cheap and simple test should retain a place in the diagnostic arsenal of emergency clinicians, not least since it helps in the differential diagnosis of SAH and meningitis.
Learning Objectives: LP is a cheap and effective test. It negates the need for invasive angiography in the majority of cases. There are cases of CT negative but LP positive SAH in early presentation, so we do not agree with the assertion that CT is always fully sensitive early post-ictus.
References:  Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study.
Perry JJ1, Stiell IG, Sivilotti ML, Bullard MJ, Emond M, Symington C, Sutherland J, Worster A, Hohl C, Lee JS, Eisenhauer MA, Mortensen M, Mackey D, Pauls M, Lesiuk H, Wells GA. BMJ. 2011 Jul 18;343:d4277. doi: 10.1136/bmj.d4277.
 Cortnum S1, Sørensen P, Jørgensen J. Determining the sensitivity of computed tomography scanning in early detection of subarachnoid hemorrhage. Neurosurgery. 2010 May;66(5):900-2; discussion 903. doi: 10.1227/01. NEU.0000367722.66098.21.