January 25, 2016

Background: Although non-contrast head CT (NCHCT) has near perfect sensitivity (98-100%) in detecting aneurysmal subarachnoid hemorrhage (SAH) when performed within 6 hours of headache onset, sensitivity declines after 6 hours. As a result of declining sensitivity, lumbar puncture (LP) continues to be part of the workup in suspected SAH. An LP gives providers the ability to perform CSF analysis for red blood cells and detect xanthochromia by visual inspection or spectrophotometry. In most of the world, including the United States, the predominant approach to identifying xanthochromia is visual detection. However, this technique is subjective and considered unreliable by many. Spectrophotometry is a more objective test but, has lower specificity, carries a higher cost and is unavailable in the majority of hospitals. In patients with SAH diagnosed by NCHCT or suspected based on LP results, angiography (CTA or MRA) is typically performed to investigate for an aneurysm that requires neurosurgical intervention. Angiography is considered to be the “gold standard” test for looking for aneurysmal SAH although it is not without it’s own limitations (a small minority of the population will have benign aneurysms and these increase with age).