Is there a role for lumbar puncture in early detection of subarachnoid hemorrhage after negative head CT?

To investigate the role of lumbar puncture (LP) after a negative head computed tomography (CT) when ruling out subarachnoid hemorrhage (SAH) within 24 h of symptom onset. In a single-center, retrospective cohort study, we studied a consecutive series of patients from 2011 to 2015. All patients underwent CT or CT following LP to rule out SAH. Patients were categorized into four groups depending on the time of symptom onset to initial head CT: 0-6 h, 6-12 h, 12-24 h, and over 24 h. Experienced radiologists interpreted all CT scans. We investigated the sensitivity, specificity, and negative predictive value (NPV) of noncontrast CT in detecting SAH. Of 539 patients with suspected SAH and negative CT, 280 (51.9%) had their CT performed within 24 h of symptom onset. None of these patients had SAH. Five (1.9%) out of 259 patients with CT performed after 24 h of symptom onset had SAH diagnosed, and two turned out to be aneurysmal. When CT was performed within 24 h of symptom onset it had a sensitivity of 100% (95% CI 95-100%), specificity of 98% (95% CI 96-99.7%), and NPV of 100% (95% CI 98-100%) in detecting SAH. Modern CT scanners seem to have high sensitivity and specificity in the diagnosis of SAH when performed within 24 h of symptom onset. Beyond this point, CT seems to lack sensitivity and further investigation with LP is required.