The Use of CT Head in Diagnosing Subarachnoid Haemorrhage

Abstract

Objectives: The aim of our audit was to assess whether a LP is necessary for a diagnosis of SAH if the CT head is negative within six hours. Methods: A retrospective analysis of 701 CT heads over 15 days was carried out at Lincoln County hospital from 1st to 15th January 2020. Provisional diagnosis of each CT head request was recorded. Radiologists’ reports were analyzed and the positive findings were recorded. Patients who had a provisional diagnosis of SAH and had a negative CT head, were further investigated to check if they had a LP and results were recorded. Timing of the CT heads from the onset of symptoms was recorded. Results: Results showed 7% of CT heads were requested to rule out SAH, 51% to rule out other intracranial bleeds and the reminder of requests were for other pathologies. Out of the 7% requests for SAH, 2% were picked up on the CT scans. The remaining 5% of the patients all had LP. All of the LPs were negative and showed no signs of a SAH. The timing of CT scans showed that only 32% of patients with provisional diagnosis of SAH had a CT head within 6 hours. 100% of patients had the CT head done within 12 hours of presentation. Conclusion: More confidence is needed in using CT heads if done within six hours from symptom onset. Due to high risks associated with LPs, pretest probability should be high before considering LPs.