Lumbar puncture and the diagnosis of aneurysmal subarachnoid haemorrhage - a ten-year service evaluation

Objectives: Aneurysmal subarachnoid haemorrhage is a life-threatening emergency that commonly presents with a sudden, severe headache. The diagnosis is usually confirmed on CT imaging, however a small subset of patients demonstrate normal imaging, particularly if presentation is delayed - in which case spectrophotometric analysis of cerebrospinal fluid (CSF) is undertaken. Nevertheless, thunderclap headache is a common presentation and the vast majority of investigated patients do not have aneurysmal subarachnoid haemorrhage. This ten-year service evaluation at a tertiary neurosurgery centre aims to estimate the utility of lumbar puncture in the diagnostic work-up of these patients. Methods: All instances of CSF spectrophotometry between 01/01/2011 and 31/12/2020 were evaluated. Clinical records of patients with positive spectrophotometry were analysed. A second method identified all coded diagnoses of non-traumatic subarachnoid haemorrhage over the same time period, with review of clinical records in cases of negative imaging. Results: Of 2158 instances of CSF spectrophotometry performed at the tertiary neurosurgery centre, four aneurysms were identified and treated by coiling or clipping, resulting in a number needed to treat of 540 patients to diagnose one case of aneurysmal subarachnoid haemorrhage. Of 648 patients with a coded diagnosis of non-traumatic subarachnoid haemorrhage (including local patients and transfers from satellite hospitals), 27 patients displayed initial negative imaging, of which 9 were found to have aneurysms and underwent neuro-intervention. Lumbar puncture was instrumental in the diagnosis and led to intervention in three patients identified by this method. Conclusion: CSF analysis resulted in diagnosis and intervention for missed (CT-negative) aneurysmal subarachnoid haemorrhage in approximately 1/540 tested patients. The estimated yield in a real-world setting may be useful for clinicians or provide a basis for discussion when counselling patients on benefit and risk.