Lumbar puncture and the diagnosis of CT negative subarachnoid haemorrhage: time for a new approach?

Objective: Because of potential risks of poor outcome, lumbar puncture (LP) is recommended to exclude the presence of blood breakdown products in patients with suspected subarachnoid haemorrhage (SAH) and a normal CT scan. The aim of this study was to document how often this test proved useful.
Method: A retrospective analysis of prospectively recorded data was conducted. Patients with suspected SAH and a normal CT scan in whom LP was recommended between May 2008 and May 2010 were identified using the neurosurgical referral database. CT scan results, LP results, inpatient stay, investigations and interventions were recorded.
Results: One hundred and sixty-three patients were identified in whom LP was recommended after a reported negative CT scan. Thirty-six of these 163 patients had a positive LP of which seven had evidence of SAH on the initial CT scan. In 66 patients, the LP was not diagnostic and 59/66 (90%) patients underwent secondary imaging in whom five with aneurysms were identified and treated.
Conclusion: LP-driven decision making in patients with a normal scan and suspected SAH is suboptimal in over a third of cases. Patients with a non-diagnostic LP harboured five aneurysms that merited treatment. These results support the need for secondary investigations following suspected SAH, but suggest that these could take the form of secondary imaging rather than a lumbar puncture.