Lesson of the week - Spectrophotometry of cerebrospinal fluid in suspected subarachnoid haemorrhage

To underline the importance of correctly examining cerebrospinal fluid, we describe two patients with subarachnoid haemorrhage for whom cranial computerised tomography was normal and on whom lumbar puncture was subsequently done. Both had clear and colourless cerebrospinal fluid, but subsequent spectrophotometry showed bilirubin. Cerebral angiography then showed a ruptured aneurysm in each patient.