Lumbar puncture is often an important investigation in certain suspected diagnoses, such as subarachnoid haemorrhage, meningitis and idiopathic intracranial hypertension. However, it has absolute and relative contraindications, many of which are encountered in raised ICP.

No patient should have a lumbar puncture without a CT scan of the brain. Decreased conscious level is a relative contraindication, and if there are concerns about the safety of lumbar puncture, specialist advice should be sought before proceeding. In the absence of an obvious mass lesion, CT or MR imaging of the brain are poor at identifying raised intracranial pressure, and should not be relied on for this purpose.