Lumbar puncture

A lumbar punctureA procedure to sample fluid that surrounds the brain and spinal cord, the cerebrospinal fluid, or CSF. may be needed in some people if a subarachnoid haemorrhageBleeding into the subarachnoid space surrounding the brain, the area between two of the three layers (meninges) surrounding the brain and spinal cord (the arachnoid mater and the pia mater). (a bleed around the brain) is suspected and a CTA scan that generates a series of cross-sectional X-ray images. scan is normal.[1]

With this procedure, also known as a spinal tap, a sample of fluid is extracted from around the brain and spinal cord - the cerebrospinal fluidThe fluid surrounding the brain and spinal cord. Abbreviated to CSF.. A hollow needle is inserted between two of the vertebrae of the spine, and a few millilitres of fluid is withdrawn.

A lumbar punctureA procedure to sample fluid that surrounds the brain and spinal cord, the cerebrospinal fluid, or CSF. can detect any bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. in the fluid round the brain and spinal cord, which may be present in the case of a subarachnoid haemorrhageBleeding into the subarachnoid space surrounding the brain, the area between two of the three layers (meninges) surrounding the brain and spinal cord (the arachnoid mater and the pia mater). . The procedure should be postponed until 12 hours after the initial onset of symptoms, to give the red bloodA fluid that transports oxygen and other substances through the body, made up of blood cells suspended in a liquid. cells enough time to break down to produce bilirubinA bile pigment, a coloured compound produced from the breakdown of haemoglobin. - the actual substance for which the lumbar punctureA procedure to sample fluid that surrounds the brain and spinal cord, the cerebrospinal fluid, or CSF. checks.[1]

If a subarachnoid haemorrhageBleeding into the subarachnoid space surrounding the brain, the area between two of the three layers (meninges) surrounding the brain and spinal cord (the arachnoid mater and the pia mater). is found to be present, then CTA scan that generates a series of cross-sectional X-ray images. angiographyX-ray imaging of the blood vessels following the injection of a dye to improve visibility. should be performed to look for any aneurysms.[1]

References: 
  1. Yew KS and Cheng E. Acute stroke diagnosisThe process of determining which condition a patient may have.. Am Fam Physician. 2009; 80: 33-40.