Brain & Nervous System Health Center

What Affects the Test

Reasons you may not be able to have the biopsy or why the results may not be helpful include:

• Not being able to lie still during the procedure.
• Having conditions such as obesity, dehydration, spinal disease, severe arthritis, or recent spinal surgery. These conditions may make it hard to do a lumbar puncture with the person lying down. The procedure may need to be done with the person sitting up and bent forward. In some cases, the procedure may need to be done with a special X-ray method called fluoroscopy. This is used to guide the placement of the spinal needle.
• Bleeding into the cerebrospinal fluid (CSF). The needle puncture can cause bleeding into the CSF. Several samples of the fluid can show the difference between bleeding from the puncture and bleeding caused by a brain hemorrhage.
• Not being able to collect a sample of the fluid. This is called a "dry tap."

What To Think About

• A lumbar puncture is not done if the person has:
  • A suspected tumor, swelling, or increased pressure in the brain. A computed tomography (CT) scan or magnetic resonance imaging (MRI) scan may be done first to see if it is safe to do the lumbar puncture.
  • A skin infection on the lower back. Doing a lumbar puncture in this case may allow the infection to spread into the spinal canal.
  • Bleeding disorders, which may increase the chance of bleeding during the procedure.
• Other tests that may be done include:
  • A cisternal or ventricular puncture. Cerebrospinal fluid (CSF) can be collected from the upper spinal canal at the base of the skull (cisternal puncture) or from within the skull (ventricular puncture) when it is not possible to get CSF from the lumbar area. These procedures are done by a trained radiologist or neurosurgeon. Special X-ray methods are used to guide the placement of the needle.
  • Bacterial marker studies. In cases of suspected bacterial meningitis, bacterial marker (bacterial antigen) studies can quickly find the common types of bacteria that cause meningitis. Antibiotic treatment for that bacteria can be started immediately.