Risks of lumbar puncture include:

• Bleeding into the spinal canal
• Discomfort during the test
• Headache after the test
• Hypersensitivity (allergic) reaction to the anesthetic
• Infection introduced by the needle going through the skin

There is an increased risk of bleeding in people who take blood thinners.

Brain herniation may occur if this test is done on a person with a mass in the brain (such as a tumor or abscess). This can result in brain damage or death. This test is not done if an exam or test reveals signs of a brain mass.

Damage to the nerves in the spinal cord may occur, particularly if the person moves during the test.

Cisternal puncture or ventricular puncture carry additional risks of brain or spinal cord damage and bleeding within the brain.

This test is particularly dangerous for people with:

• A tumor in the back of the brain that is pressing down on the brain stem
• Blood clotting problems
• Thrombocytopenia