Why is lumbar puncture contraindicated if patient has a brain abscess?

Performing a lumbar puncture (spinal tap) is contraindicated in patients with suspected or confirmed brain abscess due to the risk of herniation. A brain abscess is a collection of pus within the brain tissue, and increased intracranial pressure is often associated with it. Lumbar puncture involves inserting a needle into the spinal canal to collect cerebrospinal fluid (CSF) for analysis.

In the presence of a brain abscess, removing CSF during a lumbar puncture can rapidly decrease the pressure within the spinal canal. This sudden pressure change can cause a shift in brain tissue, leading to herniation. Herniation occurs when brain tissue is squeezed through a natural opening in the skull, such as the foramen magnum, where the brain connects to the spinal cord.

Brain herniation is a medical emergency and can have severe consequences, including coma, permanent neurological deficits, or even death. Therefore, to avoid this potential complication, a lumbar puncture is contraindicated in patients with a suspected or confirmed brain abscess.