Overview
A lumbar puncture is a medical procedure used to aid in the diagnosis of neurologic diseases and disorders of the central nervous system. During a lumbar puncture, a thin needle is inserted between the small bones of the spine, called vertebrae. This allows a sample of cerebrospinal fluid to be extracted from the spine of a patient, in a similar fashion to how blood would be drawn from a vein.
Anatomy
The Central Nervous System
The brain and spinal cord comprise the central nervous system (CNS). The CNS is responsible for processing information and coordinating the functions of your body. Due to its importance, the two parts of your CNS are well protected by bone. The skull and spine surround the brain and spinal cord, respectively.
Cerebrospinal Fluid
As its name suggests, cerebrospinal fluid (CSF) is a colorless fluid that flows freely around the brain and the spinal cord in an area called the subarachnoid space. CSF is excreted from ventricles in the brain and serves as a cushion around the CNS, while providing nutrients and removing waste products.
Procedure
Before a lumbar puncture (LP), the patient is positioned lying laterally, with the head and knees drawn toward the chest. The site is cleaned with skin disinfectant and numbed using local anesthetic. A spinal needle is inserted and slowly advanced to a depth of 3-4cm. A vial is placed below the needle, allowing the CSF to passively drip out. After the needle is withdrawn, a bandage is placed over the site. Post-lumbar puncture headache is the most commonly reported side effect.
Diagnosis
Once extracted from a patient, a sample of CSF is sent to a laboratory to be tested. When we think of body fluids that are tested, we often think of a blood test. A CSF analysis works the same way. Measurements of a variety of substances, chemicals, and cells, can be used to diagnose many conditions, including the following:
Infectious diseases (encephilitis, meningtis, tuberculosis)
Intercranial hemorrhage (brain bleed)
Autoimmune neurological disorders (multiple sclerosis, sarcoidosis)
Dementia
Remember, these conditions are only identifiable because of the presence of multiple specific biomarkers within the CSF. For example, the simultaneous presence of increased pressure, cloudy color, low glucose, elevated proteins, and certain antibodies indicate a patient is infected with tuberculosis. Because of this vital function in diagnosing patients, the lumbar puncture remains one of the most important and common procedures in neurology today.