A spinal tap, also known as a lumbar puncture, is a medical procedure that involves inserting a thin needle into the lower back to collect a sample of cerebrospinal fluid (CSF). This fluid surrounds and cushions the brain and spinal cord, aiding nutrient exchange and waste removal. Analyzing this fluid provides information about the central nervous system. The procedure is primarily used as a diagnostic tool to help identify various conditions affecting the brain and spinal cord.
Why Spinal Taps Are Performed
A spinal tap obtains cerebrospinal fluid (CSF) for analysis, offering a window into the central nervous system’s health. This analysis reveals markers for diagnosing neurological conditions. CSF examination checks clarity, color, pressure, red and white blood cells, protein, and glucose.
Spinal taps diagnose infections of the brain and spinal cord, like meningitis and encephalitis. CSF analysis identifies whether inflammations are caused by bacteria, viruses, or fungi, guiding treatment. Specific immune cells or pathogens indicate ongoing infection.
Spinal taps also identify inflammatory conditions like multiple sclerosis (MS) and Guillain-Barré syndrome. In MS, the CSF may show specific protein patterns or increased white blood cells. Guillain-Barré syndrome can be suggested by elevated protein levels without increased cell count.
The procedure detects cancers that have spread to or originated within the nervous system, including leukemia and other metastatic tumors. Abnormal cells in the CSF confirm cancer affecting the brain or spinal cord, aiding disease staging and guiding specialized treatments, such as intrathecal chemotherapy.
A spinal tap measures CSF pressure, useful for diagnosing conditions like hydrocephalus or idiopathic intracranial hypertension. It also detects bleeding around the brain, such as subarachnoid hemorrhage. Beyond diagnosis, a spinal tap can administer medications or relieve elevated CSF pressure.
How the Procedure Works
A spinal tap is typically performed in a hospital or clinic, taking 15 to 20 minutes. The patient is positioned either lying on their side with knees drawn up or sitting and leaning forward. These positions help curve the back, widening spaces between vertebrae for needle insertion.
After positioning, the healthcare professional cleanses the lower back with an antiseptic solution to minimize infection risk. A local anesthetic is then injected into the skin at the puncture site to numb the area. Patients may experience a stinging sensation.
Once numb, a thin, hollow needle is carefully inserted between two vertebrae in the lower back, usually between the third and fourth or fourth and fifth lumbar vertebrae. This location is chosen because the spinal cord ends higher up, ensuring the needle enters below it to avoid injury. Patients may feel pressure or tingling as the needle advances.
Once the needle reaches the subarachnoid space, where CSF circulates, fluid is collected into sterile tubes. CSF pressure may also be measured. After fluid collection or medication administration, the needle is removed, and a bandage is placed over the puncture site.
What to Expect Afterward
After a spinal tap, patients are advised to rest and remain lying down for a period, often an hour or more, to reduce discomfort. Mild back pain or soreness at the injection site is common and usually subsides within a few days.
A common side effect is a headache, known as a post-dural puncture headache. This headache often feels dull or throbbing, worsening when sitting or standing and improving when lying flat. It is caused by CSF leaking from the puncture site, leading to a temporary decrease in fluid pressure around the brain.
Staying hydrated and taking over-the-counter pain relievers can help manage headaches and back discomfort. Most headaches resolve within a few days to a week. Patients are advised to avoid strenuous activities for 24 to 48 hours following the procedure.
While spinal taps are generally safe, watch for signs requiring medical attention. Contact a healthcare provider immediately if you experience a severe headache that does not improve, a fever, new or worsening pain at the puncture site, or signs of infection such as redness, swelling, or discharge. Numbness, tingling, or weakness in the legs also warrant immediate medical evaluation.