Lumbar puncture and cancer

• ALSO KNOWN AS: Spinal Tap, LP

DEFINITION: Lumbar puncture is the insertion of a needle between two vertebrae in the lower back (lumbar region) into the spinal canal in order to obtain a sample of cerebrospinal fluid (CSF) for analysis.

Cancers diagnosed or treated: Cancers of the central nervous system (brain and spinal cord), such as meningeal carcinomatosis

Why performed: Lumbar punctures may be used to diagnose a condition, introduce medications, monitor treatment progress, or study a disease. Lumbar puncture results are used to help diagnose diseases such as meningitis, subarachnoid hemorrhage, Guillain-Barré syndrome, neurosyphilis, Reye's syndrome, and multiple sclerosis. Additionally, dyes for myelograms or anesthetics for pain relief may be introduced using lumbar puncture.

Patient preparation: A computed tomography (CT) scan or magnetic resonance imaging (MRI) scan is sometimes completed prior to lumbar puncture. These scans help ensure the test does not cause a significant decrease in skull pressure. Certain blood tests are taken to compare the results from the blood to the results from the CSF collected during the lumbar puncture, including serum chemistry panels (glucose) and complete blood counts (white blood cell count). Ideally, medications such as aspirin, ibuprofen, or other antiplatelet agents should be discontinued forty-eight to seventy-two hours before an elective lumbar puncture.

Steps of the procedure: The patient is placed on their side with knees drawn up toward the chest and back flexed toward the legs. The sterile procedure is completed, including sterile gloves, alcohol swabbing, iodine preparation, and isolation of the puncture area with sterile towels or paper drapes. The healthcare professional performing the procedure palpates (feels) the spine to locate the best position to insert the needle in the patient’s lower back. In adults, the spinal cord extends down to the first lumbar vertebra (five lumbar vertebrae are present, with the highest on the back labeled as number 1), so the healthcare professional locates an area below the first lumbar vertebra, usually between the third and fourth lumbar vertebrae or the fourth and fifth lumbar vertebrae. Infants require a lower insertion area since the spinal cord terminates at a lower level than in adults. A tiny needle injects a local anesthetic to numb the insertion site for the larger, hollow lumbar puncture needle. The needle goes into the spinal canal through the dura mater, and about one-half ounce (fifteen milliliters) of fluid is collected. Sometimes, an ultrasound is used to guide the needle insertion. The procedure takes about thirty to forty-five minutes.

After the procedure: The patient should lie flat on their back for about two hours following the procedure. Rising too fast after a lumbar puncture can increase the risk of the most frequent complication of a lumbar puncture, a positional headache.

Risks: A headache that changes with position is the most frequent complication, occurring in 20 to 25 percent of cases. These headaches are caused by fluid leaking into other tissues, and they usually resolve in two days to one week with rest and hydration. Uncommon complications include damage to nerves in the head and facial region that typically resolves within four months. Pain at the needle insertion site that radiates down the back of the legs is also relatively common. Rare complications include tumors and cysts that form in the area of the needle insertion site.

People with leukemia may have an increased risk of hematoma (clot) formation at or near the insertion site of the lumbar puncture needle. Leukemia patients who have a traumatic lumbar puncture (TLP+) can suffer contamination of the CSF with cancer cells, which lowers patient survival time.

The gravest complication of a lumbar puncture is herniation of the brain stem, where the lower portion of the brain is suddenly pulled down by the pressure release of opening the spinal canal to remove fluid. This can happen if a brain tumor or growth has increased pressure in the spinal canal since the fluid in the spinal canal is physically in contact with fluid surrounding the brain (hence the term cerebrospinal fluid, with cerebro referring to the brain). This rare occurrence is minimized by screening with neurological and ophthalmologic examinations and CT/MRI scanning as indicated.

Results: Normal CSF is clear and colorless. Sometimes, blood discolors the CSF, giving it a red, orange, yellow, or pink color. If blood is present, then it can indicate a very serious condition known as subarachnoid hemorrhage. Usually, if blood is present in the CSF, the blood comes from what is known as a traumatic tap, resulting from the inadvertent puncture of small blood vessels with the lumbar puncture needle. A traumatic tap is not usually a serious problem, but the blood source requires identification. Four or five small tubes of CSF are collected from a typical lumbar puncture. Blood from a traumatic tap diminishes from the first tube collected to the last tube collected. Other tests can be completed to help determine the source of blood found in a lumbar puncture. If the fluid is green, bilirubin may be present, or the patient may have an infection.

Laboratory tests routinely completed on CSF include protein, glucose, and white and red blood cell counts. Protein levels over 45 milligrams per deciliter (mg/dL), more than five white blood cells per microliter of fluid, and low glucose levels are also indicative of potential infection. Cultures and studies for bacteria, fungi, and viruses may be completed. Cells found in the CSF may be microscopically examined to determine if cancers of the brain or spinal cord are present. The pressure of the fluid as it initially drains out of the spinal canal, called the opening pressure, is measured, as is the closing pressure at the end of the procedure. Elevated pressures can indicate tumors or masses in the cranial cavity.

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