A spinal tap, also known as a lumbar puncture, is a procedure in which a long thin needle is inserted into the spinal canal that surrounds the spinal cord. It is performed in the lower back to collect cerebrospinal fluid (CSF) for laboratory analysis. This clear, watery fluid circulates around the brain and spinal cord.

A spinal tap can be used to evaluate symptoms that may be caused by infection, inflammation or certain diseases. It can also help diagnose cancers, such as leukemias, lymphomas and carcinomas that have metastasized (spread) to the brain or spinal cord. After the CSF fluid has been extracted from a patient, it is examined for cancer cells.  

In cancer patients, a lumbar puncture also may be used for a procedure known as intrathecal (IT) chemotherapy. This form of treatment provides chemotherapy drugs directly into the cerebrospinal fluid. It is typically used to treat leukemia and other cancers, such as breast cancer or lymphomas that may have metastasized to the spinal cord or brain.     

A spinal tap is an outpatient procedure, meaning it does not require an overnight hospital stay. However, the patient typically has to remain in the hospital or outpatient surgical center for several hours afterward for monitoring. Although a spinal tap is not overly painful, it can cause discomfort. A local anesthetic is used to numb the areas prior to needle insertion.

Children in particular may find the procedure to be uncomfortable and may have to be gently restrained or mildly sedated during the test. A spinal tap may also be more uncomfortable for certain patients, including obese individuals, those who have had certain back surgeries and pregnant women. Physicians may recommend other procedures for these patients, such as magnetic resonance imaging (MRI) or computed tomography (CT) scan.

A spinal tap, also called a lumbar puncture, removes a tiny amount of cerebrospinal fluid (CSF) for laboratory analysis. CSF is the clear, watery fluid that surrounds the brain and spinal cord. Spinal taps can be used to help detect or treat diseases such as cancer, and are also used to measure CSF pressure.

CSF forms in areas of the brain called ventricles and flows down into the area around the spinal cord. It is usually clear and contains small amounts of proteins and glucose (sugar). Its main function is to cushion and protect the brain and spinal cord by maintaining uniform pressure within the skull and spine.

A spinal tap may be used to help diagnose or treat certain cancers, including:

• Leukemia. When leukemia cells appear in spinal fluid, it indicates that the leukemia is advanced. More intense treatment is required to kill the leukemia cells in the central nervous system.
  
  
• Lymphoma. Lymphoma cells often spread into the spinal fluid, allowing physicians to diagnose diseases such as non-Hodgkin lymphoma and eye lymphoma (which can spread to the brain).
  
  
• Retinoblastoma. This cancer sometimes grows along the nerves between the eye and the brain. A spinal tap can reveal cancer that has spread to the surface of the brain.
  
  
• Metastatic cancer. Evidence of malignant cells in the spinal fluid may indicate that cancer from a primary site (e.g., breast cancer) has spread into the central nervous system.
  

Spinal taps also may be used to administer chemotherapy medications designed to treat or prevent brain and central nervous system cancers. In this procedure, known as intrathecal chemotherapy, the drug is injected directly into the CSF and flows freely to the brain and spinal cord.

Intrathecal chemotherapy may be beneficial for some patients to counteract the natural barrier between the bloodstream and the central nervous system. Chemotherapy given with this method may be used to destroy leukemia or lymphoma cells, as well as reduce their growth in the spinal fluid. It may be provided on a daily or weekly schedule depending on the patient’s condition.

In addition to diagnosing cancer, spinal taps can be used to detect numerous other medical conditions. These include viral or bacterial infections in the brain or spinal cord, central nervous system disorders and bleeding, abscesses or obstructions that affect the brain.

A spinal tap is usually performed in a hospital, although it can be performed in an outpatient surgical center in some cases. Prior to the procedure, patients will be asked to sign a consent form and may need to arrange for transportation. Typically, patients are advised to refrain from driving for several days following the spinal tap. Patients should also be mentally prepared for the fact that they will have to lie flat for six to eight hours following the procedure. This helps prevent headaches that sometimes occur following a spinal tap.

Patients should follow their physician’s advice about the necessary preparatory steps before undergoing a spinal tap. These may include dietary restrictions and modifications to a patient’s regimen for taking over-the-counter and prescription medications.

Just prior to the procedure, patients may be asked to change into a hospital gown and remove any jewelry. The patient then is positioned with their back to the physician and rounded out, so that the spaces between the vertebrae are as wide as possible. The optimal position will vary depending on the patient’s age. For example:

• Infants and small children. Lie on their sides curled up in a position that resembles the letter “C,” with their knees under their chin.
  
  
• Teens and adults. Lie on their sides with their knees drawn up to their chest and chin resting on their chest.

Pillows will be positioned under the patient to support the spine. To help maintain this position, patients may be instructed to place one arm around their knees and the other around their neck. Although this position may be uncomfortable, it is vital that patients remain still in the curled position. Doing so will open up the space between the vertebrae and help prevent the physician from injuring the spinal cord. Patients should also take care to breathe normally, because hyperventilation can skew pressure readings.

The lumbar area is first cleaned with an antibacterial solution and alcohol, and draped with sterile cloths to prevent any infection from entering the spine. A local anesthetic similar to that used by a dentist is used to numb the area, which may cause an initial burning or stinging feeling. A small, thin hollow needle is inserted near the waistline below the spinal cord. It is positioned between the third and fourth lumbar vertebrae and into the subarachnoid space of the spinal column.

The needle is pushed forward gently until the cerebrospinal fluid (CSF) is located. The needle may require some repositioning to locate the spinal canal. Patients will feel pressure as the needle is inserted and some brief pain as the needle penetrates the meninges – the three membranes that cover the spinal cord and brain. This pain should dissipate after a few seconds and the overall discomfort of this procedure is mild to moderate. If pain continues, patients should inform the physician performing the procedure because the needle may need to be repositioned.

The physician inserts a device called a manometer into the lumbar-puncture needle to measure the pressure of the CSF within the spinal canal. Two pressure readings are taken, one just after the initial puncture and another after the CSF has been withdrawn. One to two teaspoons of fluid are then drawn out and the needle is withdrawn and emptied into several sterile collection tubes. A bandage is placed on the injection site. The procedure usually takes less than 30 minutes.

Variations on the standard spinal tap procedure include the following:

• A sitting position may be used as an alternative, although it is rarely employed because the position is hard for patients to maintain. Any movement could lead to complication or injury from the spinal tap. In the sitting position, patients sit straight and then bend their head and chest toward their knees.
  
  
• Infants will usually be held upright for a spinal tap.
  
  
• For patients with lower back problems who cannot use either the curled or sitting position, the needle may be inserted below the occipital bone at the back of the skull (cisternal puncture).

In extremely rare cases, a physician may suspect an impending brain herniation, a condition that causes the brain to push through the opening at the back of the skull where the spinal cord is attached. In this instance, the physician will drill a hole into the skull under anesthesia and insert a needle directly into the brain. This is called a ventricular puncture.

Cancer patients who undergo a spinal tap for intrathecal chemotherapy will have variations with the procedure. It may be performed in a hospital, cancer clinic or an oncologist’s office. Patients will receive specific preparatory instructions and post-treatment information from their physician. In general, the drugs are supplied directly into the spinal canal around the spinal cord though the lumbar puncture. They will need to remain flat for several hours after the procedure to allow the chemotherapy drugs to be absorbed.

The amount of cerebrospinal fluid (CSF) removed by the spinal tap will be replaced by the body in about an hour. Some patients are prone to getting a headache after a spinal tap. To help prevent this, physicians usually tell their patients to lie flat in bed or with their head slightly raised at no more than a 30-degree elevation for several hours. However, this does not always prevent the headache and not all physicians make this recommendation. Cancer patients who receive chemotherapy through a lumbar puncture must remain flat for several hours to allow the drugs to be absorbed.

The physician will check the puncture site for redness, drainage or swelling every hour for the first four hours and then once every four hours until the patient is discharged from the hospital. The physician will also perform a neurological assessment every hour or more frequently if the patient’s CSF pressure is elevated. This elevation in pressure could indicate an increase in intracranial pressure due to a cerebral hemorrhage, tumor or swelling (edema) caused by the physical trauma of the spinal tap itself.

After discharge, patients may gradually resume regular activities, but should avoid driving for about three days and vigorously exercising for at least two weeks. During this time, patients should increase their fluid intake and be cautious when performing any activity that requires moving the head or neck to avoid the most common side effect of this procedure, which is a post-spinal-tap headache. Chemotherapy patients will receive instrutions based on the treatment and their medical conditions.

Patients may feel mild discomfort or pain at the site where the skin was punctured for a few days following the procedure. Physicians may prescribe pain-relieving medications or recommend over-the-counter pain relievers. Patients should contact their physician immediately if they:

• Notice any increased pain, swelling, redness, drainage or bleeding in the puncture area.
  
  
• Develop signs of infection, including headache, muscle aches, dizziness, fever and/or neck rigidity or unusual irritability.
  
  
• Experience any nausea or vomiting.
  

If cancer is suspected, the fluid sample is sent to a laboratory for analysis to determine if cancer cells are present. In addition, the fluid may be tested for the presence of substances released by some germ cell tumors and for infections of the central nervous system. The test analysis can include:

• Chemical composition of the fluid
• Identification of cells floating in the fluid
• Signs that the fluid is infected
  

In some cases, results can be available in as little as 30 minutes. In other cases, a physician may request a bacterial culture to look for organisms growing in the sample. It usually takes 48 to 72 hours to get these test results back. When diagnosing cancer, it may take several days to obtain a full analysis of the fluid.

Technicians who examine the fluid will note the following:

• General appearance. Cloudy spinal fluid can indicate increased cells and/or protein suspended in the fluid, which can be a sign of infection or cancer, among other things.
  
  
• Cell count. The number of red blood cells and number and type of white blood cells will be noted, because normal spinal fluid does not contain significant numbers of these types of cells. Large numbers of white cells usually indicate an infection, while the presence of red blood cells may indicate cerebral hemorrhage.
  
  
• CSF gram stain and culture.  The spinal fluid is stained and examined under the microscope to look for bacteria. To check for infection, the fluid is cultured to see if any organisms grow from the fluid.
  
  
• Presence of substances such as:
  
  
• Protein. High levels suggest hemorrhage, trauma, tumor, diabetes or polyneuritis (inflammation of several nerves).
  
  
• Glucose (sugar). Bacterial infections, cancer and hemorrhage often cause low glucose levels in the fluid.

High protein levels, low glucose levels, the presence of red blood cells and/or the appearance of blood in the CSF are indications of a hemorrhagic stroke caused by bleeding in the brain, as opposed to an ischemic stroke caused by an obstruction in the blood flow to the brain (usually caused by a blood clot).

If cancer cells are detected in the spinal fluid, the patient will likely need to undergo additional tests. These tests will vary depending on the type of cancer, the suspected location and additional factors. Tests that may be conducted include:

• Biopsy
• Bone marrow aspiration
• Blood tests
• Magnetic resonance imaging (MRI)
• Computed axial tomography (CAT) scan
• Positive emission tomography (PET) scan
• Chest x-ray
• Cytogenetics

In most cases, spinal tap procedures are quick, relatively painless and effective. The test uses a flexible needle that makes it only mildly to moderately uncomfortable. This needle is so flexible that it can be wrapped around a finger without breaking. The spinal cord is not affected, because the needle is inserted below the level where the cord ends.

As with any invasive procedure, there is a risk of infection with a spinal tap. In rare cases, patients develop meningitis, a bacterial or viral infection that causes inflammation of the meninges. Factors that increase the risk of complications from a spinal tap include alcoholism, a recent or chronic illness, a central nervous system infection or increased intracranial (within the skull) pressure. Other risks associated with the spinal tap include:

• Damage to the spinal cord, spinal canal or surrounding tissues by the spinal tap. The risk of this complication increases if the patient moves during the spinal tap.
  
  
• An allergic reaction to the anesthetic.
  
  
• Bleeding into the spinal canal. This is particularly dangerous with cancer patients. Research has found that if blood leaks into the spinal fluid, malignant cells in the blood, such as leukemia cells, may escape and grow in the fluid.
  
  
• Brain herniation, an extremely rare and potentially fatal condition in which the brain pushes through the opening at the back of the skull where the spinal cord is attached.
  

In the case of a cisternal puncture or ventricular puncture, there is the additional risk of damage to the brainstem or brain tissue causing bleeding that could result in brain damage or death. The increased risk associated with these procedures is the major reason why the spinal tap is the preferred method of collecting cerebrospinal fluid (CSF) for laboratory testing.

Less than 10 percent of patients will experience a moderate to severe post-spinal-tap headache within 48 hours of the spinal tap. Pain from the headache is typically centered around the forehead and/or the back of the head. It may be accompanied by nausea, dizziness or tinnitus (ringing in the ears). It is usually more severe when sitting or standing than when lying down. The headache usually dissipates with bed rest, but if it persists or becomes more severe, patients should contact their physician immediately. This headache can last from a few days to a few weeks. 

The post-spinal-tap headache can usually be avoided by remaining absolutely still during the spinal tap procedure and limiting the movement of both head and neck following the test. Drinking ample amounts of fluids also may help prevent a headache. Some patients may benefit from drinking caffeinated beverages such as tea or coffee after the tap to relieve their headache. The causes of a post-spinal-tap headache are unknown, but it may be the result of either leakage of the CSF or low CSF pressure in the spinal canal.

Patients who receive chemotherapy through a lumbar puncture may experience side effects from the chemotherapy drugs. These side effects will vary depending on multiple factors including the type or combination of drugs, the chemotherapy schedule, accompanying cancer treatments and the patient’s general health.

Patients with certain conditions may not be good candidates for a spinal tap. These conditions include:

• People who have had back surgery
  
  
• People with scoliosis (abnormal curvature of the spine)
  
  
• People who are overweight or obese
  
  
• Pregnant women
  
  
• People with bleeding disorders who take anticoagulant medications
  
  
• Patients with a skin infection on the lower back
  

In such cases, an MRI (magnetic resonance imaging) or CAT (computed axial tomography) scan may be used instead of the spinal tap, or the spinal tap may be used with extreme caution.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients or parents may wish to ask their doctor the following questions about spinal taps:

1. Why do I need a spinal tap?
   
   
2. Where will the test be completed?
   
   
3. How long will the procedure take?
   
   
4. What are my risks with a spinal tap?
   
   
5. Do I have any conditions that might interfere with the procedure?
   
   
6. What cancers can be detected with a spinal tap?
   
   
7. When and from whom will I receive the results?
   
   
8. If cancer is detected, what other tests will I need?
   
   
9. Is intrathecal chemotherapy necessary to treat my cancer?
   
   
10. How often and for how long will I need this type of chemotherapy?
    
    
11. What kind of side effects can I expect with this treatment?
    
    
12. How successful is this treatment for my type and stage of cancer?