A spinal tap is a procedure in which a long needle is inserted in the spinal canal in the lower back to collect cerebrospinal fluid (CSF) for laboratory analysis. This clear, watery fluid circulates around the brain and spinal cord and is tested for:
Protein. High levels of protein may indicate an infection or another condition.
White blood cells. High levels of white blood cells may indicate infection.
Glucose (blood sugar). Low glucose levels may indicate the presence of an infection.
Also known as a lumbar puncture, a spinal tap is an outpatient procedure. However, the patient typically has to remain in the hospital for several hours afterward for monitoring. Although a spinal tap is not generally painful, it can cause discomfort. Children in particular may find the procedure to be uncomfortable, and may have to be gently restrained during the test.
Spinal taps are used to diagnose several conditions. Spinal taps in children are most often performed to diagnose meningitis, an infection and inflammation of the membrane covering the brain and spinal cord. In children, spinal taps may also be used to diagnose the cause of ongoing headaches (which can result from spinal fluid pressure that is too high or too low), multiple sclerosis (chronic autoimmune disorder that can result in disability and impaired function), bleeding around the brain (subarachnoid hemorrhage), Guillain-Barre syndrome (a rare inflammatory disorder of the peripheral nerves) and various cancers of the brain and spinal cord.
About spinal taps
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. Although a spinal tap is not generally painful, it can cause discomfort.
CSF forms in the 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 (blood sugar). Its main function is to cushion and protect the brain and spinal cord by maintaining uniform pressure within the skull and spine.
Spinal taps in children are most often performed to diagnose meningitis, an infection and inflammation of the membranes (meninges) covering the brain and spinal cord. Children who have seizures caused by a high fever (febrile seizures) usually receive a spinal tap to look for signs of meningitis.
However, a spinal tap should be performed only after a neurological examination and should never delay potentially lifesaving treatment such as the administration of antibiotics and steroids to patients with suspected bacterial meningitis.
In some cases, a spinal tap may also be used to determine whether a child’s ongoing headaches are caused by spinal fluid pressure that is too high or too low.
Spinal taps also may be used to diagnose various cancers of the brain and spinal cord. For example, this test can help detect tumors of the choroid plexus, which is the tissue located in the spaces of the brain called ventricles. Such tumors are rare, but make up a significant percentage of brain tumors that affect children during the first year of life. The choroid plexus produces CSF, and a spinal tap can help determine whether cancer cells have started to spread to other parts of the body via this fluid.
A spinal tap can also be used to detect other cancers that often affect children, such as leukemia (cancer of the blood and bone marrow) and retinoblastoma (tumor of the retina). By analyzing CSF, it can be determined whether cancer has spread to the brain and spine.
In some cases, spinal taps are actually used to treat a condition rather than to just diagnose it. For example, a spinal tap can be used to remove excess CSF within the skull. This is a condition that affects some babies and is known as hydrocephalus, or “water on the brain.”
Other conditions that may be diagnosed or treated with a spinal tap include:
Viral or bacterial infections of the brain and spinal cord. In addition to meningitis, such conditions include Lyme disease, polio and neurosyphilis.
Bleeding around the brain (subarachnoid hemorrhage)and in the central nervous system (CNS).
CNS disorders characterized by tissue destruction, such as multiple sclerosis (autoimmune disease that often results in disability and impaired function) or nerve diseases, such as Guillain-Barre syndrome (a rare inflammatory disorder of the peripheral nerves).
An obstruction in CSF circulation.
Spinal taps are used to administer spinal anesthetic for some kinds of surgery. They are also sometimes 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.
Childhood issues and spinal taps
The spinal tap procedure is similar for children and adults. However, there are slight differences. For example, infants and small children lie on their sides and curl their bodies into the shape of a “C,” with their knees under their chin. A nurse or other aide may have to hold a child in the proper position. Some infants may be held upright during the procedure. Sick newborns are usually held upright because there is a risk of breathing problems if placed on the side with the body curled.
Teenagers are usually asked to lie down on their side with the knees drawn up to the chest. In some cases, teens may sit down and place their head on a pillow that is at waist level.
Spinal taps are very safe procedures that rarely result in complications. However, they can be frightening to a child. It is not unusual for children to cry during this procedure, and some children may need to be held still by a nurse or even sedated. Prior to the procedure, parents are encouraged to listen to their child’s concerns and to answer any questions honestly. Maintaining a loving and supportive presence can make the test easier for a child to endure.
Before and during the spinal tap
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, parents of the child will be asked to sign a consent form. Parents are also urged to explain to their child that it may be necessary to lie flat for six to eight hours following the procedure. This helps to prevent headaches that sometimes occur following a spinal tap. In some cases, the child will be sedated to help them relax and lie still for this long time period.
Parents should follow the physician’s advice about any other preparatory steps that the child should take before a spinal tap. These may include dietary restrictions and modifications to a child’s regimen for taking over-the-counter and prescription medications. In rare cases, a spinal tap may be performed on a child using general anesthesia. This means that the child will not be conscious during the procedure. If this type of procedure is planned, the child will not be allowed to eat or drink anything from the night before the test until after the procedure is over.
Just prior to the procedure, children are asked to remove all clothing, jewelry and glasses and to wear a hospital gown. Children are then 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, children will 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 children remain curled (to open up the space between the vertebrae) and still (to avoid injuring the spinal cord) during the procedure. Children should also take care to breathe normally, because hyperventilation can skew pressure readings.
The 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 is used to numb the area, which may cause an initial burning or stinging feeling. A small, hollow needle is inserted near the waistline (below the spinal cord) between the third and fourth lumbar vertebrae and into the spinal canal (arachnoid space).
The needle is pushed forward gently until the cerebrospinal fluid (CSF) is found. The needle may require some repositioning to locate the spinal canal. The child 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.
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 teaspoonfuls of fluid are then drawn into several sterile collection tubes and the needle is withdrawn. A bandage is placed on the injection site. The procedure usually takes at least 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, and movement could lead to complication or injury from the spinal tap. In the sitting position, children sit straight and then bend their head and chest toward their knees.
Infants may be held upright for a spinal tap.
For children 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 where the physician suspects 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), the physician will drill a hole into the skull and insert a needle directly into the brain. This is called a ventricular puncture.
After the spinal tap
The amount of cerebrospinal fluid (CSF) removed by the spinal tap will be replaced by the body in about an hour. Some patients – especially adults – are prone to developing a headache after a spinal tap. To help prevent this, the physician may tell 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. Drinking caffeinated beverages such as tea or coffee after the spinal tap may also help relieve the headache.
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.
Children who have a spinal tap while under general anesthesia will remain groggy for a short period of time following the test. In most cases, children who undergo this type of procedure do not remember it later.
Once discharged, children may gradually resume regular activities. During this time, they should increase 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 – a post-spinal-tap headache.
Children may feel mild discomfort or pain for a few days following the procedure, for which the physician may prescribe pain-relieving medications. Parents should contact their physician immediately if their child:
Has any increased pain, swelling, redness, drainage or bleeding in the puncture area.
Develops signs of infection, including headache, muscle aches, dizziness, fever and/or neck rigidity and unusual irritability.
Experiences any nausea or vomiting.
The fluid sample is sent to a laboratory for analysis. The various analytical tests:
Assess the chemical composition of the fluid
Identify cells floating in the fluid, including any potentially cancerous cells
Detect 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.
Technicians who examine the fluid will note the following:
General appearance. Normal CSF is clear. Cloudy spinal fluid can indicate increased cells and proteins suspended in the fluid, which is a sign of infection.
Cell count. The number of red blood cells and number and type of white blood cells will be noted, as normal spinal fluid does not contain significant numbers of these types of cells. Large numbers of white blood cells usually indicate an infection, whereas 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 also 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 (blood sugar). Bacterial infections 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.
Potential risks with spinal taps
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 usually 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, children can develop meningitis if a skin infection is located on the area where the needle for the spinal tap is inserted. In this situation, another diagnostic method would be performed instead ofa spinal tap. Factors that increase the risk of complications from a spinal tap include a recent or chronicillness, 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.
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.
When cerebrospinal fluid (CSF) is withdrawn during a cisternalpuncture 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 CSF for laboratory testing.
According to the National Institute of Neurological Disorders and Stroke, about one-quarter of patients experience a post-spinal tap headache within 48 hours of the spinal tap. This usually affects patients 18 to 30 years of age, and is considered rare in children. 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.
Pain is typically centered near the forehead and/or the back of the head and 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, a physician should be notified 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, drinking ample fluid afterward and limiting the movement of both head and neck following the tap. Drinking caffeinated beverages such as tea or coffee after the tap may also help replenish cerebrospinal fluids and relieve the headache. Parents are urged to consult with a child’s physician about whether caffeinated beverages are a good idea for their child. Parents may also wish to consult with their child’s pediatrician about giving a child acetaminophen, ibuprofen or another non-aspirin pain reliever.
Children with certain health conditions may not be good candidates for a spinal tap, including:
Children who have had back surgery
Children with scoliosis (abnormal curvature of the spine)
Children who are obese
Pregnant adolescents
Children with bleeding disorders who take anticoagulant medication
Children with a skin infection on the lower back
In such cases, imaging tests such as an MRI (magnetic resonance imaging) or CAT scan (computed axial tomography scan) may be used instead of the spinal tap.
Questions for your doctor regarding spinal taps
Preparing questions in advance can help parents and patients have more meaningful discussions with their physicians regarding their child’s condition. Parents and children may wish to ask the doctor the following questions related to spinal taps:
Why does my child need a spinal tap? Are there alternative, non-invasive procedures that can be used to diagnose/treat my child’s condition?
Will you need to use general anesthesia during my child’s spinal tap?
How can I prepare my child for the spinal tap?
Do I need to make changes in my child’s diet or take other preparatory steps prior to the procedure?
Will my child require a sedative during the procedure? Will my child need to be held in place?
How much discomfort is my child likely to experience?
How soon after the procedure will my child be allowed to return home?
Should I take any special steps to help prevent a headache in my child?
