Lumbar Puncture / Spinal Tap; Types, Uses, Procedures, Results

Lumbar puncture (LP) also known as a spinal tap, is a medical procedure in which a needle is inserted into the spinal canal, most commonly to collect cerebrospinal fluid (CSF) for diagnostic testing. The main reason for a lumbar puncture is to help diagnose diseases of the central nervous system, including the brain and spine. Examples of these conditions include meningitis and subarachnoid hemorrhage. It may also be used therapeutically in some conditions. Increased intracranial pressure (pressure in the skull) is a contraindication, due to risk of brain matter being compressed and pushed toward the spine.

Anatomy of Lumber Puncture

Arachnoid mater – one of three membranes that surround the brain and spinal cord; the middle web-like membrane.

Cerebrospinal fluid (CSF) – a clear fluid produced by the choroid plexus in the ventricles of the brain that bathes the brain and spinal cord giving them support and buoyancy to protect from injury.

Hemorrhage – external or internal loss of blood from damaged blood vessels. Hemorrhage is stopped by blood clotting.

Hydrocephalus – an abnormal build-up of cerebrospinal fluid usually caused by a blockage of the ventricular system of the brain. Increased intracranial pressure can compress and damage brain tissue. Also called “water on the brain.”

Meninges – the three membranes (pia mater, arachnoid mater, and dura mater) that surround the brain and spinal cord.

Meningitis – infection and inflammation of the meninges surrounding the brain and spinal cord caused by bacteria or virus.

Subarachnoid space – the space between the pia and arachnoid mater of the brain and spinal cord that contains cerebrospinal fluid (CSF).

spinal canal – the hollow space within the bony vertebrae of the spine through which the spinal cord passes.

Indications/Uses of Lumbar Puncture

A lumbar puncture procedure may be helpful in diagnosing many diseases and disorders, including:

• Meningitis – An inflammation of the membrane covering the brain and spinal cord. The inflammation is usually the result of a viral, bacterial, or fungal infection.
• Encephalitis – An inflammation of the brain that is usually caused by a virus.
• Certain cancers involving the brain and spinal cord
• Bleeding – in the area between the brain and the tissues that cover it (subarachnoid space)
• Reye syndrome – A sometimes fatal disease that causes severe problems with the brain and other organs. Although the exact cause of the disease is not known, it has been linked to giving aspirin to children. It is now advised not to give aspirin to children during illnesses, unless prescribed by your child’s healthcare provider.
• Myelitis – An inflammation of the spinal cord or bone marrow.
• Neurosyphilis – A stage of syphilis during which the bacteria invades the central nervous system.
• Guillain-Barré syndrome – A disorder in which the body’s immune system attacks part of the nervous system.
• Demyelinating diseases – Diseases that attack the protective coating that surrounds certain nerve fibers – for example, multiple sclerosis or acute demyelination polyneuropathy.
• Headaches of unknown cause – After evaluation and head imaging if necessary, a lumbar puncture may be done to diagnose certain inflammatory conditions that can result in a headache.
• Pseudotumor cerebri (also called idiopathic intracranial hypertension, or IIH) – In this condition,pressure within the subarachnoid space is elevated for reasons that are not clear. A lumbar puncture is only done in this condition after evaluation and head imaging.
• Normal pressure hydrocephalus – A rare condition affecting mainly older people in which there is a triad of loss of urinary control, memory problems, and an unsteady gait. A lumbar puncture is done to see if the pressure of the CSF is elevated or not.

Contra Indications of Lumbar Puncture

Lumbar puncture should not be performed in the following situations:

Idiopathic (unidentified cause) increased intracranial pressure (ICP)

• Rationale –  lumbar puncture in the presence of increased ICP may cause uncal herniation
• Exception – therapeutic use of lumbar puncture to reduce ICP, but only if obstruction (for example in the third ventricle of the brain) has been ruled out
• Precaution – CT brain, especially in the following situations
  • Age >65
  • Reduced GCS
  • Recent history of seizure
  • Focal neurological signs
  • Abnormal respiratory pattern
  • Hypertension with bradycardia and deteriorating consciousness
  • Ophthalmoscopy for papilledema

• Bleeding diathesis (relative)
  • Coagulopathy
  • Decreased platelet count (<50 x 10⁹/L)
• Infections
  • Skin infection at puncture site
• Vertebral deformities (scoliosis or kyphosis), in hands of an inexperienced physician.

Before the test of Lumbar Puncture

A blood test or other laboratory tests may be ordered by your doctor prior to the test. Please follow these guidelines before the test:

• If you take Plavix, stop taking it 5 days before the procedure.
• If you take Coumadin, stop taking it 5 days before the procedure.
• If you are on Lovenox injections, do not take your morning dose the day of your procedure.
• DO take your other medications as determined by your physician, especially any medications for high blood pressure.
• We may make exceptions to these recommendations based upon your specific circumstances.
• Take your usual dose of insulin and eat a light breakfast before 8:00 a.m.
• When you arrive for your test, please be sure to remind the physician that you have diabetes.
• Insulin pumps will usually be removed if X-ray is considered or if defibrillation is a possibility.
• There are no special diet restrictions associated with this procedure, unless otherwise instructed.

Procedures of Lumbar Puncture

Generally, a lumbar puncture follows this process

• Protein (15-45 mg/dl)
• You will remove any clothing, jewelry, or other objects that may interfere with the procedure.
• You will be given a gown to wear.
• You will be reminded to empty your bladder prior to the start of the procedure.
• During the lumbar puncture you may lie on the exam table on your side with your chin tucked to your chest and knees tucked to your abdomen. Or, you may sit on the edge of an exam table with your arms draped over a table positioned in front of you. In either position the back is arched, which helps to widen the spaces between your vertebrae.
• Therefore, your back will be cleansed with an antiseptic solution and draped with sterile towels. The healthcare provider will wear sterile gloves during the procedure.
• The provider will numb the skin by injecting a local anesthetic. This injection may sting for a few seconds, but makes the lumbar puncture less painful.
• The hollow needle will be inserted through the numbed skin and into the space where the CSF is located. You will feel some pressure while the needle is inserted. You must remain absolutely still during the insertion of the needle.
• The CSF will begin to drip out of the needle and a small amount, about one tablespoon, will be collected into test tubes.
• If the provider needs to inject medicine into the spinal canal, it will be given through the same needle after the CSF is collected.
• When the procedure is done, the needle will be removed and a bandage will be placed over the injection site. The test tubes will be taken to the lab for testing.
• Tell the healthcare provider if you feel any numbness, tingling, headache, or lightheadedness during the procedure.

During the test of Lumbar Puncture

• The radiologist and technologist will be in the room with you.
• Pre-medication, although rarely needed, may make you feel drowsy and relaxed.
• You will wear a hospital gown during the examination.
• You will either lie on your side with your knees bent, or on your stomach with a small pillow beneath your lower abdomen.
• Your back will be cleaned with an antiseptic solution and sterile cloths (called drapes) will be placed around the area.
• A local anesthetic (pain-relieving medication) will be injected into the area on your back. You may feel a slight burning sensation that lasts only seconds.
• When the area is numb, a hollow needle is inserted in the lower back between two lumbar vertebrae. This sometimes causes pressure, but pain will be limited by the anesthetic.
• The spinal canal is penetrated, and fluid is collected and/or medication is injected. The spinal cord is not touched by the needle during the test.
• You may feel some discomfort or have a minor headache at the end of the procedure.
• The needle is removed after the medication has been injected or fluid is removed. The area will be cleaned with an antiseptic solution and covered with a small bandage.
• You will lie on your back for 30-60 minutes, depending on the nature of the procedure.
• A blood sample may be taken from a vein in your arm and tested, along with the spinal fluid, in the laboratory.

Results of Lumbar Puncture

The spinal fluid samples are sent to a laboratory for analysis. Lab technicians check for a number of things when examining spinal fluid, including

Normal values for spinal fluid examination are as follows

• Protein (15-45 mg/dl)
• Glucose (50-75 mg/dl)
• Cell count (0-5 mononuclear cells)
• Initial pressure (70-180 mm)

• General appearance – Spinal fluid is normally clear and colorless. If it’s cloudy, yellow or pink in color, it may indicate infection.
• Protein (total protein and the presence of certain proteins) – Elevated levels of total protein — greater than 45 milligrams per deciliter (mg/dL) — may indicate infection or another inflammatory condition. Specific lab values may vary from medical facility to medical facility.
• White blood cells –  Spinal fluid normally contains up to 5 mononuclear leukocytes (white blood cells) per microliter. Increased numbers may indicate infection. Specific lab values may vary from medical facility to medical facility.
• Sugar (glucose) – A low glucose level in spinal fluid may indicate infection or another condition.
• Microorganisms –  The presence of bacteria, viruses, fungi or other microorganisms can indicate infection.
• Cancer cells – The presence of abnormal cells in spinal fluid — such as tumor or immature blood cells — can indicate certain types of cancer.

Risk Factor of Lumbar Puncture

• Post-lumbar puncture headache – Up to 25 percent of people who have undergone a lumbar puncture develop a headache afterward due to a leak of fluid into nearby tissues.
• Back discomfort or pain – You may feel pain or tenderness in your lower back after the procedure. The pain might radiate down the back of your legs.
• Bleeding – Bleeding may occur near the puncture site or, rarely, into the epidural space.
• Brainstem herniation –Increased pressure within the skull (intracranial), due to a brain tumor or other space-occupying lesion, can lead to compression of the brainstem after a sample of cerebrospinal fluid is removed.

Care after spinal tap

• Once a spinal tap is completed, you will be instructed to lie flat (the time spent flat after the tap will vary depending on why you received the procedure). A nurse will discuss post-procedure instructions with you and provide the instructions to you in written form.
• Avoid strenuous or vigorous exercise for a day or so following the lumbar puncture.
• If you have a headache, lie down as much as possible and drink plenty of fluids. Contact your health care provider if the headache persists.
• Drink 2 1/2 quarts of liquid the day of the spinal tap and the day after (regardless of headache).

References

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