Last Updated on March 7, 2021
Lumbar puncture is a medical procedure in which a thin needle is inserted into the spinal canal to collect cerebrospinal fluid (CSF).
It is called ‘lumbar puncture’ because the needle is inserted in the lumbar portion of the back and used to puncture the tissues to enter the spinal canal.
The CSF thus collected is used for diagnostic purposes ( for diagnosing diseases of the central nervous system such as bacterial meningitis or subarachnoid hemorrhage). It can also be used for therapeutic purposes (such as to inject medicines into the spinal canal).
Lumbar puncture is also known as spinal tap, spinal puncture, thecal puncture, or rachiocentesis.
The entire spinal column ( vertebral column or backbone) can be divided into 5 regions:
- Cervical spine: 7 vertebrae of the neck (C1-C7)
- Thoracic spine: 12 vertebrae of the mid-back (T1-T12)
- Lumbar spine: 5 vertebrae of the lower back (L1-L5)
The lumbar spine consists of 5 moveable vertebrae that are numbered L1-L5. Each lumbar vertebra is composed of 3 functional parts:
The vertebral body (for weight bearing)
The vertebral (neural) arch (for protecting the neural elements)
The bony processes (spinous and transverse) (for increasing the efficiency of muscle action)
The lumbar vertebral bodies are connected together by the intervertebral discs. The size of the vertebrae increases from L1 to L5, which reflects the increasing load that each lower lumbar vertebra absorbs.
What is Cerebrospinal Fluid (CSF)?
Cerebrospinal fluid or CSF is a clear, colorless fluid found in the brain and spinal cord.
It is produced by specialized ependymal cells present in the choroid plexuses of the ventricles of the brain. About 125 mL of CSF is present in the brain and spinal cord at any given time. It is continually produced, and all of it is replaced every six to eight hours. It is absorbed in the arachnoid granulations.
The pathway of the cerebrospinal fluid is as follows:
- The CSF passes from the lateral ventricles to the third ventricle through the interventricular foramen (of Monro).
- From the third ventricle, it flows through the cerebral aqueduct of Sylvius to the fourth ventricle.
- From the fourth ventricle, some CSF flows to the central canal of the spinal cord. However, the majority of CSF passes through the apertures of the fourth ventricle; the median aperture (of Magendie), and two lateral apertures (of Luschka). Through these openings, the CSF enters the cisterna magma and cerebellopontine cisterns, respectively.
- From there, the CSF flows through the subarachnoid space of the brain and spinal cord.
- Finally, it is reabsorbed through arachnoid granulation and enters the dural venous sinuses.
The main functions of CSF are:
- To act as a cushion to the brain inside the skull and spinal cord inside the vertebral column when struck with mechanical force.
- To provide immunological protection to the brain and the spinal cord.
- To remove metabolic waste, and also to transport neuromodulators and neurotransmitters.
- To autoregulate cerebral blood flow.
The normal CSF appears clear and contains substances, such as protein and glucose, along with few if any cells.
Indications of Lumbar Puncture
A lumbar puncture may be performed for diagnostic purposes or to treat a disease.
To diagnose disease
- Meningitis: An inflammation of the membranes that cover the brain and spinal cord. It could be due to viral, bacterial, tubercular, or fungal infection.
- Myelitis: An inflammation of the spinal cord. It could be due to infectious or autoimmune causes. Infectious causes include viral, bacterial, fungal, or parasitic infections.
- Encephalitis: An inflammation of the brain that is usually caused by a virus.
- Subarachnoid hemorrhage (SAH): Bleeding in the area between the brain and the tissues that cover it.
- Guillain–Barré syndrome: A disease in which the immune system of the body attacks part of the nervous system.
- Demyelinating diseases: Diseases that result in damage to the protective covering (myelin sheath) that surrounds the nerve fibers in the brain and spinal cord. Examples include multiple sclerosis and acute demyelination polyneuropathy.
- Cancers affecting the brain and spinal cord
- Headaches of unknown cause: Besides imaging techniques, a lumbar puncture may be done to diagnose certain inflammatory conditions that may be the cause of a headache.
To treat a disease
- To inject medications into the cerebrospinal fluid (intrathecal route)
- medicines such as painkillers, antibiotics, or chemotherapy.
- spinal anesthetic (epidural) to anesthetize or numb the lower part of the body before any surgery involving that area.
- contrast dye for X-ray studies as in myelography
- To remove some fluid so as to reduce pressure in the skull or spine
- idiopathic intracranial hypertension
To measure the pressure of the CSF
A special tube (called a manometer) is used to measure the pressure of the CSF during a lumbar puncture. This is useful in conditions like hydrocephalus and idiopathic intracranial hypertension.
- Skin infection at the site of puncture
- Brain abscess
- Intracranial space-occupying lesion with mass effect and posterior fossa mass as it can lead to herniation of the cerebellar tonsils
- Bleeding disorder
- Low platelet count (<50 x 109/L)
- Patient on anticoagulant therapy
- Vertebral deformities (scoliosis or kyphosis)
- Increased intracranial pressure due to the risk of cerebral herniation. However, lumbar puncture may be done for therapeutic purposes to reduce the intracranial pressure, but only if obstruction (as in the third ventricle of the brain) has been ruled out.
- Unequal pressures between the supratentorial and infratentorial compartments of the brain. This is inferred by characteristic features on CT (computed tomography) scan of the brain.
In some cases, a CT scan must be performed before lumbar puncture. These cases include:
- Elderly patients > 60 years of age
- Immunocompromised patients
- Patients with known brain lesions
- Focal findings on neurologic examination
- A recent episode of seizure
- Patients who are not fully consciousness
- Patients with papilledema as seen on physical examination
Preparation Before the Procedure
Inform your doctor regarding the following conditions:
- You are on an antibiotic course: it is better to postpone the procedure in case you have an active infection or are on antibiotic treatment for some unrelated illness.
- You are allergic to any local anesthetics
- You are on anticoagulant therapy
- You are / could be pregnant
You must take your prescribed medications as usual unless specifically instructed. For example, patients on anticoagulants (blood thinners) may be asked to withhold the medication for a few days prior to the procedure.
It is important to keep yourself hydrated before the procedure so as to avoid a dry tap ( no CSF flows during the procedure). So try to increase your fluid intake (such as water and juice) for a few days before the procedure.
On the day of the procedure, do not eat for 3-4 hours before the procedure. You may, however, have liquids and fluids during this period.
You will not be able to drive for 24 hours after the procedure. So make sure to bring a friend or family member to accompany you after the procedure.
You will be asked to empty your bladder just before the start of the procedure.
You will be instructed to remove any jewelry or other objects that may interfere with the procedure and will be given a gown to wear.
Informed written consent will be taken from you.
- The procedure may be carried out in either a lying position or a sitting position.
- Lying position: You may be asked to lie on your side with your legs pulled up and your chin tucked to your chest.
- Sitting position: You may be asked to sit on the edge of an exam table leaning forward and your arms positioned in front of you.
In both positions, the back is arched, which helps to widen the spaces between the vertebrae.
- The L3/L4 space is located by locating the superior iliac crests. The vertebral space above and below L3/L4 is palpated to determine the widest space. The widest space thus felt is chosen for the site of lumbar puncture.
- After draping the area with sterile sheets, the area is cleaned with antiseptic fluid.
- To numb the area, a local anesthetic is injected under the skin and the deeper tissues ( the anesthetic medication acts locally and hence you will be awake during the procedure).
- A spinal needle is inserted through the skin between two bones (lumbar vertebrae) at the site chosen earlier.
- You may feel slight pressure once the needle goes in.
- The needle is advanced till a ‘pop’ sensation is felt by the person performing the procedure. It indicates that the needle has pierced the duramater and reached the subarachnoid space.
- The stylet from the spinal needle is then removed and CSF will begin to drip out.
- The required amount of CSF is then collected in different vials.
- If some medicine needs to be injected into the spinal canal, it is given through the same needle after the CSF is collected.
- Once the procedure is over, the needle is withdrawn while placing pressure on the puncture site.
- A small dressing is placed over the site.
After the procedure, you will be asked to lie on your back for a few hours.
You will be asked to drink extra fluids. This is done to rehydrate the body and replace the withdrawn CSF thereby reducing the chance of developing a headache.
After observing for few hours, you may be discharged and sent home.
It is important to rest while lying on your back and limit your activity for at least 24 hours following the procedure.
You may take a mild pain-killer such as paracetamol for the relief of pain.
You may also consume drinks containing caffeine such as coffee, tea, or cola as they help to relieve headaches.
You must inform the concerned doctor, in case of the following:
- Drainage of blood or clear fluid from the injection site
- Severe pain at the injection site
- Numbness and tingling of the legs
- Inability to urinate
- Sensitivity to bright light
- Persistent or severe headache
Complications of Lumbar Puncture
It is the most common complication of lumbar puncture occurring in about 20-70 % of patients. It occurs due to leakage of CSF from the puncture site.
It usually begins after few hours or up to 24-48 hours after the procedure. The incidence can be reduced by making the patient lie flat on his/her back for several hours after the procedure.
This complication is usually self-limited and can be treated by analgesics and caffeine. If it lasts for more than two days, it can be treated by epidural blood patch, in which the person’s own blood is injected back into the site of leakage so that a clot is formed and the leak is sealed off.
There is a slight risk of infection since the needle pierces the skin’s surface, providing a possible passage for bacteria to enter the body. Strictly adhering to all sterile techniques can minimize the risk of infection.
There is a minor risk of bleeding in the spinal canal.
Pain in legs and lower back
Irritation of nerves or nerve roots by the spinal needle caused during the procedure can result in short-term numbness or pain of the legs or lower back pain.
It is the most serious complication of a lumbar puncture. It is controversial whether this complication occurs due to the withdrawal of fluid during lumbar puncture in case of high intracranial pressure. Some authorities believe that cerebral herniation can occur even due to the underlying disease for which lumbar puncture is performed and not due to lumbar puncture per se.
Till a consensus is reached reading this controversy, it is best to avoid lumbar puncture if neurological findings associated with impending cerebral herniation ( such as deteriorating consciousness, pupillary changes, posturing, irregular respirations, and a very recent seizure) are seen.
Investigations and Analysis of the CSF
- Gross examination
- Appearance: whether, clear, turbid, or hemorrhagic
- Total cell count
- WBCs- neutrophils and lymphocytes
- Biochemical tests
- Lactate dehydrogenase
- Microbiological tests
- Gram staining
- India ink test
- Microscopic examination
- to detect cancer cells
Read more about Cerebro Spinal Fluid Analysis
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- Reichman E, Simon RR. Emergency Medicine Procedures. New York, NY: McGraw-Hill; 2004.
- Roberts JR, Hedges JR. Clinical Procedures in Emergency Medicine. 4th. Philadelphia, PA: Saunders; 2004.
- Hasbun R, Abrahams J, Jekel J, Quagliarello VJ. Computed tomography of the head before lumbar puncture in adults with suspected meningitis. N Engl J Med. 2001 Dec 13. 345(24):1727-33.