Lumbar puncture (LP), also known as aspinal tap, is a medical procedure in which a needle is inserted into thespinal canal, most commonly to collectcerebrospinal fluid (CSF) for diagnostic testing. The main reason for alumbar puncture is to helpdiagnose diseases of thecentral nervous system, including the brain and spine. Examples of these conditions includemeningitis andsubarachnoid hemorrhage. It may also be usedtherapeutically in some conditions. Increasedintracranial pressure (pressure in the skull) is a contraindication, due to risk of brain matter being compressed and pushed toward the spine. Sometimes, lumbar punctures cannot be performed safely (for example due to asevere bleeding tendency). It is regarded as a safe procedure, butpost-dural-puncture headache is a common side effect if a small atraumatic needle is not used.[1]
The chief diagnostic indications of lumbar puncture are for collection ofcerebrospinal fluid (CSF). Analysis of CSF may exclude infectious,[4][6] inflammatory,[4] and neoplastic diseases[4] affecting the central nervous system. The most common purpose is in suspectedmeningitis,[7] since there is no other reliable tool with which meningitis, a life-threatening but highly treatable condition, can be excluded. A lumbar puncture can also be used to detect whether someone has Stage 1 or Stage 2Trypanosoma brucei. Young infants commonly require lumbar puncture as a part of the routine workup for fever without a source.[8] This is due to higher rates of meningitis than in older persons. Infants also do not reliably show classic symptoms of meningeal irritation (meningismus) like neck stiffness and headache the way adults do.[7] In any age group,subarachnoid hemorrhage,hydrocephalus,benign intracranial hypertension, and many other diagnoses may be supported or excluded with this test. It may also be used to detect the presence of malignant cells in the CSF, as incarcinomatous meningitis ormedulloblastoma. CSF containing less than 10red blood cells (RBCs)/mm3 constitutes a "negative" tap in the context of a workup for subarachnoid hemorrhage, for example. Taps that are "positive" have an RBC count of 100/mm3 or more.[9]
Lumbar punctures may also be done to inject medications into the cerebrospinal fluid ("intrathecally"), particularly forspinal anesthesia[10] orchemotherapy.
Serial lumbar punctures may be useful in temporary treatment ofidiopathic intracranial hypertension (IIH). This disease is characterized by increased pressure of CSF which may cause headache and permanent loss of vision. While mainstays of treatment are medication, in some cases lumbar puncture performed multiple times may improve symptoms. It is not recommended as a staple of treatment due to discomfort and risk of the procedure, and the short duration of its efficacy.[11][12]
Additionally, some people withnormal pressure hydrocephalus (characterized by urinary incontinence, a changed ability to walk properly, and dementia) receive some relief of symptoms after removal of CSF.[13]
Rationale: lumbar puncture in the presence of raised ICP may causeuncal 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
Post-dural-puncture headache withnausea is the most common complication; it often responds topain medications and infusion of fluids. It was long taught that this complication can be prevented by strict maintenance of asupine posture for two hours after the successful puncture; this has not been borne out in modern studies involving large numbers of people. Doing the procedure with the person on their side might decrease the risk.[16] Intravenous caffeine injection is often quite effective in aborting these spinal headaches. A headache that is persistent despite a long period of bedrest and occurs only when sitting up may be indicative of a CSF leak from the lumbar puncture site. It can be treated by more bedrest, or by anepidural blood patch, where the person's own blood is injected back into the site of leakage to cause a clot to form and seal off the leak.[17]
The risk of headache and need for analgesia and blood patch is much reduced if "atraumatic" needles are used. This does not affect the success rate of the procedure in other ways.[18][19] Although the cost and difficulty are similar, adoption remains low, at only 16%c. 2014.[20]
The headaches may be caused by inadvertent puncture of thedura mater.[21]
Contact between the side of the lumbar puncture needle and a spinal nerve root can result in anomalous sensations (paresthesia) in a leg during the procedure; this is harmless and people can be warned about it in advance to minimize their anxiety if it should occur.[citation needed]
Serious complications of a properly performed lumbar puncture are extremely rare.[4] They include spinal or epidural bleeding, adhesivearachnoiditis and trauma to thespinal cord[10] orspinal nerve roots resulting in weakness or loss of sensation, or evenparaplegia. The latter is exceedingly rare, since the level at which the spinal cord ends (normally the inferior border of L1, although it is slightly lower in infants) is several vertebral spaces above the proper location for a lumbar puncture (L3/L4). There are case reports of lumbar puncture resulting in perforation of abnormal duralarterio-venous malformations, resulting in catastrophicepidural hemorrhage; this is exceedingly rare.[10]
The procedure is not recommended whenepiduralinfection is present or suspected, when topical infections or dermatological conditions pose a risk of infection at the puncture site or in patients with severepsychosis orneurosis with back pain. Some authorities believe that withdrawal of fluid when initial pressures are abnormal could result in spinal cord compression orcerebral herniation; others believe that such events are merely coincidental in time, occurring independently as a result of the same pathology that the lumbar puncture was performed to diagnose. In any case,computed tomography of the brain is often performed prior to lumbar puncture if an intracranial mass is suspected.[22]
The brain and spinal cord are enveloped by a layer of cerebrospinal fluid, 125–150 mL in total (in adults) which acts as a shock absorber and provides a medium for the transfer of nutrients and waste products. The majority is produced by thechoroid plexus in the brain and circulates from there to other areas, before being reabsorbed into the circulation (predominantly by thearachnoid granulations).[27]
The cerebrospinal fluid can be accessed most safely in thelumbar cistern. Below the first or second lumbar vertebrae (L1 or L2) thespinal cord terminates (conus medullaris). Nerves continue down the spine below this, but in a loose bundle of nerve fibers called thecauda equina. There is lower risk with inserting a needle into the spine at the level of the cauda equina because these loose fibers move out of the way of the needle without being damaged.[27] The lumbar cistern extends into thesacrum up to the S2 vertebra.[27]
Illustration depicting lumbar puncture (spinal tap)Spinal needles used in lumbar punctureIllustration depicting common positions for lumbar puncture procedure
The person is usually placed on their side (left more commonly than right). The patient bends the neck so the chin is close to the chest, hunches the back, and brings knees toward the chest. This approximates afetal position as much as possible. Patients may also sit on a stool and bend their head and shoulders forward. The area around the lower back is prepared using aseptic technique. Once the appropriate location is palpated, local anaesthetic is infiltrated under the skin and then injected along the intended path of the spinal needle. A spinal needle is inserted between the lumbarvertebrae L3/L4, L4/L5[10] or L5/S1[10] and pushed in until there is a "give" as it enters thelumbar cistern wherein theligamentum flavum is housed. The needle is again pushed until there is a second 'give' that indicates the needle is now past thedura mater. Thearachnoid membrane and the dura mater exist in flush contact with one another in the living person's spine due to fluid pressure from CSF in thesubarachnoid space pushing the arachnoid membrane out towards the dura. Therefore, once the needle has pierced the dura mater it has also traversed the thinner arachnoid membrane. The needle is then in the subarachnoid space. Thestylet from the spinal needle is then withdrawn and drops of cerebrospinal fluid are collected. The opening pressure of the cerebrospinal fluid may be taken during this collection by using a simple columnmanometer. The procedure is ended by withdrawing the needle while placing pressure on the puncture site. The spinal level is so selected to avoid spinal injuries.[10] In the past, the patient would lie on their back for at least six hours and be monitored for signs of neurological problems. There is no scientific evidence that this provides any benefit. The technique described is almost identical to that used inspinal anesthesia, except that spinal anesthesia is more often done with the patient in a seated position.[citation needed]
The upright seated position is advantageous in that there is less distortion of spinal anatomy which allows for easier withdrawal of fluid. Some practitioners prefer it for lumbar puncture in obese patients, where lying on their side would cause ascoliosis and unreliable anatomical landmarks. However, opening pressures are notoriously unreliable when measured in the seated position. Therefore, patients will ideally lie on their side if practitioners need to measure opening pressure.[citation needed]
Reinsertion of the stylet may decrease the rate of post lumbar puncture headaches.[15]
Although not available in all clinical settings, use ofultrasound is helpful for visualizing the interspinous space and assessing the depth of the spine from the skin. Use of ultrasound reduces the number of needle insertions and redirections, and results in higher rates of successful lumbar puncture.[28] If the procedure is difficult, such as in people with spinal deformities such as scoliosis, it can also be performed underfluoroscopy (under continuous X-ray imaging).[29]
In children, a sitting flexed position was as successful as lying on the side with respect to obtaining non-traumatic CSF, CSF for culture, and cell count. There was a higher success rate in obtaining CSF in the first attempt in infants younger than 12 months in the sitting flexed position.[30]
The spine of an infant at the time of birth differs from the adult spine. Theconus medullaris (bottom of the spinal cord) terminates at the level of L1 in adults, but may range in term neonates (newly born babies) from L1–L3 levels.[31] It is important to insert the spinal needle below the conus medullaris at the L3/L4 or L4/L5 interspinous levels.[32] With growth of the spine, the conus typically reaches the adult level (L1) by 2 years of age.[31]
Theligamentum flavum anddura mater are not as thick in infants and children as they are in adults. Therefore, it is difficult to assess when the needle passes through them into the subarachnoid space because the characteristic "pop" or "give" may be subtle or nonexistent in the pediatric lumbar puncture. To decrease the chances of inserting the spinal needle too far, some clinicians use the "Cincinnati" method. This method involves removing the stylet of the spinal needle once the needle has advanced through the dermis. After removal of the stylet, the needle is inserted until CSF starts to come out of the needle. Once all of the CSF is collected, the stylet is then reinserted before removal of the needle.[32]
Lumbar punctures are often used to diagnose or verify an infection in very young babies and can cause quite a bit of pain unless appropriate pain control is used (analgesia).[8] Managing pain is important for infants undergoing this procedure.[8] Approaches for pain control include topical pain medications (anaesthetics such as lidocaine). The most effective approach for pain control in infants who require a lumbar puncture is not clear.[8]
Analysis of the cerebrospinal fluid generally includes a cell count and determination of the glucose and protein concentrations. The other analytical studies of cerebrospinal fluid are conducted according to the diagnostic suspicion.[4]
The CSF specimens must be sent to the laboratory immediately and examined within one hour of collection. In order to prevent cellular degradation, the cell counts should be completed within 30 to 60 minutes, just after the collection of CSF.[33]
Glass tubes are not recommended, as cells can stick to their walls and lead to underestimation of cell numbers. Samples should be drawn into four sterile tubes in the following order, tube 1 for chemistry tests, tube 2 for microbiology, tube 3 for hematology, and tube 4 for cytology or specialized studies to ensure accurate, and uncontaminated results.[33]
For culture purposes, CSF should be stored at room temperature, since refrigeration can inhibit the growth of sensitive organisms such asHaemophilus influenzae andNeisseria meningitidis.[33]
Decreased CSF pressure can indicate complete subarachnoid blockage, leakage of spinal fluid, severedehydration, hyperosmolality, orcirculatory collapse. Significant changes in pressure during the procedure can indicate tumors or spinal blockage resulting in a large pool of CSF, or hydrocephalus associated with large volumes of CSF.[27]
The presence ofwhite blood cells in cerebrospinal fluid is calledpleocytosis. A small number ofmonocytes can be normal; the presence ofgranulocytes is always an abnormal finding. A large number of granulocytes often heralds bacterialmeningitis. White cells can also indicate reaction to repeated lumbar punctures, reactions to prior injections of medicines or dyes, central nervous system hemorrhage,leukemia, recent epilepticseizure, or a metastatictumor. When peripheral blood contaminates the withdrawn CSF, a common procedural complication, white blood cells will be present along witherythrocytes, and their ratio will be the same as that in the peripheral blood.[citation needed]
The finding of erythrophagocytosis,[34] wherephagocytosed erythrocytes are observed, signifies haemorrhage into the CSF that preceded the lumbar puncture. Therefore, when erythrocytes are detected in the CSF sample, erythrophagocytosis suggests causes other than a traumatic tap, such asintracranial haemorrhage andhaemorrhagic herpetic encephalitis. In which case, further investigations are warranted, including imaging and viral culture.[citation needed]
CSF can be sent to themicrobiology lab for various types of smears and cultures to diagnose infections.
Gram staining may demonstrate gram positive bacteria in bacterial meningitis.[35]
Microbiological culture is the gold standard for detecting bacterial meningitis. Bacteria, fungi, and viruses can all be cultured by using different techniques.[citation needed]
Polymerase chain reaction (PCR) has been a great advance in the diagnosis of some types of meningitis, such as meningitis fromherpesvirus andenterovirus. It has high sensitivity and specificity for many infections of the CNS, is fast, and can be done with small volumes of CSF. Even though testing is expensive, cost analyses of PCR testing in neonatal patients demonstrated savings via reduced cost of hospitalization.[36][37]
Numerous antibody-mediated tests for CSF are available in some countries: these include rapid tests for antigens of common bacterial pathogens, treponemal titers for the diagnosis ofneurosyphilis andLyme disease,Coccidioides antibody, and others.[citation needed]
Several substances found in cerebrospinal fluid are available for diagnostic measurement.
Glucose is present in the CSF; the level is usually about 60% that in the peripheral circulation.[41] A fingerstick or venipuncture at the time of lumbar puncture may therefore be performed to assess peripheral glucose levels and determine a predicted CSF glucose value. Decreasedglucose levels[42] can indicate fungal, tuberculous[43] or pyogenic infections; lymphomas; leukemia spreading to the meninges; meningoencephalitic mumps; or hypoglycemia. A glucose level of less than one third of blood glucose levels in association with low CSF lactate levels is typical in hereditary CSFglucose transporter deficiency also known asDe Vivo disease.[44]
Increased glucose levels in the fluid can indicate diabetes, although the 60% rule still applies.[45][46]
Increased levels oflactate can occur the presence ofcancer of theCNS,multiple sclerosis, heritable mitochondrial disease, low blood pressure, lowserumphosphorus, respiratory alkalosis, idiopathic seizures,traumatic brain injury, cerebral ischemia, brain abscess, hydrocephalus, hypocapnia or bacterial meningitis.[45]
The enzymelactate dehydrogenase can be measured to help distinguish meningitides of bacterial origin, which are often associated with high levels of the enzyme, from those of viral origin in which the enzyme is low or absent.[53]
IgG synthetic rate is calculated from measured IgG and total protein levels; it is elevated in immune disorders such as multiple sclerosis, transverse myelitis, andneuromyelitis optica of Devic.Oligoclonal bands may be detected in CSF but not in serum, suggesting intrathecal antibody production.[citation needed]
The first technique for accessing the dural space was described by the London physicianWalter Essex Wynter. In 1889 he developed a crude cut down withcannulation in four patients with tuberculous meningitis. The main purpose was the treatment of raised intracranial pressure rather than for diagnosis.[57] The technique for needle lumbar puncture was then introduced by the German physicianHeinrich Quincke, who credits Wynter with the earlier discovery; he first reported his experiences at aninternal medicine conference inWiesbaden, Germany, in 1891.[58] He subsequently published a book on the subject.[59][60]
The lumbar puncture procedure was taken to the United States by Arthur H. Wentworth an assistant professor at theHarvard Medical School, based atChildren's Hospital. In 1893 he published a long paper on diagnosing cerebrospinal meningitis by examining spinal fluid.[61] However, he was criticized byantivivisectionists for having obtained spinal fluid from children. He was acquitted, but, nevertheless, he was uninvited from the then formingJohns Hopkins School of Medicine, where he would have been the first professor ofpediatrics.[citation needed]
Historically lumbar punctures were also employed in the process of performing apneumoencephalography, a nowadays obsolete X-ray imaging study of the brain that was performed extensively from the 1920s until the advent of modern non-invasiveneuroimaging techniques such asMRI andCT in the 1970s. During this quite painful procedure, CSF was replaced with air or some other gas via the lumbar puncture in order to enhance the appearance of certain areas of the brain onplain radiographs.[citation needed]
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