Lumbar Puncture

Updated: Jun 14, 2017
  • Author: Gil Z Shlamovitz, MD, FACEP; Chief Editor: Helmi L Lutsep, MD  more...
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Overview

Background

Lumbar puncture is a procedure that is often performed in the emergency department to obtain information about the cerebrospinal fluid (CSF). [1, 2, 3, 4] Although usually used for diagnostic purposes to rule out potential life-threatening conditions (eg, bacterial meningitis or subarachnoid hemorrhage), it is also sometimes used for therapeutic purposes (eg, treatment of pseudotumor cerebri). CSF fluid analysis can also aid in the diagnosis of various other conditions (eg, demyelinating diseases and carcinomatous meningitis).

Lumbar puncture should be performed only after a neurologic examination but should never delay potentially life-saving interventions, such as the administration of antibiotics and steroids to patients with suspected bacterial meningitis. [5]

Relevant Anatomy

The lumbar spine consists of 5 moveable vertebrae numbered L1-L5.The lumbar vertebrae have a vertical height that is less than their horizontal diameter. They are composed of the following 3 functional parts:

  • The vertebral body, designed to bear weight
  • The vertebral (neural) arch, designed to protect the neural elements
  • The bony processes (spinous and transverse), which function to increase the efficiency of muscle action

The lumbar vertebral bodies are distinguished from the thoracic bodies by the absence of rib facets. The lumbar vertebral bodies (vertebrae) are the heaviest components, connected together by the intervertebral discs. The size of the vertebral body increases from L1 to L5, indicative of the increasing loads that each lower lumbar vertebra absorbs. Of note, the L5 vertebra has the heaviest body, smallest spinous process, and thickest transverse process.

For more information about the relevant anatomy, see Lumbar Spine Anatomy.

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Indications

Lumbar puncture should be performed for the following indications:

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Contraindications

Absolute contraindications for lumbar puncture are the presence of infected skin over the needle entry site and the presence of unequal pressures between the supratentorial and infratentorial compartments. The latter is usually inferred from the following characteristic findings on computed tomography (CT) of the brain:

  • Midline shift
  • Loss of suprachiasmatic and basilar cisterns
  • Posterior fossa mass
  • Loss of the superior cerebellar cistern
  • Loss of the quadrigeminal plate cistern

Relative contraindications for lumbar puncture include the following:

  • Increased intracranial pressure (ICP)
  • Coagulopathy
  • Brain abscess

Indications for performing brain CT scanning before lumbar puncture in patients with suspected meningitis include the following [8] :

  • Patients who are older than 60 years
  • Patients who are immunocompromised
  • Patients with known CNS lesions
  • Patients who have had a seizure within 1 week of presentation
  • Patients with an abnormal level of consciousness
  • Patients with focal findings on neurologic examination
  • Patients with papilledema seen on physical examination, with clinical suspicion of an elevated ICP

Cranial CT scanning should be obtained before lumbar puncture in all patients with suspected SAH in order to diagnose obvious intracranial bleeding or any significant intracranial mass effect that might be present in awake and alert SAH patients with a normal neurologic examination. [9, 10]

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Technical Considerations

Complication prevention

The following measures should be taken to help minimize complications of lumbar puncture:

  • Explain the procedure, benefits, risks, complications, and alternative options to the patient or the patient’s representative, and obtain a signed informed consent
  • Before performing the lumbar puncture, ensure that patients are hydrated so as to avoid a dry tap
  • Never allow a lumbar puncture or a pre–lumbar puncture CT scan to delay administration of intravenous (IV) antibiotics; meningitis can usually be inferred from the cell count, antigen detection, or both
  • Avoid lumbar puncture in patients in whom the disease process has progressed to the neurologic findings associated with impending cerebral herniation (ie, deteriorating level of consciousness and brainstem signs that include pupillary changes, posturing, irregular respirations, and very recent seizure) [11, 12]

The smaller the needle used for the lumbar puncture, the lower the risk that the patient will experience a post–lumbar puncture headache. Data suggest an inverse linear relation between needle gauge and headache incidence, and some authors recommend using a 22-gauge needle regardless of what size needle is supplied with the kit. [13]

The use of atraumatic needles has been shown to significantly reduce the incidence of post–lumbar puncture headache (3%) when compared to the use of standard spinal needles (approximately 30%). [14, 15] In addition, it may lead to cost savings. [16] However, obtaining pressures can be more difficult with atraumatic needles.

Prophylactic bed rest after lumbar puncture has not been shown to be of benefit and should not be recommended. [17, 18, 19]

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