Abstract and Introduction
Abstract
Background: Lumbar puncture (LP) is a commonly performed procedure in pediatrics. Accurate analysis of cerebrospinal fluid (CSF) profile is essential in diagnosing and managing a variety of infectious and inflammatory conditions involving the brain, meninges, and spinal cord. It can also provide useful diagnostic information in the evaluation of possible subarachnoid hemorrhage and demyelinating syndromes, and aid in the diagnosis and management of pseudotumor cerebri.
Objectives: To review anatomic, physiologic, and pathologic aspects of performing pediatric lumbar puncture and CSF analysis.
Discussion: Although still a commonly performed procedure in the outpatient setting, effective vaccines to prevent invasive infection due to Streptococcus pneumoniae and Haemophilus influenzae type b have greatly reduced pediatric bacterial meningitis rates due to these pathogens, resulting in decreased opportunity for physician-trainees to perfect this important skill (among nonneonates) during the 3 years of supervised residency training. Success in performing pediatric LP is augmented by a thorough understanding of medical aspects related to this procedure. This article discusses technical aspects involved in successfully performing a lumbar puncture to obtain CSF, and interpreting a CSF profile in children.
Conclusion: A thorough understanding of anatomic, physiologic, and pathologic considerations regarding performing lumbar puncture and CSF analysis can augment success in diagnosing a variety of potentially serious pediatric conditions.
Introduction
Cerebrospinal fluid (CSF) is a dynamic, metabolically active body fluid that performs many important functions.[1] It provides buoyancy to the brain, reducing functional brain weight by about 75%; and also helps to buffer neural tissues from trauma. Because there are no lymphatics within the central nervous system (CNS), CSF provides an important fluid medium for chemicals and nutrients to nourish intercellular spaces, and acts as a reservoir for neural metabolites to be returned to the venous circulation.[1] Acute contraction in CSF volume can safeguard intracranial perfusion and maintain an adequate cerebral perfusion pressure despite conditions causing increased intracranial pressure. CSF contains antibacterial properties that inhibit bacterial growth and proliferation.
The CSF fills the subarachnoid space. An adult produces approximately 500 mL of CSF daily, at a rate of about 0.5 mL/min. In children ages 4–13 years, the static CSF volume ranges between 65 and 150 mL.[1] It is fully replenished approximately every 4–6 h. The volume removed by a routine lumbar puncture (LP) (3–5 mL) is reconstituted in < 1 h.
About 70% of CSF is formed in the choroid plexuses of the ventricles, a microvillus structure lined by a monolayer of epithelial cells joined by tight junctions (forming the blood–brain barrier).[2] Unlike the vascularity of other organs, brain capillary endothelia lack fenestrations or pinocytotic (transport) vesicles. Additionally, there are often different receptors and ion channels on the extracranial cell surface compared to that on the intracerebral membrane adjacent to brain parenchyma facilitating cellular transport.
CSF is an ultrafiltrate of plasma. Normal CSF is 99% water, and therefore, clear and colorless. It contains electrolytes, glucose, proteins, enzymes, antibacterial factors, and few white blood cells (WBCs); the concentration of each component varies with patient age (Table 1).
The CSF circulation dynamic is driven by unidirectional secretory pressure generated at the choroid plexus.[2] Traditional reference values for the upper limit of normal CSF pressure ranges between 70 and 180 mm H2O. A recent study of almost 500 children who underwent LP with manometer-measured CSF opening pressures found the upper limit (90th percentile) to be 280 mm H2O.[3]
This constant forward flow of newly derived CSF replenishes the subarachnoid circuit with fresh fluid and removes waste products. Magnetic resonance imaging has demonstrated that CSF movement throughout the system is pulsatile, aided by choroid plexus pulsations and by the motion of the ependymal cell cilia.[4]
CSF produced in the lateral ventricles flows through the intraventricular foramina of Monro, into the third ventricle, then through the cerebral aqueduct to the fourth ventricle, then via the foramens of Luschka and Magendie into the subarachnoid space. After exiting the ventricular system, most of the CSF flows into the subarachnoid cisterns at the base of the brain; only about 20% flows into the lower reaches of the spinal subarachnoid space, which extends caudally to the second sacral vertebra. The CSF reaching the lumbar cistern is the portion actually sampled by a routine LP.
CSF is absorbed by the arachnoid granulations located over the cerebral convexities, which drain into the venous circulation. A significant amount also drains into lymphatic vessels around the cranial cavity and spinal canal. Total CSF transit time is approximately 1 h.
J Emerg Med. 2014;46(1):141-150. © 2014 Elsevier Science, Inc.
