The cerebrospinal fluid (CSF) was first identified by Cotugno in 1764, which is a major body fluid. CSF provides a systemic mechanism for providing nutrients to the nervous tissue, eliminating metabolic waste and building a structural shield against damage to protect the brain and spinal cord.
The meninges cover the brain and spinal cord, consisting of three layers: dura mater, arachnoid, and pia mater. The outer layer is the dura mater which line the channel of the skull and the vertebral. The arachnoid is an inner layer which is filamentous (spiderlike). The pia mater is a thin layer surrounding the surfaces of the spinal cord and spine.
Formation
The choroid plexuses of the two lumbar ventricles, as well as the third and fourth ventricles, produce CSF. In adults, this includes approximately 20 mL of fluid per hour. The fluid enters the subarachnoid space between the arachnoid and the pia mater. The circulating fluid is reabsorbed back into the capillaries of the blood at a rate equal to its output in the arachnoid granulations / villae to maintain a concentration of 90 to 150 mL in adults and 10 to 60 mL in neonates in order to maintain a concentration of 90 to 150 mL in adults and 10 to 60 mL in neonates. The arachnoid granulated cells act as one-way valves that prevent fluid reflux and contribute to pressure inside the central nervous system ( CNS).
The choriod plexuses are capillary networks separating the CSF from plasma by specific filtration processes under hydrostatic pressure and active secretion of liquid. The CSF’s chemical structure also does not resemble a plasma ultrafiltrate. Capillary walls in the body are filled with poorly associated endothelial cells to facilitate the flow of soluble nutrients and waste from the fluid and tissues. The endothelial cells in the choroid plexuses have very tightly fitted junctures which prevent many molecules from moving. The tight-fitting endothelial cell arrangement is considered the blood-brain firewall in the choroid plexuses.
Function
Cerebrospinal fluid ( CSF) serves as a brain and spinal cord trauma absorber, circulates chemicals, lubricates the central nervous system ( CNS) and may lead to the maintenance of brain tissue. CSF is present in both ventricles, in the spinal cord ‘s main core, and in the subarachnoid area around both the brain and the spinal cord.
Maintaining the integrity of the blood-brain barrier is necessary to defend the brain from chemicals and other blood-circulating substances which may damage the brain tissue. The junctures, by comparison, often hinder the flow of beneficial substances like antibodies and drugs. Disruption of the blood-brain barrier triggered by disorders such as meningitis and multiple sclerosis requires the entrance of leukocytes, antibodies, and other chemicals.
CSF has four main functions:
- Serves as a mechanical buffer that prevents trauma
- Regulates the volume of the intracranial contents
- Provides nutrient medium for the central nervous system (CNS)
- Acts as an excretory channel for metabolic products of the CNS
Specimen Collection and Handling
CSF specimens need to be sent to the laboratory for review immediately. Specimens are placed in three sterile tubes in the order in which they are extracted and are numbered 1, 2 , and 3. Tubes are used for regular clinical chemistry testing, microbiology, hematology, and immunology / serology research.
CSF is normally clear, colorless, and sterile. The average, healthy adult has 90 to 150 mL of CSF, and the newborn infant, 10 to 60 mL.
Appearance
All the tubes obtained by LP are assessed for their gross appearance. Natural CSF is perfectly clear and has a comparable look to purified water. Color and transparency are observed by placing the sample on a clear white paper or written sheet amid a stream of water.
Turbidity: Slight haziness or turbidity in the specimen may suggest an increased white blood cell ( WBC) count. Turbidity in spinal fluid may result from large amounts of leukocytes (WBCs) or from bacteria, elevated protein, or lipid. If radiographic contrast media were inserted the CSF may look sticky and turbid when combined. This artifactual turbidity is not reported.
Clots: CSF should be tested for clotting, in addition to gross turbidity and color findings. The coagulation may be the product of decreased protein. Gel forming on standing is caused by decreased fibrinogen content arising from a “traumatic tap.” Rarely will subarachnoid block or meningitis be correlated with coagulation.
Color: Bloody fluid may result from a painful tap or from hemorrhage of subarachnoids. Remember the appearance of color. When blood is the product of a painful tap in a CSF test (inclusion of blood in the LP test itself), the subsequent sample tubes may reveal less muddy material, gradually being transparent. When a subarachnoid hemorrhage induces bleeding in a test, the hue of the fluid in all the sample tubes should appear the same. In fact, the appearance of xanthochromia can suggest a subarachnoid bleeding.
Xanthochromia is a term used to define a purple, orange, or yellow supernatant CSF. A number of causes may trigger xanthochromia to occur, with the most common being the involvement of RBC products for degradation. The colour ranges from pink (very small volume of oxyhemoglobin) to orange (heavy hemolysis) to yellow (conversion of oxyhemoglobin to unconjugated bilirubin) based on the quantity of blood and the period of time it was present. Certain symptoms of xanthochromia include elevated serum bilirubin, pigment carotene production, substantially raised protein concentrations, and melanoma pigmentation. Xanthochromia induced by bilirubin as a result of immature liver function is often widely seen in babies, particularly premature ones.
Cell Count
Once the specimen is collected, cell counts will be performed as quickly as possible; cells lysis on prolonged standing, and the counts are null. When the cell count can not be achieved automatically, refrigerate the tubing. Within 2 hours, 40 % of WBCs should be lysing at room temperature. WBC lysis is not avoided with refrigeration but limited to 15 %. RBCs are fairly stable at refrigeration.
RBCs are rarely found in CSF. Adult CSF contains between 0 and 5 WBCs / μL. The number is higher in infants, with as many as 30 mononuclear cells / μL considered common in newborns. Specimens containing up to 200 WBCs or 400 RBCs / μL can appear translucent, but all specimens need microscopic examination. CSF cell counts are routinely conducted in an automated Neubauer counting chamber. Electronic cell counters have not been used to count CSF cells in the past due to high background counts and poor reproducibility of low counts.
The identification of the type or types of cells present in CSF is a useful diagnostic tool. The differential counting would be done in the counting chamber. The laboratory method of documenting only the number of mononuclear and polynuclear cells present has led to missing abnormal cells of major diagnostic importance due to poor representation of the cells as they emerge in the counting chamber. To ensure the maximum number of cells available for review, the specimen will be extracted before the smear is prepared.
Predominant Cells Seen in Cerebrospinal Fluid
| Type of Cell | Major Clinical Significance | Microscopic Findings |
| Lymphocytes | Normal Viral, tubercular, and fungal meningitis Multiple sclerosis | All stages of development may be found |
| Neutrophils | Bacterial meningitis Early cases of viral, tubercular, and fungal meningitis Cerebral hemorrhage | Granules may be less prominent than in blood Cells disintegrate rapidly |
| Monocytes | Normal Viral, tubercular, and fungal meningitis Multiple sclerosis | Found mixed with lymphocytes |
| Macrophages | RBCs in spinal fluid Contrast media | May contain phagocytized RBCs appearing as empty vacuoles or ghost cells, hemosiderin granules and hematoidin crystals |
| Blast forms | Acute leukemia | Lymphoblasts, myeloblasts, or monoblasts |
| Lymphoma cells | Disseminated lymphomas | Resemble lymphocytes with cleft nuclei |
| Plasma cells | Multiple sclerosis Lymphocyte reactions | Traditional and classic forms seen |
| Ependymal, choroidal, and spindle-shaped cells | Diagnostic procedures | Seen in clusters with distinct nuclei and distinct cell walls |
| Malignant cells | Metastatic carcinomas Primary central nervous system carcinoma | Seen in clusters with fusing of cell borders and nuclei |
Chemistry Tests
Since CSF is produced by plasma filtration, one would hope to see the same low-molecular – weight chemicals present in plasma in the CSF. It is basically true; but, because the filtration method is selective and the blood-brain barrier regulates the chemical structure, standard values for CSF chemicals are not the same as those for plasma. Abnormal values derive from shifts in blood-brain boundary permeability, or decreased neuronal cell development or metabolism in reaction to a pathological disorder. Rarely should they have the same medical value as plasma irregularities. There are few clinically relevant CSF chemicals; measurement of a wider variety might be appropriate in some circumstances. There are actually several CSF metabolites under review to assess their possible diagnostic importance.
CSF Protein
Protein extracts and protein electrophoresis are standard analyzes for a range of diseases and disease states which are of diagnostic importance. Protein concentrations in CSF are usually the same as plasma percentages, but the ratios differ. The standard CSF protein differs with collection system and location, with a reference range of 12 to 60 mg / dL.
Under clinical conditions, elevated total protein levels are more commonly observed. Abnormally small values exist as fluid spills out of the CNS. The triggers of elevated CSF protein include disruption to the blood-brain barrier, immunoglobulin development inside the CNS, reduced removal of appropriate protein from the fluid, and neural tissue degeneration. Meningitis, multiple sclerosis, and conditions of hemorrhage which destroy the blood-brain barrier are the most common causes of elevated CSF protein.
The appearance in the CSF protein electrophoresis of two or more oligoclonal bands which are not present in the serum may be a helpful resource in the diagnosis of multiple sclerosis, particularly when followed by an enhanced IgG index. Certain brain conditions such as encephalitis, neurosyphilis, GuillainBarré syndrome and neoplastic diseases also occur in oligoclonal banding that may not be found in the serum. Hence the existence of oligoclonal banding in combination with clinical symptoms must be noted. Oligoclonal banding during relapse of multiple sclerosis stays healthy, but decreases in other diseases.
CSF Glucose
Glucose preferentially passes through the bloodbrain barrier to enter the CSF, resulting in a normal value of 60 to 70% of plasma glucose. When the plasma glucose level is 100 mg/dL, the CSF glucose level is usually about 65 mg/dL. For an objective assessment of CSF glucose, a blood glucose check will be conducted as a baseline. To allow for blood-fluid balance, blood glucose will be taken 2 hours before the spinal tap. The same blood glucose techniques are used to calculate CSF glucose. Since glycolysis occurs rapidly in the CSF, specimens should be tested immediately.
Having a significantly reduced CSF glucose followed by an elevated WBC count and a significant proportion of neutrophils is suggestive of meningitis with bacteria. Unless the WBCs are lymphocytes instead of neutrophils, it is thought of developing tubercular meningitis. Similarly, the treatment will support viral meningitis if a normal CSF glucose value is detected for an elevated amount of lymphocytes. Classic laboratory trends such as those already mentioned can not be observed in all meningitis situations, but can be helpful when present.
CSF Lactate
Determination of lactate concentrations in CSF can be used in meningitis diagnosis and treatment, but its utility is problematic and dependent on methodology. Bacterial, fungal, and tubercular meningitis exhibit a lactate amount higher than 25 mg / dL, which is more common with a drop in glucose rates. During initial therapy the elevated plasma lactate rates persist but a decline suggests effective care. Enhanced amounts of lactate result in lack of oxygen which are found with any situation with a reduced blood supply to the brain.
Microbiological Examination
Usually gram stain and culture are performed. Typically collections of CSF are sterile. Gram stain is particularly effective in the treatment of acute bacterial meningitis as in the Gram stained case, the pathogens can be clearly identified. Microscopic analysis of the spinal fluid can also diagnose tuberculosis (acid-fast stain) and cryptococcus infections (india ink preparations). Both bacterial and viral CSF cultures that form part of the routine procedure.