LÍQUIDO CEFALORRAQUIDIANO

Introduction to Cerebrospinal Fluid (CSF)

Overview of CSF

• The cerebrospinal fluid (CSF) is a clear, colorless, and metabolically active substance that fills the ventricles and subarachnoid space around the brain and spinal cord.

• Normal total volume of CSF ranges from 80 to 150 ml, potentially increasing up to 300 ml in elderly individuals.

• CSF production occurs through passive filtration of blood via choroidal capillary endothelium, influenced by hydrostatic pressure gradients.

Functions and Analysis Indications

• Key functions of CSF include providing essential nutrients to the brain, removing neuronal waste products, and offering mechanical protection to brain cells.

• Indications for CSF analysis include suspected meningitis, subarachnoid hemorrhage, central nervous system neoplasms, neurocysticercosis, and degenerative diseases.

Collection Techniques for CSF

Methods of Collection

• Three classical methods exist for collecting CSF: lumbar puncture (most common), cisternal puncture, and ventricular puncture.

• During lumbar puncture between L3-L4 or L4-L5 vertebrae, three sterile tubes are collected in sequence: Tube 1 for biochemical analyses; Tube 2 for microbiological analyses; Tube 3 for cellular analyses.

Importance of Collection Order

• Adhering to the collection order minimizes interference in test results across different sectors.

• Visual inspection of CSF's color before and after centrifugation can provide diagnostic insights; normal appearance is clear like water.

Analyzing Abnormalities in CSF

Color Changes in Pathological Conditions

• Xanthochromia indicates abnormal coloration due to hemoglobin presence from hemolysis or elevated protein/bilirubin levels; common in premature infants due to immature liver function.

• Distinguishing between traumatic tap versus subarachnoid hemorrhage involves analyzing tube blood content; typically more blood is present in the first tube during a traumatic tap.

Coagulation Properties

• Unlike other fluids, normal CSF does not coagulate due to lack of fibrinogen. Presence of clots suggests contamination from a traumatic tap rather than true hemorrhage.

Cell Counting Techniques

Cell Count Methodology

• Total cell count can be performed using Fuchs-Rosenthal counting chamber with specific counting strategies based on cell concentration levels.

• For low cell counts: count all squares; medium counts: four larger squares multiplied by four; high counts: one square multiplied by sixteen.

Differential Cell Count

• Differential cell count helps identify types of cells present in CSF which aids diagnosis. It requires stained smears similar to hematology practices.

Interpreting Cell Types

Significance of Predominant Cells

• A predominance of lymphocytes may indicate viral infections or early bacterial meningitis while monocyte predominance could suggest chronic conditions such as tuberculosis or fungal infections.

Analysis of Meningitis and Related Conditions

Key Biochemical Analyses in Meningitis

• Elevated protein levels are frequently observed in hemorrhagic meningitis and multiple sclerosis, indicating significant pathological processes.

• Glucose levels typically range from 60% to 70% of plasma concentration; decreased glucose is noted in bacterial, tuberculous, and fungal meningitis as these microorganisms utilize glucose for energy.

• Lactate levels above 35 mg/dL are associated with bacterial meningitis, while levels below this threshold can indicate tuberculous or fungal meningitis. Viral meningitis shows lactate levels lower than 25 mg/dL.

Microbiological Testing Methods

• Microbiological assays such as latex agglutination tests and cultures are essential for diagnosing different types of meningitis.

• Serological tests like VDRL and ELISA can also be performed to identify specific pathogens causing the infection.

Diagnostic Characteristics of Meningitis Types

• A table summarizes reference values for cerebrospinal fluid (CSF), including mandatory aspects like color, appearance, protein, glucose, and LDH.

• White blood cell counts vary by type: bacterial meningitis shows neutrophil predominance; viral shows lymphocyte predominance; tuberculous and fungal types show a mix of lymphocytes and monocytes.