In which type of body fluid are neutrophils (white blood cells) not normally seen: Cerebrospinal Fluid (CSF), synovial fluid, peritoneal fluid, or pleural fluid?

Neutrophils are Not Normally Present in Cerebrospinal Fluid (CSF)

The answer is A. CSF (cerebrospinal fluid) is the only body fluid among the options where neutrophils are not normally present.

Normal Composition of Body Fluids

Cerebrospinal Fluid (CSF)

• Normal CSF contains very few cells (<5 cells/μL) 1
• These cells are predominantly lymphocytes and monocytes
• Neutrophils are not normally found in CSF and their presence typically indicates pathology 1, 2
• Even a single neutrophil in CSF should prompt consideration of underlying pathology

Other Body Fluids

Synovial Fluid

• Normal synovial fluid contains small numbers of white blood cells (up to 200 cells/μL)
• These include neutrophils, which normally comprise <25% of cells in healthy synovial fluid 1
• Neutrophil predominance increases significantly in inflammatory arthritis

Peritoneal Fluid

• Normal peritoneal fluid contains small numbers of neutrophils
• Typically contains <250 cells/μL with a mixture of macrophages, mesothelial cells, lymphocytes, and neutrophils
• Neutrophil count increases dramatically in bacterial peritonitis

Pleural Fluid

• Normal pleural fluid contains neutrophils as part of its cellular composition
• Typically has <1000 cells/μL with mixed cell types including neutrophils
• Neutrophil predominance increases in parapneumonic effusions and empyema

Pathological Findings in CSF

When neutrophils are found in CSF, they typically indicate:

1. Bacterial meningitis: Classically shows polymorphonuclear pleocytosis with neutrophil predominance 1

   • CSF cell count typically >100 cells/μL, often >1000 cells/μL
   • Neutrophils predominate (>50%)
   • Associated with elevated protein and decreased glucose

2. Early viral meningitis: May initially show neutrophil predominance that shifts to lymphocytes within 24-48 hours 1

   • Particularly common with enteroviral infections
   • Total CSF cell count rarely exceeds 2000 cells/μL

3. Subarachnoid hemorrhage: Blood contamination can introduce neutrophils 3, 4

   • Must differentiate from true infection

4. Other conditions: Neutrophils may be seen in:

   • Partially treated bacterial meningitis
   • Early tuberculous meningitis (initially may have neutrophil predominance) 5
   • CMV radiculopathy in AIDS patients 6

Clinical Pearls and Pitfalls

• Neutrophils may be detected in CSF without pleocytosis in certain conditions:

  • Sepsis (without CNS infection) 2
  • Recent epileptic seizures 2
  • Blood contamination during lumbar puncture 2, 4

• Cytocentrifugation techniques may artificially increase the apparent proportion of neutrophils in CSF samples 7, 3

• The presence of neutrophils in CSF with normal total white cell count is not necessarily indicative of CNS infection 2

• Correction formulas for blood-contaminated CSF have limited utility and poor correlation with actual observations 4

Conclusion

Among the body fluids listed in the question (CSF, synovial fluid, peritoneal fluid, and pleural fluid), CSF is the only one where neutrophils are not normally present. The presence of neutrophils in CSF generally indicates pathology and warrants further investigation.