Features of the Cerebrospinal Fluid

1. Big picture

Cerebrospinal fluid (CSF, liquor) is one of the most important diagnostic windows into diseases of the meninges, brain, spinal cord, nerve roots, and subarachnoid space. In the state exam, CSF is usually tested through patterns:

• Bacterial meningitis → turbid CSF, high neutrophils, high protein, low glucose.

• Viral meningitis / encephalitis → clear CSF, lymphocytic pleocytosis, normal glucose, mildly increased protein.

• Subarachnoid hemorrhage → bloody or xanthochromic CSF if CT is negative or delayed.

• Guillain-Barré syndrome → high protein with normal cell count = albuminocytologic / cell-protein dissociation.

• Multiple sclerosis → oligoclonal bands and increased immunoglobulin G index.

• Malignancy / leptomeningeal metastasis → malignant cells on cytology, high protein, sometimes low glucose.

The examiner usually wants you to know the normal CSF values, how to interpret bloody CSF, how to distinguish bacterial vs viral meningitis, and when lumbar puncture is dangerous.