A xanthochromic CSF (yellow discoloration of cerebrospinal fluid) in a patient with headache most strongly suggests:
Subarachnoid hemorrhage (SAH) ⭐
Why?
* Blood enters the CSF space → RBCs break down over time.
* Hemoglobin is converted to bilirubin, causing the CSF to appear yellow (xanthochromia).
* It is especially useful when CT is negative but clinical suspicion for SAH remains high.
Classic presentation:
* “Thunderclap headache” (worst headache of life)
* Neck stiffness
* Possible loss of consciousness or neurologic deficits
CSF findings in SAH:
* ↑ RBCs
* Xanthochromia
* ↑ opening pressure
* ↑ protein