What CSF finding is consistent with subarachnoid hemorrhage?

In cases of subarachnoid hemorrhage (SAH), the cerebrospinal fluid (CSF) typically shows specific findings that help confirm the diagnosis. One of the hallmark features is the presence of xanthochromia and an increased number of red blood cells (RBCs) in the CSF.

Xanthochromia refers to a yellowish discoloration of the CSF, which occurs due to the breakdown of hemoglobin from the red blood cells that enter the CSF following a hemorrhagic event. This discoloration can take some time to develop after the initial bleeding, often becoming apparent a few hours to days post-hemorrhage. The presence of increased RBCs is also a direct reflection of the bleeding into the subarachnoid space.

These findings are crucial because they indicate that there has been recent bleeding in the subarachnoid space, thereby supporting the diagnosis of SAH. Other findings, such as elevated protein and decreased glucose, or lymphocyte predominance, are more indicative of different types of conditions, such as infections or other forms of bleeding, but do not specifically confirm SAH. Understanding these CSF characteristics is essential for differentiating among potential neurologic emergencies.