Subarachnoid Information and Courses from MediaLab, Inc.

Most cerebrospinal fluid originates in the choroid plexus. The choroid plexus is composed of a mass of tiny blood vessels which are located in the third lateral and fourth ventricles. The remaining CSF, about 30%, is formed in other sites such as the subarachnoid space and the ependymal lining of the ventricles.

When blood is present in a CSF specimen, it is necessary to determine whether the blood is due to a traumatic puncture or to a pathologic condition. There are several clues to help make this distinction: Traumatic tap:More blood is present in tube 1 than in tubes 2, 3, or 4.When sample is centrifuged within one hour, supernatant is clear.Blood clots on standing.Subarachnoid or cerebral hemorrhage:Blood is evenly distributed in all tubes.When sample is centrifuged within one hour, supernatant is pink or yellow.Blood does not clot on standing.

Two to four hours after a subarachnoid hemorrhage, the supernatant of a CSF sample will be pale pink to pale orange. The source of this color is oxyhemoglobin from lysed red cells present in the CSF before the puncture. Xanthochromia from the lysed red cells reaches its peak 24 - 36 hours after the hemorrhage and gradually disappears after four to eight days. In the same type of hemorrhage, after 12 hours yellow xanthochromia begins to appear due to the presence of bilirubin. The bilirubin is the breakdown product of oxyhemoglobin from the original lysed red cells. The yellow color in the supernatant reaches its peak in about two to four days and disappears after two to four weeks.