The presence of red blood cells (RBCs) in the cerebrospinal fluid (CSF). The CSF normally does not contain RBCs (erythrocytes).
Comment:
Erythrocytes may be seen in CSF following a traumatic lumbar tap, but in such cases RBC counts typically decrease in sequential samples. Penetration of blood into the subarachnoid space and/or CSF may be due to trauma, a ruptured aneurysm, intracerebral hemorrhage, or in connection with a tumor.