Macrophages that have phagocytized red blood cells (erythrophages) or hemosiderin (siderophages) are indications that an SAH had occurred sometime prior to collection of the CSF sample. Macrophages begin to appear in CSF approximately two hours after bleeding into the central nervous system occurs. Macrophages ingest RBCs and erythrophages (top image) may be observed on the stained CSF smear. As the RBCs degenerate further, the breakdown products are seen in the phagocytic cells as dark, granular, iron-laden hemosiderin deposits (blue arrows in bottom image) or yellow crystalline iron-free hematoidin crystals (red arrows, bottom image). The formation of these hemosiderin deposits and hematoidin crystals occurs approximately 18 hours following a subarachnoid hemorrhage. The hemosiderin deposits, hematoidin crystals, and siderophages may be present in the CSF for several months.
