The average CSF circulatory volume is approximately how many milliliters?

• A. 10-20 ml
• B. 500-750 ml
• C. 200-300 ml
• D. 100-150 ml

Answer: (D)

In adults, the total CSF volume that fills the ventricles and subarachnoid space is about 150 milliliters. This circulating reservoir stays roughly stable because CSF is continuously produced and then reabsorbed into the venous system. Production is about 0.3–0.4 mL per minute (roughly 500 mL per day), so the system turns over rather than accumulates, keeping the overall volume around that 100–150 mL range. Among the options, 100–150 mL best matches the actual circulating CSF volume. The other ranges either reflect production totals rather than the reservoir size or are far too small or large to represent the typical CSF volume.