A concept which has been difficult to dislodge from the body of medical mythology is the significance of crenated red cells in spinal fluid. Frequently on hospital records and occasionally even in medical writing a special note is made describing red cells found on microscopic examination of spinal fluid as being crenated. Unfortunately the assumption is then made sometimes that the process of crenation requires considerable time. Thus the conclusion is drawn that crenated red cells could not have resulted from the fresh bleeding of a traumatic spinal puncture but must be indicative of subarachnoid hemorrhage.
There is considerable evidence to the contrary. The red cell behaves as a perfect osmometer, gaining and losing water to remain in osmotic equilibrium with its environment.1 The spinal fluid is about 3.5% hypertonic with respect to blood plasma2 and water loss from the red cell with crenation would be expected to