It is all very much still a mystery why this happens to some patients and not others, why for some patients this is a state that persists for months or even years after successful patching. Even physiological explanations are merely theories at this point. One thought is that perhaps the blood injected to the epidural space during a blood patch acts like a kind of blood pressure cuff, squeezing the thecal sac (also called the dural sac, the protective membrane surrounding the spinal cord) and displacing the cerebrospinal fluid within it upward from the spinal canal and into the head. And yet this doesn’t explain the rebound symptoms of the patient who’s given 5 ccs of blood—which is not enough to squeeze or compress anything, really—or the complete lack of rebound symptoms in a patient who’s given 30 ccs—which is more than enough to produce pressure on the thecal sac.
Another thought is that compensatory cerebrospinal fluid production—the body’s overproduction of CSF to compensate for a leak—may be a factor. While the volume of blood used in blood patching is not a predictor of who may or may not develop rebound high pressure, one factor might be: the length of time a patient has been dealing with a spinal CSF leak. While a person is leaking, their body’s natural CSF production is increased to compensate for the leak, and the longer a person has been leaking and thus overcompensating, the longer it may take for the brain and body to adjust to more normal levels once the leak is patched. This is the hose and faucet metaphor I used to explain to my children about my new headache situation after I returned home from the procedure they’d expected to cure me of my constant headache, and it makes a lot of intuitive sense. But that doesn’t fully explain the phenomenon either.
Another thought is that people’s anatomy varies, and some people’s dura and veins are more compliant, more resilient, than others. Physiological things happen in people with spinal CSF leaks, and one of those things is that while leaking, the epidural venous plexus (a network of veins that extends from the skull base to the sacrum) dilates, meaning all those veins expand and become engorged, to compensate for the lower levels of cerebrospinal fluid. The elasticity and capacity for dilation in epidural and cranial veins varies from person to person, and that may explain why some people suffer more from rebound high pressure than others—some people’s veins may be able to dilate more without triggering any pain. The dura, too, varies: Although its medical name translates to “tough mother,” the toughness of it isn’t always uniform throughout in one person’s body, and the toughness or flexibility of one person’s dura can be different from the toughness or flexibility of another’s. Along these same lines, one person’s baseline CSF pressure may be much lower than another person’s, and so what’s high for the first person is normal-feeling for the second. Dr. Kranz explained this to me using the metaphor of a balloon: “It could be that you have a pressure of ten, and I boost it to eighteen, and then you have symptoms of rebound intracranial hypertension. But then here comes somebody off the street and I measure their pressure and they’re eighteen. You both have a pressure of eighteen, and yet you’re symptomatic and they’re not. Why is that? It may have something to do with the elasticity of the system. The person off the street, whose pressure is eighteen, may have a dura like a latex balloon that can expand and contract—but if your pressure is eighteen and your dura is like a Mylar balloon, we’ve pushed you to your limit. So every time you cough or bend over, or turn your head the wrong way or sit for too long, you’re pushing against a rigid system.”
In a small study Dr. Kranz and his team did at Duke, they found that of thirty patients with spinal CSF leaks who received blood or fibrin glue patches, about a third of those patients had no rebound intracranial hypotension symptoms afterward, 43 percent had mild symptoms (treated with Tylenol and head elevation), 17 percent had moderate symptoms (treated with Diamox, usually administered orally, though in some cases via IV), and two patients had symptoms severe enough that they had to go back to the hospital and have their spinal fluid drained to get back to normal levels. These were all patients who were followed and treated based on their symptoms within days of their patches, and even with that kind of close monitoring, treating rebound high pressure is tricky, and varies from patient to patient. For doctors without much experience in treating post-patching rebound headaches in patients with CSF leaks, especially those patients whose rebound headaches develop months afterward instead of days afterward, it can be a real challenge.
In the beginning, in the early weeks post-patching, this rebound pressure is a constant state for me, one that makes me long for the days of the leak, when lying down brought some relief, at least, however minimal, however short-lived. The rebound headache, when it surges, can’t be soothed the same way. The only thing that brings relief is time, waiting it out, surviving it. I also don’t fully understand it, I don’t understand why I still have this constant pain; although I’ve come up with that hose analogy to explain it somewhat to my kids, I haven’t fully absorbed the meaning of it for myself, I haven’t yet read about the mechanisms of rebound high pressure, I haven’t yet thought through what it is that these pain signals are trying to
