“(the cranium is) Just like carry-on luggage, only so much can fit…one pair of socks to many, and the seams start to strain.”

I’ve only lived with IIH for a few years – much less time than many, many others I encounter in support forums.  Lately I’ve taken notice of newly diagnosed patients who seem to be as perplexed at the lack of information and explanation of their condition as I remember being in 2017 when I was told “Nobody knows nothing about IIH.” (paraphrase). 

Judging by the bewildered posts of new members of our auspicious group, there hasn’t been much change.

What follows is the beginning of a “Frequently Asked Questions” section of Shuntwhisperer.  The information here is a combination of 1) my personal experience, observation of others with IIH/PTC/ETC, 2) published research that is fairly abundant for a disorder that seems to amount to a Black Hole of Understanding, 3) readily accepted tenets of human physiology, and 4) the babblings and savante-garde notions of a guy with a hole in his head and a tube in his brain.

Fair warning, take it for what its worth ; )

In all seriousness, I pray this helps those seeking answers, and as always, it’s not about me being right, it’s about getting others to think and talk about IIH in the hopes that this dialog will spark understanding and improved quality of life for everyone. 

Thus, with the timelessness of the inspired dialog of Shakespearean-trained actor Patrick Stewart,




Short Answers First, Technomedical Stuff Second


Short Answer:

“Intracranial Hypertension”, or “IIH”,  is one name for a group of complex disorders in which an individual develops physical signs and symptoms caused by abnormally high pressures of the fluids in and around the brain.* 


Geek Stuff:

The adult human brain is enclosed in a protective bony compartment of the skull known as the cranium.  The main contents of the cranium are the brain, connective tissue (meninges), and two fluids: blood and cerebrospinal fluid (CSF).

Because the cranium is rigid and has a fixed volume, net accumulations of either fluid will increase the pressure inside the cranium (Intracranial Pressure, or ICP).

“Intracranial Hypertension” results when an individual’s tolerance for normal pressure variations becomes compromised, especially high pressures.  These pressures can affect the brain itself, becoming stressed with predictable results   It is referred to by several abbreviations which likely represent individual variations of the same “disorder”:

  • IIH – “Idiopathic (‘of unknown origin’) Intracranial Hypertension
  • NPH- “Normal Pressure Hydrocephalus” –  A very misleading term that is contradictory and would only apply to true conditions of hydrocephalus, a condition where Cerebrospinal Fluid becomes trapped due to developmental or traumatic factors, allowing the very slow forming CSF to accumulate in isolated areas under significant pressure, causing deformation and/or damage to the brain tissue
  • BNPH- “Benign Normal Pressure Hydrocephalus” – Another extremely misleading term, as with “NPH”, along with the fact it is anything but “benign” (harmless)
  • PTC – “Pseudotumor Cerebri” – literally, “false brain tumor”, one of the earliest names given to this class of disorders due to the fact that a patient’s symptoms usually mimic those of a brain tumor, but upon CT/MRI, no tumor is evident.

I consider these “different” diagnoses to be representations of a similar disorder, expressing itself differently in individual patients due to their particular physiology.   Consequently, I refer to these disorders as Intracranial Pressure Dysregulation Disorders, or ICPDDs.

The Brain and its supporting anatomical structures are encased in a rigid bony protective compartment of the skull known as the cranium.  Just like carry-luggage, only so much can fit inside.  One pair of socks too many, and the seams start to strain.

*Growths of soft tissue such as tumors and cysts may also increase ICP with similar presentation; however these conditions fall into different diagnostic and treatment categories.  For the purposes of discussing the ICPDDs, the focus will be on blood and cerebrospinal fluid, assuming there are no abnormalities of the soft tissues in the cranium, including the brain itself. 



Short Answer:

Intracranial Pressure, or ICP, is the created by high volumes of blood being pumped into an extensive network of blood vessels that support the brain. (This is the foundational principal of Intracranial Pressure Dynamics, hence my appellation “Cerebrovascular ICP Dominance Principal”).**

Geek Stuff:

The brain requires more energy than any other organ in the human body.  That energy is delivered by blood containing oxygen and glucose.  Blood also carries away metabolic waste from brain cells (neurons).

  • Big Numbers Alert: The adult brain has an estimated 100 billion cells called neurons.  Getting blood to each neuron requires a vast and intricate network of blood vessels estimated to be up to 100,000 miles in total length.  The majority of the vessels are so small that blood cells must pass through one at a time.

Blood enters the brain through arteries under high pressure (Average Mean Arterial Pressure of 90 mm Hg) and volume (750-1000cc per minute).  Resistance to the flow of viscous blood (~1.8 times “thicker” than water) through the network of vessels creates pressure in the vessels.  This pressure is transferred from the blood vessels to the brain tissue and ultimately into cerebrospinal fluid in and around the brain and spinal cord, creating what is termed “Intracranial Pressure.”

**Shortly after arriving at and naming this principal “Monro-Kellie 2.0” in Millennial TechnoEvolutionary Credit to the Monro-Kellie Principal, I discovered a cheeky neurosurgeon of “Her Majesty’s Royal College of Medicine, London” had published a paper on this very subject in 2016.  His name is Wilson.  Dr. Mark Wilson.  His publication:

Monro-Kellie 2.0: The Dynamic Vascular and Venous Pathophysiological Components of Intracranial Pressure

This publication, accurate and well written, was obviously composed by MI6 as cover for “Dr. Agent” Wilson.  Subterfuge aside, it does make both Agent…excuse me, Dr. Wilson and myself seem like a pair of bright bulbs.  Nonetheless,  a pair of very stiff upper lipped chaps suggested I change the name by which I referred to this principal, in the name of the Queen…and my kneecaps.

And I do favor mine very, very dry, and of course…

Shaken…not stirred.

“Dr.” Mark Wilson, Neurosurgeon



Short Answer:

Intracranial Pressure is not a fixed, unchanging value.   ICP is dynamic by virtue of its origin in the volume and pressure of blood flowing into the brain, which is in turn inside of the rigid cranium with a limited amount of available space.  Factors affecting systemic blood pressure and an individual’s response/reaction to those factors, will cause ICP to vary as well.  “Normal” ICP is a patient-specific range of pressure determined by individual physiology.  Thus, for each of us, “Normal ICP” is any pressure that allows healthy & asymptomatic brain function.

Geek Stuff: 

While scientific studies establish an average of 110 mm of water (defined as the pressure at the base of a water column 1mm in diameter and 110mm tall), the truth is that “normal” ICP varies from person to person, again for reasons of individual physiology.  Furthermore, ICP varies in an individual over periods from as few as a few minutes to as long as years as dynamics of blood flow and CSF production fluctuate.

All aspects of ICP are dependent on the fact that blood is the only fluid that enters the cranium/brain.  Therefore the pressure and flow of that blood directly affect ICP, and hence the fact that an individual patient’s ICP varies within a personal range and is not a static value.

Finally, the brain itself ensures it receives adequate nutrient-rich blood, controlling blood flow through heart rate/contraction, as well as other critical factors including systemic blood pressure, available oxygen in the air (partial pressure of oxygen), a patient’s lung health (presence/absence of fibrosis, COPD, smoker, and other factors that affect gas exchange with blood in the lungs), health of the blood (anemia, hemoglobin, age/size of blood cells), as well as environmental factors including barometric pressure (and hence altitude), heat, humidity…the list goes on.

In a word, any condition that potentially hinders a person’s brain from getting adequate oxygen in the smallest quantity of blood possible, or which makes their tolerance for ICP fluctuations more narrow, or changes the dynamics of those fluctuations to higher ranges for longer periods potentially predisposes them to developing an ICPDD.

Chiari Malformations are essentially brains too big for the available cranium…or vice versa.  The result is less available volume to allow a patient to tolerate ICP fluctations, not to mention the potential interruption of CSF circulation between the cranium and spinal cord, aka “corking” (credit to Dr. Diana Driscoll and her ongoing body of work, “The Driscoll Theory”)

See FAQ Topic “HOW DOES ICP BECOME ELEVATED?” (coming soon to a url near you! 7/30/2019)



(That was fast!)

Short answer: too many socks in the carry-on luggage.

The adult cranium is a rigid bony case and does not expand or contract. After the bony plates of the skull fuse in adulthood, it has a defined available volume.  If one or more of the contents of the cranium accumulates without a matching decrease in the other contents, the pressure within the cranium predictably increases.*  For the purposes of discussion of ICPDDs, blood and cerebrospinal fluid (CSF) will be the only cranial contents considered to affect ICP.  Growths of soft tissue such as tumors and cysts can also increase ICP, however these conditions generally fall into different diagnoses and treatments.

Looking at blood and CSF, it becomes apparent that blood is the dominant, driving force behind ICP:

  • Blood is the only fluid to enter the cranium, at a rate of nearly one liter per minute at rest, a figure that represents approximately 20% of cardiac output.  This is because the brain demands enormous quantities of oxygen and glucose to function, and actively regulates the amount of blood it receives in real time.
  • By contrast, Cerebrospinal Fluid (CSF) is a by-product of brain function.  It is “distilled” by osmosis in specialized cells lining small hollow (normally) interconnected areas within the brain known as ventricles, as well as by similar tissue along the outside of the brain.  It is produced at a mere 0.35cc/minute from arterial blood, and as such accounts for only 0.0004% of the fluid dynamics within the cranium, with blood accounting for 99.9996%.
  • Blood and CSF are both present in the cranium in approximately equal volumes of 150 cc.  The blood volume enters and exits at approximately 6-7 times per minute; CSF is produced and replaced approximately every 7 hours.
  • CSF flow passively in and around the brain, following pressure gradients from areas of production to areas where it is absorbed by veins and lymphatic tissue.  This passive circulation is aided by pulsations of blood vessels in the brain as well as physical movement of the body.

ICP becomes elevated if blood and or ICP accumulate at a greater rate than they are removed from the cranium.  Due to the high flow rate of blood into the brain, even the smallest deficit in drainage of blood from the brain becomes a potential source for rapid elevations of ICP; this is known as (Chronic) Cerebrospinal Venous Insufficiency, or CCSVI, but could more accurately be termed Cerebrovascular Outflow Insufficiency, Acute and/or Chronic.  This is likely the source of elevated ICP in patients who do not have isolated pockets of non-draining CSF (“Non-Communicating Hydrocephalus”); however, Cerebrovascular (Blood) Dynamics and Cerebrospinal Fluid (CSF) Dynamics are inextricably linked due to the enclosed nature of the cranium**.

NIagara Falls
Cerebrovascular ICP Dynamics
frozen waterfall
CSF Dyamics


*Monro-Kellie Doctrine

**”Monro-Kellie 2.0, The Pathophysiology of Cerebrovascular Dynamics in Intracranial Pressure”, Dr. Agent Mark Wilson, Royal College of Medicine Branch, MI6