06/7/14
BrainSqueeze

Brain Squeeze

 

Brain Squeeze: The Intracranial Pressure Monster
by Edison McDaniels, MD

The skull is a closed box. Think about it. They don’t call it the cranial vault for nothing. Once past the age of a toddler, the skull is fused—it continues to grow towards the normal adult size, but the bones of the skull are knitted together and there is no mechanism whereby they can open again (short of the surgeon’s knife, or a terrible fracture) to rapidly expand the volume of the vault.

The box is closed and the volume within is, for all intents and purposes, fixed.

This, of course, presents a curious problem. There’s only so much room inside a closed box. What happens when that room is exhausted, that is, over subscribed? What happens when there’s more stuff filling the space than it was designed for?

Huh? What?

To understand this further, imagine a shoe box with an expanding balloon inside. With the lid off the box, the balloon simply expands outward, eventually expanding out of the box entirely. But with the lid on, the expanding balloon eventually destroys the box. Now imagine the box is not empty to begin with, that when the balloon is placed inside it, the box is already 90% full. What happens then? In that case, it’s the stuff filling the box that gets damaged first as the ballon expands to squeeze the contents of the box.

Now, imagine that box is the skull, already filled to near capacity by the brain. Picture the expanding balloon to be a tumor, or perhaps trapped spinal fluid (hydrocephalus), or maybe even a brain swelling out of control after a head injury.

Ouch. Not a pretty picture. Let’s look at this box and its contents more closely.

For starters, it turns out that for all practical purposes there are only three things inside this skull box: blood, brain, and spinal fluid (CSF).

CSF is a non-compressible, usually straw colored fluid that is largely water. It contains no cells under normal circumstances. It bathes the brain and spinal cord, providing a cushion in which these elements float.

Yes, the brain floats.

This is good and bad. It’s good in that under normal circumstances there is nothing pushing against the brain. It’s bad in that with a rapid acceleration or deceleration, like a fall or a blow to the head (think of a baseball bat, or a fist), the skull stops moving before the floating brain does. Or the skull starts moving while the brain is still standing still. Either way, the brain slams into the skull. As they say, it’s not the fall that gets you, nor even the sudden stop. It’s that you don’t stop all at once. Ouch again. 

Back to the CSF. The liquor cerebri, as it has been called, is produced at a constant rate of about 500 cc per day come hell or high water. Under normal circumstances it is reabsorbed into the venous system through the large vein at the top of the brain. The production and reabsorption of CSF are independent of each other however, and uncoupling of this fine balance can lead to life threatening problems within a matter of hours. This buildup of CSF is called hydrocephalus.

You might think the brain itself is a fixed volume, but you’d be wrong. The substance of the brain is composed of cells interspersed in a watery milieu, the so-called interstitial fluid that exists between the tightly packed cells. Both the cells themselves and the interstitial space they sit in are capable of changes in volume relative to a given physiological stress.

What kind of stresses? Simple breathing for one. The volume of the brain is reduced slightly with hyperventilation, i.e., rapid breathing. As a caveat, hypoventilation (very slow breathing) can cause an increase in the volume of the brain. This happens every night when we sleep (sleeping produces a relative hypoventilation—shallow breathing—leading to a slight increase in brain volume. Not enough to cause a problem in the normal circumstance, but if there is something else taking up space inside the head (hydrocephalus, a tumor, or even a slowly expanding hemorrhage—the chronic subdural of the aged), this slight change in brain volume while sleeping can cause symptoms (this is partly why patients with brain tumors tend to have a headache in the morning when they first get up—later in the process they often vomit in the mornings as well, after which they feel better because the act of vomiting has pushed a good deal of CSF out of the head and into the spine, relieving pressure within the skull).

Gravity is another stress. The volume of the brain (as well as the amount of CSF within the head itself) tends to be lower during the day when we are upright. Most of us sleep lying flat, however, and lying flat takes gravity out of the picture and fluid tends to flow back into the head during the sleeping hours. Patients with untreated brain tumors or chronic hydrocephalus learn that sleeping upright feels better and causes less trouble. Neurosurgeons often elevate the head of their patients after surgery for the same reason.

A much more significant stress is head injury. Physicians often refer to closed head injury, CHI. CHI is generally a blunt force trauma, like a fall or striking the head in an auto accident. Being hit by a thrown ball is another example. Gunshot wounds and stabbings are examples of penetrating head injuries. All of these cause swelling in various degrees, i.e., an increase in the amount of water in the brain tissue (not to mention hemorrhage—this is the definition of contusion, which is bruising).

Uncontrolled brain swelling can cause shifts of brain tissue within the skull. It turns out the intracranial space is not a simple box with a brain within. Rather, it is a complicated 3-D space with various shelves, nooks, and crannies. These divide the space into various compartments, each called a fossa (anterior, middle, and posterior—front, middle, and back), as well a right and left half with a large shelf of tissue between. Neurosurgeons spend years learning how to get in and out of these various fossas with as little injury as possible.

Swelling represents an increase in the local pressure within the brain. Simple physics dictates that material moves from an area of higher pressure to an area of lower pressure. The brain is no different. With brain swelling, injured tissue has a higher pressure than surrounding normal brain. These gradients are generally gradual and so the shift is small at first. But when the gradient increases (the swelling rises), shifts of significant magnitude can occur between and across the various shelves and compartments. This not only squeezes and distorts good brain, it also squeezes blood vessels, which may lead to stroke. All of these things can potentially turn good brain into bad brain. Bad brain swells, and the situation is potentiated until either the surgeon intervenes successfully or the patient dies. This is malignant cerebral edema (AKA malignant brain swelling).

So that’s CSF and brain. What about the third substance normally present within the skull, blood? Does the volume of blood change? Yes. In fact, the hyperventilation/hypoventilation discussed above also affects the amount of blood in the cerebral vessels. Hyperventilation reduces any pooling of blood, which is a very quick and effective way of reducing increased pressure in the head related either to brain swelling or tumors. This effect is short lived, hours to a day or so, but is quite potent and is used often in emergencies to temporize on the way to the operating room. It is one of the reasons that head injured patients are intubated so quickly.

The caveat of the above paragraph is that hypoventilation (under ventilation or shallow breathing) can kill. Hypoventilation allows pooling of blood in the head and, in the setting of brain swelling, that is very dangerous. One place this can occur is in the CT scanner in the first moments evaluating a head injured patient. This is another reason such patients are intubated early in their care, not so much because hyperventilation is necessary, but because hypoventilation is so bad.

So, the three most frequent occasions when there is a problem with the volume of brain tissue itself are tumors, brain swelling from head injury, and aging.

A brain tumor may be thought of in terms of an expansion of brain volume or brain tissue. As the tumor enlarges, it takes up valuable space inside the so-called cranial vault, space normally occupied by the normal brain. As the tumor grows, it displaces normal brain (and spinal fluid). If the tumor gets large enough, this displacement leads to shifts in brain matter (for the same reasons as above). These shifts are known as herniation. Herniation is a situation in which brain tissue is displaced out of it’s normal position. Sometimes this herniation is relatively benign and serves as a marker that there is a problem. Though the herniation itself might be relatively benign, if allowed to continue it may lead to either stroke or death—so not so benign afterall. Other types of herniation are even more significant, leading to pressure on the centers of the brain controlling heart rate, blood pressure, and breathing. Obviously, such herniations are immediately life threatening. These are sometimes irreversible.

Another situation in which blood becomes a problem inside the head is with hemorrhage (intracranial bleeding). An expanding intracranial hematoma can rapidly become lethal. This may take the form of a post-traumatic hemorrhage (epidural or sudural hematoma, hemorrhages outside the brain proper) or a spontaneous hemorrhage, which is usually within the substance of the brain itself. This latter is a form of stroke and is caused by the rupture of a small vessel within the brain substance. Sometimes such a hematoma will be amenable to removal, sometimes it occurs in an area where it cannot be reached without leaving a person devastated from a brain function perspective (in such a case, surgery is usually deferred).

Not only is the size of an expanding mass inside the skull important, but the rate of expansion of the mass is equally important. I have seen a slow growing benign tumor the size of a softball cause little in the way of problems (the young woman presented with a lump on her head she was curious about, no headaches or other symptoms!). Benign tumors can grow very, very slowly, taking many years to achieve a clinically significant size. For this reason, when such a tumor is discovered in an elderly person (whose brains have lost volume due to aging and so have extra room already), neurosurgeons often chose not to remove the tumor unless it shows evidence of significant growth over time. Depending on a person’s age, a slow growing tumor may not grow fast enough to become a problem during a person’s life.

On the other hand, an expanding epidural hematoma after a fall or other head injury may cause life-threatening problems at a relatively small size of just 25-30 cc. Sometimes a lucid interval occurs after a head injury, often seemingly minor, during which blood is accumulating in the skull until it reaches a symptomatic size, by which time it may be too late. The classic case is an epidural hematoma (bleeding outside the brain and just under the skull). Natasha Richardson, the actress, was in a lucid interval when she declined medical aid after suffering what was thought to be a minor head injury while skiing. Somewhat later, perhaps an hour or two, she collapsed when the hematoma finally reached a size where it caused one of the above noted herniations.

So, to recap. First, the skull is a closed box. Second, there are only three things inside the box: blood, brain, and CSF. Third, an increase in the volume of any one of these three substances (blood, brain, CSF) leads to a compensatory decrease in the volume of the other two. And finally, once these compensatory decreases are exhausted, the intracranial pressure rises and shift and herniation is the result. If this badness cycle isn’t interrupted at some point, death or stroke is the result.

The last paragraph is a statement of the most fundamental doctrine in all of neurosurgery, the Munroe-Kellie Doctrine. This is learned by every neurosurgery resident during the first week of training and never forgotten. In fact, there is nothing a neurosurgeon does inside the head where he or she does not have to take the Monroe-Kellie Doctrine into account.

Stated another way, as a neurosurgeon, with every intervention I make involving the brain, I have to consider the effect on intracranial pressure. Not to do so invites catastrophe, and preventing catastrophe is what treating brain squeeze is all about.

Oh, one more thing. I am often asked what happens after we lose CSF in surgery. The short answer is, nothing. As I noted above, CSF is produced at a constant rate of about 500 cc a day, which is about the volume of CSF in the head. Thus, anything lost at surgery is replenished in a matter of hours. Until then, the brain sort of sits like a lump inside the head. This might well cause a headache, though it doesn’t seem to be too bad in most patients. Sometimes nausea as well, though it’s difficult to say if this comes from the anesthesia meds, the removal of the tumor itself, or the loss of spinal fluid. Either way, the situation resolves itself before the patient goes home. This is one reason most patients don’t go dancing the night of surgery, though many are able to walk the halls of the hospital by the morning after surgery.

05/29/14
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A Most Striking Image

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A Most Striking Image
by Edison McDaniels MD

He lies on a bed, listless and naked as the day is long, the lone hand of a kind woman (a nurse? or perhaps his mother?) supporting his feeble, overly large head. Despite the sepia hue of the old photo, it is not too much to imagine his skin a sickly milk pale, his complexion sallow. He is too quiet, does not coo, and his cry is mostly a mewl. A kitten bleats louder. We can almost hear an old time gramophone scratching out a tinny version of Brahm’s lullaby in the background. If so, he gives no indication he hears it.

His scalp is thin and veiny. The spidery vessels are visible throughout, delicate streams of blue under the all but translucent skin. His hair has yet to grow, so there is nothing to obstruct the view of his bossy forehead and overgrown braincase. We can almost see the separation of the underlying skull plates, the too large and too taunt spaces between them. Indeed, the skull is overinflated, some would say grotesquely so, with the forehead protuberant and the tiny face an afterthought the way it occupies only the lowest fraction of the front side. The ears appear set too low, the crown too high.

But it is the eyes that are the most part of him. They are, quite simply, stunning. Our own eyes are drawn to them as if tugged by some unseen hand of the Almighty. There is just a hint of how big and black the pupils are, despite being buried in the lower eyelids so that the meaty whites are too visible, too obvious. Like mad doll’s eyes are those eyes. It is obvious they are forcibly deviated downward. This sunsetting is the most striking quality of the image, and conveys life to what is otherwise an unbidden stillness.

These eyes are distinctive to the point of menacing. They telegraph danger. This is a child in dire trouble, a child with infantile hydrocephalus.

At the time this photograph was taken, very likely sometime in the first or second decade of the twentieth century, hydrocephalus was akin to a death sentence. Hydrocephalus is an over accumulation of cerebrospinal fluid (CSF) in the head. The problem is one of simple plumbing. 

CSF is 98% water. It was first described by Hippocrates in ancient times, who recognized its presence but generally attributed it to disease. Even such later luminaries as Galen, Leonardo da Vinci, and Vesalius were not aware it was normally present in and around the central nervous system. A true knowledge of its significant position in neuroanatomy and physiology had to wait until the late 18th and early 19th centuries. 

CSF is normally produced within fluid filled voids within the brain, the so-called ventricles. The CSF circulates outward to bathe the brain, and is reabsorbed into the venous system over the top of the brain. Unfortunately, a number of choke points within this system serve as places where the normal circulation of CSF can be obstructed. Like water trying to flow through a crimped hose, the fluid cannot easily pass and the resultant buildup of CSF behind the obstruction (CSF is continuously produced at a steady rate independent of its reabsorption) balloons the ventricles and distorts and disturbs the brain.

The pathologic buildup of CSF is common to all forms of hydrocephalus. In the adult, this buildup can prove rapidly fatal since the skull is a solid box and cannot expand. The building fluid rapidly squeezes the brain against the skull, a fatal circumstance if not relieved.

But in infantile hydrocephalus, the infant skull is not fixed in volume because the skull plates—collapsible in order to pass through the birth canal—have not yet fused solid. Such fusion normally happens between 14 and 18 months of age. Until then, accumulating CSF distorts both the brain and the skull. The immature skull is capable of expanding to truly massive proportions, several feet in diameter in the worst cases. 

Untreated infantile hydrocephalus does not kill immediately. The expanding head becomes like a giant bag of water, one which can be trans-illuminated with a flashlight in many instances. The brain is squeezed and thinned and squeezed and thinned until just a ribbon of brain is left against the bony confines of the enlarged skull. As if the brain were nothing so much as dough and the building CSF a kind of rolling pin flattening it out. This is the very definition of trouble.

Such a dire situation causes unfathomable damage over time, of course. These children become listless and dull, unable to keep food and water down. They show an apathy to their environment, with little or no response to sounds or visual cues in the later stages. The increasing pressure inside the head presses down on the upper brainstem, against an area which controls eye movements. This leads first to an unyoking of the eyes (they look off in different directions; if the child could talk he’d perhaps complain of double vision). Later this pressure produces the characteristic downward deviation of the eyes as seen here. This is an ominous finding, suggesting the hydrocephalus is far advanced.

By this time there is another complication. The building pressure has also damaged the vision severely. Looking into these eyes with an ophthalmoscope, the doctor would see a pale, dusky, atrophic optic nerve—like a dried and shriveled prune. The optic nerve is an extension of the brain (the only part of the brain normally visible from the outside!) and its decayed condition is further evidence of the damage within. Indeed, these eyes don’t react to light, the pupils don’t constrict.

This child is very likely blind.

Hydrocephalus was largely fatal until 1960 or so. Although the problem was well described in the first part of the twentieth century, a definitive treatment proved surprisingly elusive.

The need to divert CSF out of the head for absorption elsewhere in the body was recognized, but where exactly? Just about every part of the body has been involved in one treatment or another for hydrocephalus. Physicians have tried diverting the fluid to the chest, abdomen, pelvis, and heart. One early treatment had the fluid diverted to under the scalp, where it became a bag of water outside the skull (there was not enough absorptive capacity however and the fluid simply accumulated under the skin).

A rather drastic solution, popular in the 1950s but no longer used today, was to divert the fluid to the urinary bladder. This involved removing (and sacrificing) a perfectly good kidney however (not an easy operation in itself) and passing the shunt tubing from the lumbar CSF space into the ureter (the natural tube from kidney to bladder). In addition, patients lost excess salts and water because the CSF was just peed out and not absorbed. Such a treatment would be anathema today.

Another popular treatment was to place the end of the shunt into the heart. This is called a ventriculoatrial shunt and is still used on occasion today. It has several disadvantages, chief among them being it requires periodic lengthening since the shunt does not grow with the child, but is useful in particular circumstances when the belly cannot be used.

It’s also possible to place the shunt into the chest, where the fluid spills out around the lungs. Not ideal, but again useful in certain situations. This is a ventriculopleural shunt.

By far the most common shunt in use today is the ventriculoperitoneal shunt (VP shunt). This shunt runs under the skin from the ventricles of the brain to the belly. Specifically, the end of the shunt floats in the space around the intestines—not inside the intestines or stomach themselves. This is a very useful shunt.

It wasn’t until the 1960’s that the first reasonably acceptable shunts were produced. These remarkable devices incorporate both a valve to prevent over-shunting and a hollow tube of inert material (usually silicone today) the size of a wet spaghetti noodle. The CSF is thus diverted past the obstruction to the space around the intestines, where it is reabsorbed into the blood stream just as it would have been in the head.

Today, treatment of hydrocephalus is straightforward, but requires a lifelong diligence against malfunction and infection. For most individuals these issues are not a significant problem. Most people with a ventriculoperitoneal shunt (VP shunt) live normal lives, with normal brain development.

It is very likely that if you live in the industrialized world, you know or work with somebody who has shunted hydrocephalus, though you may not know it. That’s a striking example of how far neurosurgery has come since the days of this unfortunate child, when hydrocephalus was essentially 100% fatal.

Author’s note: There are still many places in the world today where hydrocephalus is a major health concern, as a simple google search will show. In East Africa for instance, there are more than 6,000 new cases a year, most caused by infection. With about 1 neurosurgeon per 10,000,000 people in East Africa, most cases do not make it to definitive care. Those that do still have to contend with the possibility of a later shunt malfunction or infection. India is another example.

indian-baby-2

 

05/18/14
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Hydrocephalus Owner’s Manual

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Click image to download the entire Hydrocephalus Owner’s Manual as a free pdf.

Hydrocephalus: An Owner’s Manual

by Edison McDaniels II, MD

WHY I WROTE THIS MONOGRAPH

I am a brain surgeon.

Several years ago, I was confronted with a young man in the emergency room who had earlier that morning been found unconscious by his college roommates. In fact, when I met him he was essentially comatose, that is, unresponsive in any meaningful way. Fortunately, one of his roommates recalled something about him having a shunt. With this piece of information, the emergency physician quickly called for a stat head CT and a diagnosis of shunt malfunction was made. I was called, took the patient to surgery for an emergent shunt revision, and he recovered and lived happily ever after.

Well almost. It turned out he was a college student and the ordeal left him rather exhausted, though neurologically normal, and he would spend several months recovering from his near death experience. His mother, who lived in a city 160 miles away, drove over immediately and was waiting for me when I came out of the operating room. I have seldom seen a mother so grateful as that woman—unless it be virtually every other mother I have ever dealt with as a neurosurgeon.

Largely because of their children, parents are special people.

The bond between parent and child is like no other. I have seen octogenarians break down while recalling the death of a forty-year-old son or daughter—never mind that the death occurred fifteen years before. Perhaps the only bond in all of nature that can never be fully broken, it continues beyond divorce, separation, abandonment, illness, and even death. At its best, the parent-child bond drives us to be our best, to meet our full potential. Even when it is missing, entire lives are predicated, even formulated, on the basis of such a loss.

Almost without exception, the parents I meet would gladly exchange places with their child in these moments of extreme stress. These parents feel helpless and at the mercy of the situation. I am often asked What could I have done? Or Is there anything I can do to prevent this from happening again? 

I know the feeling.

I am a brain surgeon. I am also a parent. Several years ago, my oldest son died suddenly. In my years on this earth I have lost people close to me—a brother, a half-brother, both parents, several close friends—but all of their deaths paled in comparison to losing a child of my own. It was and remains the single most difficult event of my life, the defining moment if you will.

A bond which cannot be broken.

Which brings me to this monograph.

Hydrocephalus—loosely defined as a build-up of fluid in the brain—is a life-threatening, fairly common, and relatively easily treated condition. Unfortunately, with existing medical technology, the treatment requires a lifelong diligence on the part of loved ones as well as the patient himself/herself. But that being said, the treatment is not onerous on a daily basis and the benefits are dramatic. Most patients with hydrocephalus live normal lives in virtually every respect. They play sports (even extreme ones), marry, have regular jobs, carry babies through labor and delivery, and die as an old man or woman (or at least we expect they will—the technology is only fifty or so years old and thus people shunted as young children are only now reaching late middle age). With the possible exception of the more remote parts of Alaska, if you live in the United States you almost certainly have at least one friend, acquaintance, student, or co-worker with a vp shunt—though you may not know it.

So why this monograph?

Because, to put it in the simplest terms possible, failure to recognize a shunt malfunction can be fatal. The boy I took care of above had failed to get out of bed for class one morning. When his roommates returned home for lunch, they found him unresponsive and still in bed. They called an ambulance and he was taken to my hospital, where a CT of the brain showed the problem. He received prompt medical attention—but only belatedly and it nearly cost him his life.

Had his roommates known the gravity of his failure to arise that morning, his brush with death would likely have been avoided. His mother recognized this fact. She knew how close to the edge he had come. She was one of those who asked What could I have done? Is there anything I can do to prevent this from happening again?

The advice I gave her became this monograph.

Author’s note: This is not an exhaustive treatment of hydrocephalus. It’s a brief, informative, interesting, and I hope useful summation of some of the more common questions I have been asked repeatedly over the years. There are many longer, much more exhaustive books on hydrocephalus. This, however, will answer most of your questions. And it is written with the lay person in mind.

 

 

About The Author

Edison McDaniels is a writer, wordsmith, novelist, and physician living in the American midwest. His writing tends to involve ordinary people in extraordinary circumstances and is often informed by medicine. His stories showcase historical fiction and the supernatural, especially ghosts. He received honorable mention in The Seventeenth Edition of the Year’s Best Fantasy and Horror (2003), and has been published in Paradox Magazine, The Summerset Review (available online), The Armchair Aesthete, On The Premises Magazine, and others. Several of his short stories can be found online.

He is also a graduate of Stanford University and is a neurosurgeon. He is board certified in the practice of adult and pediatric neurosurgery, with over 6,000 operations to his credit.

He and his wife collect historical etchings and attend at least 1-2 baseball games a week between April and October, more if the Minnesota Twins are in town.

His novels include NOT ONE AMONG THEM WHOLE, THE BURDEN, and the forth coming THE MATRIARCH OF RUINS. His latest novella, BLADE MAN, is available as an eBook.

 

02/18/13
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2/6 Hydrocephalus Owner’s Manual

Hydrocephalus: An Owner’s Manual Part 2 of 6

A Few More Thoughts on Anatomy

Compartments

It turns out that the interior of the skull is divided into several areas, that is, it is compartmentalized. Essentially, there are three compartments: the supratentorial space, which is divided into right and left halves by a tough shelf of tissue called the falx; and the infratentorial space, which is not divided right from left but is separated from the supratentorial space by a second tough shelf of tissue call the tentorium.

The supratentorial space houses the cerebral hemispheres, within which are the right and left ventricles. We shall look at the ventricles in a moment, as they are crucial to the issue of hydrocephalus. The supratentorial space is located in the top half of the head, essentially above the level of the ear holes.

The infratentorial space is at the back of the head, below the ears. A small space, it houses the highest priced real estate in the brain: the so-called brainstem, which controls important but mundane things like breathing, swallowing, pulse, and blood pressure (to name but a few; there is also an area here seemingly devoted to vomiting—called the area postrema—and pressure here produces, you guessed it, vomiting).

 

ICP Revisited

We have already seen how the pressure inside the head, the ICP, must be at equilibrium. What this means in reality, is that pressure across the compartments mentioned above must be at equilibrium. Since every high school student knows that items move from an area of higher pressure to an area of lower pressure (this is why storms move across the atmosphere and forecasters and ship captains pay inordinate attention to barometric pressure), it stands to reason that if the pressure rises in one compartment more than another, shifts may occur inside the head. That is, the brain (or part of it), might move from one compartment to another!

In clinical terms, this is called herniation and it is deadly.

 

Herniation

As a neurosurgeon, everything I do inside the head must take into account the possibility of herniation. The last thing I want is the brain shifting around. Fortunately, it turns out one can predict these shifts fairly easily. And if one can predict them, one can prevent them. Usually.

Herniations (think of them as unwanted shifts of brain substance) occur when the ICP goes out of equilibrium because of an increase in one or more of the three important substances mentioned above (brain, blood, or CSF).

Increases in brain substance are represented by brain tumors, of which there are many kinds (some cancerous, some not).

Increases in blood substance are represented by bleeding inside the head. There are many different types of such hemorrhages, some requiring emergency surgery to remove.

Increases in CSF are represented exclusively by hydrocephalus. In fact, the definition of hydrocephalus is an unwanted and pathologic build-up of CSF within the skull, either inside or outside of the brain. The remainder of this monograph deals with hydrocephalus, a few of its variants, and how it is treated by modern neurosurgical techniques. Please note that what follows is not an exhaustive discussion but is for informational purposes only. Nothing here is meant to supersede or replace consultation with a competent expert, usually a neurosurgeon.

 

The Ventricles

The brain floats.

In the normal course of things, the brain floats in the liquor cerebrospinalis, CSF. The CSF is produced in the ventricles, which are four cavities deep within the substance of the brain, usually rather small and inconsequential.

Three of the ventricles, the right and left lateral ventricles and the IIIrd ventricle, are located in the supratentorial space. The right and left lateral ventricles are offset to the right and left of the body’s midline, and connect with the IIIrd ventricle through a small opening called the foramen of Munro. The foramen of Munro is the first choke point in the system. Choke points are areas small enough to be blocked, or at least partially obstructed, and so have the potential for trouble. The IIIrd ventricle is on the midline and is very close to the exact center of the head. It has a very small tail off of its back end, a narrow tube called the cerebral aquaduct (about the diameter of a pencil lead normally), through which every drop of CSF produced in the lateral and IIIrd ventricles must pass (a major choke point) on its way to the IVth ventricle, which is located on the midline in the infratentorial space. The IVth ventricle in turn opens into the wider spaces at the base of the brain through three openings, called foramina, which rarely cause problems.

CSF is actually absorbed into the venous system across the surface of the brain at the top of the head. Unfortunately, the absorption of CSF can fail following hemorrhage or infection (which perhaps gums up the works and thus prevents the reabsorption). This failure of absorption, combined with the continued production of CSF in the ventricles, leads to one common form of hydrocephalus called communicating hydrocephalus.

 open brain woodcut

Disclaimer: The information contained in this blog is simply that, information. I am not doling out specific medical advice. Nothing contained herein is meant to replace a complete evaluation by a qualified member of the medical establishment. This page is nonfiction.