What is a Pinched Nerve?

Pinched Nerve

There are 31 pairs of spinal nerves along the spine from the upper neck to the lower back and sacrum. Each pair exits at the level of an intervertebral disk, a flexible element situated between two rigid bones (vertebrae).

When a nerve is pinched, it becomes incapable of propagating an electrical charge in the normal fashion. For all intents, the nerve might be seen as short-circuiting. As with any wire that shorts, its function is compromised. There are two major kinds of nerves: sensory and motor. Sensory nerves provide sensation: touch, temperature, pressure, pain, etc. Motor nerves provide for movement, that is, they control muscles.

Pinching a motor nerve produces weakness. The worse the pinching, the greater the weakness. It turns out skeletal muscles are incapable of survival without nerve input in the long run, so that prolonged severe pinching leads to death of muscle cells. As the individual cells die, the muscle shrinks. This is the cause of atrophy, or muscle wasting. In a worst case scenario, a patient comes in with profound weakness and loss of muscle mass.

Pinching a sensory nerve leads to a volley of abnormal sensations. Tingling, numbness, and especially pain. The pain is generally quite disagreeable, described variously as sharp, shooting, lancinating, burning, or even a dull ache. It may be constant or intermittent, and is generally worse with activity or simply standing. Sometimes patients complain of a deep “toothache” type of discomfort. In severe cases, a patient cannot put weight on the affected leg without severe pain. In all of these cases, the pain follows the distribution of the pinched nerve, which in the most common situation is down the back of the thigh and calf, often across the top or bottom of the foot. The pain almost always runs down the leg from the back towards the foot and not vice versa. Pain running up the leg is very unlikely to be a pinched nerve. In addition, pain from a pinched nerve (the medical term is radicular pain or radiculopathy) is rarely focused around a joint, such as the knee or the hip. Joint pain often indicates a problem in the joint itself.

In reality, nerves are not entirely sensory or entirely motor, but a mixture of the two. Thus, pinched nerves often create both sensory and motor symptoms. This means most patients have both some element of radicular pain, numbness, tingling, or achiness, and a sense of weakness. Often times one aspect predominates, usually the sensory symptoms. When sensory symptoms predominate, patients may become very uncomfortable and often seek medical care early.

Cases where the weakness predominates are not rare however. In the extreme case, this is called painless weakness—a dangerous situation. Human beings respond faster to pain than to weakness. If something hurts, we tend to seek medical attention. However, if there is weakness in the absence of pain, many if not most patients ignore the weakness until it is far advanced. Read far advanced as irreversible, even with surgery. Such permanent weakness can be crippling, or at least life-changing.

As an illustration of the above, consider the difference between heart attack and stroke. Both of these are exactly the same problem—lack of blood flow—but they occur in different parts of the body. When the heart is deprived of blood flow, the result is chest pain. Heart attacks hurt and this causes the patient to seek medical attention immediately, which often prevents permanent injury. But when the brain is deprived of blood, there is no pain (the brain is the only organ in the body that does not feel pain!). The result in many cases is painless weakness of an arm or leg—which people tend to ignore, sometimes for days! In any case, delay of just a few hours is generally enough to produce permanent injury. This is, of course, a stroke.

Painless weakness caused by a pinched nerve is less dramatic, but still devastating if ignored. Patients often ignore such weakness until they notice wasting—atrophy of the thigh or calf—or they begin to fall down from the profound muscle weakness.

By far the most common cause of a pinched nerve is a herniated disk. The disk is a soft tissue element that sits between the bones of the spine, not unlike a stack of coins in which quarters (bones) and nickels (disks) alternate. The disk is the flexible element that allows the spine to bend and rotate, which means disks get a lot of wear and tear. This wear eventually catches up with a person, which is why the incidence of herniated disks increases with age. They are vanishingly rare in children (though I have operated on one in a thirteen year-old).

lumbar HNP

A fragment of herniated disk pinching nerves in the lumbar spine. The nerves are the small gray dots amid the white background in the center.

Because of wear and tear, pinched nerves are most common in the more flexible parts of the spine, the lower lumbar and mid to lower cervical spine. They are unusual in the more rigid thoracic spine.

The disk itself is composed of an outer ring of fibers and an inner meat the consistency of crab. Some folks liken this arrangement to a jelly donut, though the filling is not so squishy and does not readily flow out. Nonetheless, when the outer fibers breakdown, the inner material herniates out. Most herniations are inconsequential, since only those that actually pinch a nerve are troublesome. In fact, by some estimates, as many as 80% or more of disk herniations have no clinical significance.

Even when the herniation does pinch a nerve, surgery is not usually necessary. In most cases the pinched nerve resolves (perhaps the herniation goes back in) and the symptoms disappear. Perhaps 80% of disk herniations resolve this way, usually within a few days to six weeks or so.

Surgery for a lumbar herniation is indicated for several reasons.

First, surgery should be considered in any case with more than just mild weakness. Weakness indicates a true insult to the nerve and it is generally impossible to know if the weakness is getting better or worse at the time of initial evaluation. Because of the risk of permanent weakness with prolonged pinching, surgery is generally offered.

Second, surgery should be strongly considered whenever there is objective evidence of bladder dysfunction. The nerves to the urinary bladder are at risk only with very large lumbar herniations. True bladder dysfunction related to lumbar herniation is rare. The average neurosurgeon probably sees it only two or three times a year (out of several hundred patients). The risk of permanent injury to bladder function is high in these instances and surgery should be strongly considered on an urgent basis.

The third reason to consider surgery is for intractable pain. Radicular pain in most patients can be made tolerable with medication, enough to get them through the acute period whereupon the pain resolves on its own. In the occasional patient, the pain is so severe as to warrant surgery early on. This is a subjective call on the part of the patient and surgeon working together.

The final reason to consider surgery is for the convenience of the patient. There are many times when the pain resolves incompletely and after many months folks just get tired of it. Such residual discomfort generally (though not always) resolves with surgery. Another instance of convenience to the patient is for financial reasons, such as when the family bread winner cannot afford to miss work on and off for months waiting for pain to resolve. It is often easier and more certain a cure to operate and so return a person to gainful employment early on.

What exactly is the surgery to fix a lumbar disk herniation?

Although this will be answered more fully in another article, suffice it to say the surgery is generally straight forward, takes less than one hour, is done as an outpatient, and results in more or less immediate relief of pain. There is no risk of paralysis and only a slight risk of injuring a nerve at surgery (well under 1% with an experienced surgeon). It generally does not involve fusing the spine.


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.


The Exposed Brain



The Exposed Brain
by Edison McDaniels, MD

This is a picture of a craniotomy, one of the most ancient of all surgical procedures.

Man has been trephining the skull, that is opening a hole through the skull, for thousands of years. The purpose of those early operations is not readily apparent, though there are numerous examples of those skulls which show the patient (victim?) survived. Many more most have died during the attempt or in its aftermath.

Modern day brain surgery dates only from the early 1900s, with a few surgeries having been accomplished ten or so years before that. Many of those early patients, if not most, died as well. The road to the modern craniotomy is paved with broken skulls and enough spilled blood and spinal fluid to fill more than one olympic sized swimming pool. Perhaps many more.

Modern brain surgery, although still risky, is a remarkable undertaking. Advances in neuroimaging (see my article “A Game of Shadows” at www.surgeonwriter.com) and anesthesia have made brain surgery very safe today. Death in surgery is a very rare thing, and most patients survive with little or no deficits. There are virtually no parts of the extra-axial space, the complicated 3-D anatomic space surrounding the brain, into which a neurosurgeon’s knife cannot venture. There are areas of the brain itself which still elude our reach, but only in the most extreme circumstances, such as intrinsic tumors of the brainstem. Today, neurosurgeons routinely remove blood clots, clip aneurysms which would have killed even 20-30 years ago, excise once inoperable tumors, and selectively obliterate brain tissue to cure such ills as Parkinson’s disease and obsessive-compulsive disorder. Other neuro specialists, including therapuetic radiologists and interventional neuroradiologists, treat with radiation and endovascular therapies what were once dreaded operative diseases, such as vascular malformations, many aneurysms, and certain tumors.

What does a modern day brain surgery look like? Through the magic of photography, let us glimpse one moment in the exposure of the living, pulsating human brain.



The picture is of an exposed living brain. It’s a still photo, so one needs to imagine the brain actually pulsating with the rhythms of life, both the beating heart at perhaps eighty beats per minute, and the breathing, which in the operating room is controlled at a rate sixteen to twenty breaths per minute. These rhythms are very noticeable to the surgeon, and the surgeon learns to time his activity to them in a more or less subconsious fashion.

Blood tends to pool constantly during brain surgery, along the dependent areas of the exposure. You can see this in the lower left portion of the image. Note also the bloody sponges, which have slowly taken up the oozing blood. Along the border of the sponges are skin clips. These clips attach to the edge of the skin along the line of the incision and have only one purpose: to stop the otherwise copious bleeding from the scalp blood vessels. The scalp is quite vascular and it is very possible to bleed to death from an otherwise simple scalp laceration (as did the actor William Holden, who bled to death in his hotel room after stumbling and striking his head on the corner of his nightstand).

Accumulating blood is removed with a sucker. The sucker is a hollow tube, a straw actually, attached to a suction device. It provides a constant low level of suction that can be used to remove accumulating debris from the operative field. This debris includes not only accumulating blood, but also spinal fluid, bone dust (from drilling the skull), brain itself (sometimes, one will have to remove good brain in making a path to a tumor or other target; surgeons refer to this as ‘taking brain’), and tumor. The sucker is finely controlled by the surgeon using his nondominant hand, and comes in various shapes and configurations. One becomes very adept at its use, as a wrong swipe here or there can be quite costly.

The surgeon’s dominant hand might hold any number of devices. In this picture, it holds the yellow bipolar forceps. This is a cauterizing device. By pressing a foot pedal, the surgeon can send a gentle pulse of electricity between the tips of the bipolar. This brief pulse cauterizes whatever is between the tips of the bipolar. In the picture, the bipolar is cauterizing the edge of the dura mater. The dura mater, latin for tough mother, is a leathery membrane that encases the entire central nervous system (brain and spinal cord) in a protective envelope. Anatomically, it rests just under the bone of the skull, tending to adhere to the inner aspect of the skull in the aged. Sometimes, especially after a blow to the head which fractures the skull, bleeding can occur in the potential space between the skull and the dura (a potential space is one that normally does not exist and only arises under duress—not good). This accumulating blood is called an epidural hematoma and can be life-threatening. It’s what killed the actress Natahsa Richardson after she fell and suffered a ‘minor’ head injury on a ski slope. A craniotomy almost certainly would have saved her, though apparently the severity of the injury was not recognized. When it is, the only reasonable course in many cases is a craniotomy. Fortunately, the prognosis is excellent in most cases—if the surgery is timely.

The dura mater is perhaps a few millimeters thick and can be quite vascular. Here, the bipolar is cauterizing a bleeding point on the edge of the dura. The sucker is clearing the field of the blood so the surgeon can see what he is doing and so the bipolar can work properly. Note also that the dura mater is thick enough to hold stitches. It is often tacked up to the bone during the surgery (B in the images). The tack-ups help prevent oozing of blood from the epidural space. At the conclusion of the surgery, the dura mater will be closed with a row of closely approxiamated stitches. It will also be tacked up to the over lying bone flap, so as to prevent any accumulation of blood under the bone and above the dura. Such bleeding, an iatrogenic epidural hematoma, would necessitate a return to the operating room and reopening of the craniotomy to evacuate the accumulated blood. This is one of many potential complications of a craniotomy. It is one of the chief things neurosurgeons watch for in the first hours after a cranitomy.

Note the cut edge of the skull in our image. A large circular piece of skull has been removed to gain the exposure shown. The removal of the bone is the actual craniotomy. Drilling the skull is one of the more dramatic moments in any craniotomy, especially to the uninitiated. How is it done?

A Civil War era trephine for opening the skull.

A Civil War era trephine for opening the skull.

Drilling the skull is surprisingly easy. In the old days a trephine was used. This is a T-shaped handheld instrument with a circular base of sharp teeth. When pressed to the skull, the user presses his weight down on the T-shaped handle and simultaneously turns it, like a cookie cutter. Nowadays, at least in the United States, such a trephine is rarely used.

Another way to open the skull is with a pneumatic drill. These drills have a failsafe that causes them to stop when the bone is drilled through. The surgeon drills several holes spaced at intervals around the desired exposure area, then simply connects the dots with a saw. Today the saw is often pneumatic itself. However, another very good option is to pass a thin wire under the bone between the holes and saw through the bone with a to and fro action. This is called a gigly saw and has been used for decades. It carries the advantage of removing very little bone along its path, which makes for a better fit when the bone is replaced.

Replacing the bone is easy today. It is usually screwed in place with several tiny plates and screws. In the past it was wired or sutured.  

Craniotomy implies the bone will be returned to its proper anatomic position at the end of the operation. A craniectomy implies the bone will not, or has not been, returned to its normal position (it has been left out). Most elective operations are craniotomies. Many emergent procedures involve a craniectomy, since brain swelling or the threat of brain swelling sometimes prevents replacement of the bone flap. A decompressive craniectomy is a procedure done for uncontrolled brain swelling wherein a large portion of the overlying skull is purposely removed in an effort to control increased pressure in the head. This is often a last ditch effort to control such swelling.

Patients who have had a craniectomy will require further surgery to replace the missing bone flap if they survive. Sometimes, if the defect is especially large, they will need to wear a helmet in the interval between recovery and replacement surgery (called cranioplasty). What do we use to replace a missing bone flap? Usually, in the United States, it is a custom designed acrylic prosthesis that fits the defect more or less exactly. Such a procedure has a significant risk of infection however, and patients need to be watched for signs or symptoms of infection around the prosthesis for many months.

The patient in our image does not appear to have any brain swelling. The architecture of the surface of the brain is well preserved. Notice the large blue veins coursing over the surface of the brain, as well as the fine, spidery, red branching vessels, the arteries. The surface of the brain is composed of peaks (gyrus, or gyri for plural) and valleys (sulcus, or sulci for plural). Some surgeons prefer to operate through the depth of a sulcus in order to minimize brain tissue injury, others are more adept at going through the gyrus. When such a decision is crucial, as when working around the motor strip (which controls movement on the opposite side of the body) the brain can be mapped intra-operatively. This requires special equipment however—and an awake patient!

An awake craniotomy is possible because the brain itself does not feel any pain, despite the presence of billions of nerve cells. With awake surgery, the patient is gently sedated and the scalp is numbed with local anesthetics. Once the incision and the bone work are done, the dura mater is opened. There are many pain fibers in the dura mater, and so the patient is kept sedated until the dura mater has been incised and tacked up. Only then is the patient awakened to respond to the surgeon’s questions. The exposed brain in the image could well belong to an awake patient.

Note the glare in the image. This is caused by a thin and wispy web of issue over the brain, the arachnoid mater. The arachnoid is a flimsy membrane, generally not tough enough to hold stitches. Coursing under it, in the subarachnoid space (a true space, not a potential space) is the elusive cerebrospinal fluid, CSF. The CSF bathes the entire brain and spinal cord. It may provide nutrients and acts as a shock absorber. Infection in the CSF is called meningitis and can be life threatening.

The vessels over the brain also couse through the subarachnoid space. A subarachnoid hemorrhage is caused by the rupture of one of these vessels, often as a result of an aneurysm (a weak spot in a blood vessel). A ruptured aneurysm is a dire circumsance, fatal half the time. However, if the patient survives the initial hemorrhage, clipping the aneurysm via a craniotomy is one option. Coiling the aneurysm through an endovascular approach is another.

A simple craniotomy, as for an epidural hematoma, can be done in 60-90 minutes. Clipping an aneurysm might take three hours. Complicated tumor surgery can take 12-24 hours. These types of operations are usually done at university medical centers, with residents to assist the surgeon with the opening and closing portions of the craniotomy.

As a neurosurgeon, and a fiction writer, I’ve incorporated craniotomies into my stories several times. By way of bringing the reader into the operating room and closer to the action, I have included a scene from one of my novels below. For a graphic and dramatic depiction of a neurosurgeon in action, I refer the reader to my short story, THE CRUCIBLE, available for free at the Summerset Review website. Click the image at the end of this posting to go to the story directly.


What follows is an excerpt from NOT ONE AMONG THEM WHOLE, an audacious novel I wrote about surgeons amid the chaos and carnage of a battlefield hospital during the Battle of Gettysburg. While the scene is fictitious, it effectively portrays a trephination during the Civil War era. A trephination is not quite a craniotomy, but before one can master the rudiments of a craniotomy, one most know the trephine. Such an operation was uncommon during the Civil War, but not unheard of. At least twenty are known to have been done. 

Josiah Boyd is a tobacco chewing surgeon, Tobias Ellis his assistant surgeon, and Tiny is their hospital aide. This is a graphic scene, as is the novel itself. The trephination:

The wind howled around them, but the rain stopped abruptly. Boyd looked up from the soldier on the table, toward the cloudy sky. He didn’t pray though, knowing beyond any doubt that God had long ago abandoned him. He was not a prayerful man.

He could have been the last physician in a land besieged by plague.

He spat tobacco gruel and tried to concentrate on the problem at hand. From the corner of his eye, he saw Tobias Ellis watching him. The assistant surgeon stood directly opposite, waiting to take his cues. To Ellis’s left was a skeletally thin negro stretcher bearer named Abel. Abel’s job was to hold a lantern, to fan Boyd, to hold an umbrella, whatever might be needed. Tiny, Boyd’s long-time assistant, stood at the head prepared to administer the chloroform whenever the word was given.

The right side of Spencer’s head was discolored the blue of days-old bruised skin. Boyd smoothed the blond hair back and saw the small hole where the bullet had pierced him. Another hole just behind and above the ear where it had exited. “I guess that’s as good a place as any to cut,” he said with a lack of enthusiasm. “Sleep ‘im.”

Tiny let go a few drops of chloroform into the mask and Spencer’s heel stopped moving. The lack of movement was eerie, like he was dead. But he was only playing at dead, for every now and again he swallowed or suffered a slight cough. Boyd waited what he thought was a full minute, probably longer as he was in no hurry to get the thing started. Once started however, he was most certainly in a hurry to get it ended.

“Give me a knife.”

Tiny wiped the blade on his apron and slapped it hard into the surgeon’s outstretched palm.

Boyd sucked hard at the wad in his cheek, putting the cold edge of the steel against Spencer’s temple. He ignored the hair and pressed the blade into the skin, cutting not quite to the bone, and dragged it upward over a distance of two inches. He made a second incision at right angles to the first, the effect of which was to fashion an ‘X.’ The incisions were half in, half out of the hairline so that if Spencer survived, the marks would be forever obvious to all.

The skin parted and a brisk stream of bright blood jetted out, as if proof of life. The stream pulsed twice more in quick succession, each striking Assistant Surgeon Ellis in the belly. Ellis was quick to act though, knew the import of blood after more than a year of watching it spill. He put a stubby finger over the artery and halted the flow.

“Ligature,” Ellis said, and tied off the exposed ends of the temporal artery and vein with lengths of silk thread Tiny handed him.

Done smartly, Boyd was impressed with the assistant surgeon’s hands.

Boyd deepened the cut through the muscle over the side of Spencer’s head, running the knife over the same path as before, this time sinking the knife all the way to the skull. The wound filled to overflowing with the dark red of venous blood.


Ellis continuously swabbed the wound with a lint sponge, but the effort did little good until Boyd inserted a couple of curved metal tongs under the skin on each side of the X-shaped incision. “Here,” Boyd said, indicating Ellis should take control of them.

The assistant surgeon tugged the retractors apart from each other, opening the wound as wide as the split skin allowed. Boyd wiped again at the blood, then leaned back to spit and wiped his hand across his forehead.

“Hold that lantern up now.”

“Yassah,” Abel said and came around the table to a spot behind Boyd.

The long shadows of morning leaned lazily against the exterior of the church. The spot was the same a priest had given last rites the day before, though not a man among them had been present for that solemn observance.

Once or twice the white skull chanced into a fleeting view, but for the most part Boyd worked blindly and by feel.


The instrument was six inches long and resembled the gnawed clean bone of a chicken leg the way it flared at one end. The other tip was flat and blunt and he scraped this back and forth against the hard skull, detaching whatever muscle was there and confirming the need for the trephine. Dark blood and gray matter slowly percolated up through the bullet hole in the skull. All the while a steady stream of blood oozed from the skin edges, enough to be a nuisance but not so much the man would bleed out. Ellis pulled the skin edges taut with the retractors and the bleeding slowed to a trickle.

Boyd pushed a naked finger against the skull and felt around, rolling the digit under the skin and making a small pocket. He tried not to think too much about what he was doing, hoping only that he was making a difference.


Three minutes had passed since the incision. Boyd was exhausted.

Tiny passed the T shaped trephine to the surgeon. It had an ebony cross bar handle and a metal shaft that ended in a hollow conical drill with a flange of teeth. The whole thing was built compactly, no more than five inches long, and was solidly built, so that one could put his weight behind the turning of it; a human skull is hard, not meant to be penetrated.

He gripped the handle in his palm, the shaft between the middle and ring fingers.

Boyd knew the drilling would require muscle and backbone, though he was hesitant having never done this before—at least not in a living person where the drill could potentially plunge brainward. He thought for a moment about that word. Brainward. Like rightward or leftward, though it didn’t seem a direction one wanted to test all that often. But he was committed now, and so he leaned over the open head and pressed the teeth of the drill against the bone. He tested the unyielding nature of it, gaining confidence. Boyd simultaneously pushed down and turned the handle the way one might work a stuck door latch. The teeth bit the bone and stopped. He tried a second time using more force. The teeth moved slightly, then popped out of the skull and skittered across Spencer’s forehead, leaving a pattern of tiny bleeding nicks.

Hardy’s words haunted him: You ever trephined a man still this side of the grave?

He hadn’t pressed hard enough, that’s all. He replaced the thing and turned the drill, learning the art and work of it. It sank deeper into the bone and Hardy was at him again: I’m telling you it can’t be done without killing him.

He ignored the thought and pressed forward. The work was tedious and the minutes passed like days. At one point Spencer stirred and Tiny poured a few more drops of chloroform into the mask. Ellis too strained, holding the retractors and the head both. The assistant surgeon swallowed at the sight of the drill poking out of the head but didn’t falter when the thing skittered. 

Boyd turned the drill in small jerks, a quarter arc at a time. Simple brute force, with no way to build momentum. Despite the cool morning, sweat dripped from the tip of his nose. After every few turns, he leaned over and spat, sometimes on the floor and sometimes on the trouser leg of the man beside him.

From the post-mortem trephination he’d done and the several skull fractures he’d seen, Boyd recollected the skull to be about a quarter-inch thick. But a quarter-inch came and went and the drill was still anchored in firm bone. Several times he took the trephine out and tapped the cut skull with a mallet and chisel. Finally, on the fourth such occasion, he felt it give. He tapped again and the bone popped free and floated up, a clot of blood welling up with it.

Ellis grinned at Boyd, still holding the retractors in place. “Hot damn.”

The blood was thick and almost black. Several large chunks pushed out and slid down the side of Spencer’s head. Boyd pushed his little finger into the hole and twirled it, feeling the inside of the smooth skull and dislodging several additional pieces of clot. There didn’t look to be any fresh bleeding though, and after a few minutes he considered how he would end the operation. He decided not to put the bone back in place, there being no good way to secure it. In the case of a fracture the bone would simply be discarded and he saw no reason to deviate from that. Ellis removed the retractors, and Boyd proceeded to stitch the skin with a needle and silk thread. The entire operation had taken just under thirty minutes. When done, the right side of Spencer’s head was dimpled where the bone was missing. They wrapped his head with a length of muslin and waited for the chloroform to wear off.

Boyd spat in the dirt again and stepped back from the table. He picked up the trephine, stared at it a moment or two, then set it back down. Leaning against a wall, he closed his eyes and slept standing up for several minutes.

Another half hour passed before Spencer Hardy began to come out of his stupor. As he did so, he crossed his legs and reached up to grab his head. This was more movement than he’d done in a day and those present cheered.

Boyd at least was satisfied. He slumped to the bloody grass and slept.

Edison McDaniels, MD is a board certified neurosurgeon and practices in the American South. Follow him on twitter @surgeonwriter and read his fiction at Amazon in paperback and on kindle.


2/6 Hydrocephalus Owner’s Manual

Hydrocephalus: An Owner’s Manual Part 2 of 6

A Few More Thoughts on Anatomy


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.



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.