Microvascular decompression, the beginning

When Dr. Peter Jannetta proposed attacking TN by going inside the skull to insulate the trigeminal nerve with a mini-cushion, the idea wasn’t wholly embraced by the medical world. More than a few fellow neurosurgeons openly questioned the wisdom of risking serious complications and even death when 1) TN is not a fatal condition and 2) other, less risky, and reasonably effective treatments were available. 

A lot of patients weren’t crazy about having their head opened either. Yet five decades later, the microvascular decompression (MVD) procedure has become widely accepted and many surgeons consider it the patient’s best chance at long-term pain relief without numbness. 

MVD is the only surgical procedure that addresses the purported cause of most TN. The aim of MVD is to hunt down one or more blood vessels compressing the trigeminal nerve and to move the two apart by inserting a small pad between them. The aim of other procedures is to alter the pain-transmission ability of the nerve with a surgically-induced injury. 

The MVD approach 

The idea of MVD is to be as nondestructive as possible. However, MVD requires an opening in the skull before the surgeon can try to undo the damage the body is causing itself. If all goes well, the surgeon will get in and out with no lasting problems. This action essentially takes the offending mechanical force – a pulsating blood vessel – out of play. That alone is often enough to stop the pain in its tracks. With the vessel no longer beating on the nerve, the patient wakes up and finds the pain is gone completely. 

Other times, moving the vessel out of the way gives some improvement at first, but the nerve needs to gradually heal over days or weeks before the pain fully subsides. The longer a person has had TN pain before having an MVD, the less likely it is that pain relief will be immediate. 

Numbness sometimes occurs with MVD, but it’s not a necessary or intentional effect. In the procedures that injure the nerve, more numbness usually means better and longer-lasting pain relief but that’s also more annoying to the patient. So, surgeons try to strike a balance of injury – enough to help but not so much as to be annoying or harmful. 

In an MVD, there is no such balancing act: Having numbness doesn’t mean better pain relief. In fact, one study found that most patients with excellent relief (defined as no pain and no requirement for medicines) had no postoperative numbness at all. 

In the early years of MVD, some surgeons speculated that it wasn’t the padding action of this procedure that was stopping the pain. They theorized that the mere action of moving the vessel off the nerve was causing mild injury to the nerve and stopping pain. Long-term studies have discounted that theory. In fact, it’s now believed that irritating the nerve during surgery might be behind the numbness that sometimes occurs. Sometimes vessels can be decompressed easily but other times the surgeon must do some tugging and manipulating to separate a vessel that has adhered to the nerve or wedged itself tightly behind the nerve. When numbness does occur after MVD, it’s usually mild and clears up within a few weeks. 

The MVD procedure 

Prior to surgery, patients must be tested and screened to make sure their overall health is good enough to tolerate the stress of major surgery and the two to three hours of general anesthesia that an MVD may require. 

Once the patient is asleep, a one-inch-by-three-inch area of hair is shaved, behind the ear on the side with the pain. Positioning is important at this point. The head is secured in a surgical clamping device to prevent any movement during the procedure. After surgery, this may give patients a feeling of having had bands tightly wrapped around their heads. 

With the head in place, the surgeon cuts a half-dollar-sized hole (sometimes smaller) in the skull just behind the ear. The waterproof covering of the brain (the dura) is then opened to expose the brain. 

Using an operating microscope, the surgeon works next to the brain to locate the cranial nerves. Technically, this is cranial surgery, not brain surgery, since nothing is being done to the brain itself. The surgeon is looking for the root zone of the trigeminal nerve – the point where it connects to the pons or brainstem. That’s the spot where arteries and veins are most often found to be compressing the nerve. (An artery is a vessel that carries blood from the heart to various parts of the body; a vein carries blood back to the heart.) 

Another doctor monitors a device that continually tests the nearby auditory nerve, which lies in the path between the skull opening and the trigeminal nerve. The surgeon must work around the auditory nerve and, if it’s irritated too much, hearing damage can result. Monitoring keeps track of whether the auditory nerve is being overly stressed, so the surgeon can take corrective action before damage occurs. This step has greatly reduced the threat of hearing problems. Many surgeons require a hearing test as part of the preoperative screening so that a baseline reading is available to determine whether the MVD affected hearing. 

Finding compressions

While exploring the trigeminal nerve root through the operating microscope, the surgeon hopes to find one or more offending blood vessels. A pre surgery MRI sometimes gives surgeons an idea ahead of time where they’re likely to find compressing vessels, but not always. 

In most cases, the compressing vessel is obvious to the surgeon’s eye, but occasionally it’s well hidden. In rare cases, vessels have been found growing through the middle of the nerve. And in more than half of MVD surgeries, more than one vessel is compressing the nerve. 

In as many as l0 to 15 percent of MVD surgeries, surgeons fail to find or recognize any compressing vessels. When that occurs, many surgeons cut some of the sensory nerve fibers to bring relief without troubling numbness. (More on this below.) 

Failure to find a compressing vessel means one of two things: either something else is causing the patient’s pain or the surgeon simply hasn’t been able to locate the troublesome vessel. The better a surgeon’s training and experience, the fewer “nothing-found” cases should occur. In the early 2000s, some of the most experienced surgeons reported finding vessel compressions in 99 percent of the cases – significantly higher than even a decade before. 

Some surgeons use a camera device called an endoscope to give a magnified look inside the skull. Some use it in conjunction with the operating microscope; some use it exclusively.  

MVD advances 

Improvements are still being made in microvascular decompression surgery. Not only are many more neurosurgeons trained in the procedure, but their growing experience has led to improved techniques, fewer serious complications, less time to complete the surgery, and faster recoveries for patients. All of that is being done with smaller skull openings. 

One newer tool being used for MVDs is the endoscope, a device that employs a fiber optic tube that’s inserted into the skull opening. It gives a magnified look at the nerves and blood vessels inside. Some surgeons use it instead of the operating microscope, which also lights and magnifies the nerves and vessels but from outside the opening. Others use it in addition to the conventional microscope. 

Backers say the endoscope allows the MVD to be done with a smaller opening and doesn’t require the cerebellum to be moved. One neurosurgeon who does endoscopic MVDs, says this instrument often gives a better view of the trigeminal nerve because of better lighting, better magnification, and the endoscope’s ability to rotate and to “look around corners.” That searching ability enables the surgeon to locate compressing blood vessels that he may have missed with the standard microscope. 

Most neurosurgeons aren’t yet sold on the tool, though. Some say it gives only an occasional and marginal improvement in view, and it may be slightly more likely to lead to hearing problems. The hearing nerve is not in view when the endoscope advances toward the fifth nerve. With the smaller opening, there’s also less room to work, which could be detrimental in case of a complication, others point out. For now, few neurosurgeons are using it. Most of those who are having good success with the microscope say they are reluctant to start on a new learning curve until they’re sure the new technology will make a significant difference. Overall, most of the literature endorses the endoscope as an adjunct tool, and the practitioners who report using it solely, do report the operative approach, and intraoperative tools are similar. They also report the operation does not take any longer, compared to standard MVD. 

Surgeons also continue to look for better nerve-cushioning materials to use in MVDs and better ways to apply these materials. Shredded felt is still most commonly used today, although a few surgeons have been trying other materials, such as Gore-Tex. A few other surgeons use implanted neck muscle, which is soft and natural but tends to break down and be absorbed over time.  

Besides inserting these materials between vessels and the nerve, surgeons have tried wrapping the insulating material all the way around the nerve. The idea is to keep vessels from bumping the cushion away and to protect the nerve at all angles from any vessels that may get near it in the future. 

Other materials such as Dacron felt and Ivalon (a hard sponge) have been used in the past, but these tended to irritate the nerve. Slivers of transplanted muscle, dura, and periosteum (a fibrous connective tissue) also have been tried, but most surgeons do not use them because the body tends to break them down. 

Polytetrafluoroethylene surgical felt also occasionally has caused some scarring and adhesions on the trigeminal nerve and there have been a few reports recently about this padding causing abnormal growths (granulomas) (<1%). But at present, this has been found to be the best, least irritating material, and is widely used.  

Dealing with the vessels

In two-thirds to three-quarters of the cases, when a blood vessel is found to be compressing the nerve, that vessel is an artery. It’s important to make this distinction because arteries cannot be cut or removed but must be padded off the nerve. Veins, however, can be divided by sealing them off and cutting them out rather than padding them. Blood that had been traveling through the removed veins will find its way back to the heart through other veins. According to neurosurgeon Raymond Sekula, women between the ages of 35 and 52 seem to have a higher prevalence of veins causing their pain than other groups. This was often the case in patients presenting with isolated V2 pain. 

The problem with cutting out veins is that, in about a third of the cases, new branches will form and cause a new compression.  

To avoid some of the higher pain recurrence in vein cases, some surgeons now pad veins even though they could more easily cut them out. This seems to reduce recurrence rates, and intraoperative complications. 

Patients sometimes ask why surgeons don’t just remove all veins found anywhere near the trigeminal nerve. That can’t be done because these veins return blood to the heart from the brain, and removing too many of them (or too big a one) could lead to a stroke. 

Once the padding is in place or the vein has been eliminated, the surgeon sutures together the dura and covers the skull opening with a variety of techniques. While a thin titanium plate was initially popular, many surgeons now use bone substitutes, finding these materials easy to mold to fit the opening in the patient’s skull. It was quite common, when the opening was not repaired, to experience mild but noisome headaches probably resulting from the scarring and the muscle of the upper neck that attaches at the operative site. Whatever means are used to address the opening appear to reduce the incidence of headaches as a late complaint. 

The patient usually spends the first night in an increased care area, with a smaller nurse patient ratio. Most patients are often well enough to go home in one to two days, in part due to improved anesthetic techniques. Pain medicines are used for the first several days, and most physicians continue the preoperative medical regimen for the nerve pain. In the case of the anti-epileptic drugs (Carbamazepine, Dilantin, Neurontin, etc.) a bit of a taper for each drug is normally done after discharge. Coordination and other neurological tests are done at regular intervals for the first 24 hours. The entire MVD procedure typically takes two to four hours, although the actual repair takes more like 90 minutes. But individual cases can vary, depending on the nerve-vessel anatomy. 

Many patients can return to work within two weeks (longer if they have physically demanding jobs) and most say they are completely recovered in about two months. 

Microvascular decompression’s role in trigeminal neuralgia

Neurosurgeons often tell their patients that MVD is a procedure that sounds worse than it is. Improvements in technique, anesthesia, and technology over the past 50 years have greatly reduced the serious risks. Still, complications such as hearing loss (1%), meningitis (1%), spinal fluid leaks (2%), occur. Death from the procedure remains quite rare (<0.2%) 

On the other hand, this is the only procedure that attempts to fix the underlying problem. And it offers a high probability of complete pain relief (sometimes as much as 98 percent) with the best chance that the pain won’t come back. What it boils down to is weighing the potential risks vs. the potential benefits and carefully selecting patients who are best able to tolerate the surgery. 

MVD works best in classic TN and many TN-2 cases; it is especially good to relieve those patients that have sharp, stabbing pain and definite trigger zones. The more the pain gravitates away from that, the lower the success rate. 

Atypical or mixed cases are often helped, but the success rates for these are 50 to 65 percent as compared to 90 percent and up. What often happens is that the MVD helps the sharp, stabbing component of a person’s pain but not the more constant, burning, underlying pain. 

MVD is generally not recommended for neuropathic and deafferentation pains (these are caused by injured or disabled nerves, not blood-vessel compressions) and it’s usually not helpful for facial pain related to multiple sclerosis. The exception is if a person with MS-related pain also happens to have a blood vessel compressing their trigeminal nerve. This sometimes can be seen up on an MRI. 

General health is now considered more important than chronological age. A healthy 70-year-old is probably a better MVD candidate than a 60-year-old with heart problems. Besides those with heart problems, people who have breathing or lung problems and those with bleeding disorders are poorer risks. 

Since the whole idea of an MVD is to find and correct a compressing blood vessel, it’s important to make sure of the diagnosis before operating. Facial pains that are not TN and therefore are not being caused by a compressing blood vessel are not going to be helped by MVD. 

The arguments for and against MVD 

Most surgeons also do not advise MVD initially until medication has been given a fair trial and either has failed or is causing the patient unacceptable side effects. 

In the past, MVD was often suggested as an option of last resort – something that one should consider only if in agony or if having debilitating side effects on a handful of medicines. But that’s changed, too. Studies have found that MVD success rates seem to start dropping off after people have had their pain for more than seven or eight years. 

Some surgeons believe the prime window of opportunity is before irreparable damage is done to the nerve. This can be detected by a careful exam of the nerve function before surgery. They say that younger patients should think about earlier MVDs, even if they’re not in severe pain or having troubling side effects from their medicine. 

Not all agree with this more aggressive approach. More conservative surgeons say the success rates are still good enough in the long term that it isn’t worth the extra risk of subjecting people to MVD any sooner than necessary. Others add that radiosurgery and the through-the-cheek procedures are successful enough and repeatable enough that their lower risk outweighs MVD – at least in older, less healthy patients. They argue that if the less risky procedures fail, only then should MVD be considered – even if the success rates are a bit lower at that point. 

One neurosurgeon contends that even a 1 or 2 percent risk of death or serious complication in MVD is too high for a nonfatal pain condition. He says that is not a trivial figure for a disease with no spontaneous mortality or fixed disability when successful alternatives exist. 

On the other hand, pro-MVD surgeons argue that the other procedures have their risks as well – problems such as anesthesia dolorosa, corneal numbness, and severe numbness that are all but eliminated in MVD. And they point to several studies showing that MVD success rates are about 30 percent lower when MVD follows one of the nerve-injuring surgeries. 

Insurance

MVD surgery is routinely covered by insurance but for those without insurance, this is easily the most expensive of the TN procedures. Recent research has disclosed that the cost may represent what most shoppers already know: you get what you pay for. The researchers found the most utilized procedures were also the costliest, though lower cost does not always mean better results. In fact, the researchers found that MVD, the costliest procedure, also had the most quality-adjusted life years (QALY) score, as defined as complete freedom of pain, not including facial numbness or a partial reduction in pain symptoms. The late Steven Graff-Radford, DDS, treated TN extensively at the Cedars-Sinai Pain Center in Los Angeles, California, and served on the board of the Trigeminal Neuralgia Association. Dr. Graff-Radford said the most successful surgical procedure has consistently been MVD. 

Pain relief

The medical literature is relatively consistent regarding MVD. Microvascular decompression achieves the most sustained pain relief with 90% of patients reporting initial pain relief and over 80% still pain free after 1 year, with 75% after 3 years and 73% after 5 years remaining pain free. In most cases, pain relief is immediate. Once the pressure of the blood vessel is removed, the nerve’s fibers are no longer pressed together and signals from the light-touch fibers stop jumping onto the pain-signaling fibers. 

However, in some cases – especially in those who have had pain for a long time – the pain may take a few days or even weeks to resolve. 

What isn’t always spelled out in the studies is whether success means no pain or whether it also includes people who are significantly improved but still in some pain. One of the few to try and sort out the pain-free cases from those who are much improved is a prospective, long-term 1996 study of 1,185 patients who underwent MVD surgery at the University of Pittsburgh. That study found that 82 percent of patients had no pain and 16 percent had at least a 75 percent reduction of pain. The remaining 2 percent either had no relief or only minor improvement. 

In a study of MVD patients by patients themselves, the Australia TN support group surveyed 71 Australians, Americans, and Canadians who had undergone MVDs and found that 80 percent were pain-free immediately after surgery. 

Pain recurrence in MVD 

As with the other procedures, pain can return after an MVD. When the pain does come back, it tends to come back soon after the surgery. Several studies have found that more than half the people whose pain ultimately recurs after an MVD get it back within the first two years. 

Long-term studies have found the MVD pain recurrence rate goes down as time passes. On average, about 6 percent of MVD patients get recurrence in the first year, 3 percent a year get it in years two through four, fewer than 2 percent get pain back in years five through nine, and fewer than 1 percent get it in year 10. One recent review noted recurrent symptoms typically occur after a mean of 1.9 pain-free years, with a yearly recurrence risk of 1 to 4%. In addition, refractory and recurrent symptoms can occur after radiosurgery or radiofrequency ablation. After the latter procedure, 21 to 50% of patients have recurrent TN and 15% require retreatment. After radiosurgery, approximately 13 to 22% of patients require repeated treatment for recurrent symptoms. 

Counting the initial failures along with those who have pain recurrence, one pain specialist came up with the following prospects for MVD patients: 81 percent will be pain-free at two years, 76 percent will be pain-free at five years, and 71 percent will be pain-free at 10 years. 

Initial failures may happen for several reasons, such as the surgeon was unable to find the offending vessel (or vessels), the nerve wasn’t sufficiently cushioned, or the patient didn’t have TN in the first place. 

Causes of pain recurrence

When pain recurs, it’s not because the effects of the MVD wear off. Rather, the most likely reason is that a divided vein sends out new branches and sets up a compression problem all over again. Or it could be that a different blood vessel elongates with age and causes an altogether new compression point. And sometimes these vessels don’t cause a new compression but instead push away the implanted cushion from between the nerve and the vessel. 

Other possible causes of pain recurrence include adhesions that form to cause new damage to the trigeminal nerve or failures of the implant. (Adhesions are fibrous growths that sometimes occur along with scar tissue around the surgical site and implanted pad. Implants occasionally can be absorbed by the body – one example of failure.) 

In the long-term study mentioned above, patients with vein compressions were more likely to have a recurrence of pain. Also, female patients and those who didn’t get immediate pain relief from the MVD were slightly more likely to have their pain return. 

Although MVDs can be done following other procedures that have failed, the success rates are reportedly lower, but several recent papers did not support that concern. The best MVD results come when MVD is the first procedure. 

Repeated MVDs also can be done following a failed MVD. Those success rates also are a bit lower than the first surgery – around 80 percent compared to the 85 to 95 percent range for first- time patients. 

The possible drawbacks 

MVD patients can expect to be stiff, have a headache, and have some pain around the incision for the first couple of weeks. Those after-effects are common. 

Occasionally, patients experience one or more of the following: blurred or double vision, muffled hearing, an outbreak of cold sores, nausea, dizziness, lack of coordination, fluid in the middle ear, or ringing in the ears. These almost always go away on their own in a matter of days or weeks. 

A few other possible complications may require medical treatment. These may include meningitis (an infection of the membranes covering the brain), cerebrospinal fluid leaks, lung difficulties, and wound infections. The modern series reflect low complication rates.

 [ Infection-1%, fluid leaks 2%, Meningitis, non-bacterial 8%. These also are almost always short-term problems. Among the more serious risks are hearing loss on the surgery side (<1%), brain swelling, intracranial bleeding, stroke, blood clot, facial paralysis, and even death. 

• Hearing loss is the most likely of the serious complications. The most recent reports estimate hearing loss at 1 percent or less. 
• The chance of nonfatal stroke or cranial bleeding is also estimated at about 1 percent. 
• As for the chance of dying, that rate remains low at 0.2%. Deaths have occurred due to brain seizures, cranial bleeding, heart attack, stroke, and pulmonary embolism. 
• Facial numbness occurs in very few patients (0.15%). But this is almost always mild and almost always greatly improves or clears up within a few weeks. Permanent facial numbness in any part of the face occurs but is quite rare. 
• About 5 percent of MVD patients report sensations of tingling or crawling in the face, in the first few weeks. 

The complications rates are related to the number of procedures performed at an institution- more procedures result in fewer complications. The Medicare report concluded that discharge to home versus a rehabilitation facility is also affected by the number of procedures performed. (more procedures=more discharge to home). 

An alternative: partially cutting the nerve 

There’s one more surgical procedure that’s sometimes used, short of completely disconnecting the trigeminal nerve at its roots. It’s called a partial root section or partial sensory trigeminal rhizotomy(PSR). This can be confusing, as some centers use that acronym to refer to Percutaneous Sensory Rhizotomy. So, it is important to clarify that with your physician.  

The idea of this procedure is to cut just enough trigeminal nerve fibers near where the nerve first exits the brainstem to stop or lessen the pain, while preserving at least some feeling in the face. This was a common surgical treatment for TN from the early 1900s until the 1960s. 

Partial root sections are primarily employed today as a backup strategy in cases when an MVD surgeon finds no offending blood vessel to decompress. Rather than do nothing, one option (discussed with the patient beforehand, of course) is to cut some of the nerve fibers near their roots. 

A partial root section also may be done if a vessel or vessels are found that cannot be safely moved away from the nerve. That may be the case, for example, when a vessel has grown into the nerve fibers. Another time a partial root section may be done is when pain comes back after a prior surgery and the surgeon goes back in, only to find no new compression or a situation that’s unlikely to be helped by a second MVD. And occasionally it’s done when all other procedures have failed and the patient is willing to trade the almost-certain numbness for pain relief. 

In a 1993 report, 70 percent of 83 patients who underwent this partial cutting of the trigeminal nerve root had no pain or well controlled pain for an average of six years after surgery. About half of these patients reported mild numbness and 18 percent had severe numbness, but the remaining one-third had little or no loss of feeling. 

A British comparative study in 2003 of 220 MVD patients and 53 partial-root-section patients found that 89 percent of the MVD patients were satisfied with their situation five years later, compared to only 72 percent of the partial-root-section patients. 

More than one in five of the partial-root-section patients said they were worse off than five years earlier. The study attributed that dissatisfaction largely to complications, primarily numbness. 

As with the through-the-cheek procedures, partial root sections involve a bit of a balancing act. The more nerve fibers that are cut, the greater the chance of lasting pain relief but also the greater the chance of dense and permanent numbness. Lighter cuts may limit numbness but increase the chance that pain will come back. 

A few surgeons routinely do partial root sections along with an MVD because they believe it reduces the chance that the pain will recur. Others say that approach needlessly increases the chance of numbness, because there’s no way to tell how much is too much. 

Because this is an open-skull procedure much like an MVD, a partial root section is an option open only to those healthy enough to undergo major surgery. one surgeon also adds routine nerve bruising in addition to the section but most practicing surgeons do not feel it offers any additional benefit.