Tarlov and other spinal cysts
There are several kinds of cysts that occur in and around the spine. The most common and the least understood occur in the sacrum or tail bone. These are commonly called Tarlov cysts after the neurosurgeon who described them over 70 years ago. These are the most common of all the sacral cysts. They are also called perineural because of their location with relation to the nerves. They may occur anywhere along the spine. However, they are much more common in the tail bone. There are not any very extensive studies of these cysts, so the actual incidence in the general population is not known with certainty. The best paper currently available estimates that between 1.5% and 2.0% of people have such cysts. A much smaller percentage of pesons have cysts which cause symptoms.
The history of Tarlov cysts is quite interesting. Tarlov first thought they did not cause symptoms, but by the 1950’s he had identified patients with these cysts who could be cured by surgery, and other surgeons began to report the same kinds of patients successfully treated by surgery. Over the next 50 years or so, there have been a number of reports of individual patients and small groups of patients benefited significantly by surgical repair of symptomatic cysts. For reasons which are unclear from the literature, the mythology has grown up over the past 20 years that these cysts never cause symptoms. There is no paper which I can find published in the medical literature which supports this statement. However, two generations of physicians have been taught that these cysts do not cause symptoms and radiologists often make the statement that the cysts do not cause symptoms in their reports without any knowledge of the individual patient. How this all came about in the absence of any papers supporting the position is uncertain. It is true that many cysts occur in patients without symptoms. However, it is equally true that some cysts are symptomatic, injure nerves, and can cause serious neurological deficits with time. The key issue is to determine when the cysts are symptomatic and when they are not. It is the experience from many reports that some of these cysts are symptomatic and can be successfully treated. These cysts occur most frequently in women,7-9 to 1.
Dural ectasias are large dilatations of the normal spinal sac and can often form large cysts around nerve roots. Many of these penetrate the tailbone and present in the abdomen or pelvis as very large cysts. Some are big enough to fill the entire abdomen. These cysts occur predominately in woman and they usually are present in patients who have what are called connective tissue disorders. Many of these are well known. Marfan’s syndrome and Ehlers-Danlos syndrome are the most common, but there are many other diseases that also affect ligaments and connective tissue. Many of these are inherited. Back pain is the most common symptom, but a small number of patients develop severe involvement of nerves. Loss of bowel, bladder, and sex function can occur and in extreme cases, paralysis of the legs has been reported. When symptomatic, these cysts frequently cause slowly progressive abnormities with increasing pain and increasing loss of function. Many patients just have back pain or local pain around the few nerves. The progression to serious disability is fortunately very rare.
There is a third group of cysts which have been called meningoceles. These are typically in the midline of the tail bone and involve all the nerves on both sides. They are often associated with other abnormalities called the tethered cord syndrome and the Chiari malformation. These occur more commonly in men while the Tarlov cysts and ectasias are more common in women.
With all these cysts, the diagnostic evaluation is usually reversed from the usual patient presentation. That is, the cysts are usually seen on the imaging study and the diagnosis is made before their clinical significance is known. The typical patient comes to me with complaints, a diagnosis of the cyst, and uncertainty about whether the cyst is related to the complaints or not.
The first step in determining when these cysts are symptomatic is a careful history. There is nothing specific about the complaints we have identified with these cysts that differentiates them from other spinal abnormalities on the basis of the description of the symptoms alone. However, patients commonly have local pain right over the cyst, disturbance of bowel and bladder function, and pain in the distribution of the nerves involved. Leg pain is common, typically sciatica. Pain in the pelvis and pelvic area is common; internal pain involving bowel, bladder and sexual function are the most common. Neurological changes can be slowly progressive and lead to serious abnormalities if unrecognized and left untreated. Fortunately this is rare; most just cause pain.
One of the unfortunate consequences of the fact that physicians have ignored these cysts over a long period of time is that their natural history remains unknown. Once cysts could be easily identified with MRI, it should have been possible to study these cysts over time to determine their natural history. That is, when do they increase in size, when do they decrease, and how often do they cause symptoms? These facts are simply unknown at present. Therefore, even when treatment is not required, we recommend that regular MRI’s be done over at least five years to determine what the cyst is doing in any individual patient. Once neurological changes occur, the situation becomes more serious, though we have no evidence that it is urgent to proceed with treatment yet. Nevertheless, the presence of a neurological deficit should lead to treatment in my opinion, if that neurological deficit is significant.
Once it seems probable that the cyst is the cause of the symptoms or if that is strongly suspected, there are several possibilities for management. If symptoms are minor and there is no neurological deficit there is no reason that anything needs to be done other than observation. Treatment can follow when symptoms warrant therapy.
If there is question whether the cysts are involved in the complaints several strategies have been employed to try to determine if the cyst is the cause of the symptoms. One of these is to simply carry out an anesthetic block of the nerve. Using CT or fluoroscopy control, a needle is passed to the nerve above the cyst and local anesthetic is injected. If local blockade of that nerve relieves the pain on at least two occasions then it is probable that the cyst is related to the pain. This has never been tested, but it makes logical sense and has been shown to be true in other diseases, if not for cysts specifically. Aspiration of the fluid from the cyst may relieve the pain temporarily and thus lead to treatment.
Another technique and the one we favor is to carry out the aspiration first, but then to obliterate the cyst by an injection. Using CT-control, a needle is passed into the cyst. With the large cysts, a second venting needle is also put in place. The cyst is aspirated and then filled with a liquid which sets up into a soft solid filling the majority of the cyst. The idea is to exclude spinal fluid from the cyst, and the hope is that the scarring which occurs around the injected material will keep spinal fluid from entering the cyst permanently.
This is an outpatient procedure done with sedation, but no anesthesia. It typically takes about 30 minutes and the patients are allowed to leave after the sedation has worn off. We are in the process of evaluation of all of the patients treated. At present, our series is about 250 patients treated over six years. Our first evaluation of the original 130 patients indicated about 70% improvement rate by the injection, to the point they did not want or need anything else done. Some of them have had recurrence of pain after months to years and a few have been retreated. A few others have gone to surgery. The needle procedure has not been associated with many serious side effects. We have not yet seen an infection or a nerve injury. A small number of people felt their pain was worse for a few weeks afterwards and then improved. A very small number, at present no more than two or three have thought their pain was permanently worse. Thus, we believe this is a reasonable treatment to offer. It is both diagnostic and therapeutic. That is, if we do the procedure and there is no benefit we have to question whether the cyst is really the cause of the pain or not. At the same time the aspiration is done we have carried out the injection which has treated the cyst. If we achieve long-term relief of symptoms then we know the cyst was the cause.
Another possibility is to go directly to surgery. This is favored by two of the most experienced surgeons. They also think that the injections may interfere with subsequent surgery. That was not my experience when operating upon these cysts, so I still think the injection is a reasonable first alternative.
Sometimes there may be other abnormalities which could also cause the pain besides the cyst. In such cases we try to decide which abnormality is most likely to cause the problem and focus our attention upon the one that seems the most clinically important. If treatment of that problem fails then we move to the other problem and examine that.
We have discussed the management of Tarlov cysts in some detail. As we go forward with our examination of outcomes for patients treated by aspiration we will have more information to present in the literature and on the web. At present we think the aspiration- obliteration technique has the potential of helping many patients, and to date has had very little risk. However, at least one-third of patients with apparently symptomatic cysts are not helped and a small number think they have been worsened by the procedure.
Surgery for cysts had been employed for more than 50 years. The surgical treatment of Tarlov cyst is relatively straight forward and in my experience has not had many complications. In my series the infection rate for the true Tarlov cyst has been 0. We have seen no nerve injury. The biggest problem has been an occasional spinal fluid leak. The typical cyst, which is a candidate for aspiration has a very small opening to the spinal fluid. The larger cysts, which require surgery, often have a large opening and that opening can be difficult to close surgically. Spinal fluid leak is the biggest problem after surgery.
The repair of the dural ectasias is in its infancy. Only a few have been treated. We first reported seven, and have now added three other exceptionally large cysts which will be reported in the literature shortly. These cysts are huge and the openings to the spinal fluid are often several inches across. Closing them permanently and obliterating an enormous cyst which can fill the pelvis and abdomen can be very difficult. Spinal fluid leak is the biggest concern. At present surgery is the only therapy possible.
Repair of the internal meningoceles is much more straightforward, but the connections with the spinal fluid can still be large. Just as with the other abnormalities, spinal fluid leak is the biggest risk. Sometimes, these are associated with what is called a tethered cord syndrome and treatment of that entity is well known to neurosurgeons. Sometimes, these are associated with the Chiari malformation and a separate surgery for that problem may be required. Most neurosurgeons are familiar with this condition and the abnormalities associated with it. The surgical repairs are well accepted.
The greatest problem for patients with sacral cysts is that so many physicians do not believe any of the cysts are symptomatic. Treatments are not recommended. The majority of the physicians think the cysts do not cause symptoms and therefore ignore them in the evaluation. Even when serious neurological deficits are occurring, the cysts tend to still be ignored as a potential cause. The key issue is to determine when the cysts are symptomatic and when they are not, so that an appropriate therapy can be chosen for those in whom the cyst are causing the symptoms and an appropriate diagnosis can be made in those patients in which the cysts are not.