Tarlov cysts, or perineural cysts, were first described by I.M. Tarlov in 1938 as an incidental finding during his autopsy studies of the filum terminale.1 These cysts are characterized as closed cerebrospinal fluid (CSF)-filled sacs that form at the junction of the dorsal ganglion and the nerve root.1 Tarlov cysts can be further distinguished from other lesions by their formation between the endoneurium and perineurium, as well as by the fact that their lining contains nerve fibers and/or ganglion cells.1
In the general population, it has been estimated that 1.5% of people have ≥1 Tarlov cysts, with about 13% of those being symptomatic.2 It is generally accepted that the majority of Tarlov cysts are small, multiple, and asymptomatic, whereas large symptomatic cysts are considered rare.3 It is not known whether the prevalence of Tarlov cysts differs by sex, age, or other demographics.
The origin, causes, and risk factors of these cysts is also unknown, and several hypotheses have been proposed.1 Tarlov suggested that these cysts could form from the restriction in blood supply to tissues due to degradation, inflammation, or hemorrhage caused by infiltration from the subarachnoid space or trauma.1 Another hypothesis for the origin of Tarlov cysts is that they are a result of arachnoidal proliferation, the rapid multiplication of a specific type of cell, or due to an obstruction of perineural lymphatic flow.1 A final hypothesis is that Tarlov cysts form due to an increase in CSF hydrostatic pressure (pressure exerted by a fluid due to the force of gravity).1 There are examples of patients within all of these hypotheses, but a singular cause of Tarlov cysts remains unknown.1 As there is not a single biological explanation for the cause of Tarlov cysts, it is also difficult to identify risk factors associated with these cysts.1
The majority of Tarlov cysts are asymptomatic.1 Symptomatic patients often complain of pain in the lower back, coccyx, lower extremities, or groin.1 Other symptoms include hypesthesia (reduced sensation) or paresthesia (tingling sensation) over the buttocks, between the legs and into the lower body, bladder incontinence, motor weakness, and impotence.1
Tarlov cysts are usually diagnosed using diagnostic imaging.4 Under traditional radiographic imaging, Tarlov cysts may be visualized as causing erosion of the sacrum, bone scalloping, or a rounded paravertebral shadow.4 When using oil-based pantopaque contrast-enhanced myelography, Tarlov cysts demonstrate a unique characteristic in that they do not immediately fill with contrast.4 Instead, these cysts have been shown to fill with contrast hours, days, and even weeks after.4 This characteristic helps distinguish Tarlov cysts from other lesions.4
Computed tomographic (CT) scanning with and without contrast can also be used in the detection of Tarlov cysts.4 The use of postmyelography CT scanning can be used to further characterize the cyst, as a filling of the cyst would indicate that communication exists between the cyst and the spinal subarachnoid space.4
Finally, magnetic resonance imaging can be used in the diagnosis of Tarlov cysts and is considered the recommended form of diagnostic imaging in the initial identification of these cysts.4 This is due to the absence of bone interference and the enhanced resolution of tissue density.4
A number of treatment options are available for symptomatic Tarlov cysts. The objective of treatment is to relieve nerve stimulation and compression, stop bone erosion, and reduce symptoms.5 Treatment options include lumbar CSF drainage, microsurgical excision of the cyst,6 clipping of the cyst to prevent CSF leakage,7 and CT-guided percutaneous cyst aspiration.5
A 2001 study of 10 cases reported that surgery resulted in 7 patients experiencing complete or substantial resolution of their symptoms and that all of these patients had Tarlov cysts >1.5 cm in diameter. The authors concluded that large cysts (>1.5 cm) and the presence of associated radicular symptoms strongly correlated with excellent outcome.1 Further studies have cited these findings promoting the theory that the size of the cyst may be the essential element responsible for symptoms.6,8
Despite a range of options for treatment, there is debate about when, and how to optimally treat individuals with Tarlov cysts among clinicians, and among policy decision makers. There is no known systematic review on the effectiveness or optimal treatment of Tarlov cysts; 1 review including 10 studies was published in early 2016; however, it was not systematic or comprehensive.9 The purpose of this research is to summarize all of the current evidence on treatment of Tarlov cysts.
A systematic review was completed. MEDLINE, PubMED, Cochrane CENTRAL Register of Controlled Trials, EMBASE, and PsycINFO, Cochrane Database of Systematic Reviews, HTA Database, CINAHL, and SOCIndex were searched from inception until January 6, 2016. Terms aimed at capturing the target diagnoses such as “tarlov cyst,” “meningeal cyst,” “sacral root cyst,” and “perineurial or perineural cyst” were combined using the Boolean operator “or.” Results were limited to English and French language studies, and a filter was used to exclude animal model studies. No other limitations or filters were applied (full search strategy in Online Appendix, Supplemental Digital Content 1, http://links.lww.com/CLINSPINE/A41).
All abstracts were screened in duplicate. Abstracts proceeded to full-text review if: they assessed safety/effectiveness/efficacy of treatments for Tarlov cysts; were written in English or French; and were randomized, quasi-randomized, observational cohort, case control, or case series design including ≥2 participants. Abstracts were excluded if they failed to meet any of the above inclusion criteria, or if they: were an animal model; reported nonoriginal data; or were case reports, editorials, opinions, or qualitative studies. Abstracts selected for inclusion by either reviewer proceeded to full-text review. This initial screen was intentionally broad to ensure that all relevant literature was captured.
Studies included after abstract review proceeded to full-text review in duplicate. Studies were included if they met all inclusion criteria and failed to meet any of the criteria for exclusion presented in Table 1. Full-text review was completed in duplicate. Any discrepancy between reviewers was resolved through discussion, consensus, and a third reviewer if necessary.
For all studies, year of publication, country, patient selection, patient characteristics, description of treatment, research methods, and outcomes measured were extracted using standardized data extraction forms. Safety outcomes including pain, infection, weakness, nausea, and discomfort, were also extracted. Discrepancies between reviewers during data extraction were resolved through consensus.
During data extraction, quality assessment using the Downs and Black checklist10 was completed in duplicate. Using this checklist, each study was assessed based on 27 criteria, widely covering areas reporting quality, external and internal validity, and power. Studies are assigned a value of “1” if they meet the question criteria, “0” if they do not or if it is not possible to determine whether they meet the criteria; with an exception where 1 question may be given “2” points. In some cases, a question may not be applicable, due to study design, and not applicable (NA) is used. Any discrepancy between reviewers on quality assessment was resolved through discussion and consensus.
Following best practice, published systematic reviews were hand-searched to ensure that all relevant papers were captured in the literature search. Transparent Reporting of Systematic Reviews and Meta-Analyses guidelines and reporting standards were used.
Some studies reported patient-level data. Where available we collected patient-level data on age, sex, size of cyst, location, outcome, the time of the outcome assessment, duration of symptoms, types of symptoms, and treatment. Logistic regression analysis was undertaken to understand the association between the size of the cyst and whether symptoms were completely relieved. All patient-level data collected were considered and tested as a covariate.
In total, 1018 unique citations were identified. Two additional citations were identified through hand searching. In all, 922 were excluded and 98 proceeded to full-text review. After full-text review 67 studies were excluded leaving 31 studies in the final analysis (Fig. 1).
All 31 studies were case series assessing the effectiveness of surgical treatment in reducing symptoms associated with Tarlov cysts. None of the included studies used nonsurgical treatment methods. The included studies were conducted in France,11,12 Canada,13 the United States,1,14–19 Germany,20–22 India,3,23 China,5,24–28 Saudi Arabia,29 Japan,8,30,31 Italy,7 Argentina,32 Korea,6,33 and Croatia34 between 196713 and 201519,23,26,35 (Table 2). In total, these studies reported data on 646 participants who had an intervention to improve symptoms from a Tarlov cyst. The studies ranged from including 2 to 213 participants. The mean age of participants ranged from 32 to 66.5. For detailed characteristics of included studies, see Table 1 in the Online Appendix, Supplemental Digital Content 1, http://links.lww.com/CLINSPINE/A41.
A variety of interventions were used in the included studies, such as laminectomy, hemilaminectomy, cyst remodeling by titanium clips, and cyst aspiration and excision (Table 2). Some studies also used fibrin gel or gelfoam during surgery, which may be used to seal the cyst and prevent it from filling with fluid.
All studies included only symptomatic patients. Before surgery, the included participants suffered from a variety of symptoms. Back pain was the most common (n=382), followed by urinary or bowel dysfunction (n=258), perianal/perineal pain or numbness (n=250), neuropathy (n=179), sexual dysfunction (n=92), and sensory/motor disturbances of the lower extremities (n=78). A number of patients had less common symptoms such as night pain, sciatica, coccydynia, leg pain, pain in the groin, cauda equine compression, postural changes, pelvic pressure, numbness, decreased reflex, and claudication.
Among the 646 included participants, 210 experienced complete resolution of symptoms (32%), 327 had partial resolution (50%), 106 did not have any improvement or worsening of symptoms (16%) and 3 had their symptoms worsen after surgery (0.4%) (Fig. 2). One of the participants experienced worsening of urinary incontinence which disappeared after 1 month.28 Although the worsening symptoms of the remaining 2 were not reported.27
A number of adverse events were reported among the 31 studies. The most commonly reported adverse events were CSF leak (n=11),23,24,28,30,35 temporary increase in pain (n=7),35 mild inflammation (n=3),35 worsening of preoperative symptoms (n=3),35 temporary urinary dysfunction (n=2),1,24 and headache (n=2).19 Other adverse events (each n=1) include mild transient postoperative urticaria,16 mild allergic reaction,35 CSF fistula,22 aseptic meningitis,17 incisional erythema,19 superficial seroma,19 pulmonary embolus,19 pseudomeningoceles,19 prostatisis,31 and cerebellar bleeding.31 All surgery-related adverse events resolved either naturally or through further intervention.
Follow-up time in the included studies ranged from 2 to 180 months (15 y). Broadly, cyst recurrence was rare in the included studies during this follow-up time. Three studies noted cyst recurrence during follow-up; 2 patients experienced recurrence after 6 years of follow-up,35 1 experienced recurrence after 30 days,32 and 1 experienced recurrence 8 months after surgery.28 On the basis of the included studies, recurrence of cysts seems to be rare, occurring in 4 of 646 participants.
The literature is of low quality. Using the Downs and Black Checklist, studies scores range from 7 to 16, out of a possible 28 points. All of the studies clearly describe their objectives. Nearly all describe characteristics of included participants, intervention(s), and main findings. In all studies, the statistical tests used are appropriate, and compliance with the intervention was reliable. None of the studies provided estimates of random variability, actual P-values, blinded participants or the researchers measuring the outcomes, and none randomized participants. The poor quality is predominantly due to the weak study designs of the included studies; all of the studies are case series, and therefore neither randomization nor comparative control occur. The full results of the quality assessment can be found in Table 2 in the Online Appendix, Supplemental Digital Content 1, http://links.lww.com/CLINSPINE/A41.
Patient-level data were available for 97 patients, however, only 49 patients had complete data on cyst size. The sample size was smaller for those who also had information on the type of surgery undertaken (47) and whether the cyst was in the sacral or lumbar region (30). These variables were not used in the final analysis due to their effect on the sample size.
Contrary to previously published findings the odds of having complete resolution after surgery was lower for those with larger cysts odds ratio=0.53, controlling for age and sex and using cyst size as a continuous variable; for every increased centimeter in size the likelihood of success decreased by 0.53. However, this analysis did not result in a statistically significant finding, P-value=0.107 (Table 3). Controlling for cyst location or type of treatment also resulted in lower odds of complete resolution although neither result was statistically significant at alpha level of 0.05. When cyst size is considered as a binary variable using a cut-off of 1.5 cm the odds of complete relief were also 0.36 lower than those with a cyst size of <1.5 cm, controlling for age and sex, but still not statistically significant, P-value=0.190.
The odds of part or complete resolution after surgery was higher for those with larger cysts, odds ratio=1.17, controlling for age and sex, but not statistically significant, P-value=0.631.
The most common symptoms associated with Tarlov cysts include back pain, urinary or bowel dysfunction, and perianal/perineal pain or numbness. There was only evidence found on surgical interventions for Tarlov cysts. Combining the evidence from 31 case series we found that after surgical treatment, the symptoms attributed to Tarlov cysts were either completely or partially relieved in 83% of the cases. Complete resolution was experienced in 32% of cases, 50% had partial resolution, 16% had no improvement or worsening of symptoms and 0.4% had worsening of symptoms after surgery. Although adverse events were reported postoperatively, all were temporary. No significant long-term safety concerns were reported and recurrence of cysts seems to be rare, even with studies reporting up to 15 years of follow-up.
There is considerable debate around whether Tarlov cysts are responsible for the pain attributed to them.2 It has been reported that in most cases, the pain attributed to a Tarlov cyst is not responsible for the pain, with suggestions that there is another pathology that is causing the symptoms near the Tarlov cyst, and that Tarlov cysts are not clinically important.2 The results found in this systematic review point to a correlation between pain and Tarlov cysts, as the majority of individuals included experienced partial or complete relief after surgical treatment targeting only Tarlov cysts.
It has been suggested that larger Tarlov cysts result in more severe symptoms. Moreover, these larger cysts respond better to surgical treatment. Voyadzis and colleagues found that all patients who had cysts >1.5 cm experienced partial or complete relief (7 patients), and all patient who had cysts <1.5 cm did not experience significant relief from surgery (3 patients). In a logistic regression of 49 patients with information on cyst size we found that patients with larger cysts did not have statistically significant higher odds of partial or complete relief and that patients with larger cysts had lower odds of complete relief, although the finding was not statistically significant.
Although these studies seem to show a trend that surgical treatment of Tarlov cysts is effective at relieving symptoms, this effectiveness and safety evidence comes from a study type that is prone to bias. In addition, this study design does not provide information about how well surgery performs in comparison with other treatments. Case series are level 3 evidence in the hierarchy of research evidence, which is the lowest level of evidence.36 On the basis of the mixture of outcomes and a general lack of consensus from the clinical community, it is reasonable to expect that higher levels of evidence may become available on surgical treatment of symptomatic Tarlov cysts. For example, it is possible that a randomized controlled trial (level 1 evidence36) be completed with patients randomized to receive either surgical intervention or nonsurgical care. Higher levels of evidence are required to understand the effectiveness of surgery in comparison with other types of management.
There was large heterogeneity in the methodologies used to relieve symptoms of Tarlov cysts. Remodeling by titanium clips, endoscopic surgery, and laminectomy were some of the techniques used. Fibrin glue was used in some, but not in others. This heterogeneity in technique could be due in part to the improvement in technique and technology over time, and/or neurosurgical preferences. Surgery and diagnosis of Tarlov cysts has changed significantly since the first study of Tarlov on this subject in 1970.37 Without comparative literature, the optimal management of Tarlov cysts remains unknown. Primary studies comparing a variety of intervention strategies would be a unique and useful addition to the literature.
One limitation is worth noting. Some included studies reported complete relief from symptoms and partial relief together (eg, “16 of the 19 patients experienced complete or substantial resolution of preoperative symptoms…”7). For the purpose of data extraction in this research, when there was not enough information to separate complete and partial relief, they were recorded as partial relief to ensure that the estimate of effect was conservative and not overstated. As not all symptoms of Tarlov cysts are equal, partial resolution will be clinically different between patients and the impact of the unresolved symptoms on patient’s lives will vary.
The evidence suggests that surgery for symptomatic Tarlov cysts may be an effective option for partially or completely relieving symptoms. However, the effectiveness of surgery has not been compared with other treatment options and well-designed comparative studies are needed to determine the most effective treatment. There is no evidence on which types of surgery are more effective, and no evidence on when surgery is indicated.
Special thanks Jason Plemel of the University of Calgary for his help.
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tarlov cysts; treatment outcome; postoperative complications; cysts
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