Abstract
Objective
The aim of this study was to evaluate the long-term efficacy of fistula laser closure (FiLaC®) in the treatment of cryptoglandular anal fistula.
Methods
Data from Parks I-II cryptoglandular anal fistula patients in Parks I-II who underwent FiLaC® in our department between September 2017 and December 2019 were retrospectively analyzed. Demographic data, perioperative data, and postoperative data were collected and statistically analyzed.
Results
A total of 52 patients were included in the study. The success rate at 3 months, 1 year, and 5 years was 76.9% (40/52), 75% (39/52), and 71.2% (37/52), respectively. The differences between the internal orifice location subgroups were statistically significant (P = 0.013), with the anterior type demonstrating a lower success rate than the bilateral and posterior types. No statistically significant differences were observed between the subgroup of Parks classification and the treatment of internal orifices. All scores, including visual analogue scale pain score (VAS-PS), Cleveland Clinic Florida Incontinence Score (CCF-IS), and the quality of life in patients with anal fistula questionnaire score (QoLAF-QS), showed no obvious difference.
Conclusion
FiLaC® technique can significantly relieve postoperative pain, reduce the incidence of anal incontinence and improve the postoperative quality of life in long-term follow-up. Patients with bilateral and posterior anal fistula are more likely to benefit from this technique.
Keywords: Fistula laser closure, 1470 nm diode laser, Cryptoglandular anal fistula, Long-term outcomes, Internal orifice location
Introduction
Anal fistula is defined as an abnormal tract connecting the anal canal to the perianal skin, predominantly originating from an infection of the anal glands [1]. Its incidence has been reported as 18.4 cases per 100,000 population, with a marked male predominance [2]. According to the Parks classification, anal fistulas are categorized into four types: intersphincteric, transsphincteric, suprasphincteric, and extrasphincteric (types I–IV). Among them, the intersphincteric and transsphincteric types are the most common. Surgery is the primary treatment. Fistulotomy remains the standard treatment with a low recurrence rate, but increases the risk of anal incontinence. Consequently, there has been a shift in focus towards sphincter- preserving procedures, including ligation of the inter-sphincteric fistula tract (LIFT), endorectal advancement flap (ERAF), video-assisted anal fistula treatment (VAAFT), and fistula laser closure (FiLaC®) [2–5].
The FiLaC® technique was first introduced by Wilhelm in 2011 [6]. This technique employs laser energy to ablate the fistula tract epithelium and simultaneously close the internal opening. Moreover, Studies have reported favorable efficacy for this procedure, with success rate ranging from 71% to 82% [7–9]. This technique is attractive to patients because it is minimally invasive and has less impact on daily activities compared to conventional methods.
This retrospective study reported more than 5 years of experience in using laser ablation for anal fistula at a single center in China, with a specific focus on the association between internal orifice location and surgical success.
Methods
Study design and patients
All patients with anal fistulas who were treated using laser ablation therapy from September 2017 to December 2019. Ethical approval was obtained by the ethics committee of Yueyang Hospital of Integrated Traditional Chinese and Western Medicine, affiliated with to Shanghai University of Traditional Chinese Medicine (No. 2017-033). Written informed consent was obtained from all participants.
Inclusion criteria: Patients with Parks I-II cryptoglandular anal fistulas assessed on endoanal ultrasound or magnetic resonance imaging.
Exclusion criteria: Patients who are pregnant, lactating, or in the menstrual period; Patients with concurrent other anorectal diseases, such as Crohn’s disease; Patients with severe comorbidities, including those affecting the cardiovascular, cerebrovascular, respiratory, or hematopoietic systems, as well as patients with malignant tumors.
Operative technique
All patients received preoperative preparation and underwent hair removal before surgery, which was performed using the FiLaC® technique. All laser procedures were performed under general anesthesia. We used Leonardo DUAL 45 laser (Biolitec AG, Germany) with power (12 W) and wavelength (1470 nm). Parameter settings were configured according to the recommendations from FiLaC RDG [10]. Firstly, we inserted a 360° single-ring diode laser fiber from the external orifice to the internal orifice. The fiber was then withdrawn at a constant speed of 1 mm/s to ensure continuous and uniform energy delivery along the tract. The internal opening was sutured closed with absorbable suture material if its diameter exceeded 2 mm [11, 12]. Finally, the external opening was either excised or minimally debrided to ensure adequate postoperative drainage, depending on its size and characteristics (Figure 1).
Fig. 1.
Flowchart
Outcome measures
Baseline demographic data encompassed sex, age, disease duration body mass index (BMI), internal and external orifice positions, Parks classification, and fistula diameter. Perioperative parameters included American Society of Anesthesiologists score (ASA), surgical time and postoperative complications. Furthermore, we collected observational indicators including the primary and secondary outcomes.
Primary outcomes included success rates at 3 months, 1 year, 5 years, visual analog scale pain score (VAS-PS) and Cleveland Clinic Florida Incontinence Score (CCF-IS) [13, 14]. The success criteria were closure of the external opening and absence of pain and discharge from both the external and internal orifices. Postoperative pain was measured using VAS-PS. The severity of fecal incontinence symptoms was evaluated using the CCF-IS. Secondary outcomes included the quality of life in patients with anal fistula questionnaire score (QoLAF-QS) [15], stool consistency as assessed by the Bristol Stool Chartand, and postoperative complications [16].
Data analysis
Statistical analysis was performed using SPSS Statistics 25.0 software (IBM Inc., IL, USA). Continuous variables were presented as mean ± standard deviation (SD) or median with interquartile range (IQR) based on the distribution. The independent t-test was used to compare normally distributed continuous variables, whereas the Mann-Whitney U test was used to compare non-normally distributed continuous variables. Categorical data were expressed as number of cases and percentages. A value of P < 0.05 indicated a statistically significant difference.
Results
This study included a total of 52 patients, comprising 41 men (78.8%) and 11 women (21.2%). The median age was 38.7(31, 44) years, and the median disease duration was 8.23(1.5, 12) months. According to the Parks classification, there were 40 transsphincteric (76.9%) and 12 intersphincteric (23.1%) fistulas. The distribution of internal opening locations was as follows: anterior in 8 cases (15.4%), bilateral in 29 cases (55.8%), and posterior in 15 cases (28.8%) (Table 1).
Table 1.
Comparison of patient demographics and outcomes
| Variables | Laser group (n=52) |
|---|---|
| Sex, n (%) | |
| Male | 41 (78.8) |
| Female | 11 (21.2) |
| Age, y [M (P25, P75)] | 38.7 (31,44) |
| Disease duration, m [M (P25,P75)] | 8.23 (1.5,12) |
| BMI, kg/m2 [M (P25, P75)] | 24.6 (22.6,26.3) |
| The location of internal orifice, n (%) | |
| Anterior type | 8 (15.4) |
| Bilateral type | 29(55.8) |
| Posterior type | 15(28.8) |
| Parks classification, n (%) | |
| Intersphincteric fistula | 12 (23.1) |
| Transsphincteric fistula | 40 (76.9) |
| ASA scorea, n (%) | |
| I | 51 (98.1) |
| II | 1 (1.9) |
| The treatment of internal orifice, n (%) | |
| Suture | 24 (46.2) |
| None | 28 (53.8) |
| Follow-up duration, m [M (P25,P75)] | 76.5(59, 84) |
| Success rate, n (%) | |
| 3-month | 40(76.9) |
| 1-year | 39(75) |
| 5-year | 37(71.2) |
Postoperative pain was mild, with no patients requiring analgesic medication, and overall satisfaction was high. No major complications were reported. The median follow-up time was 76.5(59, 84) months. The internal opening was sutured closed in 24 cases (46.2%) and left unsutured in 28 cases (53.8%). The primary success rate at 3 months, 1 year and 5 years postoperatively was: 76.9% (40/52), 75.0% (39/52), and 71.2% (37/52), respectively (Figure 2). Patients who experienced recurrence were successfully treated with fistulotomy, with no further recurrence reported thereafter (Figure 3).
Fig. 3.
Kaplan-Meier curve demonstrating the time to successful healing
Fig. 2.
Schematic diagram of laser ablation. A Preoperative image of the external orifice of the anal fistula. B The operation of continuous release of energy from fibers during surgery. C Image of the healing of the external orifice
Univariate analysis of potential factors associated with recurrence showed no statistically significant associations for gender, fistula type, history of prior fistula surgery, or management of the internal opening. However, there were statistical differences in the location of the internal orifice(P = 0.013). As is shown in Table 2. The results indicated that fistulas with an anterior internal opening had a significantly lower success rate compared to those with bilateral(P = 0.04) and posterior sides(P = 0.012), while no significant difference was observed between bilateral and posterior locations (P = 0.675). The results of the multivariate analysis indicated that the location of the internal opening is an independent risk factor for the long-term outcomes of FiLaC® (OR = 7.473, 95% CI: 1.382–40.427, P = 0.020) (Table 3).
Table 2.
Univariate analysis of potential predictive factors
| Variables | Success | Failed | p |
|---|---|---|---|
| Sex, n (%) | |||
| Male | 31(75.6) | 10（24.4） | 0.67 |
| Female | 9（81.8） | 2 (18.2) | |
| Type of fistula n (%) | 0.86 | ||
| Intersphincteric fistula | 9(75) | 3 (25) | |
| Transsphincteric fistula | 31(77.5) | 9 (22.5) | |
| Closure of internal orifice (n, %) | 0.83 | ||
| Suture (16) | 12(75) | 4(25) | |
| Without suture (36) | 28(77.8) | 8(22.2) | |
| Previous fistula surgery | 0.93 | ||
| Yes (4) | 3 (75) | 1 (25) | |
| No (48) | 37(71.1) | 11(28.9) | |
| The location of internal orifice | 0.013 | ||
| Anterior type (8) | 3 (37.5) | 5 (62.5) | |
| Bilateral type (29) | 25 (86.2) | 4 (13.8) | |
| Posterior type (15) | 12 (80.0) | 3 (20.0) | |
Anterior: Located anterior to a transverse line through the anal canal (between the 9 o'clock and 3 o'clock positions in the lithotomy position). Posterior: Located posterior to this transverse line
Table 3.
Multivariate Logistic Regression Analysis of Factors Affecting Success
| Variable | β | SE | Waldχ | P | OR | 95% CI |
|---|---|---|---|---|---|---|
| BMI | 0.034 | 0.172 | 0.040 | 0.841 | 1.035 | 0.739–1.450 |
| Length of fistula | 0.032 | 0.044 | 0.523 | 0.469 | 1.032 |
0.947–1.125 1.382–40.427 |
| The location of internal orifice | 2.011 | 0.861 | 5.453 | 0.020 | 7.473 |
A post hoc power analysis was conducted using G*Power 3.1. Based on the observed success rates between the anterior internal opening subgroup (37.5%) and the non-anterior subgroup (84.1%), with sample sizes of 8 and 44 and α = 0.05, the achieved statistical power was approximately 64%, indicating inadequate power for subgroup comparisons.
The patient reports mild postoperative pain with minimal impact on CCF-IS and QoLAF-QS scores (Table 4).
Table 4.
Comparison of perioperative scores. (Score, x ± s)
| Variables | Laser group (n = 52) |
|---|---|
| VAS⁃PS | |
| PRD | 0.8 ± 0.7 |
| POD 1d | 2.3 ± 1.3 |
| POD 3d | 1.0 ± 0.7 |
| POD 7d | 0.2 ± 0.4 |
| POD 30d | 0.2 ± 0.4 |
| POD 90d | 0.2 ± 0.4 |
| POD 1y | 0.2 ± 0.4 |
| POD 5y | 0.1 ± 0.3 |
| CCF⁃IS | |
| PRD | 1.0 ± 1.2 |
| POD 1d | 1.3 ± 1.5 |
| POD 3d | 1.4 ± 1.5 |
| POD 7d | 1.4 ± 1.4 |
| POD 30d | 0.8 ± 1.1 |
| POD 90d | 0.8 ± 1.0 |
| POD 1y | 0.2 ± 0.5 |
| POD 5y | 0.2 ± 0.1 |
| QoLAF⁃QS | |
| PRD | 17.2 ± 1.8 |
| POD 1d | 21.6 ± 5.0 |
| POD 3d | 19.5 ± 3.1 |
| POD 7d | 17.7 ± 2.4 |
| POD 30d | 18.3 ± 2.6 |
| POD 90d | 17.6 ± 2.6 |
| POD 1y | 16.1 ± 1.7 |
| POD 5y | 15.8 ± 2.0 |
PRD Preoperative day, POD Postoperative day, CCF-IS Cleveland Clinic Florida Incontinence Score, VAS-PS Visual analog scale pain score, QoLAF-QS Quality of life in patients with anal fistula questionnaire score
Discussion
Numerous treatment modalities exist for anal fistula; however, the primary therapeutic challenge lies in balancing complete lesion eradication with the preservation of anal sphincter function. Accordingly, a growing number of sphincter-preserving surgical approaches have emerged in clinical practice. These modalities include cutting seton (with a healing rate ranging from 82% to 100%), fibrin glue (14%–69%), anal fistula plug (14%–83%), mucosal advancement flap (0%–75%), and ligation of the intersphincteric fistula tract (60%) [17].
As a sphincter-preserving technique, FiLaC® is being increasingly adopted by clinicians. FiLaC® is a new sphincter-preserving surgery that achieves the purpose of treatment by closing the anal fistula after ablation. It was found that the primary healing rate of the modified FiLaC® technique (combined with ERAF) was 64.1%, and the secondary healing rate was 88% [18]. Giamundo conducted a retrospective analysis of 180 patients who underwent the FiLaC® procedure. The results showed that the cure rates of the primary operation and the second operation were 66.8% and 73.7%, respectively [12]. Other studies have shown that the success rates of FiLaC® technique range from 22% to 82% [6, 19–21]. This variation is likely attributable to differences in patient populations and specific technical approaches. Notably, when FiLaC® is combined with closure of the internal opening, success rates can be as high as 82%. The studies are shown in Table 5. The recent meta-analysis, which included 8 studies enrolling 476 patients, demonstrated a pooled success rate of 63% (95% CI:50–75) for this technique. The pooled complication rate was 8% [22].
Table 5.
Comparison of laser data in various literature
| Study | Patients | Energy (W) | Success rate(%) |
|---|---|---|---|
| Wihelm (2011) | 11 | 13 | 81.8 |
| Giamundo (2013) | 35 | 10–13 | 71.4 |
| Ôzturk (2014) | 50 | 15 | 82.0 |
| Giamundo (2015) | 45 | 12 | 71.7 |
| Wilhelm (2017) | 10 | 13 | 64.0 |
| Terzi (2017) | 103 | 12 | 40.0 |
| Lauretta (2018) | 30 | 12 | 33.3 |
| Brabender (2019) | 18 | 10–14 | 22.0 |
| Bonnechose (2020) | 100 | 13 | 44.6 |
| Sluckin (2022) | 162 | 13 | 55.6 |
| Lara Blanco Teres (2024) | 36 | 12 | 55.6 |
| Current study | 52 | 12 | 71.2 |
Our study also confirmed that the FilaC® is an effective therapeutic option for anal fistula. The success rate at 3 months postoperatively was 76.9%. No one developed anal incontinence. This favorable outcome can be attributed to several factors. First, our cohort was exclusively composed of Parks I-II fistulas, which are less complex. Second, all patients underwent MRI or ERUS to precisely delineate the fistula anatomy, thereby minimizing the risk of missing secondary tracts. The FilaC® destroys the fistula tract epithelium using laser energy, promotes postoperative contraction of the fistula, and closes the fistula without damaging the surrounding sphincter. The patient’s postoperative pain is mild, and there is no significant effect on CCF-IS and QoLAF-QS after surgery, and the satisfaction level is high. However, this study also found that the number of patients with recurrence gradually increased over time, with a 5-year success rate of 71.2%. The FiLaC® technique treats the internal orifice with laser ablation, which causes the internal orifice to shrink and local protein denaturation [23]. During the postoperative healing process, the unhealed wound remains susceptible to contamination by stool, potentially leading to recurrence. This hypothesis aligns with the assertions of Giamundo and Wilhelm, who emphasized the critical importance of adequate internal opening management for successful healing [6, 8]. However, in our study, no significant differences were found between surgeries regardless of whether the internal orifice was closed or not, which needs to be supported by further studies.
Our analysis revealed that anterior internal orifices had a significantly lower success rate compared to bilateral locations and posterior sides. This finding is consistent with a study by Emile, which identified an anterior fistula location as a risk factor for recurrence [5]. This may be related to the complex anatomy of the anterior perianal region. In males, the anterior external sphincter is intertwined with the bulbocavernosus muscle, and in females, the anatomical proximity to the vaginal sphincter creates surgical challenges. This complex muscular architecture can make complete ablation of deep or branching tracts more challenging. Furthermore, the proximity of critical structures like the urethra and vagina may necessitate the use of lower laser energy levels in anterior fistulas, potentially increasing the risk of incomplete ablation.
Limitations
Our study has several limitations that should be acknowledged. The main limitations of this study include its retrospective design, relatively small sample size, and the associated risk of selection bias. In particular, the statistical power for subgroup analyses based on internal opening location (e.g., the anterior subgroup with only 8 patients) is significantly inadequate. Therefore, conclusions drawn from these subgroup comparisons should be considered preliminary and hypothesis-generating, necessitating validation through larger prospective studies. Additionally, a time-dependent failure bias should be noted: the recurrence rate gradually increased over the 5-year follow-up period (from 76.9% at 3 months to 71.2% at 5 years), indicating that treatment failure is not randomly distributed across time. This time-dependent nature may affect the interpretation of long-term efficacy, as late recurrence could be related to cumulative exposure to confounding factors (e.g., repeated stool contamination, unrecognized micro-tracts) that were not fully accounted for in the analysis. In addition, regarding internal opening management, future studies may optimize the surgical strategy by resecting and suturing large or fibrotic internal openings following laser closure.
Conclusion
FiLaC® is shows potential for cryptoglandular anal fistula with internal orifices located bilaterally and posteriorly. It can significantly reduce postoperative pain, lower the rate of anal incontinence and improve patients’ postoperative quality of life at long-term follow-up.
Abbreviations
- CCF-IS
Cleveland Clinic Florida Incontinence Score
- ERAF
Endorectal Advancement Flap
- FiLaC®
Fistula Laser Closure
- LIFT
the Ligation of the Inter-sphincteric Fistula Tract
- QoLAF-QS
the Quality of Life in Patients with Anal Fistula Questionnaire Score
- VAAFT
Video Assisted Anal Fistula Treatment
- VAS-PS
Visual Analog Scale Pain Score
Authors’ contributions
Zhicheng Li and Lei Jin: Conceptualization, Data curation, Formal analysis, Writing – original draft. Jingyi Zhu: Methodology, Investigation, Visualization. Can Cui: Resources, Validation, Project administration. Zhenyi Wang: Supervision, Writing – review & editing, Funding acquisition. Jiong Wu: Supervision, Writing – review & editing, Final approval of the version to be published. All authors reviewed the manuscript.
Funding
This work was supported by the Shanghai Science and Technology Committee (No. 20Y21901200) and Shanghai Shenkang Hospital Development Center (SHDC12017124) and Shanghai Institute of Traditional Chinese Medicine(24YJS14).
Data availability
Data available on request from the corresponding author on reasonable request.
Declarations
Approval for this study was obtained and signed informed consent forms were obtained from all patients.
Ethics approval and consent to participate
The study was approved by the institutional ethics board of Yueyang Hospital of Integrated Traditional Chinese and Western Medicine, Shanghai University of Traditional Chinese Medicine (No. 2017–033). Informed consent was obtained from all patients. This study was performed following the Declaration of Helsinki.
Consent for publication
was obtained from all participants.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Zhicheng Li and Lei Jin are contributed equally to this work.
Zhenyi Wang and Jiong Wu are contributed equally to this work.
Contributor Information
Zhenyi Wang, Email: drxinhuo@163.com.
Jiong Wu, Email: 12491947@qq.com.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Data available on request from the corresponding author on reasonable request.