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. 2021 Jan 2;25(4):385–399. doi: 10.1007/s10151-020-02385-5

Simple fistula-in-ano: is it all simple? A systematic review

F Litta 1,#, A Parello 1,#, L Ferri 1,#, N O Torrecilla 2, A A Marra 1, R Orefice 1, V De Simone 1, P Campennì 1, M Goglia 1, C Ratto 1,3,✉
PMCID: PMC8016761  PMID: 33387100

Abstract

Background

Simple anal fistula is one of the most common causes of proctological surgery and fistulotomy is considered the gold standard. This procedure, however, may cause complications. The aim of this systematic review was to assess the surgical treatment of simple anal fistula with traditional and sphincter-sparing techniques.

Methods

A literature research was performed using PubMed, Cochrane, and Google Scholar to identify studies on the surgical treatment of simple anal fistulas. Observational studies and randomized clinical trials were included. We assessed the risk of bias of included studies using the Jadad scale for randomized controlled trials, and the MINORS Scale for the remaining studies.

Results

The search returned 456 records, and 66 studies were found to be eligible. The quality of the studies was generally low. A total of 4883 patients with a simple anal fistula underwent a sphincter-cutting procedure, mainly fistulotomy, with a weighted average healing rate of 93.7%, while any postoperative continence impairment was reported in 12.7% of patients. Sphincter-sparing techniques were adopted to treat 602 patients affected by simple anal fistula, reaching a weighted average success rate of 77.7%, with no study reporting a significant postoperative incontinence rate. The postoperative onset of fecal incontinence and the recurrence of the disease reduced patients’ quality of life and satisfaction.

Conclusions

Surgical treatment of simple anal fistulas with sphincter-cutting procedures provides excellent cure rates, even if postoperative fecal incontinence is not a negligible risk. A sphincter-sparing procedure could be useful in selected patients.

Keywords: Simple anal fistula, Fistula-in-ano, Fistulotomy, Incontinence

Introduction

Anal fistula (AF), one of the most common causes of proctological surgery [1], is a condition that can have impact on patients’ anorectal function and quality of life (QoL) [2].

The classification of AFs into “simple” or “complex” has the greatest practical and surgical significance. Usually, the majority of simple AFs are considered to have “low” tracts. However, the definition of low fistula has changed over time, with a trend towards lowering the percentage of the external anal sphincter (EAS) crossed by the fistula tract [3]. According to several guidelines [4–6], an AF is defined “simple” when the tract is intersphincteric, or low transsphincteric (crossing < 30% of the EAS). Instead, AFs are defined as complex in cases of––high transphincteric tract (crossing > 30% of the EAS); in patients considered at risk for postoperative fecal incontinence (anterior fistula in women, recurrent fistula, or pre-existent fecal incontinence) even though with low transphincteric tract; suprasphincteric or extrasphincteric tracts; and in AFs with multiple tracts in a horseshoe fashion or those associated with inflammatory bowel disease (IBD), radiation, malignancy, tuberculosis, or chronic diarrhea [4–6].

Surgical treatment of AFs is therefore usually based on the amount of the sphincters involved, and, based on this concept, anal fistulotomy is considered the gold standard to treat simple AFs. This procedure, however, may have side effects such as deformities and esthetic alterations [7], together with detrimental effects on continence and on patient satisfaction [2, 4–8].

For these reasons, several minimally invasive techniques have been developed, even if their adoption (mainly in simple AFs) is limited by a higher failure rate. They also tend to be more expensive and are rarely used in real practice scenarios [9]. Reflecting this, guidelines do not offer specific indications regarding the clinical application of these techniques in simple AFs [4–6].

The aim of this systematic review was to assess the surgical treatment of simple AFs by sphincter-cutting and sphincter-sparing techniques, and specifically—(1) peri-operative features and morbidity, (2) clinical results in terms of efficacy, (3) the risk of postoperative continence impairment and impact of surgery on patients’ QoL.

Materials and methods

Literature review and eligibility criteria

This review was carried out according to the Preferred Reporting Items for Systematic reviews and Meta-Analyses Statement (PRISMA) guidelines [10]. A literature research was performed using PubMed, Cochrane, and Google Scholar. “Simple anal fistula”, “low anal fistula”, “intersphincteric fistula”, “low transphincteric fistula”, “fistulotomy” were the search terms used. Studies were included if they provided any number of cases analyzing any surgical treatment for simple AFs as defined by commonly adopted guidelines [4–6]. Prospective, retrospective, observational studies, and randomized clinical trials were included, while reviews, meta-analyses, trial proposals, thesis articles, technical notes, commentaries, letters, and meeting abstracts were excluded. The time range covered was 1990–April 2020, and only articles written in English were selected. Additional articles responding to the inclusion criteria were extrapolated from the bibliography of relevant material via backward citation tracking.

All articles concerning complex, recto-vaginal or ano-vaginal, tuberculosis- and IBD-related AFs were excluded, as well as any study where data on simple AFs could not be extrapolated.

Database research was performed by three authors individually (FL, AP, LF) and the results were then discussed and merged by a working group. Article inclusion, when in doubt, was decided on a per-case basis after discussion.

Data extraction

Data from eligible literature was thus extracted and inserted in tables using SPSS® version 21.0 for Windows® software (SPSS, Chicago, IL, USA), including publication data (author, year of publication, study type), type of intervention, characteristics of participants (number of patients, mean age, male-to-female ratio), perioperative details, and other outcomes (operating time, hospital stay, mean healing time, complications, recurrence, and/or success rates, continence impairment, pre- and postoperative anorectal manometry, QoL scores).

Data extraction was performed by two reviewers (AP, LF) and independently assessed by another (FL) for completeness and accuracy. Surgical procedures were summarized as sphincter-cutting procedures (fistulotomy, fistulectomy, and cutting setons) or sphincter-sparing techniques [glues/pastes, laser, flap, ligation of intersphinctericv fistula tract (LIFT), etc.].

Risk of bias assessment

A risk of bias and quality assessment was performed for each article. For randomized studies, the Jadad scale was used (1–5 points, 1 = poor and 5 = excellent) [11], while for non-randomized studies, the Methodological Index for Non-Randomized Studies (MINORS) Scale for comparative (0–24 points, 0 = poor and 24 = excellent) or non-comparative (0–16 points, 0 = poor and 16 = excellent) studies was applied [12].

Data reporting and statistical analysis

Descriptive statistics have been reported as absolute frequencies and percentages for qualitative data; quantitative variables have been described as mean value (standard deviation) or median (range), based on availability. For means, the weighted averages were calculated as follows: (single study average × study cohort size) 1, 2, …, n/pooled cohort size. This was done to minimize the effect of the different cohort sizes of the studies on the calculated averages and to provide an overall value for the outcome measures evaluated.

Results

Study selection and risk of bias

The search returned 456 records of interest. After removal of duplicated records, 437 were screened; after title and abstract evaluation, 343 were excluded according to the inclusion criteria. Finally, 94 full text articles were assessed for eligibility; however, 28 of them were excluded, mainly because of the impossibility of isolating data on patients affected by simple AFs from mixed case reports. Therefore, a total of 66 articles [2, 8, 13–76] were found to be eligible (Fig. 1). The publication dates of the articles range from 1994 to 2020. Among the included studies, 28 were prospective studies [21–25, 29, 38–40, 42, 44, 48, 51, 53, 56, 58–62, 64, 65, 68, 70, 71, 74–76], 19 were retrospective series [2, 8, 13–15, 18, 26–28, 33, 43, 45, 57, 63, 66, 67, 69, 72, 73], and 19 were randomized clinical trials (RCT) [16, 17, 19, 20, 30–32, 34–37, 41, 46, 47, 49, 50, 52, 54, 55] (Tables 1–2). The quality of the studies was generally low with a consistent risk of bias; the median score of the Jadad Scale for RCT was 3 (1–5), and only 2 studies had the highest possible score [52, 55]; the median MINORS score for non-comparative studies was 12 (3–16), with only one study that could be regarded as excellent [44], while the median MINORS score for comparative studies was 17 (8–21) (Tables 1, 2). Risk of bias of the selected studies could be attributed mainly to a retrospective design, difficulty or impossibility of patients’ and operators’ blinding, small sample size, short follow-up, heterogeneity of the analyzed variables, absence of uniform definition of the main outcomes (success rate, continence impairment).

Fig. 1.

Fig. 1

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PRISMA flow diagram of the included studies

Table 1.

Patient and study characteristics—sphincter-cutting procedures

Authors Year Study type Intervention Patients Age (years) Sex
(M:F)		 Quality of the studya
Sangwan et al. [13] 1994 R Fistulotomy 461 42 310:151 8/16
Lentner and Wienert [14] 1996 R Long-term indwelling seton 108 NR NR 6/16
Hongo et al. [15] 1997 R Coring out 319 NR NR 4/16
Ho et al. [16] 1998 RCT Fistulotomy 52 41.1 49:3 3/5
Fistulotomy with marsupialization 51 41.2 41:10
Ho et al. [17] 2001 RCT Chemical ayurvedic seton 46 42 21:2 3/5
Fistulotomy 54 37 5:1
Isbister and Al Sanea [18] 2001 R Cutting Seton 31 42 14.5:1 12/16
Shahbaz et al. [19] 2002 RCT Fistulectomy 25 32.1 24:1 1/5
Fistulectomy with primary closure 25
Lindsey et al. [20] 2002 RCT Fistulotomy 7 NA NA 3/5
Chang and Lin [21] 2003 P Fistulotomy 45 54.2 29:16 14/16
Gupta [22] 2004 P Radiofrequency fistulotomy 232 NR NR 11/16
Hammond et al. [23] 2006 P Snug seton 18 42* 26:3 13/16
Van Der Hagen et al. [24] 2006 P Fistulotomy 62 40* 22:9 11/16
Mahajan et al. [25] 2007 P Fistulectomy and skin graft 25 NR 24:1 3/16
Van Koperen et al. [26] 2008 R Fistulotomy 109 39 71:38 14/16
Jordàn et al. [27] 2009 R Fistulotomy, fistulectomy 76 NA NA 12/16
Bokhari and Lindsey [28] 2010 R Fistulotomy 57 NA NA 17/24
Bhatti et al. [29] 2011 P Fistulotomy 25 NR 46:4 15/24
Fistulectomy 25 NR
Sahakitrungruang et al. [30] 2011 RCT Fistulotomy 25 43.2 23:2 3/5
Fistulotomy with marsupialization 25 40.6 4:1
Nazeer et al. [31] 2012 RCT Fistulectomy 75 NR NR 3/5
Fistulotomy 75 NR NR
Jain et al. [32] 2012 RCT Fistulectomy 20 34.5 4:1 3/5
Fistulotomy with marsupialization 20 34.3 9:1
Salem [33] 2012 R Fistulectomy 146 NR 190:82 14/24
Fistulotomy 126 NR
Kamal [34] 2012 RCT Fistulotomy 32 NR 15:4 1/5
Fistulectomy 44 NR
Wang et al. [35] 2012 RCT SDPC suture dragging and pad compression 6 NA NA 3/5
Fistulotomy 5 NA NA
Chalya and Mabula [36] 2013 RCT Fistulectomy 82 37.8 76:6 3/5
Fistulotomy with marsupialization 80 38.6 74:6
Gottgens et al. [8] 2015 R Fistulotomy 537 45.5 379:158 12/16
Sheikh et al. [37] 2015 RCT Fistulotomy 131 32.5 All M 1/5
Fistulectomy 131 33.5 All M
Visscher et al. [2] 2015 R Fistulotomy 68 NA NA 13/16
Abramowitz et al. [38] 2016 P Fistulotomy 133 48 107:133 14/16
Elsebai et al. [39] 2016 P Fistulectomy 15 35.3 23:7 21/24
Fistulotomy 15 37.4
Limongelli et al. [40] 2016 P Fistulotomy 29 41 40:13 20/24
Fistulotomy with marsupialization 44
Saber [41] 2016 RCT Fistulotomy 100 NR All M 3/5
Fistulectomy 100 NR All M
Vyas et al. [42] 2016 P Fistulotomy 38 45.2 7.3:1 17/24
Fistulectomy 37
Wang and Rosen [43] 2016 R Fistulotomy 26 46.4 23:3 13/16
Jayarajah et al. [44] 2017 P Multiple techniques 34 42.5 30:14 16/16
Murtaza et al. [45] 2017 R Fistulotomy 96 40.5 81:15 21/24
Fistulectomy 96 41.4 92:4
Ganesan et al. [46] 2017 RCT Fistulotomy 30 NR NR 3/5
Fistulectomy 30 NR NR
Shahid et al. [47] 2017 RCT Fistulectomy 30 35.8 4:1 3/5
Fistulectomy and suture 30 38.4 13:1
Vyas et al. [48] 2017 P Fistulotomy 92 38.5 85:7 8/16
Mittal et al. [49] 2018 RCT Fistulotomy 38 41.5 31:6 3/5
Fistulectomy 37 45.2 35:3
Gupta et al. [50] 2018 RCT Fistulectomy 30 35.5 28:2 1/5
Mallik et al [51] 2018 P Fistulotomy 25 39.6 23:2 13/24
Fistulectomy 25 24:1
Anan et al. [52] 2019 RCT Fistulotomy 30 38.3 4:1 5/5
Fistulotomy with marsupialization 30 43.5 13:2
Bhatia [53] 2019 P Fistulectomy 50 NR  > 2:1 12/16
Sahai et al. [54] 2019 RCT Fistulotomy 28 41 5:1 1/5
Sanad et al. [55] 2019 RCT Fistulotomy + phenytoin 2% and sitz baths 30 41.4 5:1 5/5
Fistulotomy + sitz baths 30
Basa and Prakash [56] 2020 P Open Fistulectomy 25 NR 2:1 21/24
Fistulectomy with primary closure 25 NR
De Hous et al. [57] 2020 R Fistulectomy and suture 24 52.8 2:1 14/16
Total 4883
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P prospective study, R retrospective study, RCT randomized clinical trial, NR not reported, NA not available

*Values are median

aRandomized studies assessed according to JADAD scale [11] (maximum score: 5); non-randomized studies assessed according to MINOR Scale [12] (maximum score 16 for non-comparative studies. 24 for comparative studies)

Table 2.

Patient and study characteristics—sphincter-sparing techniques

Authors Year Study type Intervention Patients (no.) Age (years) Sex (M:F) Quality of the studya
Cintron et al [58] 2000 P Fibrin glue 11 NA NA 19/24
Lindsey et al [20] 2002 RCT Fibrin glue 6 NA NA 3/5
Mohammed [59] 2004 P Laser 6 32 All M 11/16
Gisbertz et al [60] 2005 P Fibrin glue 27 43 23:4 13/16
Barillari et al [61] 2006 P Cyanoacrylate glue 7 NA NA 13/16
Rojanasakul et al [62] 2007 P LIFT 13 NA NA 12/16
Chew and Adams [63] 2007 R Advancement flap 6 46 2:1 11/16
Jain et al [64] 2008 P Cyanoacrylate glue 20 26 3:1 12/16
Bokhari and Lindsey [28] 2010 R Flap and glue 9 NA NA 17/24
Mishra et al [65] 2013 P Fibrin glue 16 NA NA 11/16
Van Onkelen et al [66] 2013 R LIFT 22 45.5 13:9 14/16
Oztürk and Gülcü [67] 2014 R Laser 44 NR NR 13/16
Cestaro et al [68] 2014 P Fibrin glue 6 NR NR 12/16
Malakorn et al [69] 2017 R LIFT 167 NR NR 13/16
Wilhelm et al [70] 2017 P Laser 8 NA NA 13/16
Gupta et al [50] 2018 RCT SLOFT 30 33.5 23:7 1/5
Giordano et al [71] 2018 P Permacol paste 27 NA NA 12/16
Terzi et al [72] 2018 R Laser 61 NA NA 15/16
Marinello et al [73] 2018 R OTSC clip 3 58.3 All F 9/16
Bayrak et al [74] 2018 P Permacol paste 11 NA NA 11/16
Sahai et al [54] 2019 RCT LIFT 22 41 5:1 1/5
Iqbal et al [75] 2019 P 1% silver nitrate 76 32 31:7 11/16
Vander Mijnsbrugge et al [76] 2019 P LIFT 4 NA NA 15/16
Total 602
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P prospective study, R retrospective study, RCT randomized clinical trial, NR not reported, NA not available, LIFT ligation of the intersphincteric fistula tract, SLOFT submucosal llgation of fistula tract

*Values are median

aRandomized studies assessed according to JADAD scale [11]; non-randomized studies assessed according to MINOR scale [12] (maximum score 16 for non-comparative studies. 24 for comparative studies)

Patient characteristics and surgical procedures

A total of 4883 patients (weighted average age: 41.3 years; M:F ratio 6:1) underwent a sphincter-cutting procedure, which was usually fistulotomy or fistulectomy (Table 1). Main technical variations reported were marsupialization [16, 30, 32, 36, 40, 52] or primary sphincteroplasty [19, 35, 47, 56, 57].

Sphincter-sparing techniques were adopted to treat 602 patients (weighted average age: 36.2 years; M:F ratio 4:1) with a simple AF (Table 2). Among those, glues/pastes (fibrin glue, Permacol® collagen paste, and cyanoacrylate glue) were the most frequently analyzed procedures with ten records [20, 28, 58, 60, 61, 64, 65, 68, 71, 74]. LIFT and the laser closure of fistula tracts were reported in five [54, 62, 66, 69, 76] and four studies [59, 67, 70, 72], respectively. Other procedures adopted are detailed in Table 2.

Perioperative details

When reported, the weighted average duration of the sphincter-cutting procedures was 21.9 (8.0–43.0) minutes, and the weighted average duration of hospital stay was 3.1 (0–13.0) days. The weighted average healing time was 41.0 (8.0–183.0) days (Table 3). The most frequent complication reported was wound infection (123 cases, 6%), followed by bleeding (53 cases, 2.9%) and urinary retention (40 cases, 2.6%) (Table 3).

Table 3.

Perioperative details—sphincter-cutting procedures

Authors Technique Operation time (minutes) Hospital stay (days) Healing time (days) Morbidity (no. %)
Bleeding Urinary retention Infection Other
Lentner and Wienert Long term indwelling seton NR 0.3 NR NR NR NR NR
Ho et al Fistulotomy 8.0 2.0 42.0 0 (0) 0 (0) 0 (0) 0 (0)
Ho et al Fistulotomy with marsupialization 10.0 1.0 70.0 0 (0) 0 (0) 0 (0) 0 (0)
Ho et al Chemical ayurvedic seton NR 1* 54* 0 (0) 0 (0) 1 (2.2) 0 (0)
Ho et al Fistulotomy NR 1* 45* 0 (0) 0 (0) 0 (0) 0 (0)
Isbister and Al Sanea Cutting Seton NR NR 183.0 NR NR NR 0 (0)
Shahbaz et al Fistulectomy NR NR 31.8 NR NR NR 0 (0)
Shahbaz et al Fistulectomy with primary closure NR NR 8.0 NR NR NR 0 (0)
Lindsey et al Fistulotomy NA NA NA NA NA NA 0 (0)
Gupta Radiofrequency fistulotomy 13.0 0 67.0 0 (0) 0 (0) 0 (0) 1 (0.4)
Hammond et al Snug seton NA NA NA NR NR 1 (5.6) 2 (11.1)
Mahajan et al Fistulectomy and skin graft 41.2 9.2 13.8 NR NR NR NR
Van Koperen et al Fistulotomy NR NR NR 1 (0.9) 0 (0) 1 (0.9) 0 (0)
Bhatti et al Fistulotomy NR 1.5 24* 1 (4) 0 (0) 0 (0) 0 (0)
Bhatti et al Fistulectomy NR 2.5 35* 3 (12) 0 (0) 0 (0) 0 (0)
Sahakitrungruang et al Fistulotomy NR NR NR 2 (8) 2 (8) 1 (4) 0 (0)
Sahakitrungruang et al Fistulotomy with marsupialization NR NR NR 0 (0) 0 (0) 0 (0) 0 (0)
Nazeer et al Fistulectomy NR 3.5 40.0 5 (6.7) 0 (0) 0 (0) 0 (0)
Nazeer et al Fistulotomy NR 2.0 28.0 1 (1.3) 0 (0) 0 (0) 0 (0)
Jain et al Fistulectomy 28.0 NR 47.3 NR NR NR NR
Jain et al Fistulotomy with marsupialization 28.2 NR 34.0 NR NR NR NR
Salem Fistulectomy NR 2.0 21.0 NR NR NR NR
Salem Fistulotomy NR 3.0 28.0 NR NR NR NR
Kamal Fistulotomy 17.3 NR 26.4 0 (0) 0 (0) 1 (3.1) 0 (0)
Kamal Fistulectomy 33.0 NR 38.6 1 (2.3) 0 (0) 1 (2.3) 0 (0)
Chalya e Mabula Fistulectomy 28.4 3.9 36.4 0 (0) 0 (0) 27 (32.9) 0 (0)
Chalya e Mabula Fistulotomy with marsupialization 29.2 4.2 28.6 0 (0) 0 (0) 28 (35) 0 (0)
Gottgens et al Fistulotomy NR NR 37* NR NR NR NR
Sheikh et al Fistulotomy 14.3 3.7 28.8 1 (0.8) NR 3 (2.3) NR
Skeikh et al Fistulectomy 25.9 4.9 32.0 4 (3.1) NR 5 (3.8) NR
Abramowitz et al Fistulotomy NR NR 56* 1 (0.8) 0 (0) 0 (0) 0 (0)
Elsebai et al Fistulectomy 40.7 NR 45.3 0 (0) 2 (13.3) 1 (6.7) NR
Elsebai et al Fistulotomy 19.4 NR 28.5 0 (0) 1 (6.7) 2 (13.3) NR
Limongelli et al Fistulotomy NR NR NR 14 (48.3) NR NR NR
Limongelli et al Fistulotomy with marsupialization NR NR NR 7 (15.9) NR NR NR
Saber Fistulotomy 27.0 1.0 30.0 NR NR NR NR
Saber Fistulectomy 37.0 1.0 41.7 NR NR NR NR
Vyas et al Fistulotomy NR 2.9 28.6 NR NR 4 (10.5) NR
Vyas et al Fistulectomy NR 4.3 48.5 NR NR 15 (40.5) NR
Murtaza et al Fistulotomy 17* NR 15* NR NR NR NR
Murtaza et al Fistulectomy 25* NR 30* NR NR NR NR
Ganesan et al Fistulotomy 12.1 1.8 24.2 0 (0) 3 (10.0) 1 (3.3) NR
Ganesan et al Fistulectomy 22.2 2.6 31.5 2 (6.7) 5 (16.7) 3 (10) NR
Vyas et al Fistulotomy NR NR 28.0 NR NR 7 (7.7) NR
Mittal et al Fistulotomy NR 2.9 28.6 NR NR 4 (10.5) NR
Mittal et al Fistulectomy NR 4.3 48.5 NR NR 15 (40.5) NR
Gupta et al Fistulectomy 43.0 NR 32.0 NR NR 2 (6.7) NR
Mallik et al Fistulotomy 9.7 3.9 16.8 NR 0 (0) NR NR
Mallik et al Fistulectomy 15.2 4.2 24.4 NR 0 (0) NR NR
Anan et al Fistulotomy 16.8 NR 46.9 2 (6.7) 1 (3.3) 0 (0) 0 (0)
Anan et al Fistulotomy with marsupialization 18.4 NR 35.7 0 (0) 2 (6.7) 0 (0) 0 (0)
Bhatia Fistulectomy 26.4 2.0 39.0 3 (6) 6 (12) 0 (0) 6 (12)
Sanad et al Fistulotomy + phenytoin 2% and sitz baths 13.0 0 41.2 3 (10) 1 (3.3) 0 (0) 0 (0)
Sanad et al Fistulotomy + sitz baths 14.0 0 42.0 2 (6.7) 1 (3.3) 0 (0) 0 (0)
Basa and Prakash Fistulectomy NR 1.0 31.0 0 (0) 10 (40) 0 (0) 0 (0)
Basa and Prakash Fistulectomy with primary closure NR 7.0 8.0 0 (0) 6 (24) 0 (0) 0 (0)
De Hous et al Fistulectomy and suture 20* 0 NR 0 (0) NR 0 (0) 6 (25)
Total 53 (2.9) 40 (2.6) 123 (6) 15 (4)
Weighted average 21.9 3.1 41.0
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NR not reported, NA not available

*Values are median

The overall weighted average operation time of sphincter-sparing procedures was 34.5 (19.0–52.5) minutes, with a weighted average postoperative hospital stay of 0.8 (0–1.5) days. Only 3 studies reported healing time [50, 59, 62]; the weighted average was 15.1 (7.7–28.0) days (Table 4). The morbidity rate was very low, with a total of 6 complications registered (Table 4).

Table 4.

Perioperative details—sphincter-sparing techniques

Authors Technique Operation time (minutes) Hospital stay (days) Healing time (days) Morbidity (no. %)
Bleeding Urinary retention Infection Other
Lindsey et al Fibrin glue NA NA NA NA NA NA 1 (16.7)
Mohammed Laser 19.0 0 7.7 0 (0) 0 (0) 0 (0) 0 (0)
Gisbertz et al Fibrin glue 20.0 NR NA 0 (0) 0 (0) 0 (0) 0 (0)
Barillari et al Cyanoacrylate glue NR NR NR 0 (0) 0 (0) 0 (0) 0 (0)
Rojanasakul et al LIFT 40 1.3 28.0 0 (0) 0 (0) 0 (0) 0 (0)
Chew e Adams Advancement flap 52.5 1.0 NR 0 (0) 0 (0) 0 (0) 0 (0)
Jain et al Cyanoacrylate glue NR 0.0 NR 0 (0) 0 (0) 0 (0) 0 (0)
Mishra et al Fibrin glue NA NA NA 0 (0) 0 (0) 0 (0) 1 (6.3)
Oztürk and Gulcü Laser NR 1.5 NR 0 (0) 0 (0) 0 (0) 0 (0)
Cestaro et al Fibrin glue NR 1.0 NR 0 (0) 0 (0) 0 (0) 0 (0)
Gupta et al SLOFT 46.0 NR 11.0 0 (0) 0 (0) 1 (3.3) 0 (0)
Marinello et al OTSC clip 21.7 NR NR 0 (0) 0 (0) 0 (0) 3 (100)
Iqbal et al 1% silver nitrate NR NR NR 0 (0) 0 (0) 0 (0) 0 (0)
Vander Mijnsbrugge et al LIFT NA NA NA 0 (0) 0 (0) 0 (0) 0 (0)
Total 0 (0) 0 (0) 1 (0.004) 5 (0.02)
Weighted average 34.5 0.8 15.1
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NR not reported, NA not available, LIFT ligation of the intersphincteric fistula tract, SLOFT submucosal ligation of fistula tract

* Values are median

Success rate and continence status

After a weighted average follow-up of 14.7 (1–77) months, the weighted mean success rate after a sphincter-cutting procedure was 93.7% (61.0–100%), while any postoperative continence impairment was reported in 12.7% of patients (0–45.7%) (Table 5).

Table 5.

Results—sphincter-cutting procedures

Author Technique Follow-up (months) Success (%) Preoperative continence impairment (%) Postoperative continence impairment (%)
Any impairment Incontinence to liquid Incontincence to gas Major incontinence
Sangwan et al Fistulotomy 34.0 93.5 NR NA 2.8 NR 0.0
Lentner and Wienert Long term Indwelling seton 15.6 88.0 0 1 0 1 0.0
Hongo et al Coring out NR 98.7 NR 6.4 NR NR NR
Ho et al Fistulotomy 9.0 96.0 NR 12.0 NR NR NR
Ho et al Fistulotomy with marsupialization 10.2 98.0 NR 2.0 NR NR NR
Ho et al Chemical ayurvedic seton 2.3* 97.8 NR 10.9 6.5 4.3 0.0
Ho et al Fistulotomy 1.9* 98.2 NR 5.6 3.7 1.9 0.0
Isbister and Al Sanea Cutting seton 13 96.8 NA 7.1 0 7.1 0
Shahbaz et al Fistulectomy NR 88.0 NR 12.0 NR 12.0 NR
Shahbaz et al Fistulectomy with primary closure NR 92.0 NR NR NR NR NR
Lindsey et al Fistulotomy 18 100.0 NA 0 0 0 0
Chang and Lin Fistulotomy 9.5 100.0 NR 38 NR NR NR
Gupta Radiofrequency fistulotomy 15.0 99.2 NR 0 0 0 0
Hammond et al Snug seton NA 100.0 0 25.0 0 25.0 0
Van Der Hagen et al Fistulotomy 75* 61.0 4.8 9.7 0 0 0
Van Koperen et al Fistulotomy 77* 93.0 2.8 41.0 NR NR 4.8
Jordàn et al Fistulotomy, fistulectomy 19.2 97.4 NA 8.1 NA NA NA
Bokhari and Lindsey Fistulotomy NR 93.0 NR 16.0 NR 11.0 5.0
Bhatti et al Fistulotomy NR 100.0 NR 0 0 0 0
Bhatti et al Fistulectomy NR 100.0 NR 0 0 0 0
Sahakitrungruang et al Fistulotomy NR 100.0 NR 0 0 0 0
Sahakitrungruang et al Fistulotomy with marsupialization NR 100.0 NR 0 0 0 0
Nazeer et al Fistulectomy 10.0 100.0 NR 0 0 0 0
Nazeer et al Fistulotomy 10.0 100.0 NR 0 0 0 0
Jain et al Fistulectomy 3.0 100.0 NR 0 0 0 0
Jain et al Fistulotomy with marsupialization 3.0 100.0 NR 0 0 0 0
Salem Fistulectomy 12 94.0 NR NR NR NR NR
Salem Fistulotomy 12 90.0 NR NR NR NR NR
Kamal Fistulotomy 12.0 93.7 NR 6.3 0 6.3 0
Kamal Fistulectomy 12.0 93.2 NR 11.4 0 11.4 0
Wang et al SDPC suture dragging and pad compression 12 96.7 0 0.0 NA NA NA
Wang et al Fistulotomy 12 100.0 0 1.0 NR NR NR
Chalya and Mabula Fistulectomy 3.0 100.0 NR 0 0 0 0
Chalya and Mabula Fistulotomy with marsupialization 3.0 100.0 NR 0 0 0 0
Gottgens et al Fistulotomy 38.9* 83.6 1.3 45.7 NA NA 28.0
Sheikh et al Fistulotomy 6 89.3 NR NR NR NR NR
Skeikh et al Fistulectomy 6 84.7 NR NR NR NR NR
Visscher et al Fistulotomy NA 84.0 NR 27.9 3.0 24.0 3.0
Abramowitz et al Fistulotomy 12.0 99.2 NR NA NA NA NA
Elsebai et al Fistulectomy 8.0 100.0 0.0 6.7 0.0 6.7 0.0
Elsebai et al Fistulotomy 8.0 100.0 0.0 13.3 0.0 13.3 0.0
Limongelli et al Fistulotomy 39.4 96.6 NR NR NR NR NR
Limongelli et al Fistulotomy with marsupialization 39.4 95.5 NR NR NR NR NR
Saber Fistulotomy NR 98.0 NR 2.0 NA NA NA
Saber Fistulectomy NR 100.0 NR 4.0 NA NA NA
Vyas et al Fistulotomy NR 94.7 NR 0 NA NA NA
Vyas et al Fistulectomy NR 81.1 NR 0 NA NA NA
Wang e Rosen Fistulotomy 11.9 100.0 NR NR 0 NA 0
Jayarajah et al Multiple techniques 27.5 NR 18.0 38.0 NR NR NR
Murtaza et al Fistulotomy 6.0 96.9 NR 5.3 NR NR NR
Murtaza et al Fistulectomy 6.0 95.8 NR 12.5 NR NR NR
Ganesan et al Fistulotomy 8.0 96.7 NR 1.0 0.0 6.7 0.0
Ganesan et al Fistulectomy 8.0 100.0 NR 0.0 3.3 13.3 0.0
Shahid et al Fistulectomy 1.5 93.3 NR NR NR NR NR
Shahid et al Fistulectomy and suture 1.5 100.0 NR NR NR NR NR
Vyas et al Fistulotomy NR 96.8 NR 0.0 NR NR NR
Mittal et al Fistulotomy NR 94.7 NR 0 0 0 0
Mittal et al Fistulectomy NR 81.1 NR 0 0 0 0
Gupta et al Fistulectomy NR 100.0 NR 3.3 NR NR NR
Mallik et al Fistulotomy 18.0 96.0 NR 0 0 0 0
Mallik et al Fistulectomy 18.0 100.0 NR 0 0 0 0
Anan et al Fistulotomy 11.3 96.7 NR 3.3 0 3.3 0
Anan et al Fistulotomy with marsupialization 11.5 100.0 NR 0 0 0 0
Bhatia Fistulectomy NR 96.0 NR 8.0 0 8.0 0
Sahai et al Fistulotomy 2–6 86.0 NR 0 NA NA NA
Sanad et al Fistulotomy + phenytoin 2% and sitz baths 8.2 100.0 NR 0 NA NA NA
Sanad et al Fistulotomy + Sitz baths 7.6 100.0 NR 0 NA NA NA
Basa and Prakash Open Fistulectomy 1 96.0 NR 0 NA NA NA
Basa and Prakash Fistulectomy with primary closure 1 100.0 NR 0 NA NA NA
De Hous et al Fistulectomy and suture 3* 95.8 NR 20.8 NR NR NR
Weighted average 14.7 93.7 2.1 12.7 1.1 3.7 6.0
Open in a new tab

NR not reported, NA not available

*  Values are median

Overall, sphincter-sparing techniques reached a weighted average success rate of 77.7% (25.0–100%) after a weighted average follow-up of 13.2 (2.3–71.0) months. No study reported any postoperative continence deterioration, with the exception of a retrospective study reporting minor incontinence in 1 out of 9 patients (11.1%) with a simple AF and treated with a sphincter-saving technique [28] (Table 6).

Table 6.

Results—sphincter-sparing procedures

Author Technique Follow-up (months) Success (%) Preoperative continence impairment (%) Postoperative continence impairment (%)
Any impairment Incontinence to liquid Incontincence to gas Major incontinence
Cintron et al Fibrin glue NA 82.0 NR NR NR NR NR
Lindsey et al Fibrin glue NA 50.0 NA 0 0 0 0
Mohammed Laser 2.3 100.0 NR 0 0 0 0
Gisbertz et al Fibrin glue 6.8* 33.0 7.4 0 0 0 0
Barillari et al Cyanoacrylate glue 18.0 71.4 0 0 0 0 0
Rojanasakul et al LIFT NR 94.4 NR 0 0 0 0
Chew e Adams Advancement flap 8.1 98.0 0 0 0 0 0
Jain et al Cyanoacrylate glue 6.0 95.0 0 0 0 0 0
Bokhari and Lindsey Flap and glue NR 60.0 NR 11.1 0 11.1 0
Mishra et al Fibrin glue NA 81.0 NA 0 0 0 0
Oztürk e Gülcü Laser NA 86.4 NR NR NR NR NR
Cestaro et al Fibrin glue 12 66.7 NR 0 0 0 0
Van Onkelen et al LIFT 19.9* 82.0 0 0 0 0 0
Malakorn et al LIFT 71* 91.0 NR 0 0 0 0
Wilhelm et al Laser NA 100.0 NA 0 0 0 0
Gupta et al SLOFT NR 100.0 NR 0 0 0 0
Giordano et al Permacol paste 12 70.4 NA NA NA NA NA
Terzi et al Laser 28.3 39.0 NR 0 0 0 0
Marinello et al OTSC clip 22.7 100.0 NR NR NR NR NR
Bayrak et al Permacol paste 12 NA NA 0 0 0 0
Sahai et al LIFT 2–6 68.2 NR 0 0 0 0
Iqbal et al 1% silver nitrate 2.5 76.3 NR NR NR NR NR
Vander Mijnsbrugge et al LIFT 45 25.0 NA 0 0 0 0
Weighted average 13.2 77.7 2.4 0.2 0 0.2 0
Open in a new tab

NR not reported, NA not available, LIFT ligation of the intersphincteric fistula tract, SLOFT submucosal ligation of fistula tract

* Values are median

Only four studies reported anorectal manometry data in patients affected by simple AFs—unfortunately, differences in the instruments and units of measurement adopted (mmHg, cmH2O or kPa) made it impossible to pool the manometric results. In 3 studies, resting and squeeze pressures did not change [17, 20, 35], while a prospective study reported a significant reduction of postoperative resting and squeeze pressures [21].

QoL and patient satisfaction

Seven studies [2, 38, 41, 44, 51, 71, 76] evaluated the effects of surgery on patients’ QoL and satisfaction, even if the data for simple AFs could not be extrapolated for two of them [51, 71]. The postoperative onset of fecal incontinence reduced patients’ QoL in a retrospective series [2], while it had no significant effect in another prospective study [44]; the recurrence of the disease had a negative impact on QoL in a recent prospective study [76]; finally, two reports [38, 41] stated that patient satisfaction after surgery for a simple AF was high or very high in 86.4% and 90.6% of patients, respectively.

Discussion

Surgical treatment of simple AFs is usually considered “simple” by definition. However, over time, the definition of “simple” AFs has led to a reduction in the percentage of the sphincters that is involved, mainly due to the feared risk of postoperative continence impairment [3]. Moreover, it must be considered that the lack of an univocal definition of "simple" fistula can make it difficult to pool the results of the different studies available. However, the selection of studies in this review was performed considering the definition of “simple” fistula provided by the most important international guidelines [4–6]. Only a few of the studies analyzed reported the adoption of imaging techniques (magnetic resonance imaging or endoanal ultrasound) to define the diagnosis, although this probably reflects the infrequent use of these techniques in this kind of anal fistula.

From this systematic review, it emerged that fistulotomy/fistulectomy is by far the most suitable surgical intervention to treat simple AFs. The use of these procedures was constant over the years, and they provide a very high overall success rate (Table 5). However, it should be noted that many of the studies analyzed had a short follow-up, and the healing rate seems to decrease in some studies with a long follow-up. Van der Hagen et al. [24] stated that the recurrence rate after fistulotomy for low AFs gradually increased over time, being 7%, 16%, and 39% after 12, 24, and 72 months of follow-up, respectively. The same study underlined that in more than half of the cases, the recurrence occurred in a different location from the previous fistula tract. Therefore, the authors hypothesized that the recurrence in patients with a simple AF was "more likely a matter of patient disease than a failure of the treatment" [24]. Another large retrospective series on 537 patients showed that the healing rate at the 5-year follow-up was about 83% [8], while a study by van Koperen et al. failed to identify a significant risk factor for fistula recurrence [26].

Concerning the sphincter-sparing procedures, the pooled healing rate calculated in this review was 77.7% (Table 6); however, it should be considered that small sample sizes, short follow-up, and the heterogeneity of the evaluated procedures do not allow us to draw definitive conclusions. LIFT is an attractive recently developed procedure which has proven to be effective (91% success rate) also in a study on simple AFs with a long mean follow-up (71 months) [69]. However, other investigations on this topic are needed to really assess the efficacy of this procedure specifically to treat simple AFs.

Our study confirmed that fistulotomy is a simple and quick procedure (mean operation time: 21 min), with an acceptable mean wound healing time (41 days), although a certain amount of morbidity has been registered (Table 3). In contrast, sphincter-sparing techniques are sometimes more technically demanding and therefore operating time can be longer, even if postoperative complications are almost absent (Table 4). Several new sphincter-sparing techniques have been developed, mainly to reduce the most feared complication of fistulotomy, which is postoperative fecal incontinence. In fact, even this systematic review has confirmed that this complication is almost absent if one of the above-mentioned procedures is used (Table 6). On the other hand, techniques that are not sphincter-sparing could cause continence impairment in approximately 13% of patients with simple AFs (Table 5). Moreover, studies with longer follow-up showed that the incontinence rate after fistulotomy could be higher [2, 8, 21, 44], much more than expected for such a "simple" operation. A study by Visscher et al. [2] reported about 25% of continence impairment (mainly minor) in simple AF patients, with a significant reduction of QoL. Similarly, a high postoperative incontinence rate (about 45%) emerged from a study on 537 patients [8].

There is still debate about how to reduce or contain the risk of fecal incontinence even in simple AFs. Some studies suggest using preoperative anorectal manometry to evaluate baseline anorectal function. Chang and Lin [21] analyzed 45 patients with low intersphincteric fistula with anorectal manometry performed at baseline and at least 6 months after surgery. They found that maximum anal resting pressure significantly decreased, and a lower preoperative anal resting pressure was the only independent predictive factor of postoperative continence disturbances. Similarly, Toyonaga et al. [77] recommend avoiding a fistulotomy in patients with intersphincteric fistulas and with a preoperative low anal squeeze pressure at the anorectal manometry. Therefore, a sphincter-sparing procedure in this kind of patient could be advisable. A technical variation of lay-open fistulotomy to reduce postoperative fecal incontinence seems to be immediate sphincter reconstruction, both for simple and complex fistulas [78].

Some issues regarding the length of hospital stay (3.1 days in the fistulotomy group and 0.8 in the "sphincter-sparing" group) must be considered—the "sphincter-cutting" group includes a relevant number of studies that were carried out decades ago (1990–2000), when protocols on shorter hospital stay were not yet fully implemented. Furthermore, the series with a longer hospital stay were often conducted in specific geographic areas (mainly Asia). We could therefore hypothesize that in both cases, the length of stay was due to hospital requirements. However, we believe that today, in most centers, it is possible to perform both "sphincter-cutting" and "sphincter-sparing" procedures in a day-hospital setting.

Strengths and limitations

This systematic review pooled a large number of patients undergoing surgery for simple AF and analyzed clinically relevant outcomes of different kinds of procedures. As far as we could gather from the literature, an analysis of this size regarding the treatment of simple AFs has never been carried out. The interrogation of multiple search databases allowed us to collect articles from countries with different ranges of income and cultural impact of the disease providing an extensive coverage of both population and procedure types.

The implementation of quality assessment allowed more accurate quantification of selection bias and partially moderated the inhomogeneity of reports.

Nonetheless, a number of limitations of the articles included in this systematic review have surfaced. A large number of studies are low quality and many report a small sample size and/or short follow-up. Additionally, a substantial heterogeneity of the examined procedures, concerning mainly sphincter-sparing techniques was observed. Finally, it must be emphasized that in many of the studies analyzed the continence impairment assessment was performed without the adoption of validated incontinence scores.

Conclusions

Surgical treatment of simple AFs by sphincter-cutting procedures provides excellent cure rates, even if a certain morbidity should be expected. Postoperative continence impairment is not a negligible risk, which could have a detrimental effect on both patients’ QoL and satisfaction. The adoption of sphincter-sparing procedures could be useful in selected patients, and this should be better evaluated in future prospective studies with adequately long follow-up.

Acknowledgements

We thank Dr. Franziska Michaela Lohmeyer for English language editing of this manuscript.

Funding

Open access funding provided by Università Cattolica del Sacro Cuore within the CRUI-CARE Agreement.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest, and no funding from any organization for the submitted work.

Ethical approval

This article does not contain any study with human participants performed by any of the authors.

Informed consent

For this type of study, formal consent is not required.

Footnotes

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Francesco Litta, Angelo Parello and Lorenzo Ferri contributed equally to this article.

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