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Contemporary Management
https://t.me/med1917
of Fistula in Ano
Philip Tozer and Lillian Reza
Abstract
Fistula in ano poses a common yet challenging clinical scenario in colorectal
surgery, necessitating optimal management strategies for improved outcomes.
This chapter offers a concise overview of contemporary approaches to fistula in
ano management, focusing on advancements in surgical techniques and adjunctive therapies. Highlighting the significance of individualized treatment plans, it
discusses options such as seton placement, fistulotomy, fistulectomy, and emerging techniques like the LIFT procedure and biologic agents. Emphasis is placed
on achieving durable fistula closure while minimizing recurrence and preserving
anal continence. Overall, the abstract underscores the importance of evidencebased practice and multidisciplinary collaboration in the successful management
of fistula in ano.
Keywords
Fistula in ano•Anorectal abscess•Surgical management•Seton placement
Fistulotomy•Fistulectomy•Fistula plug•Fibrin glue•LIFT procedure
•
(Ligation of Intersphincteric Fistula Tract)
Biologics
14
•
Key Points
•
Potentially debilitating symptoms affecting QOL.
•
Heterogeneity in definitions exist which hinders comparative analyses.
P. Tozer (B)
St Mark’s Hospital, Watford Road, London HA1 3UJ, UK
e-mail: philtozer@nhs.net
L. Reza
North East Thames London Deanery, Whittington Hospital, Magdala Avenue, London N19 5NF,
UK
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
M. Evans e t al. (eds.), Coloproctology, https://doi.org/10.1007/978-3-031-59630-8_14
337
338 P. Tozer and L. Reza
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•
Most patients present with a ‘non-healing wound’ after drainage of an abscess.
•
Classified as intersphincteric (IS) fistula, transsphincteric (TS), extrasphincteric
(ES) and suprasphincteric (SS).
•
Careful assessment necessary in three dimensions to exclude complex tracts or
horseshoe collections.
•
Clinical assessment complemented with imaging with MRI and EAUS.
•
Fistulotomy gives most reliable results but effect on continence must be
paramount.
•
Other options include seton, sphincter preserving procedures, LIFT, advancement
flap, video assisted anal fistula treatment and and laser ablation of fistula tract.
14.1 Introduction
An anal fistula (sometimes called perianal) is an epithelialized tract which forms
between the anal canal or rectum, and perianal skin. In Europe, the incidence of
anal fistula is reported at 1.2–2.80 per 10,000 people per year [1] and the prevalence is 1.69 per 10,000 population [2]. Cryptoglandular and Crohn’s disease are
the most common aetiologies with prevalence rates of 0.86 and 0.76 per 10,000
population [2].
Anal fistulation is thought to be a sequela of perianal abscess following
infection of an intersphincteric anal gland. The cryptoglandular theory of fistula
formation begins with chronic infection of a blocked anal gland, leading to a tract
traversing the sphincter complex to varying degrees with an internal opening (IO)
usually at the dentate line, and an external opening (EO) on the perianal skin [3].
The next most common cause is Crohn’s disease, and a third of Crohn’s patients
develop perianal disease, which represents an aggressive phenotype [4]. Anal
fistula associated with perianal Crohn’s disease may develop due to chronic transmural inflammation, particularly when they arise in the rectum, but there is no
evidence that those arising from IOs at the dentate line do not develop through
cryptoglandular sepsis, albeit at a higher rate than in the absence of IBD. They are
more likely to be complex in morphology, have a higher rate of recurrence and
shorter time to recurrence [5].
A study using Hospital Episode Statistics identified the rate of fistula persistence following perianal abscess due to cryptoglandular disease to be 16%
compared to 42% with inflammatory bowel disease [6]. Perianal abscess most
commonly presents at a mean age of 40 with predominance in males [7]. Inflammatory bowel disease, female gender, age of first abscess (41–60 years), intersphincteric and ischiorectal location of abscess are associated with an increased
risk of developing a fistula following perianal abscess [6]. Other causes of anal fistula development include iatrogenic injury to the anal canal secondary to surgical
instrumentation, traumatic vaginal birth, radiotherapy, tuberculosis [8], actinomycosis [9] and malignancy. In this chapter we will focus on the management of
cryptoglandular anal fistula.
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14.2 Clinical Presentation of Anal Fistula
Patients with anal fistula can suffer with debilitating symptoms such as persistent
pain, discharge, recurrent perianal sepsis, and reduced continence, which significantly affect quality of life (QoL). Most patients present with a ‘non-healing
wound’ after drainage of an abscess. This external opening prompts clinical
and often radiological assessment, identifying and anatomically characterising the
fistula. Some patients present de novo with an EO without ever having an abscess.
14.3 Clinical Assessment of Anal Fistula
Clinical assessment should include history and clinical examination to elicit features which may be suggestive of inflammatory bowel disease or other underlying
aetiology. An assessment of the frequency of bowel movement, consistency of
stools, and continence should be made and these features will contribute to
planning surgical intervention.
The primary focus of clinical assessment of the fistula itself is assessing morphological complexity which determines chances of achieving long term healing
and management options. Complex cryptoglandular anal fistula, rectovaginal fistula and fistulas in the presence of an ileoanal pouch are associated with treatment
failure and persistence [10]. Several classification systems have been developed
to describe the morphological complexity of anal fistula. Parks classification [11],
St James University Hospital (SJUH) [12], Standard Practice Task Force (SPTF)
classification from the American Society of Colon and Rectal surgeons [13], and
most recently the Garg classification [13] attempt to grade the extent of complexity on clinical examination or MRI depending on the degree of involvement of
the sphincter complex. Globally, Parks classification (Fig. 14.1) is most commonly
reported although the SJUH classification has been found to have better correlation
between fistula anatomy and outcomes [14].
Anal fistulas have also been classified as ‘high’ or ‘low’, and ‘complex’ or
‘simple’. There is no agreed definition of ‘high’ anal fistula and considerable heterogeneity in definitions exist which hinders comparative analyses of outcomes of
interventional studies [15].
‘Simple’ anal fistulas have one external opening, with no extensions and are
below the dentate line. These may be subcutaneous, inter or transsphincteric fistulas. ‘Complex’ fistulas may have several extensions, more than one external
opening, or horseshoe collections in the intersphincteric, ischioanal or supralevator spaces. These fistulas may traverse the sphincter complex above the dentate
line. They may also be intersphincteric when they involve greater than 50% of the
internal anal sphincter, high transsphincteric with greater than 30% of the external
anal sphincter involvement, suprasphincteric or extrasphincteric [16]. Another way
to consider fistula height is to identify the length of good quality muscle which
would be left behind after lay open. This may be more clinically useful.
340 P. Tozer and L. Reza
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Fig.14.1 Parks classification includes extrasphincteric (ES), suprasphincteric (SS), transsphincteric (TS) and intersphincteric (IS) fistula
The degree of involvement of the sphincter complex, bowel habit, history of
previous sphincter injury or perianal surgery and baseline continence determine
whether fistulotomy could be offered. Fistulotomy is associated with the highest
rate of successful cure [17, 18]. A third of patients may experience minor incontinence (loss of fine control—flatus incontinence, minor mucus leakage/soiling)
following fistulotomy if any sphincter is divided, and this deficit is related to IAS
division. Sphincter preserving procedures (SPP) are considered where the fistula
involves a large proportion of the sphincter complex making fistulotomy untenable, or where the minor incontinence risk described above is unacceptable to the
patient, but cure is sought.
14.4 Imaging
Imaging provides precise and objective evaluation of anal fistulas that are thought
to be complex in morphology. Imaging aids surgical planning with a visual representation of the anal fistula and its relation to the sphincter complex. ‘Simple’ anal
fistulas on clinical assessment may not require further imaging [19]. Our practice
is to image any fistula which is not completely appreciable from external to internal opening, or in whom a sphincter preserving procedure is planned, or in the case
of recurrence. In practice, this means the vast majority of fistulae will be scanned,
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Fig.14.2 Clinical assessment aid for managing anal fistula
and only low, simple fistulae destined for lay open will not. Depending on local
practice and availability, various imaging modalities are used in clinical practice
including magnetic resonance imaging (MRI), endoanal ultrasound scan (EAUS),
computed tomography (CT) and fistulography. CT and fistulography are not commonly utilised and have a very limited role. MRI is the gold standard for the
assessment of anal fistula [16, 19]. EAUS is highly sensitive (97%) in identifying
the internal opening and fistulas of all classifications apart from suprasphincteric
fistulas [20]. EAUS is recommended for the assessment of specific features such
as the internal opening and the relation of the fistula to the sphincter complex [19].
Although sensitivity for EAUS is comparable to MRI, MRI is better at identifying complex anal fistula [21]. MRI is superior to examination under anaesthetic
(EUA) and endoanal ultrasound scan (EAUS) as occult collections and secondary
extensions can be readily identified [22, 23]. These features are associated with
fistula persistence or recurrence [24] therefore use of MRI in preoperative planning is recommended in complex anal fistula [22, 23, 25]. The clinical assessment
aid below summarises the pertinent points to consider for surgical management of
anal fistula (Fig. 14.2).
14.5 Surgical Management
The management options for anal fistula centre around the suitability of 3 options
(and of course, doing nothing). If the fistula can be safely laid open with no greater
risk than 1 in 3 minor continence impairment, and the patient consents to this, it
will give them the greatest chance of successful fistula eradication. If lay open
would present a greater risk to continence (due to loose, frequent stools, underlying bowel pathology, pre-existing continence impairment, inadequate good quality
342 P. Tozer and L. Reza
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muscle above the fistula) or if the patient does not accept the 1 in 3 risk, then two
alternatives exist.
Traditionally, a permanent loose seton would be offered to prevent recurrent
abscess formation and reduce fistula symptoms. The tract may mature, but caudad
migration of the tract, despite anecdotal reports, has not been proven.
The other option is a sphincter preserving procedure (SPP). These do not always
preserve the sphincter, and suffer from a lower success rate than lay open. Nevertheless, they can offer fistula cure without substantial sphincter injury. They
require a specific fistula morphology, usually without substantial complexity, and
some fistula are more suitable for some SPPs than others. In general, a straight,
unbranching transsphincteric fistula with a small IO is suitable for most SPPs.
Rationalisation
Fistulae can be simplified or rationalised either to improve symptoms by reducing
the total surface area of the tract and its inflammatory burden or to make them
suitable for an attempt at repair, usually with a sphincter preserving procedure.
Consider, for example, a tract with a secondary extension which precludes repair
with an advancement flap. Eradication of that extension will facilitate the repair.
Rationalisation can usually be undertaken by wide drainage or lay open of that
component, particularly when no muscle would be involved for example in the
rectal wall, or in the ischioanal fossa.
However, an IS extension might require lay open through the internal sphincter, giving the patient the minor continence impairment risk associated with IAS
division, but not yet offering them a cure. Some patients may feel that the chance
of fistula eradication is enough to justify this risk, but others may not. This is the
‘point of no return’ in fistula rationalisation and is a moment which the patient
must understand. Video assisted anal fistula treatment (VAAFT) can be used to
attempt eradication of fistula extensions avoiding this risk, although the efficacy
of this technique is unclear, and is probably low.
Fistulotomy
Fistulotomy or ‘laying open’ of the fistula involves dividing the fistula tract along
its length, including any involved sphincter muscle, and allowing the tract to heal
by secondary intention. This is usually recommended in patients with intersphincteric or low transsphincteric fistula with less than 30% involvement of the external
anal sphincter and at least 2 cm of good quality, contractile muscle cephalad to
the fistula. A fistula tract passing through the intersphincteric space on an oblique
cephalad course may involve far more sphincter muscle than is clinically appreciable. In these patients, preoperative MRI is useful to recognise the increased risk
of fistulotomy [26].
In patients with normal preoperative continence and bowel function, success
rates of fistulotomy are reportedly between 80 and 100% [17, 27, 28]. Continence
is often poorly assessed in clinical research, and when carefully sought, a usually minor impairment is found in around a third of patients, where 2 cm of EAS
remains. Wound shaping is important to allow adequate drainage and avoid early
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bridging of the wound. Marsupialisation of the divided tract edges has been associated with shorter time to wound healing [29] and a Salmon Back Cut may also
be valuable to aid drainage.
Caution must be exercised in female patients with anterior tracts as they have a
shorter muscle length, and that length is also harder to judge. They are therefore
more prone to significant continence impairment with fistulotomy and this should
generally be avoided. Sphincter preserving procedures in simple anal fistulas have
a variable success rate between 25 and 100% compared to fistulotomy at 61–100%
[30] but the heterogeneity in success rates belies a generally disappointing success
rate of SPPs in real world data. The balance for patients therefore lies between
greater efficacy with greater risk, and less risk but a lower chance of success. This
is the essence of the decision for most fistula patients and surgeons should help
patients decide what is most important to them, rather than determine the correct
answer on behalf of the patient.
Fistulotomy in complex anal fistula (high transsphincteric and suprasphincteric)
is associated with higher rates of impairment of continence compared to simple
anal fistulas [31]. In the recent cryptoglandular fistula guideline developed by the
European society of Coloproctologists (ESCP) [32], fistulotomy is recommended
for the management of intersphincteric and low transsphincteric fistulas. Fistulotomy may be used with caution by experienced proctologists in well consented
patients with higher tracts.
Setons
Setons are inert materials primarily used for draining sepsis in perianal fistula. In
the longer term, setons can be used for symptom control (the ‘permanent loose
seton’) or as a bridge to surgery, to reduce inflammation and ‘mature’ the tract
prior to attempts at repair.
Use of a bridging seton prior to surgery has been associated with higher rates of
fistula healing with LIFT (60% with bridging seton compared to 49% without) [33]
and LAFT (70% with bridging seton compared to 52% without) [34], probably
through better control of sepsis and a reduction in inflammation. Permanent loose
setons can be used as a long term solution in patients with good symptom control,
and who wish to avoid further surgery, or in whom fistula eradication is very
unlikely.
Cutting setons have been used in the belief that they cause limited impairment
to the sphincter complex by dividing the tract through slow caudad migration and
allowing the sphincter to heal cranially during the process. There is not good evidence to support this assertion [16, 35]. Although, short term studies reported high
rates of success with cutting seton [36], it is associated with more pain than fistulotomy, with recent long term cohort studies reporting significant impairment
of continence in 8.5% [37], gas incontinence in 21% and liquid incontinence in
5.4% from a median follow up of 38.6 months [38]. Cutting seton is not recommended for the management of anal fistula and this was also strongly advocated by
both clinicians and the patient advisory group of the ESCP cryptoglandular fistula
guideline [32].
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Partial sphincter preserving procedures
Fistulotomy and fistulectomy with immediate sphincter reconstruction
Fistulotomy and fistulectomy with immediate sphincter reconstruction (FISR)
involves division of a high anal fistula tract with primary repair of the divided
sphincter complex to avoid ‘keyhole’ deformity. In high anal fistula (high
transsphincteric, suprasphincteric and extrasphincteric), FISR is reported to have
a fistula healing rate of 89% with disturbance to continence reported in 16% [15].
There is a concern that a sphincter dehiscence after repair following high fistulotomy could drive profound incontinence, and that the existing literature has
not adequately allayed these fears through careful assessment of the technique in
a sufficient number of very high tracts [15]. Systematic reviews are limited by
heterogeneity in fistula height and in outcome reporting, including the lack of
distinction between minor and major incontinence, and the lack of reporting preoperative and postoperative continence using validated scores [15, 39]. Patients
with a fistula, a sphincter defect and existing continence impairment may be well
served by this technique.
Sphincter preserving procedures
Rectal advancement flap
Rectal advancement flaps (RAF) can be mucosal, partial, or full thickness
involving the entire internal anal sphincter/rectal wall. A degree of laxity or intussusception is required. A flap of healthy bowel wall is mobilised proximal to the
internal opening. The opening itself is excised or debrided, along with curettage
or core out of the primary tract. The flap is then secured distal to the internal
opening. Variations include the Delorme’s-style advancement flap, in which the
muscular wall is plicated rather than incised and transposed, and the Church-style
flap, in which the distal tissues are mobilised and the anastomosis takes place at
the site of the internal opening. This latter technique is suitable for lower internal
openings.
RAF is not feasible in patients with poor quality internal anal sphincter,
large internal openings (>2.5 cm is cited) but even slightly smaller openings are
problematic, very high technically inaccessible or low internal openings with inadequate space for distal anastomosis [40, 41]. Fistula healing rates approach 75%
with a pooled incontinence rate of 7.8% [42]. The fistula recurrence rate reduces
with increasing thickness of the flap, but with an inverse impact on continence.
Full thickness flaps are associated with a higher rate of minor incontinence at 20%
compared to mucosal flaps at 9% [43]. Although in the literature distinctions have
been made between full thickness and partial thickness flaps, it is unlikely there
is a standard of thickness that would be applicable for every patient. In practice,
clinicians should ascertain the extent of flap thickness that may be possible in an
individual patient by thorough preoperative examination of tissue laxity and quality of the internal anal sphincter. The trade-off between lower recurrence rates and
greater risk of minor continence impairment should be discussed with the patient.
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Fig.14.3 Illustration from Rojanasakul et al. demonstrating the LIFT technique. Dissection in the
intersphincteric space (A), ligation of the tract on the IAS (B) and EAS (B) side and tract division
[44]
Ligation of intersphincteric fistula tract
Ligation of intersphincteric tract (LIFT) (Fig. 14.3) involves dissection in the intersphincteric space to identify the intersphincteric portion of the tract which is then
ligated from within the IS space on the side of the internal and external anal sphincter, and then the tract is divided in between. The external opening is curetted and
sufficiently deroofed to allow free drainage [44].
LIFT is appropriate in patients with a single tract, without intersphincteric
extensions or collections, and a small internal opening that has not invaded the
entire thickness of the internal anal sphincter causing a large defect. Cranially there
must also be sufficient space between the anorectal junction and the intersphincteric portion of tract for dissection and fixation of the intersphincteric portion, to
avoid iatrogenic injury to the rectal or vaginal wall [40].
LIFT is associated with a fistula healing rate of 69%, with a minor incontinence
rate of 2% at a median follow up of 12 months [42]. Minor incontinence following
LIFT may occur due to direct injury to the internal anal sphincter during dissection
in the intersphincteric space [45]. When LIFT fails, it may do so with the same TS
tract persisting, or with the addition of a new IS tract through the LIFT incision
(upstaging) or with a new IS tract alone (downstaging).
Randomised controlled trials comparing LIFT to RAF found no significant differences in fistula healing or rates of incontinence but LIFT was associated with
less post operative pain [46, 47]. LIFT is technically less challenging to perform
compared to RAF but requires suitable fistula morphology to ensure success.
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Video assisted anal fistula treatment
Video assisted fistula treatment (VAAFT) is a new addition to the armamentarium of fistula surgeons. The fistuloscope is a rigid, straight scope with a diameter
of 3.3 × 4.7 mm which allows direct visualisation of extensions, collections, and
identification of high internal openings. VAAFT also enables fulguration of the
fistula tract and curettage of its extensions [48]. VAAFT has been used to guide
setons into high or sharply angulated anal fistulas [49]. Curative (c)VAAFT is usually combined with direct closure of the internal opening. Various techniques have
been reported in the literature, including suture closure, over the scope clip or
mucosal flap [50]. The rigid nature of the scope is a limiting feature which prevents its deployment in fistulas with long horseshoe extensions or side branches
with an acute angle. Very narrow tracts and suprasphincteric tracts are also not
suitable for VAAFT. Fistula healing rates have been reported between 53 and 93%
[50, 51]. Studies reporting high rates of healing with VAAFT have always used
VAAFT in combination with another sphincter preserving procedure to close the
internal opening.
VAAFT can also be used to reduce symptoms and allow ablation and debridement of complex tracts (pVAAFT), initially reported in Crohn’s disease [49], and
to rationalise tracts without requiring muscle division (dVAAFT).
Laser ablation of fistula tract
Laser ablation of fistula tract (LAFT) is also a relatively new therapeutic procedure
utilising a radial emitting laser diode of 1.8 mm diameter to fulgurate the fistula
tract and promote fistula healing [52]. In the literature, studies use a laser fibre
with a wavelength of 1470 nm with a wattage ranging between 10 and 12 Watts
[53]. LAFT is deployed in combination with simple suture closure of the internal
opening or advancement flap. The underlying aim of IO closure is to disconnect
the tract from the gut and prevent luminal microbes from propagating inflammation [54]. The laser fibre has demonstrated better results in tracts that are greater
than 4 cm in length with a diameter of ≤5 mm. LAFT also demonstrates higher
success rates with intersphincteric tracts. Tracts with associated complexity such
as extensions or unrecognised collections suffer treatment failure [52] therefore
the tract should be rationalised prior to attempting LAFT by draining sepsis and
using a bridging seton [34]. Fistula healing rates have been reported between 63
and 69% with a median 12 month follow up. Minor incontinence is reported at
1%. Theoretically thermal damage may impair continence [34, 53, 55]. LAFT is a
suitable option for patients with an intersphincteric or transsphincteric fistula who
are keen to avoid the risk of minor incontinence. As with VAAFT, thermal energy
can penetrate the fistula wall and close proximity to other organs (e.g. vaginal wall,
urethra) should prompt caution.
Fistula Plug
Fistula plugs have been used in intersphincteric and transsphincteric fistulas in
the absence of associated complexity such as collections or extensions. The fistula
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