Fig. 6.1
(a) Transsphincteric fistula . (b) Intersphincteric fistula . (c) Suprasphincteric fistula . (d) Extrasphincteric fistula
(a)
Transsphincteric
(b)
Intersphincteric
(c)
Suprasphincteric
(d)
Extrasphincteric
Horseshoe fistulas deserve special mention but are actually variations of transsphincteric or intersphincteric fistulas. The intersphincteric fistulas are the commonest type of fistula (70 %). They are typically a simple low tract that traverses only the internal sphincter but can be complicated by secondary tracts. Transsphincteric fistulas (20–25 %) pass through both internal and external sphincter before exiting to the skin. A supralevator extension of a transsphincteric fistula may also occur.
Suprasphincteric fistula are unusual fistulas (even though Parks and colleagues reported them to comprise 20 % of their series, other series have reported that this type of fistula is very rare), approximately 1–3 % of fistulas [1]. The fistula pathway starts as an intersphincteric fistula and tracks superiorly between puborectalis and the levator ani muscles. It then traverses downward through the ischiorectal fossa to the skin.
Extrasphincteric fistulas are rare (1–2 %). This fistula is generally associated with an unusual etiology such as trauma, Crohn’s disease, pelvic inflammatory disease, or carcinoma. It can also result from a supralevator abscess (or a transsphincteric fistula with supralevator extension) that spontaneously drains into the rectum.
6.4 Preoperative Assessment
6.4.1 Physical Examination
An examination in the office may identify any potential external fistulous openings. Palpation may reveal a thick tract proceeding towards the anal canal. Intersphincteric fistulas are the most likely to be identified in this fashion. Transsphincteric fistulas are deeper and less likely to be able to be felt. A careful digital rectal exam can also sometimes identify the internal opening in more chronic fistulas. An anoscopy should be done in the office as well. The yield for identifying internal openings is rather low but it allows for evaluation of any other coexisting pathology. Tell-tale signs of perianal Crohn’s (edematous skin tags, multiple unusual fissures) can be seen at this time and give insight to the etiology of the fistula.
6.4.2 Goodsall’s Rule
This rule is designed to help identify the internal opening and the course of the primary tract of a fistula-in-ano (Fig. 6.2). When the external opening lies anterior to the transverse anal line drawn across the tuberosities transecting the anal verge, the internal opening tends to be located in a straight radial tract into the anal canal. If the opening is posterior to the transverse anal line, the internal opening is usually located in the posterior midline.
Fig. 6.2
Goodsall’s rule : anterior fistulas track radially; posterior fistulas track to the midline
Cirocco and Reilly analyzed the predictive accuracy of this rule by reviewing 216 patients who underwent fistula surgery. While only 49 % of those who had an external opening anterior to the traverse plane had radially directed fistulas, the accuracy rate of Goodsall’s rule regarding posterior secondary openings was much greater [2].
6.4.3 Fistula Probes
One can attempt passage of a probe gently from the external opening to the internal opening. However, this maneuver is best left for the operating room due to patient discomfort. The probing should be done gently to avoid creating another tract.
6.4.4 Injection of the Fistula Tract
Various products have been described to inject into the fistula tract in order to help identify the internal opening and any unusual secondary tracts or extensions. Milk, methylene blue, and hydrogen peroxide are examples used by various authors. Usually these are adjuncts used in the operating room rather than in the office setting.
6.4.5 Imaging Studies
Imaging studies are not used routinely for all fistulas or in all practices; these modalities are most useful for complex or recurrent fistulas, especially in the setting of multiple previous surgeries and significant scar.
6.4.5.1 Fistulography
Fistulography consists of the radiologic delineation of a fistula tract with a water-soluble contrast agent. It has been replaced in most cases with newer technologies such as CT scan, MRI, and endoluminal sonography [3]. In unusual cases, fistulography may help delineate an extrasphincteric fistula of pelvic origin or may help evaluate patients with recurrent fistula [4] However, previous studies have found fistulograms to be inaccurate in many cases when compared to surgical findings.
6.4.5.2 Endoanal Ultrasound (EAUS )
This technique is simple to perform, noninvasive, inexpensive, and well tolerated and provides excellent definition of anatomy. However, it does depend to a large degree on the examiner’s experience. 3D imaging has been available since the late 1990s [5] and has further enhanced the accuracy of ultrasound examination.
The ultrasound probe may be used with two frequency settings: 7 or 10 MHz. The higher frequency (e.g., 10 MHz) does not penetrate as deeply, but gives higher-resolution images close to the probe. For this reason, it is ideally suited for ultrasound within the anal canal, but may not be as well suited for deeper fistula tracks passing at some distance from the rectum [6].
One report noted that the surgical procedure was influenced by ultrasonographic finding in up to 38 % of cases [7]. In another study that compared digital examination with ultrasound, the two were equally able to identify intersphincteric and transsphincteric tracts, but the ultrasound was unable to assess superficial, suprasphincteric, extrasphincteric, and supralevator or infralevator tracts [7].
Cataldo et al. evaluated their experience with intrarectal ultrasonography (IRUS) in 24 patients with suspected perianal abscess and fistula. At operation, 19 of 24 patients were found to have perirectal abscesses, with all 19 cases correctly identified preoperatively by IRUS [8].
Fistula tract enhancement using hydrogen peroxide provides excellent definition of the fistula tract anatomy. Cheong et al. reported that hydrogen peroxide enhancement of fistula tract is simple, effective, and safe method of improving the accuracy of endoanal ultrasonographic assessment of recurrent anal fistula [9]. There are several “tricks” to properly perform injection of hydrogen peroxide at the time of EUS. Gas bubbles can create artifact and obscure anatomy. Therefore, a minimum amount of hydrogen peroxide should be used during the examination. The authors prefer to use 12 mL of 1.5 % hydrogen peroxide injected after first clearing the fistula tract of any debris by flushing with saline. Pressure must be applied to the external opening at the time of injection to prevent retrograde extravasation and increased bubbling. This maneuver may require help by an assistant. The fistula probe is then passed into and out of the fistulous trajectory following the tract. If 3D ultrasound is used, it may be cycled at this point. The internal opening of a fistula tract is defined by the presence of a hyperechoic breach at the level of the internal sphincter [10]. The inability to identify all extensions of complex fistulas or even primary tracts when they are beyond the reach of the instruments is a limitation of this technique [11]. Scar or inflammatory tissue and presence of abscess may limit the ability to distinguish the anatomic structure that otherwise is usually seen on endoanal ultrasound. Abscess, in particular, can appear similar to adipose tissue seen in the ischiorectal fossa. It has also typically been difficult to identify the internal opening of a fistula in the mucosa.
6.4.5.3 Magnetic Resonance Imaging
MRI appears to have the greatest concordance with clinical and surgical finding when compared with EAUS or CT, with reported accuracy rates of 85 % or greater [12, 13]. It has the advantage of not being user dependent for interpretation, as well as the ability to evaluate fistula tracts that course distant from the anus [14]. It may be performed with or without contrast medium and/or using an endorectal coil. One problem with the endorectal coil is that it requires transanal insertion [14]. Specific characteristics that may be seen were outlined by Buchanan et al. who showed that acute angulation from the internal opening tended to be found in high transsphincteric tracts, whereas those exhibiting obtuse angulation tended to be lower fistulas [15].
Buchanan found that disease recurrence after surgery in patients with fistula-in-ano was decreased by 75 % in those who underwent preoperative MRI. Sahni et al. [16] found MRI to be superior to EUS with regard to specificity and sensitivity (97 % and 96 % vs. 92 % and 85 %,respectively). EUS is less accurate in detecting disease extending into the pelvis or ischiorectal fossa [17]. In the setting of Crohn’s disease, Schwartz prospectively demonstrated equivalent accuracy between MRI, EUS, and EUA (87, 91, and 91 %, respectively) for determining fistula anatomy.
6.5 Surgical Treatment
Despite advances in technology and new options for surgery, the goal of curing fistulas while maintaining continence and minimizing recurrence can be challenging. Most surgical options for treatment of an anal fistula are performed on an outpatient basis. Following the induction of adequate anesthesia, the patient is placed in position of surgeon’s choice. A thorough examination of the anorectal region is always the first step. As mentioned earlier in the evaluation section, simple examination and digital rectal exam are an invaluable part of determining the course of the fistula and location of the internal opening. A fistula probe can then be utilized to identify the tract. The probe is usually placed through the external opening, but it can also be used retrograde in the anal canal to help identify the involved crypt. If the fistula tract cannot be delineated in this way, the next step is to use hydrogen peroxide (the author’s favorite) or other dye to help find the internal opening. While examining the anal canal with a Hill-Ferguson retractor, a syringe with an 18-gauge catheter is used to infuse hydrogen peroxide through the external opening until it can be seen emanating from an internal opening.
If the tract and the internal opening cannot be defined after all these maneuvers, the best option is to stop at this point and reevaluate the patient at a later date. If imaging (MRI, ERUS) had not been done preoperatively, this would be an opportune time to obtain one of these studies.
The surgical treatment of fistula-in-ano is very dependent on the classification of the fistula. In the following section on the treatment of intersphincteric and transsphincteric fistulas, it is assumed that the underlying etiology is due to cryptoglandular disease.
6.5.1 Intersphincteric Fistulas
For an intersphincteric fistula , the most common choice is a fistulotomy. In the setting of an intersphincteric fistula, the cure rates are high. Because there is a relatively limited amount of muscle divided, the most feared complication (incontinence) is not often seen. However, if there is already impaired anal function, one can still consider the muscle-sparing techniques discussed below.
6.5.2 Fistulotomy
Performing a fistulotomy is a straightforward procedure once the tract has been defined and the internal opening found. A fistula probe is passed along the entire length of the fistula tract. The tract is opened down to the fistula probe using electrocautery or a scalpel. The tract can then be curetted and packed. Any unusual tissue can be sent for histologic evaluation.
6.5.3 Transsphincteric Fistulas
There are many treatment choices and considerable controversy surrounding transsphincteric fistulas . Much of the difficulty in making a decision for transsphincteric fistulas revolves around the issue of incontinence.
6.5.4 Fistulotomy
Fistulotomy , described above, can still be a good choice for treatment of a transsphincteric fistula. For a relatively low transsphincteric fistula in the posterior midline of a healthy young male, fistulotomy can result in high cure rates with little risk of incontinence. However, the same procedure done for the same fistula in the anterior midline of a woman with the sphincter already compromised by a difficult vaginal delivery could result in debilitating incontinence.
6.5.5 Fistulectomy
There is little reason to consider doing a fistulectomy rather than a fistulotomy. Although recurrence rates may be similar, healing times are longer and there is more incontinence associated with fistulectomy. One could consider an excision of a small section of the tract for biopsy purposes in the case of suspected Crohn’s disease or malignancy in a long-standing fistula [18].
6.5.6 Setons
Setons can be used in primarily two ways: a marking (non-cutting seton) or a cutting seton (Fig. 6.3a, b).
Fig. 6.3
Seton placement in transsphincteric fistula
1.
Marking (non–cutting) seton
The marking seton will not damage or cut the sphincter, and as the name implies it is placed in the tract and tied loosely. The purpose of the marking seton is to control local sepsis by providing a drainage channel and ensuring that the tract does not temporarily close and lead to an abscess. It is used to either set the stage for a second more definitive procedure (including all the muscle-sparing techniques discussed below) or in the setting of Crohn’s it can be used as a definitive treatment.
2.
Cutting seton
The cutting seton is used for a controlled division of the sphincter to aid in healing of the fistula. Inflammatory reaction and fibrosis of the transection site are thought to prevent retraction of the sphincter complex during the cutting process [19]. This mechanism is supposed to minimize risks of incontinence. The analogy used to describe this technique is that of pulling a wire through an ice block. As the wire passes through, the ice reforms behind the wire.
The technical aspects of placing a seton are straightforward. The procedure starts in the usual fashion: after anesthesia is induced, exam is carried out to identify the pathway of the tract and the internal opening. Once this is accomplished, the seton can be passed through the tract and tied to itself. A marking (non-cutting) seton is tied loosely. For a cutting seton, the skin and anal canal mucosa between the openings must be initially incised and then seton tied down firmly in place around the muscle encompassed by the fistula tract. Multiple alternatives for the seton exist such as double no. 2 silk, elastic bands, vessel loops, or a ¼-in. Penrose drain [20], and the commercially available silastic Comfort Drain™ (AMI).
The cutting seton must be sequentially tightened to gradually cut through the muscle. There are alternatives such as a rubber ring ligator to tighten the ligature [21], use of hangman’s knot [22], or inserting multiple setons initially, securing only one.
Cutting setons do not eliminate the risk of incontinence. Parks and Stitz assessed function in 68 patients in whom a seton was used. Of those patients who had a seton inserted but removed without further division of muscle, 17 % complained of partial loss of control, whereas 39 % of patients who later had division of the seton-contained muscle experienced problems with control [23]. William and colleagues reviewed their experience with 74 patients who underwent seton division of high anal fistulas by four techniques: staged fistulotomy, cutting seton, short-term drainage, and long-term drainage for Crohn’s disease [24]. None of the patients treated with a cutting seton (n = 13) developed a recurrence. Minor instances of incontinence developed in 54 % of those treated by two-staged fistulotomy or by a cutting seton. Kuypers reported his experience with the use of the seton in the treatment of extrasphincteric fistula [25]. No recurrences were observed in his ten patients; six experienced slight soiling, and one was incontinent. A meta-analysis of 37 different studies that examined the incidence of incontinence following cutting seton use reported a rate of 12 %, increasing proportionally with the height of the internal opening [26]. Van Tets and Kuijpers cautioned against the use of setons for fistulas with high anal or rectal openings. In a review of 34 patients with a two-stage seton procedure (16 extrasphincteric and 18 transsphincteric), there were two recurrences but all transsphincteric fistulas healed. Of 29 patients with preoperative normal fecal control who were available for follow-up, postoperative continence was normal in 12 patients (category A according to Browning and Parks classification [27]), 5 patients had no control over flatus (category B), 11 were incontinent for liquid stool or flatus (category C), and 1 had continued fecal leakage (category D).
6.5.7 Muscle Sparing Approaches to Treat Transsphincteric Fistulas
There are several surgical techniques for the treatment of fistulas that do not involve dividing any muscle: advancement flaps, fibrin glue, fistula plugs, and LIFT (ligation of the intersphincteric fistula tract) procedure.
6.5.7.1 Fibrin Glue
The efficacy of fibrin sealant was markedly improved through the addition of bovine thrombin to fibrinogen in 1944 [28]. Instilling fibrin glue in the presence of local sepsis or active inflammation is not recommended. A marking seton should be placed for 6–8 weeks prior to the fibrin glue treatment.
As in all surgery involving treatment of an anal fistula, the procedure is started by identifying the internal and external opening of the fistula. The tract is debrided and cleaned using a curette. Fibrin glue is then injected into the external opening using a syringe and 18-gauge angiocath until the fibrin glue can be seen coming out of the internal opening in the anal canal.
Initial reports were impressive, with a 75 % healing rate without loss of continence. More recent studies have been less promising (Table 6.1) with only one recent study, by Maralcan et al. in 2006 demonstrating a strong healing rate of 78 % [44].
Table 6.1
Results of fibrin glue repair
Author | N | Etiology | % success |
|---|---|---|---|
Hjortrup et al. [29] | 23 | Crypto, postoperative | 74 |
Venkatash et al. [30] | 30 | Crypto, RVF, HIV, Crohn’s, urethro-vesicorectal | 60 |
Cintron et al. [31] | 26 | Crypto, Crohn’s | 85 |
Cintron et al. [32] | 79 | Crypto, HIV, Crohn’s RVF | 54 |
64 | |||
Sentovich [33] | 48 | Crypto, Crohn’s | 69 |
Lindsey et al. [34] | 19 | Crypto, Crohn’s | 63 |
Chan et al. [35] | 10 | Crypto | 60 |
Sentovich et al. [36] | 48 | Crypto, Crohn’s | 69 |
Buchanan et al. [37] | 22 | Crypto | 14 |
Vitton et al. [38] | 14 | Crohn’s | 57 |
Witte et al. [39] | 34 | Crypto, IBD, HIV | 55 |
Hammond et al. [40] | 16 | Crypto | 80 |
Maralcan et al. [41] | 46 | Crypto | 87 |
de Oca et al. [42] | 28 | Crypto | 68 |
Herreros et al. [43] | 59 | Crypto | 37 |
60 | 52 |
Healing rates have been reported in the range of 14–80 % [31, 45, 46]. When compared with other techniques that do not cut the sphincter, fibrin glue was better only than seton drainage alone. The healing rate with glue was 39.1 %, whereas the fistula plug, advancement flap, and seton drainage had healing rates of 59.3, 60.4, and 32.6 % at 12 weeks of follow-up, respectively [47]. Several recent meta-analyses of the literature have been published and demonstrate no advantage for the use of fibrin glue over conventional surgical therapies (Table 6.1).
6.5.7.2 Advancement Flap
The advancement flap was first described by Elting in 1912 [29]. The procedure usually is done after first minimizing local sepsis by use of a marking seton. Following induction of anesthesia, an examination confirms the location of the internal opening. The most common flap is a widely based anorectal mucosa flap that is developed starting just below the internal opening. The epithelialized internal opening is excised, the tract is excised or curetted, the internal opening closed, and then the flap mobilized over the internal opening and sutured in place (Fig. 6.4).
Fig. 6.4
Advancement flap repair: fistula is identified, a wide-based flap raised, the fistula closed, and the flap advanced over the closure
Because the advancement flap has been in use for so long, considerable experience has been gained using the technique of advancement flap. Success rates range from 60 to 80 % (Table 6.2). One advantage of advancement flap repairs is that they are quite versatile and can be used in the presence of Crohn’s disease and for other fistulas such as rectovaginal and rectourethral fistulas. However, it should be noted that even though the sphincter muscle is not directly divided, Soltani et al. reported that the success and incontinence rates were 80.8 %/13.2 % for cryptoglandular and 64 %/9.4 % for Crohn’s fistulas. Mizrahi et al. found an increased risk in the presence of prior attempts at repair [62]. Schouten et al. found no difference in risk of incontinence based on age, sex, or the number of prior repairs [56]. Abbas et al. found an increased risk of incontinence with older age and high transsphincteric fistulas; however, the majority of the patients in this study had a fistulotomy, with only 10.6 % of patients having advancement flaps [63].
Table 6.2
Results of advancement flap repairs
Author | N | % success |
|---|---|---|
Chung et al. [47] | 96 | 60 |
Dubsky et al. [48] | 54 | 76 |
Golub et al. [49] | 164 | 97 |
Zbar et al. [50] | 11 | 81.8 |
Mitalas et al. [51] | 162 | 59 |
Mitalas et al. [52] | 80 | 68 |
Ortiz et al. [53] | 91 | 82 |
Ortiz et al. [54] | 16 | 88 |
Perez et al. [55] | 30 | 93 |
Schouten et al. [56] | 44 | 75 |
van Koperen et al. [57] | 54 | 83 |
Wang et al. [58] | 26 | 64 |
Christoforidis et al. [59] | 43 | 63 |
Uribe et al. [60] | 56 | 92.9 |
Abbas et al. [61] | 36 | 76 |
6.5.7.3 Anal Fistula Plug
The first anal fistula plug developed was the Cook Surgisis Biodesign fistula plug. Made from lyophilized porcine intestinal submucosa, this device has an inherent resistance to infection, does not initiate immune response, and becomes repopulated with host cell tissue during a period of 3 months [64]. The surgical technique for placing the fistula plug is straightforward but certain steps must be rigidly adhered to in order to minimize the risk of early technical failure.
As with the other techniques described in this section, it is recommended that this procedure should not be done in a field of ongoing sepsis. Most authors suggest placement of a seton prior to proceeding with a fistula plug. Once in the operating room, the fistula plug is pulled into the fistula tract through the internal opening (using a hemostat or suture to guide it) until the larger caliber fistula plug has been wedged into the internal opening of the fistula. Once in place, the proximal end of the fistula plug is anchored into the internal sphincter at the level of the internal opening using an absorbable suture. A common cause of early failure is that of plug dislodgment and migration out of the fistula tract. Although initial reported success rates were very promising, subsequent experience has not been as good with healing rates range between 13.9 and 87 % [65].
A second option for a fistula plug is the Gore BIO–A Fistula Plug, which was also approved in 2009. It is a porous, fibrous polymer composed of 67 % polyglycolide and 33 % trimethylene carbonate. It is nonantigenic and biocompatible because it is degraded via a combination of hydrolytic and enzymatic pathways. The device consists of a disk 16 mm in diameter, attached to six tubes, each 9 cm in length. The size of the plug can be tailored by changing the number and length of the tubes so that it occupies the fistula tract until the bioabsorbable nature of the material allows the body to fill the defect with native tissue [66]. Similar to the Cook Surgisis product, the BIO-A has had some success in healing fistulas with healing rates ranging from 14 to 88 % [65, 67]. In a study directly comparing the Cook Surgisis Biodesign and Gore BIO-A products over a 28-month period [65], Buchbery and colleagues found that the healing time was similar. However, the overall success rates were 12.5 % with the BIO-A, compared with 54.5 % for the Cook Surgisis plug (Table 6.3).
Table 6.3
Results of fistula plug
Author | N | % |
|---|---|---|
Ratto et al. [68] | 11 | 72.7 |
Ommer et al. [69] | 40 | 57.5 |
De la Portilla et al. [66] | 19 | 15.7 |
Johnson et al. [70] | 25 | 87 |
Champagne et al. [71] | 46 | 83 |
O’Connor et al. [72] | 20 | 80 |
Ellis et al. [73] | 18 | 78 |
Safar et al. [74] | 35 | 14 |
Lawes et al. [75] | 20 | 24 |
El-Gazzaz et al. [76] | 33 | 25 |
6.5.7.4 Ligation of Intersphincteric Fistula Tract (LIFT)
The LIFT procedure is a relatively recent addition to the options for treatment of anal fistulas.
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