**2. Goals of anal fistula treatment**

#### **2.1 Pathogenesis**

To delve into the intricacies of anal fistulas, one must first understand hypotheses that currently exist. The most widespread hypothesis is the cryptoglandular one which states that infected or inflamed anal glands are the cause of anal abscess and fistula [6]. This could be due to the ascending inflammation originating in the anal canal or blockage of discharge. Over almost 150 years, much research was done to find out exact relationship between anal glands and anal fistula, and while some researchers found them to correlate, others weren't even able to prove the existence of anal glands or found them to be very variable at best [7]. Nevertheless, this is the predominant theory that surgeons adhere to throughout the modern surgery era, and anal glands seem to be the likely culprit. Despite this, etiology remains uncertain or unknown, but the inflammatory process seems to play a crucial role.

From the anatomical standpoint, it was stated by Parks that anal fistula is the chronic manifestation of anal abscess that is an acute condition. Fistula forms as a consequence of the medio-lateral spread of infection that subsequently may perforate the anal sphincter complex and extend to the perianal skin, thus forming a fistula [3]. More recently, Garg has shown that intersphincteric space plays a major role in anal fistula pathology, stating that almost all complex fistulas have some degree of intersphincteric involvement and that fistula in closed intersphincteric space acts like an abscess and must be treated accordingly [8, 9].

Molecular analyses of an anal fistula are scarce. One study has shown abundant expression of pro-inflammatory cytokine IL-1b in 93 % of the cryptoglandular anal fistulas, along with increased levels of cytokines IL-8, IL-12p40 and TNF-α in anal fistulas [10]. IL-1, especially IL-1β are strong pro-inflammatory cytokines that can be stimulated by other cytokines, microbial products and even IL-1β by auto stimulation, which can play a role in the recurrence or persistence of anal fistula. Tozer et al. showed immunological differences between cryptoglandular and Crohn's disease-associated fistula [11]. While those are undoubtedly valuable findings that advance our understanding of anal fistula pathology, they still don't change anything in our management of this problem.

#### **2.2 Diagnostic methods for anal fistulas**

To achieve best results, accomplish a higher primary healing rate, prevent recurrence and risk of postoperative continence disturbance, it is essential to identify the entire course of fistula tract including infected anal gland in intersphincteric space, main and possible secondary tracts. In that way, one can decide which surgical option is best for the patient.

After performing DRE, additional usage of the metal probe with insertion through fistula canal should be done to identify which type of fistula patient has so one can decide which surgical option should be performed. In case of pain, this can be performed under anesthesia (EUA: examination under anesthesia) [12]. In the case of a simple anal fistula, it is usually sufficient to examine as mentioned above, but in cases of a complex anal fistula in most cases, additional diagnostic methods should be done.

Some diagnostic methods that have previously been used to verify the course of fistula tracts, have since been abandoned. One of these techniques is X-ray fistulography. This technique is not performed anymore because it does not show the correlation of the fistula tract to the anal sphincter complex, so in that way, surgeon does not know which type of anal fistula the patient has [13].

Possible options to verify the correlation of the fistula tract with anal sphincter complex are: CT fistulography, endoanal ultrasound (EUS) and MRI fistulography.

CT fistulography can be more accurate in cases associated with acute inflammations and abscesses, but it somewhat deficient in cases of mature anal fistula.

Endoanal ultrasound (EUS) is a very good option to verify fistula tract correlation with sphincter complex and possible secondary branches but it is a highly operatordependent technique [14–16].

For now, the golden standard for anal fistula diagnosis and classification is magnetic resonance imaging (MRI). MRI helps not only to accurately demonstrate disease extension but also to predict prognosis, make therapy decisions and can be used in some cases in follow-up periods especially in the patient suffering from Crohn´s disease or recurrent fistula (**Figure 2**) [16–21].

One other possibility in the verification of main fistula tract and possible secondary branches is using fistuloscope during the diagnostic phase of VAAFT procedure (video-assisted anal fistula treatment) but the technique can also be considered as operator-dependent [22]. VAAFT procedure will be discussed later in this chapter.

#### **2.3 Management principles**

It is stated that the ideal treatment for anal fistula lies on two principles. The first is the eradication of sepsis and promotion of fistula tract healing, and the second is preserving the sphincter complex and continence mechanism [23]. With simple fistulas, this can be achieved by laying open the fistulous tract with high healing rates and with no significant continence disturbance [24]. While simple fistulas have simple treatment solutions, the concept of treatment for complex fistulas is somewhat different, and while the above-mentioned principle holds, certain aspects should be explained.

Colorectal surgeons' postulate that internal fistula openings should always be identified and closed. This was shown in a meta-analysis by Mei et al. with class I

**Figure 2.** *MR fistulography clearly shows horseshoe fistula on axial view.*

evidence for significant association between anal fistula recurrence and failure to identify and close internal fistula opening. The same meta-analysis also showed the connection between horseshoe fistula extensions and recurrence [25]. Both of these problems could be solved by applying video-assisted approach in treatment. This covers the first principle.

To achieve the second principle in complex anal fistula, sphincter preserving techniques should be used to address the anal continence problem. Currently, no study compares lay open techniques and sphincter preserving techniques for complex anal fistula treatment but other studies have shown that, in this case, lay open techniques have an unacceptably high incidence of continence disturbance, up to 25% [4]. Meanwhile, sphincter preserving techniques for complex fistulas, with the possible exception of rectal advancement flap, have shown to have no or only minor continence disturbances in up to 1.7% patients [26].

A somewhat different approach, arising from analysis of modern sphincter preserving techniques, to the ideal treatment of anal fistulas was described by Garg. He hypothesized that in order to successfully heal anal fistula, we should bear in mind three principles:


This may be the reason why most sphincter preserving treatment methods still do not have healing results comparable to lay open techniques.
