A perianal fistula is an epithelialized tract that connects the luminal surface of the anal canal or rectum with the perineal skin. Tract formation in anal fistula requires disruption of the epithelial barrier and anal mucosa-associated immune cells; the precise mechanism of this physical disruption and immunologic obstacles to the development of anal fistulas have yet to be determined. However, there were hints that matrix metalloproteinases and cytokines, defined as epithelial-mesenchymal transition, may all play a role (6, 7). Anal fistula disease is thought to be caused by activation of the inflammatory process independently of the abscess; most of these studies are based on preclinical studies of fistulas associated with Crohn's disease, whose inflammatory processes are relatively well characterized. Currently, inflammatory markers such as CRP are used in scoring systems to determine the severity of uncomplicated Crohn's disease (8). In addition, many publications have proven CRP's efficacy in evaluating the perianal fistula activity (9, 10). CAO ratio, a combination of markers for systemic inflammation and nutritional status, has been extensively studied as an independent prognostic marker in infection, malignancy, and other inflammatory diseases (11-13). In addition, NLO and CAO ratios in patients with acute cholecystitis (14), NLO ratio in patients with acute appendicitis (15), and CAO ratio in patients with acute pancreatitis (16) were significant as prognosis and severity scores. In colorectal cancers, the LCO ratio was an excellent prognostic marker (17-19). In our study, CAO, NLO, LCO, LCO, NCO, LMO, and TLO parameters were compared separately with tract length, tract thickness, presence of perifistular inflammation, and presence of abscess, which are the criteria for complex fistula formation, and cutoff values were created. Among these scoring values, CAO, LCO, and NCO ratios were statistically significant in predicting the tract characteristics defined for complex fistula with a high probability of recurrence.
Fistula morphology and the relationship between the fistula and the anal sphincter complex are crucial in determining the feasibility of any surgical treatment. The optimal surgical strategy should offer the best chance of cure with the lowest risk of recurrence and an acceptable risk of continence disturbance. Fistulas can be categorized as simple or complex. Simple fistulas are intersphincteric or low trans sphincteric fistulas and involve less than 30% of the external sphincter complex. Complex fistulas include high trans sphincteric, suprasphincteric, extrasphincteric, recurrent and horseshoe fistulas, multiple fistulas, inflammatory bowel disease, radiation history, and those associated with pre-existing incontinence or chronic diarrhea (20). In addition, another defined form of complex anal fistula is a fistula that is difficult to manage, carries a higher risk of recurrence, and poses a more significant threat to continence (21). The definition of complex fistula includes high localization of the fistula, multiple tracts, tract length, sphincter relationship, presence of an associated abscess, absence of an internal orifice, presence of concomitant disease, and recurrent fistulas (21). In our study, it was found that all of the criteria defined as components of complex fistula showed a homogenic correlation with each other; in patients with more than one tract, trans sphincteric sphincter relationship, presence of abscess and presence of perifollicular inflammation were found to be more frequent, and the tract length was also found to be higher. In patients with perifistular inflammation, trans sphincteric fistula and the presence of abscess were more frequent, and the thickness of the tract was higher. Therefore, these criteria were compared with inflammatory indices separately.
Although many surgical methods have been tried to treat perianal fistula, recurrence rates are variable and do not tend to decrease (recurrence rates are 3-57%) (22). The reasons for recurrence in the literature include previous anal surgery, fistulas related to Crohn's disease, patients receiving immunosuppressive therapy, diabetes mellitus, steroid users, high trans sphincteric fistulas, wrong choice of surgical procedure, failure to reveal the internal patency completely, presence of secondary tract, presence and persistence of abscess pouches, and inability to remove the primary tract (23, 24). Our study observed recurrence in 33 (25%) patients. In addition, recurrence rates were found to be more frequent in patients with perifistular inflammation and increased tract thickness. One of the main perioperative problems is the inability to detect the inner mouth of the fistula in the anal epithelium and the presence of a second tract that is not detected by imaging methods (21). In our study, the internal opening could not be detected intraoperatively in 16 (22%) patients. In addition, a secondary tract was observed in 14 (11%) patients. Therefore, the importance of preoperative diagnosis of complex fistula and the importance of utilizing routine examination methods that may raise the suspicion of complex fistula in terms of preoperative preparation-diagnosis algorithm were seen.
In some cases of perianal fistula, in addition to superficially located acute abscess foci, there may be collections in chronic abscess formation that cause deep recurrences or formation of other fistula tracts that cannot be detected by complicated physical examination. In our study, the trans sphincteric sphincter relationship and perifistular inflammation were observed more frequently in abscess patients. We also found that abscess patients had more extended hospital stays and more frequent recurrences. Our study also found that the distributions between the history of previous abscess drainage and tract thickness were homogeneous. This was another indicator of the link between abscess and complex fistula.
In various publications, recurrence and incontinence rates have been reported to be lower with surgeries performed by considering MRI findings; the most important reason for this is that the surgical plan is shaped according to the preoperative fistula tract course (25-27). However, one of the most commonly used methods for intraoperative visualization of the internal orifice is determining where it will exit through the lumen by giving colored fluids through the external orifice. However, this method may not be adequate in all patients. In such a case, it is recommended to advance the probe to the dentate line and perforate the mucosa closest to the epithelium. However, this method is highly likely to find a false internal orifice. It has been reported that such a method is the most important cause of recurrence (28). Determination of the fistula tract is vital in determining the presence of additional fistula tracts and determining the patients to be further investigated in terms of preoperative shaping of the surgical procedure to be applied. Our study with routine inflammatory parameters showed us that based on this information, the presence of abscess, tract length, tract thickness, tract thickness, number of tracts, presence of highly located tracts, additional inflammatory disease, and perifistular inflammation are the main factors that increase the likelihood of complex fistulas. As a result, these factors closely affect the possibility of recurrence, and our study has shown that inadequate preoperative and perioperative patient evaluation increases the likelihood of recurrence regardless of the type of technique used. Based on this information, preoperative differentiation of complex/straightforward fistula, identification of the fistula tract, determination of the presence of additional fistula tracts, and identification of patients to be further investigated for preoperative shaping of the surgical procedure to be performed are of significant importance.