**6.2 Setonage and fistulotomy**

Setonage and fistulotomy represent the gold standard for the treatment of anorectal fistulas and can be performed both in an outpatient setting and in an operating room, depending on fistula anatomical features. The placement of a seton can be considered when the internal opening is identifiable. Fistulotomy can be carried out with a simultaneous drainage of the abscess in case of a simple fistula, or can be performed as a second stage procedure 4–8 weeks after drainage [56, 57].

Fistulotomy is performed with the patient laying on a left lateral position. After a probe is inserted into the external opening and gently passed along the fistula tract to the internal opening, an incision is made over the entire length of the fistula using the probe as a guide. The tract is then gently curetted and is left opened to heal for second-intention healing or marsupialised to promote healing, depending on surgeons preference. The most critical step in this procedure is to identify and curette the internal opening to reduce the risk of recurrence, since concomitant induration due to inflammation may obscure the internal opening. Hydrogen peroxide injected through the external orifice may help to identify the internal opening [66], while overzealous attempts with a fistula probe should be discouraged as they can cause iatrogenic damage [71].

The most concerning potential complication of a fistulotomy is incontinence (either to solid faeces or liquid faeces or gas) from procedure-related damageto the external anal sphincter. The reported rates of incontinence are highly variable, ranging from 0 to 82% [72, 73], with an increased risk if the fistulotomy is performed at the time of the drainage of an acute abscess [74]. Nevertheless, when fistulotomy is used forsimple anal fistulas in properly selected patients, the risk of faecal incontinence is minimal or none [75, 76].

This treatment is indicated to manage simple fistulas, thus superficial fistulas, intersphincteric fistulas and low transsphincteric fistulas, involving less than 30% of the sphincter complex. For these fistula it is an effective treatment with a high success rate ranging from 79 to 100% [77–79] and low recurrence rates [66, 72, 80, 81].

In females and in patients with preoperative impairment of continence, a high or recurrent fistula, previous fistula surgery or Crohn's disease, any division of the sphincter should be undertaken with caution and by an experienced surgeon [82]. The location of the internal opening per se, whether high or low in the anal canal, should not be used as a guide to "safe fistulotomy".

As fistulotomy, also the insertion of a seton through the fistula track is performed with the patient laying on a left lateral position and requires fistula track probing. Once the seton lays through the fistula track it can be used in different ways. A loose seton purpose is to facilitate drainage preventing an acute exacerbation of abscess formation and to allow healing of any secondary tracts, allowing local assessment some weeks later [57, 83]. A cutting seton purpose is to allow a gradual division of the sphincter, thank to a progressive tightening [57, 84]. Recently reported data of patients undergoing fistulotomy with a cutting seton tightened every 6–8 weeks, reported healing rates over 90% with only minor disturbances in anal sphincter function in 4% of patients [85–87].

Complex fistula treatment, including ligation of intersphincteric fistula tract (LIFT) [88, 89], advancement flap [90, 91], diversion, proctectomy and modified Haley procedure, cannot be performed in an office-based setting.
