Consent: Lay Open Fistula or Seton Insertion

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Last updated: March 12, 2021
Revisions: 4

Last updated: March 12, 2021
Revisions: 4

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This article is for educational purposes only. It should not be used as a template for consenting patients. The person obtaining consent should have clear knowledge of the procedure and the potential risks and complications. Always refer to your local or national guidelines, and the applicable and appropriate law in your jurisdiction governing patient consent.

Overview of Procedure

A fistula-in-ano typically results from presence of a previous peri-anal abscess, however, other causes such as inflammatory bowel disease (Ulcerative Colitis or Crohn’s Disease), trauma, or radiation changes should be considered.

As part of the procedure, a digital rectal examination should be performed to feel for any sinus tract or presence of deeper abscess. Rigid sigmoidoscopy or proctoscopy should also be performed to assess the integrity of the bowel mucosa for signs of inflammatory bowel disease and any evidence of internal fistula openings.

Definitive surgery for fistula-in-ano should not be performed if there is presence of an anorectal abscess, unless being performed by a experienced colorectal surgeon. If there is difficulty in determining presence of a fistula, the tract can be delicately probed and / or injection of hydrogen peroxide into the tract can help identify presence of another internal or external opening. Pre-operatively, a pelvic MRI can also be performed to identify presence of fistula and allow for planning.

A seton can be placed in the tract is probed and the tract is higher in the sphincter mechanism (Fig. 2). These are tied loosely into place initially, however can be slowly tightened at subsequent outpatient follow-up, to allow the gradual closure of fistula tracts

Laying open of a fistula (fistulotomy) is effective in 85-95% of primary fistula. A fistula probe is passed through the tract and the overlying tissues are divided with a knife or diathermy.

Figure 1 – A seton in place

The Goodsall Rule

The Goodsall rule (FIg. 1) can be used clinically to predict the trajectory of a fistula tract, depending on the location of the external opening:

  • External opening posterior to the transverse anal line – fistula tract will follow a curved course to the posterior midline
  • External opening anterior to the transverse anal line – fistula tract will follow a straight radial course to the dentate line

Figure 2 – The Goodsall rule, used clinically to predict the course of a fistula tract  



Complication Description of Complication Potential Ways to Reduce Risk
Bleeding Typically there is minimal or no blood loss
Damage to the anal sphincter complex Always do circum-anal incisions (unless an experienced colorectal surgeon) to avoid the risk of sphincter damage
Anaesthetic risks Includes damage to the teeth, throat and larynx, reaction to medications, nausea and vomiting, cardiovascular and respiratory complications Forms a part of the anaesthetist assessment before the operation



Complication Description of Complication Potential Ways to Reduce Risk
Pain Pudendal nerve block with local anaesthesia can help with post-operative pain
Bleeding There is a small chance of bleeding and bruising post operatively
Infection Superficial wound infection abscess formation is possible, which may necessitate further surgery or a course of antibiotics
Scarring Any incision will result in a scar, which may form a keloid scar, particularly in high risk ethnicities
Blood clots DVTs and PEs are a possibility in any operation, however are low risk as the duration of the procedure is short The patient will be given anti-embolism stockings and low molecular weight heparin peri-operatively to minimise this risk as deemed appropriate.



Complication Description of Complication Potential Ways to Reduce Risk
Recurrence Previous fistula or peri-anal abscess can predispose patients to developing a recurrence in the future Ensure appropriate investigations have been performed to exclude underlying pathology e.g. Crohn’s
Anal stenosis Healing of the fistula tract can lead to fibrosis of the anal canal Use of bulking agents can help prevent narrowing
Delayed wound healing Usually healing should occur within 12 weeks unless there is underlying pathology e.g. Crohn’s