A fistula an abnormal opening between one hollow organ and another or between a hollow organ and the surface of the skin, caused by ulceration, congenital malformation, etc. Anal fistulae originate from the anal glands, (The anal glands or anal sacs are small glands found near the anus ), which are located between the two layers of the anal sphincters and which drain into the anal canal. If the outlet of these glands becomes blocked, an abscess can form which can eventually point to the skin surface. The tract formed by this process is the fistula. Abscesses can recur if the fistula seals over, allowing the accumulation of pus. It then points to the surface again, and the process repeats.
Anal fistulas per se do not generally harm, but can be very painful, and can be irritating because of the pus-drain (it is also possible for formed stools to be passed through the fistula); additionally, recurrent abscesses may lead to systemic spread of infection.
CAUSES AND TYPES
Fistula-in-ano is nearly always caused by a previous anorectal abscess. Main cause of this is an injury at external anal area due to scratching, shaving and infected hair roots etc. After injury, infection occurs and an abscess is formed. Usually that abscess drains spontaneously making an opening which may be a Fistula in ano. After spontaneous drainage or surgical occasionally a tract is left behind, causing recurrent symptoms.
Occasionally, they develop secondary to trauma, Crohn disease, fissures, cancer, radiotherapy, tuberculosis, and other infections.
Anal fistulae can present with many different symptoms:
Diagnosis is by examination. The examination can be an anoscopy.
DIAGNOSIS AND INVESTIGATIONS
The diagnosis can be made by inspection, palpation, and/or Proctoscopic examination by a Specialist Doctor.
These are not performed for routine fistula evaluation. They can be helpful when the primary opening is difficult to identify or in the case of recurrent or multiple fistulae to identify secondary tracts or missed primary openings.
This involves injection of contrast via the external opening, which is followed by x-ray images to outline the course of the fistula tract.
MRI (Most reliable investigation )
Findings show 80-90% concordance with operative findings when observing a primary tract course and secondary extensions. It is the most reliable investigation to show if the fistula is HIGH (i.e. extending above the sphincter muscles that control the continence/ holding control of feces) or LOW (i.e. not involving the muscles).
This above finding is crucial as it decides if the surgery would be in 1 or multiple stages.
A CT scan is more helpful in the setting of perirectal inflammatory disease than in the setting of small fistulae because it is better for delineating fluid pockets that require drainage than for small fistulae.
This is useful for patients with multiple fistulae or recurrent disease to help rule out inflammatory bowel disease.
No definitive medical therapy is available; long-term antibiotic prophylaxis may have a role in recurrent.
Fistulotomy/fistulectomy: The laying-open technique (fistulotomy) is useful for 85-95% of primary fistulae. Complete fistulectomy creates larger wounds that take longer to heal and offers no recurrence advantage over fistulotomy.
Seton placement: A seton (thread tie) can be placed alone, combined with fistulotomy, or in a staged fashion. This technique is useful in patients with the following conditions:
- Complex fistulae (ie, high transsphincteric, suprasphincteric, extrasphincteric) or multiple fistulae
- Recurrent fistulae after previous fistulotomy
With time, healing occurs above the seton as it gradually cuts through the muscles. The seton is tightened on subsequent weekly visits until it falls out. This could take 2-5 visits to cure.