ANORECTAL FISTULA

ANORECTAL FISTULA - Timothy L.Black, MD
BASICS
DESCRIPTION
Inflammatory track with one opening in the anal canal and another in perianal skin. Fistulas occur spontaneously or secondary to perirectal abscess. Most fistulas originate in the anal crypts at the anorectal junction.
• Goodsall's rule
- If external opening is anterior to an imaginary line drawn horizontally through anal canal, fistula usually runs directly into anal canal.
- If external opening is posterior to line, fistula usually curves to posterior midline of anal canal.
- For Goodsall's rule: Anterior fistulae, PPV is ~70%, for Posterior fistulae, PPV is ~40%.
- In children, track is usually straight.
• Classification (1)[C]
- Intersphincteric: Fistula is confined to the intersphincteric plane (most common).
- Transsphincteric: Fistula connects intersphincteric plane with ischiorectal fossa by perforating the external sphincter.
- Suprasphincteric: Fistula connects intersphincteric plane with ishiorectal fossa but loops over external sphincter.
- Extrasphincteric: Fistula connects rectum to perineal skin but passes external to sphincter.
• System(s) Affected: Gastrointestinal; Skin/Exocrine
• Synonym(s): Fistula-in-ano; Anal fistula
ALERT
Geriatric Considerations
Constipation is a common complication.
Pediatric Considerations
• Most common in infants
• More frequent in males
GENERAL PREVENTION
Prevention or prompt treatment of anorectal abscess
EPIDEMIOLOGY
• Predominant age: All ages
• Predominant sex: Male = Female
Incidence
Common
RISK FACTORS
• Injection of internal hemorrhoids, puncture wound from eggshells or fish bones, foreign objects, enema tip injuries
• Ruptured anal hematoma
• Prolapsed internal hemorrhoid
• Acute appendicitis, salpingitis, diverticulitis
• Inflammatory bowel disease (chronic ulcerative colitis, Crohn disease)
• Previous perirectal abscess
• Radiation treatment to perineum/pelvis
• Trauma, either internal or external
• Carcinoma
ETIOLOGY
• Erosion of anal canal
• Extension from infection from a tear in lining of anal canal
• Infecting organism is commonly Escherichia coli
ASSOCIATED CONDITIONS
• Possibly associated with penetrating injury, intestinal tuberculosis, ulcerative colitis
• Hidradenitis suppurativa
• Crohn disease


DIAGNOSIS
SIGNS AND SYMPTOMS
• Constant or intermittent drainage or discharge
• Firm tender perianal lump
• External anal sphincter pain during and after defecation
• Spasm of external anal sphincter during and after defecation
• Anal bleeding
• Discoloration of skin surrounding fistula
• Fistulous opening frequently granulose or scarred
• Possible fever
• Recurrent anorectal abscesses in identical locations
History
• History of perianal drainage
• History of perianal pain
• History of recurrent perianal abscesses
Physical Exam
• Perineal or perianal draining orifice
• Recurrent perianal abscesses in identical location
• Small palpable lesion sometimes identified on rectal exam at level of anal crypts
TESTS
Lab
• Complete blood count (usually not indicated)
• Prometheus first step serology for inflammatory bowel disease (if Crohn disease suspected)
• Consider RPR for recurrent fistulas in sexually active patients.
Imaging
• Lower gastrointestinal series if inflammatory bowel disease suspected
• Pelvic MRI or endorectal ultrasound may be useful in complex or recurrent fistulas
Diagnostic Procedures/Surgery
• Proctoscopy
• Sigmoidoscopy
• Probe inserted into tract to determine its course (be careful not to create an artificial opening)
• Injection of dilute methylene blue into abscess cavity may be helpful in demonstrating fistula (1)[C]
Pathological Findings
• Fistulous tract may be simple or multiple
• Fistulous tract has primary opening in anal crypt; secondary opening in anal skin, para-anal skin, perineal skin, or in rectal mucus membrane
• Anal sinus: Opens in anal crypt
• Termination of sinus is blind and located in para-anal or pararectal tissue.
DIFFERENTIAL DIAGNOSIS
• Pilonidal sinus
• Perianal abscess
• Urethroperineal fistulas
• Ischiorectal abscess
• Submucous or high muscular abscess
• Pelvirectal abscess (rare)
• Rule out: Crohn disease; carcinoma; retrorectal tumors
TREATMENT
GENERAL MEASURES
• Appropriate health care: Outpatient surgery
• Sitz baths 3-4 times per day until definitive surgery
Diet
Clear liquid diet until gastrointestinal function returns
Activity
Resume work and normal activity as soon as possible.
MEDICATION (DRUGS)
• Broad-spectrum antibiotic if active infection
- Cephalexin (Keflex)
- Cefadroxil (Duricef)
- Ampicillin-sulbactam (Unasyn)
- Amoxicillin-clavulanate (Augmentin)
• Stool-softening laxative
• Contraindications
- Refer to manufacturer's literature
• Precautions
- Refer to manufacturer's literature
• Significant possible interactions
- Refer to manufacturer's literature
SURGERY
• Fistulotomy
- Surgical incision of entire length of fistula (unroofing) (2)[A]
- Mucosal tract should be cauterized or curetted
- Sphincterotomy
• Fistulectomy
- Complete excision of tract (rarely indicated, because of extensive tissue loss)
- Sphincterotomy
• Consider Seton stitch placement (especially for suprasphincteric or transsphincteric fistulas). (2)[A]
• Endorectal advancement flap closure for complex fistulas. (2)[A]
• General anesthesia or regional anesthesia usually required (usually done as outpatient procedure in children)
• Consider use of fibrin glue in selected cases of anal fistulas (2)[A], (3)[C]
• Fistulas in Crohn Disease (2)[A]
- Asymptomatic fistulas may not need treatment.
- Simple fistulas treated with unroofing
- Complex fistulas treated with advancement flap or long term setons
- May require a stoma
• Postoperative: Sitz baths
• Avoid constipation.
FOLLOW-UP
PROGNOSIS
• Surgical results usually excellent
• Postoperative healing
- 4-5 weeks for perianal fistulas
- 12-16 weeks for deeper fistulas
• Postoperative healing may occur within 2-3 weeks in children.
• Recurrence rates 2-9% in simple fistulas (2)[A]
COMPLICATIONS
• Constipation (urge to defecate may be suppressed due to pain)
• Rectovaginal fistula
• Partial incontinence of fecal material if sphincter is divided
• Delayed wound healing
• Low-grade carcinoma may develop in long-standing fistulas.
• Recurrent anorectal fistula if fistula is incompletely opened or excised
• Chronic intermittent infections
• Sepsis (rarely)
PATIENT MONITORING
Frequent follow-up examinations following surgery to ensure complete healing and assess continence
REFERENCES
1. Townsend C, Beauchamp RD, Evers BM, et al., eds. Sabiston Textbook of Surgery, 17th ed. Philadelphia: Elsevier Saunders; 2006.
2. Whiteford MH, Kilkenny J, Hyman N, et al. Practice parameters for the treatment of perianal abscess and fistula-in-ano (Revised). Dis Colon Rectum. 2005;48:1337-1342.
3. Hammond TM, Grahn MF, Lunniss PJ. Fibrin glue in the management of anal fistulae. Colorectal Dis. 2004;6:308-319.