You are in: eMedicine Specialties >
General Surgery > Colorectal
Fistula-in-Ano
Article Last Updated: Nov 9, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 12  
Author: Dennis F Zagrodnik II, MD, FACS, Consulting Staff, Wisconsin Vein Center
Dennis F Zagrodnik, II, is a member of the following medical societies: American College of Chest Physicians, American College of Surgeons, American Medical Association, Phi Beta Kappa, and Society of American Gastrointestinal and Endoscopic Surgeons
Editors: Oscar Joe Hines, MD, Assistant Professor, Department of Surgery, University of California at Los Angeles School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; David L Morris, MD, PhD, Professor, Department of Surgery, St George Hospital, University of New South Wales, Australia; Paolo Zamboni, MD, Professor of Surgery, Chief of Day Surgery Unit, Chair of Vascular Diseases Center, University of Ferrara, Italy; John Geibel, MD, DSc, MA, Professor, Department of Surgery, Section of Gastrointestinal Medicine and Department of Cellular and Molecular Physiology, Yale University School of Medicine; Director of Surgical Research, Department of Surgery, Yale-New Haven Hospital
Author and Editor Disclosure
Synonyms and related keywords:
anorectal fistula, perianal fistula, anorectal abscess, to trauma, Crohn disease, Crohn's disease, anal fissures, carcinoma, radiation therapy, actinomycoses, tuberculosis, chlamydial infections, anorectal sepsis, intersphincteric fistula, transsphincteric fistula, trans-sphincteric fistula, suprasphincteric fistula, supra-sphincteric fistula, extrasphincteric fistula, extra-sphincteric fistula, hemorrhoidectomy, sphincterotomy, Goodsall rule, Parks classification
History of the Procedure
References to fistula-in-ano date to antiquity. Hippocrates made reference to surgical therapy for fistulous disease. The English surgeon John Arderne (1307-1390) wrote Treatises of Fistula in Ano; Haemmorhoids, and Clysters in 1376, which described fistulotomy and seton use. Historical references indicate that Louis XIV was treated for an anal fistula in the 18th century. In the late 19th and early 20th centuries, prominent physician/surgeons, such as Goodsall and Miles, Milligan and Morgan, Thompson, and Lockhart-Mummery, made substantial contributions to the treatment of anal fistula. These physicians offered theories on pathogenesis and classification systems for fistula-in-ano.
Since this early progress, little has changed in the understanding of the disease process. In 1976, Parks refined the classification system that is still in widespread use. Over the last 30 years, many authors have presented new techniques and case series in an effort to minimize recurrence rates and incontinence complications. Despite 2500 years of experience, fistula-in-ano remains a perplexing surgical disease. For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education articles Anal Abscess, Rectal Pain, and Rectal Bleeding.
Problem
A fistula-in-ano is a hollow tract lined with granulation tissue connecting a primary opening inside the anal canal to a secondary opening in the perianal skin. Secondary tracts may be multiple and from the same primary opening.
Frequency
The prevalence rate is 8.6 cases per 100,000 population. The prevalence in men is 12.3 cases per 100,000 population. In women, it is 5.6 cases per 100,000 population. The male-to-female ratio is 1.8:1. The mean age of patients is 38.3 years.
Etiology
Fistula-in-ano is nearly always caused by a previous anorectal abscess. Anal canal glands situated at the dentate line afford a path for infecting organisms to reach the intramuscular spaces.
Other fistulae develop secondary to trauma, Crohn disease, anal fissures, carcinoma, radiation therapy, actinomycoses, tuberculosis, and chlamydial infections.
Pathophysiology
The cryptoglandular hypothesis states that an infection begins in the anal gland and progresses into the muscular wall of the anal sphincters to cause an anorectal abscess. Following surgical or spontaneous drainage in the perianal skin, occasionally a granulation tissue–lined tract is left behind, causing recurrent symptoms. Multiple series have shown that the formation of a fistula tract following anorectal abscess occurs in 7-40% of cases.
Clinical
History
Patients often provide a reliable history of previous pain, swelling, and spontaneous or planned surgical drainage of an anorectal abscess.
Signs and symptoms (in order of prevalence)
- Perianal discharge
- Pain
- Swelling
- Bleeding
- Diarrhea
- Skin excoriation
- External opening
Past medical history
Important points in the history that may suggest a complex fistula include the following:
- Inflammatory bowel disease
- Diverticulitis
- Previous radiation therapy for prostate or rectal cancer
- Tuberculosis
- Steroid therapy
- HIV infection
Review of symptoms
- Abdominal pain
- Weight loss
- Change in bowel habits
Physical examination
Physical examination findings remain the mainstay of diagnosis. The examiner should observe the entire perineum, looking for an external opening that appears as an open sinus or elevation of granulation tissue. Spontaneous discharge via the external opening may be apparent or expressible upon digital rectal examination.
Digital rectal examination may reveal a fibrous tract or cord beneath the skin. It also helps delineate any further acute inflammation that is not yet drained. Lateral or posterior induration suggests deep postanal or ischiorectal extension.
The examiner should determine the relationship between the anorectal ring and the position of the tract before the patient is relaxed by anesthesia. The sphincter tone and voluntary squeeze pressures should be assessed before any surgical intervention to delineate whether preoperative manometry is indicated. Anoscopy is usually required to identify the internal opening.
Differential diagnoses
The following do not communicate with the anal canal:
- Hidradenitis suppurativa
- Infected inclusion cysts
- Pilonidal disease
- Bartholin gland abscess in females
Therapeutic intervention is indicated for symptomatic patients. Symptoms usually involve recurrent episodes of anorectal sepsis. An abscess develops easily if the external opening on the perianal skin seals itself.
If patients are without symptoms and a fistula is found during a routine examination, no therapy is required.
A thorough understanding of the pelvic floor and sphincter anatomy is a prerequisite for clearly understanding the classification system for fistulous disease (see Media file 1). The external sphincter muscle is a striated muscle under voluntary control by 3 components. These are submucosal, superficial, and deep muscle. Its deep segment is continuous with the puborectalis muscle and forms the anorectal ring, which is palpable upon digital examination. The internal sphincter muscle is a smooth muscle under autonomic control and is an extension of the circular muscle of the rectum. In simple cases, the Goodsall rule can help to anticipate the anatomy of fistula-in-ano. The rule states that fistulae with an external opening anterior to a plane passing transversely through the center of the anus will follow a straight radial course to the dentate line. Fistulae with their openings posterior to this line will follow a curved course to the posterior midline (see Media file 2). Exceptions to this rule are external openings more than 3 cm from the anal verge. These almost always originate as a primary or secondary tract from the posterior midline, consistent with a previous horseshoe abscess. Parks classification system (see Media file 3) The Parks classification system defines 4 types of fistula-in-ano that result from cryptoglandular infections. - Intersphincteric
- Common course - Via internal sphincter to the intersphincteric space and then to the perineum
- Seventy percent of all anal fistulae
- Other possible tracts - No perineal opening; high blind tract; high tract to lower rectum or pelvis
- Transsphincteric
- Common course - Low via internal and external sphincters into the ischiorectal fossa and then to the perineum
- Twenty-five percent of all anal fistulae
- Other possible tracts - High tract with perineal opening; high blind tract
- Suprasphincteric
- Common course - Via intersphincteric space superiorly to above puborectalis muscle into ischiorectal fossa and then to perineum
- Five percent of all anal fistulae
- Other possible tracts - High blind tract (ie, palpable through rectal wall above dentate line)
- Extrasphincteric
- Common course - From perianal skin through levator ani muscles to the rectal wall completely outside sphincter mechanism
- One percent of all anal fistulae
Current procedural terminology codes classification - Subcutaneous
- Submuscular (intersphincteric, low transsphincteric)
- Complex, recurrent (high transsphincteric, suprasphincteric and extrasphincteric, multiple tracts, recurrent)
- Second stage
Unlike the current procedural terminology coding, the Parks classification system does not include the subcutaneous fistula. These fistulae are not of cryptoglandular origin but are usually caused by unhealed anal fissures or anorectal procedures, such as hemorrhoidectomy or sphincterotomy.
Surgery for fistula-in-ano should not be performed for definitive repair of the fistula in the setting of anorectal abscess (ie, unless the fistula is superficial and the tract is obvious). In the acute phase, simple incision and drainage of the abscess are sufficient. Only 7-40% of patients will develop a fistula.
Lab Studies
- No specific laboratory studies are required; the normal preoperative studies are performed based on age and comorbidities.
Imaging Studies
- Radiologic studies: 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.
- Fistulography
- This involves injection of contrast via the internal opening, which is followed by anteroposterior, lateral, and oblique x-ray images to outline the course of the fistula tract.
- The accuracy rate is 16-48%.
- The procedure is well tolerated but requires the ability to visualize the internal opening.
- Except in the case of recurrent disease, fistulography may be slightly more useful than a careful examination under anesthesia.
- Endoanal/endorectal ultrasound
- These studies involve passage of a 7- or 10-MHz transducer into anal canal to help define muscular anatomy differentiating intersphincteric from transsphincteric lesions.
- A standard water-filled balloon transducer can help evaluate the rectal wall for any suprasphincteric extension.
- Studies show that the addition of hydrogen peroxide via the external opening can help outline the fistula tract course. This may be useful to help delineate missed internal openings.
- These studies are reported to be 50% better than physical examination alone to help find an internal opening that is difficult to localize.
- This modality has not been used widely for routine clinical fistula evaluation.
- MRI: Findings show 80-90% concordance with operative findings when observing a primary tract course and secondary extensions. MRI is becoming the study of choice when evaluating complex fistulae. It has been shown to improve recurrence rates by providing information on otherwise unknown extensions.
- CT scan
- 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.
- CT scan requires administration of oral and rectal contrast.
- Muscular anatomy is not delineated well.
- A barium enema/small bowel series: This is useful for patients with multiple fistulae or recurrent disease to help rule out inflammatory bowel disease.
Other Tests
- Anal manometry
- Pressure evaluation of the sphincter mechanism is helpful in certain patients.
- Decreased tone observed during preoperative evaluation
- History of previous fistulotomy
- History of obstetrical trauma
- High transsphincteric or suprasphincteric fistula (if known)
- Very elderly patients
- If decreased, surgical division of any portion of the sphincter mechanism should be avoided.
Diagnostic Procedures
- Examination under anesthesia
- An examination of the perineum, digital rectal examination, and anoscopy are performed after the anesthesia of choice is administered.
- This examination is necessary before surgical intervention, especially if outpatient evaluation causes discomfort or has not helped delineate the course of the fistulous process.
- Several techniques have been described to help locate the course of the fistula and, more importantly, identify the internal opening.
- Inject hydrogen peroxide, milk, or dilute methylene blue into the external opening and watch for egress at the dentate line. In the authors' experience, methylene blue often obscures the field more than it helps identify the opening.
- Traction (pulling or pushing) on the external opening may also cause a dimpling or protrusion of the involved crypt.
- Insertion of a blunt-tipped crypt probe via the external opening may help outline the direction of the tract. If it approaches the dentate line within a few millimeters, a direct extension likely existed. Care should be taken to not use excessive force and create false passages.
- Proctosigmoidoscopy/colonoscopy
- Rigid sigmoidoscopy can be performed at the initial evaluation to help rule out any associated disease process in the rectum.
- Further colonic evaluation is performed only as indicated.
Medical therapy
No definitive medical therapy is available; long-term antibiotic prophylaxis and infliximab may have a role in recurrent fistulae in patients with Crohn disease.
Surgical therapy
Fistulotomy/fistulectomy (see Media file 4) - The laying-open technique (fistulotomy) is useful for 85-95% of primary fistulae (ie, submucosal, intersphincteric, low transsphincteric).
- A probe is passed into the tract through the external and internal openings.
- The overlying skin, subcutaneous tissue, and internal sphincter muscle are divided with a knife or electrocautery, thereby opening the entire fibrous tract.
- At low levels in the anus, the internal sphincter and subcutaneous external sphincter can be divided at right angles to the underlying fibers without affecting continence. This is not the case if the fistulotomy is performed anteriorly in female patients. If the fistula tract courses higher into the sphincter mechanism, seton placement should be performed.
- Curettage is performed to remove granulation tissue in the tract base.
- Complete fistulectomy creates larger wounds that take longer to heal and offers no recurrence advantage over fistulotomy.
- Opening the wound out on the perianal skin for 1-2 cm adjacent to the external opening with local excision of skin promotes internal healing before external closure.
- Some advocate marsupialization of the edges to improve healing times.
- Perform a biopsy on any firm, suggestive tissue.
Seton placement A seton 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
- Anterior fistulae in female patients
- Poor preoperative sphincter pressures
- Patients with Crohn disease or patients who are immunosuppressed
Setons have 2 purposes beyond giving a visual identification of the amount of sphincter muscle involved. These are (1) to drain and promote fibrosis and (2) to cut through the fistula. Setons can be made from large silk suture, silastic vessel markers, or rubber bands that are threaded through the fistula tract. - Single-stage seton (cutting)
- Pass the seton through the fistula tract around the deep external sphincter after opening the skin, subcutaneous tissue, internal sphincter muscle, and subcutaneous external sphincter muscle.
- The seton is tightened down and secured with a separate silk tie.
- With time, fibrosis occurs above the seton as it gradually cuts through the sphincter muscles and essentially exteriorizes the tract.
- The seton is tightened on subsequent office visits until it is pulled through over 6-8 weeks.
- A cutting seton can also be used without associated fistulotomy. See Media file 5.
- Two-stage seton (draining/fibrosing)
- Pass the seton around the deep portion of the external sphincter after opening the skin, subcutaneous tissue, internal sphincter muscle, and subcutaneous external sphincter muscle.
- Unlike the cutting seton, the seton is left loose to drain the intersphincteric space and to promote fibrosis in the deep sphincter muscle.
- Once the superficial wound is healed completely (2-3 mo later), the seton-bound sphincter muscle is divided.
- Two studies (74 patients combined) support the 2-stage approach with a 0-nylon seton. Once wound healing is complete, the seton is removed without division of the remaining encircled deep external sphincter muscle. The researchers reported eradication of the fistula tract in 60-78% of cases.
Mucosal advancement flap - Mucosal advancement flap is reserved for use in patients with chronic high fistula but is indicated for the same disease process as seton use.
- Advantages include a 1-stage procedure with no additional sphincter damage.
- A disadvantage is poor success in patients with Crohn disease or acute infection.
- This procedure involves total fistulectomy, with removal of the primary and secondary tracts and complete excision of the internal opening.
- A rectal mucomuscular flap with a wide proximal base (2 times the apex width) is raised.
- The internal muscle defect is closed with an absorbable suture, and the flap is sewn down over the internal opening so that its suture line does not overlap the muscular repair.
Preoperative details
- Rectal irrigation with enemas should be performed on the morning of the operation.
- Anesthesia can be general, local with intravenous sedation, or a regional block.
- Administer preoperative antibiotics.
- Prone jackknife position with buttocks apart is the most advantageous position.
Intraoperative details
- Examine the patient under anesthesia to confirm the extent of the fistula.
- Identifying the internal opening to prevent recurrence is imperative.
- A local anesthetic block at the end of the procedure provides postoperative analgesia.
Postoperative details
Most patients can be treated in an ambulatory setting with discharge instructions and close follow-up care.
Follow-up
- Sitz baths, analgesics, and stool bulking agents (eg, bran, psyllium products) are used in follow-up care.
- Frequent office visits within the first few weeks help ensure proper healing and wound care.
- Importantly, ensure that the internal wound does not close prematurely, causing a recurrent fistula. Digital examination findings can help distinguish early fibrosis.
- Wound healing usually occurs within 6 weeks.
Early postoperative
- Urinary retention
- Bleeding
- Fecal impaction
- Thrombosed hemorrhoids
Delayed postoperative
- Recurrence
- Incontinence (stool)
- Anal stenosis: The healing process causes fibrosis of the anal canal. Bulking agents for stool help prevent narrowing.
- Delayed wound healing: Complete healing occurs by 12 weeks unless an underlying disease process is present (ie, recurrence, Crohn disease).
Following standard fistulotomy, the reported rate of recurrence is 0-18% and the rate of any stool incontinence is 3-7%.
Following seton use, the reported rate of recurrence is 0-17% and the rate of any incontinence of stool is 0-17%.
Following mucosal advancement flap, the reported rate of recurrence is 1-10% and the rate of any incontinence of stool is 6-8%.
Future Recent advances in biotechnology have led to the development of many new tissue-adhesive and biomaterials. Reported series exist of fibrin glue treatment of fistula-in-ano, with 1-year follow-up success rates approaching 60%. By its less invasive nature, this therapy leads to decreased postoperative morbidity. The Surgisis fistula plug has also proven successful in direct clinical trials.1, 2 Long-term success rates vary with methodology but with minimal morbidity can easily be repeated for recurrence. Controversies Crohn disease of the perineum with multiple and often complex fistulae requires careful surgical treatment. Acute perianal abscess requires incision and drainage. Definitive repair of fistulae in these patients requires that the intra-abdominal disease be under control with medical therapy. If controlled, routine therapy, as outlined in Treatment, is warranted. Recurrent fistulous disease to the rectum and perineum with persistent anorectal sepsis is an indication for panproctocolectomy. Studies have identified a role for medical therapy with infliximab, the monoclonal antibody to tumor necrosis factor, with 50-60% response rates for perianal fistulae.
| Media file 1:
Fistula-in-ano. Anatomy of the anal canal and perianal space. |
 |  View Full Size Image | |
Media type: Image
|
| Media file 4:
Fistula-in-ano. Schematic of intersphincteric and low transsphincteric fistulotomy. |
 | View Full Size Image | |
Media type: Image
|
| Media file 5:
Fistula-in-ano. Schematic of high transsphincteric fistulotomy with seton. |
 | View Full Size Image | |
Media type: Image
|
- Champagne BJ, O'Connor LM, Ferguson M, Orangio GR, Schertzer ME, Armstrong DN. Efficacy of anal fistula plug in closure of cryptoglandular fistulas: long-term follow-up. Dis Colon Rectum. Dec 2006;49(12):1817-21. [Medline].
- Johnson EK, Gaw JU, Armstrong DN. Efficacy of anal fistula plug vs. fibrin glue in closure of anorectal fistulas. Dis Colon Rectum. Mar 2006;49(3):371-6. [Medline].
- American Society of Colon and Rectal Surgeons. Practice parameters for treatment of fistula-in-ano--supporting documentation. The Standards Practice Task Force. Dis Colon Rectum. Dec 1996;39(12):1363-72. [Medline].
- Beckingham IJ, Spencer JA, Ward J, Dyke GW, Adams C, Ambrose NS. Prospective evaluation of dynamic contrast enhanced magnetic resonance imaging in the evaluation of fistula in ano. Br J Surg. Oct 1996;83(10):1396-8. [Medline].
- Belliveau P. Anal fistula. In: Current Therapy in Colon and Rectal Surgery. Philadelphia: BC Decker; 1990:22-7.
- Buchanan GN, Bartram CI, Phillips RK. Efficacy of fibrin sealant in the management of complex anal fistula: a prospective trial. Dis Colon Rectum. Sep 2003;46(9):1167-74. [Medline].
- Buchanan GN, Halligan S, Williams AB, Cohen CR, Tarroni D, Phillips RK, et al. Magnetic resonance imaging for primary fistula in ano. Br J Surg. Jul 2003;90(7):877-81. [Medline].
- Cosman BC. All's Well That Ends Well: Shakespeare's treatment of anal fistula. Dis Colon Rectum. Jul 1998;41(7):914-24. [Medline].
- Hancock BD. ABC of colorectal diseases. Anal fissures and fistulas. BMJ. Apr 4 1992;304(6831):904-7. [Medline].
- Ho YH, Tan M, Leong AF, Seow-Choen F. Marsupialization of fistulotomy wounds improves healing: a randomized controlled trial. Br J Surg. Jan 1998;85(1):105-7. [Medline].
- Hämäläinen KP, Sainio AP. Incidence of fistulas after drainage of acute anorectal abscesses. Dis Colon Rectum. Nov 1998;41(11):1357-61; discussion 1361-2. [Medline].
- Loungnarath R, Dietz DW, Mutch MG, Birnbaum EH, Kodner IJ, Fleshman JW. Fibrin glue treatment of complex anal fistulas has low success rate. Dis Colon Rectum. Apr 2004;47(4):432-6. [Medline].
- McCourtney JS, Finlay IG. Setons in the surgical management of fistula in ano. Br J Surg. Apr 1995;82(4):448-52. [Medline].
- Parks AG, Gordon PH, Hardcastle JD. A classification of fistula-in-ano. Br J Surg. Jan 1976;63(1):1-12. [Medline].
- Present DH, Rutgeerts P, Targan S, Hanauer SB, Mayer L, van Hogezand RA, et al. Infliximab for the treatment of fistulas in patients with Crohn's disease. N Engl J Med. May 6 1999;340(18):1398-405. [Medline].
- Ratto C, Gentile E, Merico M, Spinazzola C, Mangini G, Sofo L, et al. How can the assessment of fistula-inano be improved?. Dis Colon Rectum. Oct 2000;43(10):1375-82. [Medline].
- Rosen L. Anorectal abscess-fistulae. Surg Clin North Am. Dec 1994;74(6):1293-308. [Medline].
- Ross ST. Fistula in ano. Surg Clin North Am. Dec 1988;68(6):1417-26. [Medline].
- Sainio P. Fistula-in-ano in a defined population. Incidence and epidemiological aspects. Ann Chir Gynaecol. 1984;73(4):219-24. [Medline].
- Sangwan YP, Rosen L, Riether RD, Stasik JJ, Sheets JA, Khubchandani IT. Is simple fistula-in-ano simple?. Dis Colon Rectum. Sep 1994;37(9):885-9. [Medline].
- Seow-Choen F, Nicholls RJ. Anal fistula. Br J Surg. Mar 1992;79(3):197-205. [Medline].
- Topstad DR, Panaccione R, Heine JA, Johnson DR, MacLean AR, Buie WD. Combined seton placement, infliximab infusion, and maintenance immunosuppressives improve healing rate in fistulizing anorectal Crohn's disease: a single center experience. Dis Colon Rectum. May 2003;46(5):577-83. [Medline].
- Weisman RI, Orsay CP, Pearl RK, Abcarian H. The role of fistulography in fistula-in-ano. Report of five cases. Dis Colon Rectum. Feb 1991;34(2):181-4. [Medline].
Fistula-in-Ano excerpt Article Last Updated: Nov 9, 2007
|
