Anal Fistulotomy
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Anorectal abscess, which can be an incapacitating condition, originates from a cryptoglandular infection in the anal canal. Anal fistula, or fistula-in-ano, is a persistent, abnormal tract from the anal canal to the perianal skin; it is estimated to occur in 50% of patients with anorectal abscess. [1]
Anal fistulae are hollow tracts lined with granulation tissue connecting a primary (internal) opening inside the anal canal to a secondary (external) opening in the perianal skin. Obstruction of anal crypt glands leads to suppuration, which then forms a tract into an anorectal space; the direction taken determines the anorectal abscess location and hence the type of fistula. To understand the different types of anal fistulae (see Technical Considerations), clinicians must be familiar with the different anorectal spaces from which abscesses arise (see the image below).
Whereas treating an abscess can be rather straightforward, treating an anorectal fistula can be difficult for the surgeon and frustrating for the patient. Treatment of anorectal fistulae also varies according to the location, severity, and chronicity of the fistula tract.
All anal fistulae should be treated surgically. The goal of treatment is to obliterate the internal fistulous opening, including associated epithelialized tracts, with minimal sphincter division (preservation of sphincter function) and prevention of recurrence.
The type of procedure performed depends on the type of fistula (see Technical Considerations). Thus, the first step in surgical treatment is to identify the anatomy, including the external and internal opening, and define the course of all tracts relative to the sphincter muscles. This maneuver almost always requires that the patient be anesthetized. The external opening is usually more apparent, and identifying the internal opening can be challenging.
Many principles and maneuvers have been devised to assist in this task, including the Goodsall rule, which is as follows (see the image below):
According to the literature, Goodsall’s rule accurately predicts the location of the internal opening in 49-81% of patients. [2] The external opening location can be a poor predictor of fistula location in patients with long fistula tracts, recurrent fistulae, or Crohn disease. [3, 4, 5]
All symptomatic anorectal fistulae require anal fistulotomy. The only exceptions are in patients with Crohn disease. The primary treatment for perianal Crohn fistulae is medical (eg, immunologic agents), and surgery is reserved for control of perianal sepsis, where less (eg, placement of draining setons) is more. [6]
Anatomy of anal canal and surrounding structures
A solid knowledge of the anatomy of the anal canal, the perirectal tissues, and the sphincteric muscles is a prerequisite for any operative treatment of anal fistula.
The surgical anal canal, which is approximately 2-4 cm long, is located between the anorectal ring (a palpable convergence of the internal sphincter, the deep external sphincter, and the puborectalis) superiorly and extends inferiorly to the anal verge (the junction of the anal canal and the hair-bearing keratinized perineal skin). The lining of the anal canal is composed of columnar cells, transitional epithelium, and non-hair-bearing squamous epithelium.
The anal canal is surrounded by two layers of funnel-shaped musculature. The inner muscular structure is the internal anal sphincter, which is the lowermost continuation of the inner, circular muscle layer of the rectum and is under involuntary control. The outer musculature is formed by the puborectalis (innermost fibers of the levator ani) and the external anal sphincter. The external anal sphincter has three parts—subcutaneous, superficial, and deep—and is under voluntary control.
The dentate line, which is about 1-2 cm proximal to the anal verge or the midportion of the anal canal, is the embryologic fusion point between endoderm and ectoderm and marks a separation between innervation, arterial-venous blood supply, and lymphatic drainage. At the level of the dentate line there exists a cryptoglandular complex, consisting of four to eight apocrine anal glands from the intersphincteric space that empty via anal ducts through the internal anal sphincter into the anal canal.
The intersphincteric groove is the space between the internal and external anal sphincters. It can be palpated approximately 1 cm below the dentate line near the level of the anal verge. The anal margin is outside of the anal verge, and is characterized by radial skin folds, thicker skin, pigmentation, and skin with adnexal tissues.
For more information about the relevant anatomy, see Anal Canal Anatomy.
Classification of fistula types
The Parks classification system, which describes the fistula tracts in relation to the anal sphincter complex, defines the following four types of fistula-in-ano resulting from cryptoglandular infections [7] :
Intersphincteric fistulae (see the image below) account for about 70% of all anal fistulae; they usually result from a perianal abscess. The tract extends via the internal sphincter to the intersphincteric space and then out to the perineum. No external sphincter is involved. Other possible tracts include a blind tract with no perineal opening and a high tract to the lower rectum or pelvis.
Transsphincteric fistulae (see the image below) account for about 25% of all anal fistulae; they usually arise from an ischioanal abscess. The tract traverses both internal and external sphincters and passes into the ischiorectal fossa and then to the perineum. Other possible tracts include a high tract with perineal opening and a high blind tract.
Suprasphincteric fistulae (see the image below) account for about 5% of all anal fistulae; they usually result from a supralevator abscess. The tract arises in the intersphincteric space and courses superiorly above the puborectalis into the ischiorectal fossa and then to the perineum.
Extrasphincteric fistulae (see the image below) account for only about 1% of all anal fistulae. Causes include iatrogenic injury from probing or penetrating injury to the perineum or rectum, Crohn disease, and carcinoma (or treatment thereof). The tract passes from the rectum above the levators and through the levator ani muscles to the perianal skin completely outside the sphincter mechanism.
Additionally, anal fistulae can be classified as either simple or complex, as follows [5] :
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Vassiliki Liana Tsikitis, MD, MCR, FACS, FASCRS Associate Professor of Surgery, Medical Director of Digestive Health Center, Department of Surgery, Division of Gastrointestinal and General Surgery, Oregon Health and Science University School of Medicine
Vassiliki Liana Tsikitis, MD, MCR, FACS, FASCRS is a member of the following medical societies: Alpha Omega Alpha, American College of Surgeons, American Society of Clinical Oncology, American Society of Colon and Rectal Surgeons, Association for Academic Surgery, European Society of Coloproctology, International Society for Digestive Surgery, International Society of Surgery, Pacific Coast Surgical Association, Society for Surgery of the Alimentary Tract, SWOG
Disclosure: Nothing to disclose.
Ragavan V Siddharthan, MD General Surgery Resident, Department of Surgery, Oregon Health and Science University
Ragavan V Siddharthan, MD is a member of the following medical societies: American College of Surgeons
Disclosure: Nothing to disclose.
Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Nothing to disclose.
Kurt E Roberts, MD Assistant Professor, Section of Surgical Gastroenterology, Department of Surgery, Director, Surgical Endoscopy, Associate Director, Surgical Skills and Simulation Center and Surgical Clerkship, Yale University School of Medicine
Kurt E Roberts, MD is a member of the following medical societies: American College of Surgeons, Society of American Gastrointestinal and Endoscopic Surgeons, Society of Laparoendoscopic Surgeons
Disclosure: Nothing to disclose.
Kurt E Roberts, MD Assistant Professor, Section of Surgical Gastroenterology, Department of Surgery, Director, Surgical Endoscopy, Associate Director, Surgical Skills and Simulation Center and Surgical Clerkship, Yale University School of Medicine
Kurt E Roberts, MD is a member of the following medical societies: American College of Surgeons, Society of American Gastrointestinal and Endoscopic Surgeons, Society of Laparoendoscopic Surgeons
Disclosure: Nothing to disclose.
Nicole EK Wieghard, MD Resident Physician, Department of Surgery, Oregon Health and Science University School of Medicine
Nicole EK Wieghard, MD is a member of the following medical societies: Alpha Omega Alpha, American College of Surgeons, Association of Women Surgeons
Disclosure: Nothing to disclose.
The authors and editors of Medscape Drugs & Diseases thank Francisco Javier Reyes Martin, MD, Resident Physician, Department of Surgery, University of Arizona College of Medicine, for his contributions to an earlier version of this topic.
Anal Fistulotomy
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