Anorectal Abscesses


Anorectal Abscesses

  1. Anatomic Spaces
    • perianal space: surrounds the anus, continuous with the fat of the buttocks
    • intersphincteric space: separates the internal and external sphincters, is continuous with the perianal space, extends cephalad into the rectal wall
    • ischiorectal space: lateral and posterior to the anus
    • deep postanal space: between the levator ani and anococcygeal ligament, connects the two ischiorectal spaces posteriorly
    • supralevator space: lies above the levator ani

    Anorectal Spaces
  2. Pathophysiology
    • the infection originates from an obstructed anal crypt, which communicates with the body of an anal gland which lies in the intersphincteric plane
    • initial result of an infected anal gland is an intersphincteric abscess
    • as this abscess enlarges, it may spread in one of several directions
    • if the pus spreads downwards to the anal margin (the most common route), then a perianal abscess results
    • if the infection spreads horizontally across the external sphincter, then an ischiorectal abscess results
    • if the infection remains in the intersphincteric plane, then an intersphincteric abscess results
    • vertical spread upwards across the levator muscle results in a supralevator abscess (least common route)
    • an abscess that forms posterior to the anal canal may extend into one or both ischiorectal or supralevator spaces (horseshoe abscess)
    • all abscesses other than a perianal abscess are termed perirectal abscesses
    • ~50% of anorectal abscesses will result in a chronic fistula that connects the anal gland with the skin overlying the drainage site

    Anorectal Abscesses
  3. Clinical Manifestations
    • severe anal pain is the most frequent symptom
    • pain is constant and not associated with bowel movements
    • fever is common
    • occasionally, a patient will present with sepsis (diabetics)
    • a fluctuant mass is usually visible for perianal and ischiorectal abscesses
    • intersphincteric abscesses may not cause visible perianal skin changes, but they can be palpated on rectal exam as a painful fluctuant mass protruding into the lumen

    1. Supralevator Abscess
      • can be difficult to diagnose since some patients may have only minimal discomfort and no external manifestations
      • other patients may have perianal pain and fever
      • a palpable mass or area of induration may be felt on rectal exam above the anal ring
      • may also originate from an intraabdominal source
      • CT scan is often necessary to make the diagnosis

      Anorectal Spaces
      Supralevator Abscess

  4. Treatment
    1. Perianal Abscess
      • requires incision and drainage with a cruciate-type incision
      • incision should be placed as close to the anal verge as possible to minimize the length of a future fistula
      • no need to perform immediate fistulotomy
      • wound packing is not necessary postop
      • antibiotics are usually not necessary unless the patient is febrile, diabetic, or immunocompromised

    2. Ischiorectal Abscess
      • abscess cavity is often large
      • usually drained through a cruciate type incision
      • all loculations must be broken up digitally
      • no evidence that wound packing reduces the incidence of recurrence or fistula formation

    3. Intersphincteric Abscess
      • should be drained into the anal canal by performing an internal sphincterotomy below the dentate line
      • abscess cavity is left open to drain
      • sitz baths postop will keep the wound clean

    4. Supralevator Abscess
      • CT scan prior to drainage is helpful to rule out an abdominal source
      • should be drained internally (transanally) by incising the rectal wall overlying the abscess
      • should not be drained externally because a supralevator fistula may result that often requires a colostomy to heal

    5. Horseshoe Abscess
      • requires draining the deep postanal space
      • an incision is made midway between the coccyx and anus
      • the anococcygeal ligament must be divided at the posterior midline to adequately drain the abscess
      • counter incisions are made to drain the extensions into the ischiorectal spaces

      Horseshoe Abscess
      Horseshoe Abscess and Drainage

Anorectal Fistulas

  1. Pathophysiology
    • occurs in up to 50% of patients with a previous perianal abscess
    • the fistula tract is the epithelialized communication between the internal opening in the anal canal and the external opening through which the abscess was drained
    • Parks identified 4 major types of fistula that traverse the sphincter muscles: intersphincteric (45%), transphincteric (30%), suprasphincteric (20%), extrasphincteric (5%)
    • in addition, a superficial fistula that doesn’t involve the sphincter muscles exists

    Parks Classification of Anorectal Fistulas
  2. Clinical Manifestations
    • patients present with persistent purulent drainage from the external opening

  3. Diagnosis
    • successful treatment requires identification of the internal opening and the course of the fistula tract – this is best done in the operating room as an exam under anesthesia
    • a blunt probe should be carefully passed through the external opening to identify the course of the tract and the internal opening, taking care not to create a false passage
    • if the internal opening is not apparent, then hydrogen peroxide may be injected through the external opening while looking for the bubbles in the anal canal to identify the internal opening
    • Goodsall’s rule can be of help when looking for the internal opening: anterior fistulas will connect to the internal opening by a short, direct tract; posterior fistulas follow a curved tract to the posterior midline
    • an exception to this rule occurs for anterior fistulas that have an external opening 3 cm or more from the anal verge - these fistulas tend to have an internal opening in the posterior midline

    Goodsall's Rule
    Goodsall's Rule

  4. Initial Management
    • dependent on identifying the internal and external openings, the course of the track, and the amount of sphincter muscle involved

    1. Simple Fistulas
      • majority of cases (90%)
      • superficial fistulas, transphincteric fistulas below the anal ring, intersphincteric fistulas

      1. Fistulotomy
        • contraindicated if the patient has preexisting incontinence
        • a probe is passed from the internal opening to the external opening, and the tract is completely opened up and curetted
        • some surgeons marsupialize the tract to promote healing
        • cure rate is 90%
        • incontinence rate is minimal in properly selected patients

        Anorectal Fistulotomy
    2. Complex Fistulas
      • cannot be treated by simple fistulotomy because of the risk of incontinence
      • suprasphincteric and extrasphincteric fistulas
      • fistulas proximal to the dentate line
      • any fistula involving >30% of the external sphincter
      • complicated fistulas (Crohn’s disease, HIV, radiation)
      • anterior fistulas in women
      • preexisting incontinence

      1. Drainage Seton
        • should be the first step in a patient with a complex fistula
        • used to encircle the tract and provide drainage of the septic process before definitive surgery
        • promotes fibrosis and maturation of the tract
        • can provide long-term control of anorectal sepsis in Crohn’s patients with multiple fistula tracts
        • silastic vessel loops are ideal for draining setons

        Drainage Seton
  5. Definitive Management of Complex Fistulas
    1. Cutting Setons
      • used to gradually transect the fistula tract on the leading edge of the seton while allowing scarring on the trailing edge
      • must divide the skin and subcutaneous tissue between the two openings
      • goal is to preserve sphincter continuity and preserve continence
      • tightened at regular intervals (every 2 weeks)
      • cure rates are high, but incontinence is a major risk (30%)

    2. Advancement Flaps
      • used as an alternative to a cutting seton
      • performed in high transphincteric fistulas or persistent fistulas
      • internal opening is excised
      • a flap of mucosa, submucosa, and superficial circular muscle is created for 4 – 6 cm proximal to the internal opening to allow for a tension-free closure
      • the external opening is widened and curetted
      • success rates reported to be 75% - 98%

      Anorectal Fistula Advancement Flap
    3. Fibrin Glue
      • advantages include no risk of incontinence and repeatability
      • drainage seton is usually placed first to drain any infection
      • sealant is injected through the external opening into the internal opening
      • success rates are poor (14% - 69%)

    4. Fistula Plug
      • bioprosthetic plug serves as a matrix for tissue ingrowth and to obliterate the fistula tract
      • plug is inserted from the internal opening to the external opening
      • no risk of incontinence
      • healing rates are < 50%

    5. Ligation of the Intersphincteric Fistula Tract (LIFT)
      • ideal for transphincteric fistulas with mature tracts (prior seton drainage)
      • internal and external sphincters are separated in the intersphincteric space
      • fistula tract is identified, ligated proximally and distally, and then divided
      • success rates reported between 57% - 89%

      Ligation Intersphincteric fistula Tract (LIFT)

Anal Fissures

  1. Pathogenesis
    • results from a tear in the anoderm
    • 90% occur in the posterior midline; 10% occur in the anterior midline
    • caused by local trauma, most often from a hard bowel movement
    • majority of patients with nonhealing fissures are found to have high anal sphincter pressures on anal manometry – this reduces perfusion of the anoderm and impairs healing

  2. Clinical Manifestations
    • tearing pain on defecation
    • blood on the toilet paper or stool is common
    • since the condition is so painful, an adequate examination may only be possible under anesthesia
    • anoscopy will demonstrate the fissure with the hypertrophied fibers of the internal sphincter visible at the base
    • associated findings include a ‘sentinel pile’ externally and an enlarged anal papilla internally
    • fissures in atypical locations should raise suspicions of Crohn’s disease or sexually transmitted diseases

    Acute and Chronic Anal Fissures
    Acute and Chronic Anal Fissures

  3. Management
    1. Medical Management
      • acute fissures will usually heal (90%) with stool softeners, bulking agents, and warm sitz baths
      • topical nitroglycerin or topical nifedipine have been used in chronic anal fissures to relax the internal sphincter, which promotes healing by improving blood flow to the anal canal
      • medical therapy is not as efficacious as surgery, but it is not associated with the risk of incontinence

    2. Surgical Management
      • reserved for patients who fail medical therapy

      1. Lateral Internal Sphincterotomy
        • procedure of choice for chronic fissures that have failed medical therapy
        • may be done with an open or closed technique
        • internal sphincter is completely divided, relieving the spasm
        • usually done on the right side between the anterior and posterior hemorrhoidal cushions
        • a concomitant fissurectomy may also be performed
        • healing occurs in 90% to 95%
        • minor incontinence (leakage of mucus or gas) occurs in 10% to 20%

        Lateral Internal Sphincterotomy
      2. Botulinum Toxin Injection
        • relaxes the hypertonic anal sphincter, which increases blood flow and improves healing in chronic fissures
        • risk of mild incontinence is low
        • recurrence rate is 40% - 50%
        • procedure may be repeated

      3. Fissurectomy
        • low recurrence rate and low risk of incontinence
        • often combined with other procedures

      4. Anal Advancement Flap
        • does not divide the internal sphincter
        • used in patients who are risk for incontinence after a sphincterotomy
        • also used to treat anal fistulas

        V-Y Advancement Flap for Anal Fissure






References

  1. Sabiston 20th ed., pgs 1402 – 1412
  2. Schwartz, 10th ed., pgs 1225 – 1232
  3. Cameron 11th ed., pgs 262 – 274
  4. UpToDate. Perianal and Perirectal Abscess. Ronald Bleday, MD. Feb 24, 2020. Pgs 1 – 27.
  5. UpToDate. Operative Management of Anorectal Fistulas. Bradley Champagne, MD, FACS, FASCRS. Dec 17, 2019. Pgs 1 – 32.
  6. UpToDate. Anal Fissure: Surgical Management. C. Neal Ellis, MD, FACS, FASCRS, FACG. Jun 24, 2019. Pgs 1 – 20.