You are in: eMedicine Specialties > General Surgery > Colorectal Perianal AbscessArticle Last Updated: Mar 3, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Andre Hebra, MD, Chief, Division of Pediatric Surgery, Medical University of South Carolina Andre Hebra is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American College of Surgeons, American Medical Association, American Pediatric Surgical Association, Association for Academic Surgery, Society of Laparoendoscopic Surgeons, South Carolina Medical Association, Southeastern Surgical Congress, and Southern Medical Association Coauthor(s): Patrick B Thomas, MD, Fellow, Department of Pediatric Surgery, Texas Children's Hospital Editors: Marc D Basson, MD, PhD, Chief of Surgery, John D Dingell VA Medical Center; Professor, Department of Surgery, Wayne State University School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Amy L Friedman, MD, Professor of Surgery, Director of Transplantation, State University of New York Upstate Medical University College of Medicine, Syracuse; 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: anal abscess, perianal abscess, anorectal abscess, ischiorectal abscess, perianal fistula, digital rectal examination, DRE, rectal pain INTRODUCTIONSection 2 of 12
  Perianal abscess represents an infection of the soft tissues surrounding the anal canal, with formation of a discrete abscess cavity. The severity and depth of the abscess are quite variable, and the abscess cavity is often associated with formation of a fistulous tract. For that reason, both perianal abscess and perianal fistula are discussed in this article. For excellent patient education resources, visit eMedicine's Esophagus, Stomach, and Intestine Center. Also, see eMedicine's patient education articles Anal Abscess and Rectal Pain. ProblemAnorectal abscesses originate from infection arising in the cryptoglandular epithelium lining the anal canal. The internal anal sphincter is believed to serve normally as a barrier to infection passing from the gut lumen to the deep perirectal tissues. This barrier can be breached through the crypts of Morgagni, which can penetrate through the internal sphincter into the intersphincteric space. Once infection gains access to the intersphincteric space, it has easy access to the adjacent perirectal spaces. Extension of the infection can involve the intersphincteric space, ischiorectal space, or even the supralevator space. In some instances, the abscess remains contained within the intersphincteric space. The variety of anatomic sequelae of the primary infection is translated into variable clinical presentations. FrequencyThe peak incidence of anorectal abscesses is in the third to fourth decades of life. Men are affected more frequently than women, with a male-to-female predominance of 2:1 to 3:1. Approximately 30% of patients with anorectal abscesses report a previous history of similar abscesses that either resolved spontaneously or required surgical intervention. A higher incidence of abscess formation appears to correspond with the spring and summer seasons. While demographics point to a clear disparity in the occurrence of anal abscesses with respect to age and sex, no obvious pattern exists among various countries or regions of the world. Although suggested, a direct relationship between bowel habits, frequent diarrhea, and poor personal hygiene and the formation of anorectal abscesses remains unproved. The occurrence of perianal abscesses in infants also is quite common. The exact mechanism is poorly understood but does not appear to be related to constipation. Fortunately, in infants this condition is quite benign and rarely requires any operative intervention other than simple drainage. EtiologyPerirectal abscesses and fistulas represent anorectal disorders arising predominately from the obstruction of anal crypts. Infection of the now static glandular secretions results in suppuration and abscess formation within the anal gland. The abscess typically forms initially within the intersphincteric space and then spreads along adjacent potential spaces. PathophysiologyPerirectal abscesses and fistulas represent anorectal disorders that arise predominately from the obstruction of anal crypts. Normal anatomy demonstrates anywhere from 4-10 anal glands drained by respective crypts at the level of the dentate line. Anal glands normally function to lubricate the anal canal. Obstruction of anal crypts results in stasis of glandular secretions and, when subsequently infected, suppuration and abscess formation within the anal gland results. The abscess typically forms in the intersphincteric space and can spread along various potential spaces. Common organisms implicated in abscess formation include Escherichia coli, Enterococcus species, and Bacteroides species; however, no specific bacterium has been identified as a unique cause of abscesses. Less common causes of anorectal abscess that must be considered in the differential diagnosis include tuberculosis, cancer, Crohn disease, trauma, leukemia, and lymphoma. ClinicalThe classic locations of anorectal abscesses listed in order of decreasing frequency are as follows: perianal 60%, ischiorectal 20%, intersphincteric 5%, supralevator 4%, and submucosal 1% (see Media file 1). Clinical presentation correlates with the anatomical location of the abscess. Patients with perianal abscesses typically complain of dull perianal discomfort and pruritus. Their perianal pain often is exacerbated by movement and increased perineal pressure from sitting or defecation. Physical examination demonstrates a small, erythematous, well-defined, fluctuant, subcutaneous mass near the anal orifice. Patients with ischiorectal abscesses often present with systemic fevers, chills, and severe perirectal pain and fullness consistent with the more advanced nature of this process. External signs are minimal and may include erythema, induration, or fluctuance. On digital rectal examination (DRE), a fluctuant indurated mass may be encountered. Optimal physical assessment of an ischiorectal abscess may require anesthesia to alleviate patient discomfort that would otherwise limit the extent of the examination. Patients with intersphincteric abscesses present with rectal pain and exhibit localized tenderness on DRE. Physical examination may fail to identify an intersphincteric abscess. Though rare, supralevator abscesses present a similar diagnostic challenge. As a result, clinical suspicion of an intersphincteric or supralevator abscess may require confirmation by CT scan, MRI, or anal ultrasonography. The latter is limited to confirming the presence of an intersphincteric abscess. INDICATIONSSection 3 of 12
As a rule, the presence of an abscess is an indication for incision and drainage. Watchful waiting while administering antibiotics is inadequate. RELEVANT ANATOMYSection 4 of 12
Classification of anorectal abscess Abscesses are classified based on their anatomical location. The most commonly described locations are perianal, ischiorectal, intersphincteric, and supralevator. Media file 1 illustrates the different anatomical locations of anorectal abscesses. Perianal abscesses represent the most common type of anorectal abscesses, accounting for approximately 60% of reported cases. These superficial collections of purulent material are located beneath the skin of the anal canal and do not transverse the external sphincter. The next most common types of abscesses in descending order of frequency are ischiorectal, intersphincteric, and supralevator. An ischiorectal abscess forms when suppuration transverses the external sphincter into the ischiorectal space. Intersphincteric abscesses result from suppuration contained between the internal and external anal sphincters. A supralevator abscess results either from suppuration extending cranially through the longitudinal muscle of the rectum from an origin in the intersphincteric space to reach above the levators or as a result of primary disease in the pelvis (eg, appendicitis, diverticular disease, gynecological sepsis). Horseshoe abscesses, while rare, result from circumferential infiltration of pus within the intersphincteric planes. The Goodsall rule for perianal fistulas The Goodsall rule states that the external opening of a fistulous tract located anterior to a transverse line drawn across the anal verge is associated with a straight radial tract of the fistula into the anal canal/rectum. Conversely, an external opening posterior to the transverse line follows a curved fistulous tract to the posterior midline of the rectal lumen. This rule is important for planning surgical treatment of the fistula (see Media files 2-3). CONTRAINDICATIONSSection 5 of 12
Clinical suspicion of anorectal abscess warrants aggressive identification and surgical drainage. Delayed surgical intervention results in chronic tissue destruction, fibrosis, stricture formation, and may impair anal continence. Delayed incision and drainage of an anorectal abscess is contraindicated. WORKUPSection 6 of 12
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TREATMENTSection 7 of 12
Medical therapyIn most patients with anorectal abscess, adjuvant medical therapy with antibiotics generally is not necessary. The presence of a systemic inflammatory response, diabetes, or immunosuppression justifies concomitant use of antibiotics. Surgical therapyTreatment of anorectal abscesses involves early surgical drainage of the purulent collection. Primary antibiotic therapy alone is ineffective in resolving the underlying infection and simply postpones surgical intervention. Any delay in surgical drainage of anorectal abscesses prolongs infection, augments tissue damage, may impair sphincter continence function, and may promote stricture and/or fistula formation. The ability to drain an anorectal abscess depends on location, patient comfort, and accessibility of the abscess. Drainage of perianal or superficial abscesses usually can be accomplished in the office or emergency department using local anesthetics. A small incision is made over the area of fluctuance in close proximity to the anal verge. Pus is collected and sent for culture. Hemostasis is achieved with manual pressure, and the wound is packed with iodophor gauze. The gauze is removed after 24 hours, and the patient is instructed to take sitz baths 3 times a day and after bowel movements. Postoperative analgesics and stool softeners are prescribed to relieve pain and prevent constipation. The patient typically will follow up with his/her physician in 2-3 weeks for wound evaluation and inspection for possible fistula in ano. A potential complication of anorectal abscess drainage is the formation of fistulous tracts. Management of fistulas will be addressed later in this review. The type of organism cultured from an anorectal abscess is an important predictor of fistula formation following surgical incision and drainage. Underlying anal fistulas are present in 40% of abscess cultures positive for intestinal bacteria; however, cultures growing Staphylococcus species are associated with perianal skin infections and typically have no subsequent risk of developing anal fistulas. Treatment of ischiorectal, intersphincteric, and supralevator abscesses is performed best under general or regional anesthesia. In the case of ischiorectal abscess, a cruciate incision is made at the site of maximal swelling. Pus is drained and cultured. The ischiorectal fossa is probed with a finger or hemostat to disrupt loculations and facilitate drainage. Placement of a drain only is indicated for management of complex or bilateral abscesses. To drain an ischiosphincteric abscess, a transverse incision is made within the anal canal below the dentate line posteriorly. The intersphincteric space is identified, and the plane between the internal and external sphincters is exposed. The abscess is opened to allow drainage, and a small mushroom catheter is sutured in situ to assist drainage and prevent premature wound closure. Location and etiology will determine the drainage technique of supralevator abscesses. Failure to manage supralevator abscesses with consideration of the primary etiology may result in iatrogenic fistula formation. Evaluation with MRI or CT scan can exclude intra-abdominal or pelvic pathology as possible sources. If the supralevator abscess evolved from the extension of an ischiorectal abscess, external drainage through the ischiorectal fossa is indicated. If the abscess resulted from an upward extension of an intersphincteric abscess, appropriate drainage is created through the rectal mucosa. In cases of posterior supralevator abscess collections, a transverse incision is made in the posterior anal canal below the dentate line. The dissection extends from the intersphincteric plane through the puborectalis sling into the posterior anal space. A mushroom catheter then is sutured in place to ensure adequate drainage. Anterior supralevator abscesses are superficial and more common in women. Surgical drainage may be approached using an anteriorly directed transanal incision or by a transvaginal approach entering the posterior cul-de-sac. A mushroom catheter is placed to ensure adequate drainage of the abscess collection. Patients with systemic signs of toxicity are admitted to the hospital and treated with intravenous antibiotics. If the patient does not improve clinically over the next 24-48 hours, reevaluation of the supralevator abscess by CT scan or reoperation may be indicated. In the face of recurrent, severe supralevator abscesses, some patients may require a diverting colostomy for optimal management. Preoperative detailsBecause of the acute nature of anorectal abscesses, preoperative bowel preparation is not possible and typically is unnecessary. Intraoperative detailsDecisive management of anal fistulas relies on therapeutic interventions. Healing rarely is spontaneous, and failure to achieve adequate treatment often results in recurrent abscess, persistent drainage, and even malignancy. The main paradigms to follow in the management of anorectal fistulas include the following: determine the anatomy of the fistula, provide adequate drainage, eradicate the fistula tract, prevent recurrence, and preserve sphincter function. Preservation of sphincter function relies on maintaining integrity of the anorectal ring. Once the external opening of the anorectal fistula has been identified and the surrounding tissue palpated, probing of the fistula tract is warranted. Aggressive probing of the fistula is discouraged to prevent formation of false channels. Using a blunt probe (eg, a small lachrymal probe), the internal origin of a primary fistula can be identified in the majority of cases. When searching for the opening within the anal canal of a fistulous tract the Goodsall rule is an excellent guideline. This rule states that an external opening anterior to a transverse line drawn across the anal verge is associated with a straight radial tract into the canal. An external opening posterior to the transverse line follows a curved fistulous tract to the posterior midline rectal lumen. Horseshoe fistulas occasionally are associated with both anterior and posterior openings within the anal canal. Treatment options for the management of fistulas are aimed at providing definitive therapy while minimizing the morbidity of the procedure. For example, 2 widely accepted treatment interventions include fistulectomy and fistulotomy. Studies have demonstrated that removal of the entire fistula tract along with the surrounding scar tissue (ie, fistulectomy) unnecessarily results in a larger wound, prolonged healing time, and higher risks of incontinence. As a result, the more conservative approach of unroofing the tract without excision of all surrounding tissue (fistulotomy) usually is preferred and decreases the risks of incontinence and fistula recurrence, as well as shortens wound healing time. A fistulectomy is performed as a primary procedure for superficial fistulas that require minimal dissection of the fistula from the surrounding sphincter musculature. In contrast, simple fistulotomy for repair of high-level fistulas is contraindicated as the primary treatment. Use of loose Setons is warranted in high-level fistulas (ie, trans-sphincteric and suprasphincteric) to reduce the risk of incontinence or in cases in which poor wound healing is anticipated. A Seton is a nonabsorbable nylon or silk suture that is guided through the fistula tract and tied exteriorly to maintain suture placement within the tract and to cause compression of the tract. The ischemic compression by the Seton and the local inflammatory reaction of adjacent tissues initiates fibrosis. Once fibrosis of the surrounding tissue develops, it helps maintain the integrity of the sphincter musculature during subsequent fistulotomy. Setons often are used in patients with fistulas secondary to inflammatory bowel disease (IBD). In addition, the Seton allows epithelialization of the fistulous tract, thereby preventing secondary closure and facilitating drainage of abscesses. Another commonly used type of Seton is the cutting Seton, which can be used to gradually transect the anal sphincter musculature underlying the fistula by externally tightening the suture to induce pressure necrosis. Typically, retightening the Seton over a period of several days is necessary (this can be performed in the outpatient setting). The cutting Seton may eliminate the need for subsequent fistulotomy. While the cutting Seton is used as an effective therapeutic option for high-level fistulas, it is contraindicated in patients with IBD. Postoperative detailsPostoperatively, administer analgesics for pain, stool bulking agents, and stool softeners to prevent constipation. Follow-up evaluation of an incised anorectal abscesses is important to assess not only adequate healing but also the potential development of anorectal fistulas. The patient typically will follow up with his/her physician in 2-3 weeks for wound evaluation and inspection for possible fistula in ano. Antibiotics are used in adjunct to surgical therapy for patients with comorbidities such as diabetes, valvular heart disease, or immunodeficiencies. Follow-upThe patient typically will follow up with his/her physician in 2-3 weeks for wound evaluation and inspection for possible fistula in ano. COMPLICATIONSSection 8 of 12
Anorectal fistulas Anorectal fistulas occur in 30-60% of patients with anorectal abscesses. The intersphincteric glands lie between the internal and external anal sphincters and are associated most commonly with abscess formation. Anorectal fistulas arise through obstruction of anal crypts and/or glands and are identified by purulent drainage from the anal canal or from the surrounding perianal skin. Other etiologies of anorectal fistulas are multifactorial and include diverticular disease, IBD, malignancy, and complicated infections such as tuberculosis and/or actinomycosis. The Parks classification system defining the 4 major types of anorectal fistulas in order of decreasing frequency is as follows: intermuscular (70%), trans-sphincteric (23%), extrasphincteric (5%), and suprasphincteric (2%). The intersphincteric fistula is found between internal and external sphincters. The trans-sphincteric fistula extends through the external sphincter into the ischiorectal fossa. An extrasphincteric fistula passes from rectum to skin through the levator ani. Lastly, the suprasphincteric fistula spans from the intersphincteric plane through the puborectalis muscle, exiting the skin after traversing the levator ani. The Goodsall rule states that an external opening of a fistulous tract anterior to a transverse line drawn across the anal verge is associated with a straight radial tract of the fistula into the anal canal/rectum. Conversely, an external opening posterior to the transverse line demonstrates a curved fistulous tract to the posterior midline rectal lumen. This rule is important for the planning of surgical treatment of the fistula, and it is illustrated in Media files 2-3. OUTCOME AND PROGNOSISSection 9 of 12
Approximately two thirds of patients with rectal abscesses treated by incision and drainage or by spontaneous drainage will develop a chronic anal fistula. The recurrence rate of anorectal fistulas after fistulotomy, fistulectomy, or use of a Seton is about 1.5%. The overall incidence of major fecal incontinence after surgical management of complex suprasphincteric fistulas is estimated at approximately 7%. FUTURE AND CONTROVERSIESSection 10 of 12
Some surgeons advise performing a complementary colostomy to facilitate management of complex anal fistulas. This may be of some benefit in selected cases, but the perirectal infection may continue despite a diverting colostomy. Adequate drainage of the abscess is the most important factor in controlling progressive perirectal infection. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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