Anorectal Abscess 

Updated: Jul 24, 2020
Author: Andre Hebra, MD; Chief Editor: John Geibel, MD, MSc, DSc, AGAF 



An anorectal abscess originates from an 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 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, fistulas are also discussed in this article where relevant.

The variety of anatomic sequelae of the primary infection is translated into variable clinical presentations. The relatively simple perianal abscess is to be distinguished from the more complex perirectal abscesses. Treatment also differs according to the type of abscess present.

For patient education resources, see the Esophagus, Stomach, and Intestine Center and the Digestive Disorders Center, as well as Anal Abscess, Rectal Pain, and Rectal Bleeding.


Normal anatomy demonstrates anywhere from four to 10 anal glands lying at the level of the dentate line, which divides the squamous epithelium distally and the columnar epithelium proximally. Obstruction of these anal glands by debris leads to stasis, bacterial overgrowth, and abscess formation that extends into the intersphincteric groove between the internal and external anal sphincters.[1] From this space, the abscess can spread along various potential spaces.

Anorectal abscesses are classified according to their anatomic location; the following are the most common locations (see the image below):

  • Perianal
  • Ischiorectal
  • Intersphincteric
  • Supralevator
Illustration of major types of anorectal abscesses Illustration of major types of anorectal abscesses (submucosal type not pictured).

Perianal abscesses represent the most common type of anorectal abscesses, accounting for approximately 60% of reported cases.[1, 2, 3, 4] These superficial collections of purulent material are located beneath the skin of the anal canal and do not transverse the external sphincter.

Ischiorectal abscesses are the next most common type. These abscesses form when suppuration transverses the external anal sphincter into the ischiorectal space. An ischiorectal abscess may traverse the deep postanal space into the contralateral side, forming a so-called horseshoe abscess.

Intersphincteric abscesses, the third most common type, result from suppuration contained between the internal and external anal sphincters. They may lie completely within the anal canal, leading to severe pain, and may only be found by digital rectal examination or anoscopy.

Supralevator abscesses, the least common of the four major types, may form from cephalad extension of the intersphincteric abscess above the levator ani or from caudal extension of a suppurative abdominal process (eg, appendicitis, diverticular disease, gynecologic sepsis) into the supralevator space. These abscesses may be diagnosed by means of computed tomography (CT), and they cause pelvic and rectal pain.

According to the widely used Parks classification system, anorectal fistulas may also be classified into four major types, as follows[5] :

  • Intersphincteric (70%) - Found between the internal and external sphincters
  • Transsphincteric (23%) - Extends through the external sphincter into the ischiorectal fossa
  • Extrasphincteric (5%) - Passes from the rectum to the skin through the levator ani
  • Suprasphincteric (2%) - Extends from the intersphincteric plane through the puborectalis, exiting the skin after traversing the levator ani

The characteristics of perianal fistulas vary according to their anatomic location. According to the Goodsall rule, 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, whereas an external opening posterior to the transverse line follows a curved, fistulous tract to the posterior midline of the rectal lumen (see the image below). This rule is important for planning surgical treatment of the fistula (see Treatment).

Goodsall rule for anorectal fistulas. Fistulas tha Goodsall rule for anorectal fistulas. Fistulas that exit in posterior half of rectum generally follow curved course toward posterior midline, whereas those that exit in anterior half of rectum usually follow radial course to dentate line.


Perirectal abscesses and fistulas represent anorectal disorders arising predominantly (~90% of cases) from the obstruction of anal crypts,[4]  possibly involving increased sphincter tone.[6]  Infection of the now static glandular secretions results in suppuration and abscess formation within the anal gland. Typically, the abscess forms initially in the intersphincteric space and then spreads along adjacent potential spaces.


Both aerobic and anaerobic bacteria have been found to be responsible for abscess formation. The anaerobes most commonly implicated are Bacteroides fragilis, Peptostreptococcus, Prevotella, Fusobacterium, Porphyromonas, and Clostridium. The aerobes most commonly implicated are Staphylococcus aureus, Streptococcus, and Escherichia coli.[7] More recent studies have noted community-acquired methicillin-resistant S aureus (MRSA) as a pathogen leading to abscess formation.[8, 9]

Approximately 10% of anorectal abscesses may be caused by reasons other than anal gland infection, including Crohn disease, trauma, immunodeficiency resulting from HIV infection or malignancy (both hematologic and anorectal cancer), tuberculosis, hidradenitis suppurativa, sexually transmitted diseases, radiation therapy, foreign bodies, perforated diverticular disease, inflammatory bowel disease, or appendicitis (a rare cause of supralevator abscesses).[1]


United States and international statistics

Approximately 30% of patients with anorectal abscesses report a previous history of similar abscesses that either resolved spontaneously or required surgical intervention.

The incidence of abscess formation appears to be higher in spring and summer. Whereas 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 it has been suggested that there is a direct relation between the formation of anorectal abscesses and bowel habits, frequent diarrhea, and poor personal hygiene, this relation remains unproven.

Age- and sex-related demographics

The peak incidence of anorectal abscesses is in the third and fourth decades of life.[10] These abscesses are also quite common in infants (see Anorectal Abscesses in Children). The exact mechanism is poorly understood but does not appear to be related to constipation. Fortunately, this condition is quite benign in infants, rarely necessitating any operative intervention other than simple drainage.[11]

Men are affected more frequently than women are, with a male-to-female predominance of 2:1 to 3:1.[10]


Overall mortality from anorectal abscesses is quite low.[2]

Early data indicated that abscess formation recurred in approximately 10% of patients, with chronic fistula-in-ano occurring in as many 50% of patients.[1, 2, 12] A later study found that 37% of patients developed chronic anal fistula or recurrent sepsis.[6] In this study, risk factors were age younger than 40 years and nondiabetic status; no difference in these complications was noted with regard to HIV status, sex, antibiotic usage, or smoking status.

Approximately two thirds of patients with rectal abscesses who are treated by incision and drainage or by spontaneous drainage will develop a chronic anal fistula. After fistula formation, multiple complications may develop after surgery. As many as 43% of patients may experience fecal incontinence after surgical repair for complex fistula-in-ano.[13] Other postoperative complications include temporary postejaculation urethral irritation and postoperative urinary retention.[14] Constipation may also occur as a result of pain on defecation.

The recurrence rate of anorectal fistulas after fistulotomy, fistulectomy, or the use of a seton is about 1.5%. The success rate of primary surgical treatment with fistulotomy appears to be fairly good.[15]




The classic locations of anorectal abscesses, listed in order of decreasing frequency, are as follows:

  • Perianal (60%)
  • Ischiorectal (20%)
  • Intersphincteric (5%)
  • Supralevator (4%)
  • Submucosal (1%)

The clinical presentation correlates with the anatomic location of the abscess (though it should be kept in mind that a perianal abscess sometimes is not an isolated superficial lesion but represents the point of a more involved perirectal abscess).

Almost all perirectal abscesses are associated with perirectal pain that is indolent in nature. Patients with a perianal abscess typically complain of dull perianal discomfort and pruritus. The pain often is exacerbated by movement and increased perineal pressure from sitting or defecation. Those with an ischiorectal abscess 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.

As many as 50% of patients with perirectal abscesses may present with swelling around the rectum, and as many as one quarter may present with rectal or perirectal drainage that may be bloody, purulent, or mucoid.[2, 4] These patients may also present with constipation, most likely due to pain on defecation, but the absence of constipation or even diarrhea does not rule out the diagnosis. Most of them report no history of fever or chills.

In many cases, these patients delay presentation to a physician, or they have already presented to a physician and have been given alternative diagnoses.[2, 4] Furthermore, complaints of abdominal pain are rare in these patients.

In addition to these symptoms, various case reports in the literature describe patients with perirectal abscesses who present with penile discharge, hip pain, or an ingested foreign body.[16, 17, 18]

Physical Examination

Patients with anorectal abscesses usually have normal vital signs on initial evaluation, with only 21% reporting fevers or chills. Physical examination demonstrates a small, erythematous, well-defined, fluctuant, subcutaneous mass near the anal orifice. On digital rectal examination (DRE), a fluctuant, indurated mass may be encountered. In one study, however, clinicians were unable to identify abscesses in 10% of patients on rectal examination; 4% of patients showed no signs of perirectal abscesses on initial examination.[2]

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 an intersphincteric abscess present with rectal pain and exhibit localized tenderness on DRE. Physical examination may fail to identify an intersphincteric abscess.

Although rare, supralevator abscesses present a similar diagnostic challenge. As a result, clinical suspicion of an intersphincteric or supralevator abscess may require confirmation by means of computed tomography (CT), magnetic resonance imaging (MRI), or anal ultrasonography (see Workup).

Digital examination with anesthesia can be helpful in certain cases, because patient discomfort can significantly limit physical assessment. For example, optimal evaluation for an ischiorectal abscess is performed in this manner. A fistula tract can be injected with peroxide solution at the time of examination under anesthesia in order to facilitate visualization of the internal opening of the fistula.


Complications of anorectal abscesses may include the following:

  • Fistula formation
  • Bacteremia and sepsis, including seeding of the infection to other areas by hematogenous spread
  • Fecal incontinence
  • Malignancy [19]

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. Fistulas arise through obstruction of anal crypts or glands and are identified by purulent drainage from the anal canal or from the surrounding perianal skin. Other potential causes of anorectal fistulas include diverticular disease, inflammatory bowel disease,[20] malignancy, and complicated infections (eg, tuberculosis or actinomycosis).





Approach Considerations

No specific laboratory studies are indicated in the evaluation of a patient with a perianal or anorectal abscess. Certain patients, such as individuals with diabetes and those who are immunocompromised, are at high risk for developing bacteremia and possibly sepsis, as a result of an anorectal abscess. In such cases, complete laboratory evaluation is important. Laboratory evaluation of the septic patient is not the focus of this article.

When an anorectal abscess is not obviously apparent but a high degree of clinical suspicion exists, imaging (eg, computed tomography [CT], ultrasonography, or magnetic resonance imaging [MRI]) may be necessary for the diagnosis. Plain films are of little utility for this purpose and should not be obtained unless other diagnoses are being considered.

Laboratory Studies

Many patients with perianal abscesses present as outpatients and need no laboratory blood tests; incision and drainage will be sufficient. For patients with such abscesses who present to the emergency department (ED) with no signs of systemic disease, this management strategy may be adequate, in that laboratory data will yield very little additional information of practical use.

In patients with suspected perirectal abscess or systemic disease, a complete blood count with differential may be obtained and may show leukocytosis or a left shift, but the absence of these findings does not preclude either of these entities. As many as 23% of patients with diagnosed perirectal abscesses have a normal temperature and a normal white blood cell count with a normal differential.[2]

Even though presumptive antibiotics are not required with routine incision and drainage of uncomplicated perianal abscesses,[21, 22] wound cultures should be collected in all patients in whom incision and drainage is performed; newer strains of bacteria (eg, methicillin-resistant S aureus) are being recognized as causes of perirectal abscesses,[8, 9] and recurrence rates are as high as 10%.[1] Blood cultures may be obtained but may have little to no diagnostic yield; one study reported no growth on blood cultures.[2]

CT, Ultrasonography, and MRI

Although imaging studies usually are not necessary in the evaluation of patients with an anorectal abscess (which will be perianal in the majority of cases), clinical suspicion of an intersphincteric or supralevator abscess may require confirmation by means of CT, anal ultrasonography, or MRI.[23, 24] As a rule, use of anal ultrasonography is limited to confirming the presence of an intersphincteric abscess, though this modality can also be used intraoperatively to help identify a difficult abscess or fistula.

CT is readily available in most EDs and is commonly used in the diagnosis of perirectal abscesses. In one retrospective study, CT for perirectal abscesses confirmed by surgical drainage yielded a sensitivity of 77%, with the false-negative scans being significantly more likely to come from immunocompromised patients.[25]

Although not readily used for this purpose in the ED, transperineal ultrasonography has shown good results for the detection of fistulous tracts and fluid collections in preoperative planning, with sensitivities ranging from 85%[26, 27, 28] to 100%[29] or the detection of surgically significant disease.

MRI is the criterion standard for imaging of perirectal abscesses; its 91% sensitivity makes it useful in preoperative planning.[30] In the ED, however, its use is restricted.


Evidence suggests that the use of endoscopic visualization (transrectal and transanal) is an excellent way of evaluating complex cases of perianal abscess and fistula. With the endoscopic technique, the extent and configuration of the abscess and fistulas can be clearly visualized. Endoscopic visualization has been reported to be as effective as fistulography.[31]

In experienced hands, endoscopic evaluation is the preferred diagnostic procedure in patients with perirectal pathology because of the low risk of bacterial dissemination and the low incidence of patient discomfort. Performing an endoscopic evaluation after nonsurgical treatment is also effective for documenting the patient’s response to therapy.



Approach Considerations

As a rule, the presence of an abscess is an indication for incision and drainage. Watchful waiting while administering antibiotics is inadequate. Clinical suspicion of anorectal abscess warrants aggressive identification and surgical incision and drainage. Delaying surgical intervention results in chronic tissue destruction, fibrosis, and stricture formation and may impair anal continence. Simple perianal abscesses may be treated in the emergency department (ED); more complex perirectal abscesses are treated by an experienced surgeon in an operating room.

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.

A patient with a perirectal abscess should be admitted to the surgical service unless other medical conditions or complications from the abscess necessitate a primary medical admission, with the surgeon acting as a consultant. Consider admitting a patient with a perirectal abscess to a medical service with the surgeon as a consultant should be considered if the patient is elderly, febrile, hypotensive, or immunocompromised or has significant comorbidities.

Transfer, if warranted, may be safely carried out if the patient is hemodynamically stable. Instability resulting from a concurrent condition or sepsis makes transfer to another institution inappropriate (and possibly illegal under the Emergency Medical Treatment and Active Labor Act [EMTALA]) unless transfer to allow delivery of a higher level of care is in the patient’s best interest.

Pharmacologic Therapy

The need for routine use of antibiotics in patients with anorectal abscesses has not been established; they have not been shown to improve healing times or reduce recurrence rates. In most of these patients, therefore, adjuvant medical therapy with antibiotics is considered unnecessary. However, concomitant use of antibiotics may be warranted in patients with conditions such as the following[1] :

  • Systemic inflammatory response or sepsis
  • Extensive cellulitis
  • Diabetes
  • Immunosuppression
  • Heart valve abnormalities or prostheses

Predisposing or comorbid factors may guide empiric antibiotic selection. If antibiotics are considered, the increasing prevalence of methicillin-resistant S aureus should be taken into account; according to a 2009 study, both vancomycin and trimethoprim-sulfamethoxazole provide excellent coverage.[9]

Surgical Intervention

Preparation for surgery

Because of the acute nature of anorectal abscesses, preoperative bowel preparation is not possible and typically is unnecessary.

Tetanus immunity status should be ascertained. When acceptable immunity cannot be established, the currently recommended guidelines for high-risk wounds should be followed.

Adequate analgesia before aspiration is mandatory. Lidocaine 2% with epinephrine injected subcutaneously over and around the periphery of the abscess and intramuscular (IM) or intravenous (IV) narcotics are recommended. Ethylene chloride spray applied to the suspected area immediately before aspiration may also help decrease the discomfort of aspiration. The cooling effect of ethylene chloride renders pain receptors temporarily unable to transmit pain signals to the cerebral cortex.

Conscious sedation is also an option if the physician is trained and prepared to manage the airway. If this route is taken, cardiac monitoring, pulse oximetry, and airway management equipment must be available, including suctioning devices, bag-valve-mask, and endotracheal intubation equipment. This technique should be used only by physicians highly skilled in cardiac and airway management.

Management of abscess

Treatment of anorectal abscesses involves early surgical drainage of the purulent collection.[32, 33, 34, 35, 36, 37, 38] Primary antibiotic therapy alone is ineffective in resolving the underlying infection and simply postpones surgical intervention. Any delay in surgical intervention prolongs infection and augments tissue damage, and it may impair sphincter continence function and promote stricture or fistula formation. The ability to drain an anorectal abscess depends on patient comfort and on the location and accessibility of the abscess.

When the abscess is perianal or superficial, drainage can usually be accomplished in the office or ED with local anesthesia. A small incision is made over the area of fluctuance; to shorten the length of any fistula that may form, the incision should be made as close to the anus as is compatible with safety.[1] Pus is collected and sent for culture. Hemostasis is achieved with manual pressure, and the wound is packed with iodophor gauze.

After 24 hours, the gauze is removed, and the patient is instructed to take sitz baths three times a day and after bowel movements. Postoperative analgesics and stool softeners are prescribed to relieve pain and prevent constipation. Typically, the patient follows up with the physician in 2-3 weeks for wound evaluation and inspection for possible fistula-in-ano. (A short fistula-in-ano coursing through a minimal amount of external sphincter is best treated with a fistulotomy.)

The formation of fistulous tracts (see below) is an important potential complication of anorectal abscess drainage. The type of organism cultured from an anorectal abscess is an important predictor of fistula formation after surgical incision and drainage. Underlying anal fistulas are present in 40% of abscess cultures that are positive for intestinal bacteria; however, cultures growing Staphylococcus species are associated with perianal skin infections and typically indicate that there is no risk of subsequent fistula formation.

Treatment of ischiorectal, intersphincteric, and supralevator abscesses typically requires general or regional anesthesia. To drain an 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 is indicated only for the management of complex or bilateral abscesses.

To drain an intersphincteric abscess, a transverse incision is made in 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.

The optimal drainage technique for a supralevator abscess is determined by the location and etiology of the lesion. Failure to take the primary etiology into account in the management of a supralevator abscess may lead to iatrogenic fistula formation. Evaluation with magnetic resonance imaging (MRI) or computed tomography (CT) 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 would be indicated. If the abscess resulted from an upward extension of an intersphincteric abscess, appropriate drainage would be 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 and into the posterior anal space. A mushroom catheter is then sutured in place to ensure adequate drainage.

Anterior supralevator abscesses are superficial and are more common in women than in men. Surgical drainage may be accomplished via an anteriorly directed transanal incision or by way of 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 IV antibiotics.

If the patient’s clinical condition does not improve over the following 24-48 hours, reevaluation of the supralevator abscess by means of CT or reoperation may be indicated. Some patients with recurrent, severe supralevator abscesses may require a diverting colostomy for optimal management.[39]

Management of fistula

Although the anal fistula has been reported since the time of Hippocrates, there is little systematic evidence to establish optimal management. Different treatment modalities have been evaluated in more than 400 reported trials. Approaches that have been researched include the following:

  • Fistulotomy versus fistulectomy
  • Seton treatment [40]
  • Marsupialization
  • Glue therapy
  • Anal flaps
  • Radiosurgical approaches
  • Fistulotomy/fistulectomy at time of abscess incision
  • Intraoperative anal retractors

Two reported meta-analyses compared incision and drainage alone with incision plus fistulotomy. Evidence suggests that after fistulotomy, marsupialization reduces bleeding and permits faster healing. Results from small trials indicate that healing rates after flap repair may be no worse than those after fistulotomy, though this has not yet been proved.[41] Failure rates may be higher when flap repair has been combined with fibrin glue treatment of fistulas.[42]

Radiofrequency fistulotomy results in less pain on the patient’s first postoperative day and may permit faster healing.[43] However, a great deal is not yet understood about surgical treatment of anal fistulas.[35]

Decisive 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
  • Preserve sphincter function (preservation depends on maintaining the integrity of the anorectal ring)

Once the external opening of the anorectal fistula has been identified and the surrounding tissue has been palpated, probing of the fistula tract is warranted. To prevent formation of false channels, aggressive probing is discouraged. By 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 one is searching for a fistula tract’s opening in the anal canal, 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, whereas an external opening posterior to the transverse line follows a curved fistulous tract to the posterior midline rectal lumen (see the image below). Horseshoe fistulas occasionally are associated with anterior and posterior openings in the anal canal.

Goodsall rule for anorectal fistulas. Note curved Goodsall rule for anorectal fistulas. Note curved nature of posterior fistulas and radial (straight) orientation of anterior fistulas.

Treatment options for the management of fistulas are aimed at providing definitive therapy while minimizing the morbidity of the procedure. For example, two widely accepted treatment interventions are fistulectomy (removing the entire fistula tract along with the surrounding scar tissue) and fistulotomy (unroofing the tract without excising all surrounding tissue).

Studies have demonstrated that fistulectomy results in a larger wound, prolonged healing time, and higher risks of incontinence. As a result, the more conservative procedure, fistulotomy, is usually preferred; it decreases the risk of incontinence and fistula recurrence and also shortens wound healing time. Fistulotomy 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 is contraindicated as primary treatment of high-level (ie, transsphincteric and suprasphincteric) fistulas. For high-level fistulas, the use of loose setons is warranted to reduce the risk of incontinence or in cases where poor wound healing is anticipated.

Setons may also be used as temporary initial intervention in the management of a fistula. A seton is a nonabsorbable nylon or silk suture that is guided through the fistula tract and tied exteriorly, in this way compressing and maintaining suture placement in the tract. A soft vessel loop may also be used for seton placement. The seton suture must be left in place for a prolonged period (weeks to months).

The ischemic compression created by the seton and the local inflammatory reaction of adjacent tissues initiate fibrosis. Once fibrosis of the surrounding tissue develops, it helps to 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, setons allow epithelialization of the fistulous tract, thereby preventing secondary closure and facilitating the 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, the seton must be retightened over a period of several days; this can be done in the outpatient setting. Use of a cutting seton may eliminate the need for subsequent fistulotomy. Whereas the cutting seton can be an effective therapeutic option for high-level fistulas, it is contraindicated in patients with IBD.

Other treatment modalities include resection with coverage by advancement tissue flaps (used for more complex cases) and placement of a bioprosthetic fistula plug (made of porcine submucosa). The plug technique is indicated in selected cases with long fistulous tracts; the success rate is variable (50-70%).

Patients with anal fissures can be treated with topical nifedipine gel and onabotulinumtoxinA injections. Occasionally, sphincterotomy (incision of the lateral internal anal sphincter) may be necessary.

Postoperative Care

Postoperatively, analgesics are given for pain, and stool bulking agents and stool softeners are given to prevent constipation. After appropriate wound care, patients may be discharged home with instructions for sitz baths and routine follow-up. Adequate outpatient analgesia (eg, codeine with acetaminophen or an oxycodone-containing compound) should be provided. Outpatient antibiotics may be indicated and are best chosen on the basis of culture and sensitivity testing of pathogens derived from the abscess.


Simple perianal abscesses can generally be managed in the ED. When the diagnosis of a more complex perirectal abscess is made or is being entertained, however, expeditious consultation with a surgeon is mandatory. Timely and appropriate operative treatment prevents more serious complications, such as extension of the abscess or serious systemic infection. Appropriate surgical treatment of perirectal abscess should not be undertaken in the ED. General or spinal anesthesia is necessary to obtain the optimal result.

Long-Term Monitoring

An otherwise healthy patient with a simple isolated perianal abscess may be treated in the ED with incision and drainage and released with timely follow-up care. If inpatient surgical treatment is required, surgical follow-up is necessary; acute abscesses recur in 10% of patients, and chronic fistula-in-ano may occur in as many as 50%.[1] Typically, the patient follows up with the physician in 2-3 weeks for wound evaluation and inspection for possible fistula-in-ano.

If any unusual symptoms arise, such as persistent pain or fever, patients should be advised to return immediately to the ED or to another provider.



Medication Summary

Antibiotics are unnecessary in otherwise healthy individuals. The practitioner should provide appropriate empiric intravenous (IV) antibiotic coverage for patients who are elderly or immunosuppressed, patients who have comorbidities, patients with a heart valve abnormality or prosthetic valve who are likely to benefit from antibiotic prophylaxis, and patients in whom infection has become systemic.

Analgesia is necessary for pain control and may be given orally (PO) or IV, in conjunction with anesthetics if needle aspiration or incision and drainage of an abscess are performed. Anxiolytics may help certain patients who are apprehensive about needle aspiration, incision and drainage, imaging studies, or surgery.


Class Summary

Appropriate IV antibiotic coverage should be provided preoperatively and postoperatively, either on the basis of Gram staining or on an empiric basis, as a preventive measure, for elderly patients, patients with immunosuppression, patients with a heart valve abnormality or prosthesis, and patients with comorbid states.

Ampicillin-sulbactam (Unasyn)

Ampicillin-sulbactam represents a combination of a beta-lactamase inhibitor with a penicillin. It interferes with bacterial cell-wall synthesis during active replication, causing bactericidal activity against susceptible organisms. It is used as an alternative to amoxicillin when a patient is unable to take medication PO. Ampicillin-sulbactam covers skin, enteric flora, and anaerobes; it is not ideal for nosocomial pathogens.

Imipenem-cilastatin (Primaxin)

Imipenem-cilastatin should be used empirically for more severely ill intensive care unit (ICU) patients. Pus or blood culture and sensitivity results, once available, should guide antibiotic selection. Predisposing and comorbid diseases may also guide empiric antibiotic selection.


Ampicillin, a broad-spectrum penicillin, interferes with bacterial cell-wall synthesis during active replication, causing bactericidal activity against susceptible organisms. It is used as an alternative to amoxicillin when a patient is unable to take medication PO. Patients with prosthetic heart valves who are at risk for endocarditis should receive IV prophylactic antibiotics before any procedure. Ampicillin is preferred for this application, unless the patient is penicillin-allergic, in which case cefazolin or clindamycin is an appropriate choice.


Cefazolin is a first-generation semisynthetic cephalosporin that binds to one or more penicillin-binding proteins, arresting bacterial cell wall synthesis and inhibiting bacterial replication. It has poor capacity to cross the blood-brain barrier. Cefazolin is primarily active against skin flora, including Staphylococcus aureus, and is typically used alone for skin and skin-structure coverage. Regimens for IV and intramuscular (IM) dosing are similar. This agent is used in penicillin-allergic patients with prosthetic heart valves who are at risk for endocarditis.

Clindamycin (Cleocin)

Clindamycin is a semisynthetic antibiotic produced by 7(S)-chloro-substitution of the 7(R)-hydroxyl group of the parent compound, lincomycin. It inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest. Clindamycin is widely distributed in the body without penetrating the central nervous system (CNS). It is protein-bound and excreted by the liver and kidneys. This agent is used in penicillin-allergic patients with prosthetic heart valves at risk for endocarditis.


Class Summary

Anesthetics may help blunt the pain of a diagnostic needle aspiration but are only partially effective.

Lidocaine 1% (Xylocaine with Epinephrine)

Lidocaine 1-2% with or without epinephrine (1:100,000 or 1:200,000 concentration) is used. Lidocaine is an amide local anesthetic used in 1-2% concentration. The 1% preparation contains 10 mg of lidocaine for each 1 mL of solution; the 2% preparation contains 20 mg of lidocaine for each 1 mL of solution. Lidocaine inhibits depolarization of type C sensory neurons by blocking sodium channels. Epinephrine prolongs the duration of the anesthetic effects from lidocaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

Lidocaine decreases permeability to sodium ions in neuronal membranes. This results in inhibition of depolarization, blocking the transmission of nerve impulses. Epinephrine prolongs the duration of the anesthetic effects from lidocaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

Ethylene chloride may be used in conjunction with lidocaine to blunt the pain of a diagnostic needle aspiration but is only partially effective. It should be sprayed over the area to be aspirated immediately before aspiration.

Bupivacaine and epinephrine (Marcaine with Epinephrine, Vivacaine, Sensorcaine with Epinephrine)

Bupivacaine decreases permeability to sodium ions in neuronal membranes. This results in the inhibition of depolarization, blocking the transmission of nerve impulses. Epinephrine prolongs the duration of the anesthetic effects from bupivacaine by causing vasoconstriction of the blood vessels surrounding the nerve axons.

Pain Medications

Class Summary

Pain control is essential to quality patient care. Analgesics ensure patient comfort, promote pulmonary toilet, and possess sedating properties, which are beneficial for patients who experience pain. These agents are used for comfort and sedation and to blunt the discomfort of diagnostic needle aspiration.

Meperidine (Demerol, Meperitab)

Meperidine is an analgesic with multiple actions similar to those of morphine; it may produce less constipation, smooth muscle spasm, and depression of cough reflex than similar analgesic doses of morphine. Meperidine may be used in combination with promethazine to provide a synergistic effect.


Class Summary

Antiemetic agents are used to treat vomiting. In combination with analgesics like meperidine, it may produce a synergistic effect.

Promethazine (Phenergan)

Promethazine is an antidopaminergic agent that is effective in treating emesis. It blocks postsynaptic mesolimbic dopaminergic receptors in the brain and reduces stimuli to the brainstem reticular system. It may be used in combination with meperidine to provide a synergistic effect.


Class Summary

By binding to specific receptor sites, benzodiazepines appear to potentiate the effects of gamma-aminobutyric acid (GABA) and to facilitate neurotransmission of GABA and other inhibitory transmitters. These agents are anxiolytics that may help patients who are apprehensive about needle aspiration, imaging studies, or surgery. Conscious sedation may be considered by the emergency physician with equipment and experience necessary to manage the patient’s airway if spontaneous ventilation becomes compromised.


Midazolam is a shorter-acting benzodiazepine sedative-hypnotic that is useful in patients who require acute or short-term sedation. It is also useful for its amnestic effects.

Lorazepam (Ativan)

Lorazepam is a sedative-hypnotic that increases the action of GABA, thereby potentially depressing all levels of the CNS, including the limbic system and reticular formation. It has a short onset of effect and a relatively long half-life. When patient needs to be sedated for longer than 24 hours, this medication is excellent.


Questions & Answers


What is an anorectal abscess?

How is an anorectal abscess characterized?

What is the anatomy of anal glands relative to anorectal abscess?

What are the most common locations of an anorectal abscess?

What is the most common type of anorectal abscess?

What is the second most common type of anorectal abscess?

What are the third most common type of anorectal abscess?

What is the least common type of anorectal abscess?

How are anorectal abscesses classified?

What are the characteristics of a perianal fistula associated with an anorectal abscess?

What is the pathophysiology of anorectal abscess?

What causes an anorectal abscess?

What causes of anorectal abscess other than anal gland infection?

How common are recurrent cases of anorectal abscess?

Is there a seasonal or demographic pattern to the incidence of anorectal abscess?

What are the age-related demographics for anorectal abscess?

Is anorectal abscess more common in men or women?

What is the mortality from anorectal abscess?

What are the risk factors for chronic or recurrent anorectal abscess?

What is the prognosis of anorectal abscess after fistula formation?

What is the recurrence rate of anorectal fistulas?


Where do anorectal abscesses occur?

What features of an anorectal abscess determine the clinical presentation?

What are the signs and symptoms of anorectal abscess?

What is commonly found in the physical exam of patients with anorectal abscess?

When is anesthesia indicated in the physical exam of anorectal abscess?

When is imaging indicated in the diagnosis of anorectal abscess?

What is the role of DRE during exam for anorectal abscess?

What are the complications of anorectal abscess?

How common are fistulas due to anorectal abscess?


What are the differential diagnoses for Anorectal Abscess?


What are the approach considerations in the workup of anorectal abscess?

Which lab studies are indicated in the workup of anorectal abscess?

What is the role of CT in the workup of anorectal abscess?

What is the role of ultrasonography in the workup of anorectal abscess?

What is the role of MRI in the workup of anorectal abscess?

How is endoscopy used in the workup of anorectal abscess?


When is incision and drainage indicated for treatment of anorectal abscess?

What is the role of colostomy in the treatment of anorectal abscess?

Are patients with anorectal abscess admitted to the surgical or medical service?

When is transfer indicated for the treatment of anorectal abscess?

Are antibiotics indicated in the treatment of anorectal abscess?

What is the role of predisposing or comorbid factors in the selection of antibiotic therapy for the treatment of anorectal abscess?

How are patients reevaluated if treatment does not resolve an anorectal abscess?

How are patients with anorectal abscess prepared for surgery?

How is anorectal abscess treated?

How is incision and drainage performed in the treatment of anorectal abscess?

When are fistulas a potential complication of anorectal abscess?

When is general or regional anesthesia required for the treatment of anorectal abscess?

How is an intersphincteric anorectal abscess drained?

How is a supralevator anorectal abscess drained?

What are the surgical approach options for the treatment of supralevator anorectal abscess?

Which surgical approach is used in the treatment of posterior supralevator anorectal abscesses?

Which surgical approach is used for the drainage of anterior supralevator anorectal abscess?

What are the surgical management options for the treatment of anorectal abscess?

Which fistulotomy techniques are most effective in the treatment of anorectal abscess?

What is the role of radiofrequency fistulotomy in the treatment of anorectal abscess?

What are the main principals of management of anorectal fistulas in the treatment of anorectal abscess?

What is the Goodsall rule for the management of fistulas in the treatment of anorectal abscess?

What are the treatment options for the management of fistulas due to anorectal abscess?

Is fistulotomy or fistulectomy preferred in the treatment of anorectal abscess?

When is fistulotomy contraindicated for the treatment of anorectal abscess?

What is a seton and how is it used in the treatment of anorectal abscess?

How is a cutting seton used in the treatment of anorectal abscess?

What are other treatment options for anorectal abscess?

What is the postoperative care for anorectal abscess?

When is surgical consultation indicated in the treatment of anorectal abscess?

What follow-up is included in the treatment of anorectal abscess?


Which medications are indicated in the treatment of anorectal abscess?

Which medications in the drug class Benzodiazepines are used in the treatment of Anorectal Abscess?

Which medications in the drug class Antiemetics are used in the treatment of Anorectal Abscess?

Which medications in the drug class Pain Medications are used in the treatment of Anorectal Abscess?

Which medications in the drug class Anesthetics are used in the treatment of Anorectal Abscess?

Which medications in the drug class Antibiotics are used in the treatment of Anorectal Abscess?