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Synonyms and Keywords: Anorectal abscess, Ischiorectal abscess, Supralevator abscess, Horse shoe abscess
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Anorectal abscess is secondary to blockade of the anal gland ducts, resulting in a infection of the gland. The anatomical position of the anal glands in relation to the anal canal is responsible for the variation in the location of the abscess. Initial infection occurs in the anal gland duct and it takes the path of least resistance. The anorectal abscess are classified into low abscess and high based on the location of the abscess. Patients with low abscess present with anal pain associated with bowel movement, and patients with high abscess present systemic manifestations such as fever and malaise in addition to anal pain. On examination tenderness and flactulance suggest anorectal abscess. It is an emergency condition and must be treated promptly within 24 hours of presentation as spread of infection can result in perineal cellulitis and sepsis. Incision and drainage is the definitive treatment and should be performed under local or general anesthesia based on the location of the abscess. With treatment prognosis is good but a risk of recurrence and formation of a fistula is high in patients with improper drainage and failure to identify existing fistula. Antibiotic therapy does not help with treatment of the infection and wound healing.
- In 1880, Herman and Desfosses described the anal glands within the internal sphincter, sub-mucosa and their opening into the anal crypts and demonstrated that the infection of these glands and the spread of the infection through the intersphincteric space can result in the formation of a anorectal abscess.
- Tucker and Hellwig, provided evidence that the initial infection occurs in the anal ducts allowing the infection to spread from the anal lumen into the anal canal wall.
- In 1950, Goligher described the treatment for anorectal abscess with incision and curettage with antibiotic bath and primary closure.
- Perianal abscess: When the infection reaches the anal verge passing between the internal sphincter and external sphincter, it results in the formation of a perianal abscess.
- Ischiorectal abscess: If the infection ruptures through the external sphincter it results in a formation of a ischiorectal abscess.
- Supralevator abscess: If the infection extends superiorly, it can form a supralevator abscess.
- Horseshoe abscess: Extension of the abscess to both the ischiorectal fossa results in the formation of a horseshoe abscess.
Based on the location the abscesses can also be classified into:
- High anorectal abscess: These include intersphincteric, perianal, and ischiorectal abscesses.
- Low anorectal abscess: These incude submucosal, supralevator abscesses.
- Anal canal is a 2 to 4cm in length, starts at the anorectal junction to the end of anal verge.
- It is divided into a upper and a lower part by transition zone that is seen at the dentate line or pectinate line which is surrounded by longitudinal mucosal folds, called columns of morgagni.
- Each of this fold contains anal crypts, each of which contains 3 to 12 anal glands, the distribution of these glands is not uniform with most of the glands present anterior to the position of the anal canal and fewer in the posterior position.
- The initial infection occurs in the ducts of the anal glands and the spread of infection results in the formation of the abscess, various theories were put forward to describe the pathogenesis and the most accepted one is the cryptoglandular theory.
- The crytoglandular theory states that obstruction of anal gland duct results in a infection and due to the presence of these glands deep in relation to the anal canal and sphincter, the infection follows the path of least resistance resulting in abscess formation at the termination of the gland.
Source of Infection
- Supralevator abscess can be caused by the spread of infection from abdominal infections such as appendicitis, diverticulitis, or gynecologic sepsis.
- Spread of infection of ano-rectal Crohn's disease.
- Trauma to the anal canal
- Cancer of the anal canal or the anal glands
Organisms commonly causing anorectal abscess include:
Epidemiology and Demographics
- The incidence of anorectal abscess is estimated to be around 68,000 to 96,000 cases per year in the United States.
- Anorectal abscesses are two times more frequently seen in men than women.
- Patients with anorectal abscess present between ages of 20 to 60 years with a mean age of 40 in both sexes.
- There are limited epidemiological studies which studied the frequency of anorectal abscess with race differences, however a study in Chicago reported a 92% of the patients presented with anorectal abscess were of African-American origin.
- Crohn's disease
- Diabetes mellitus
- History of abscess in the ischiorectal location
- HIV infection
- Receptive anal sex
Anorectal abscess must be differentiated from other causes of anal pain including anal fissure, thrombosed hemorrhoids, levator spasm, sexually transmitted disease, proctitis, hidradenitis suppurativa, infected skin furuncles, herpes simplex virus, tuberculosis, syphilis, actinomycosis and cancer.
|Fistula in ano||
|Thrombosed External Hemorrhoids||
|Infected skin furuncle||
|Disease||History||Physical exam findings||Sample image|
Digital rectal examination
Natural History, Prognosis, Complications
Prognosis of patients is good with incision and drainage and most patients do not require any antibiotic therapy after the procedure, except for patients with HIV infection, Crohn's disease. Majority of patients have relief of pain after abscess drainage and healing takes time as it heals by secondary intention.
History and Symptoms
- Patients with low abscess typically present with anal pain. Other findings include:
- Patients with high abscess present with :
Digital Rectal Examination
- It is difficult to perform digital rectal examination due to the severe pain, therefore patient should be examined under local anesthesia to identify the location of the abscess and also if suspicion of a high abscess (Supralevator abscess) is present.
- Anoscopy should not be performed.
- Anorectal abscess is a clinical diagnosis and presence of induration, tenderness and fluctulance are diagnostic of perianal and ishciorectal abscess. In patients with intersphincteric or supralevator abscesses external findings are minimal only pelvic or rectal tenderness or fluctulance on digital rectal examination can be demonstrated.
(Images courtesy of Charlie Goldberg, M.D., UCSD School of Medicine and VA Medical Center, San Diego, CA)
- Anorectal abscess is a clinical diagnosis and physical examination is sufficient to make the diagnosis, therefore complete laboratory testing is not done in most of the patients.
- Complete blood count will demonstrate a neutrophilia and elevated ESR.
- Bleeding time and clotting time and routine pre-operative evaluation must be performed.
- Culture and gram staining of the necrotic tissue is done to establish cause of infection.
- Endoanal ultrasound is useful in detecting horse-shoe abscesses extension and presence of fistula tracts with high sensitivity.
- Three dimensional ultrasound is useful in patients to identify the anatomical locations of complex perianal abscesses and fistula tracts.
- CT scan is useful in patients with complex suppurative anorectal conditions such as supralevator abscess and to identify other etiologies causing anorectal abscess such as pelvic infections, appendicitis, Crohn's disease and diverticulitis.
- Medical therapy is not recommended in patients with anal abscess as the antibiotics have poor penetration in to the abscess cavity and are not helpful to in treatment of the infection or wound healing.
- Antibiotics may be considered in patients with extensive cellulitis, HIV infection and diabetes mellitus.
- Patients with low neutrophil count (500-1000/mm³) and also in patients with no fluctulance medical therapy can be helpful in resolution of the abscess, however in patients with neutrophil count of >1000/mm³ and with fluctulance surgical drainage is a better option for treatment.
- Prophylactic antibiotics prior to incision and drainage is recommended by American Heart Association, in patients with prosthetic valves, previous bacterial endocarditis, congenital heart disease, and heart transplant recipients with valve pathology.
- Management of anal abscess should be prompt as the risk of involving the surrounding tissue resulting in perineal cellulitis and sepsis is high.
- Primary treatment for anorectal abscess is incision and drainage and it should be performed within 24 hours of presentation.
- Patients with perianal abscess and ischiorectal abscess can be treated in a outpatient setting under local anesthesia using 1% lidocaine or bupivacaine with epinephrine is injected subcutaneously into the area affected by the abscess to provide adequate infilteration into the skin. 
- Patients with loculations or large ischiorectal, intersphincteric, supralevator, or horseshoe abscesses should be admitted to the hospital and the procedure should be performed under anesthesia.
- Under aseptic precautions a scalpel is used to make a cruciate or elliptical incision over the area of flactulance. The incision should be close to the anal verge to minimize the length of a potential fistula.
- After incision is made the necrotic tissue is removed and loculations are broken using a hemostat or a finger.
- After the procedure the wound is packed with a gauze sponge which is removed after 24 hours.
- Regular sitz bath is recommended after the surgery, it will help in local cleansing and wound healing.
- A variation in the incision and drainage is using a small latex catheter (Pezzer catheter). After a small incision is made the catheter is inserted into the cavity and is left in place for a duration of 3 to 10 days till the abscess cavity is drained and the cavity closes around the catheter.
- Recurrence of the abscess: The recurrence rate depends on the location of the abscess and the duration of follow-up, the rate ranges from 3% to 44%. Other factors influencing the recurrence rate include incomplete initial drainage, failure to break up loculations within the abscess, missed abscess undiagnosed fistula. Recurrence rates are high in horseshoe abscess with a range from 18% to 50% which require multiple surgeries.
- Urinary retention
- Postoperative bleeding
- Abstain from anal intercourse
- Adequate treatment of Crohn's disease and HIV infection
- Maintaining proper hygiene
- Early incision and drainage, with regular sitz bath is adviced in all patients.
- Identification of pre-existing fistula tract and fistulotomy during incision and drainage decreases the risk of recurrence and fistula formation.
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