A 48-year-old man with a history of hepatitis C and IV drug use presents complaining of left buttocks pain for two weeks. The pain is sharp, and is worse with sitting and defecation. He claims that he has “white stuff” draining from the anus, which is not always associated with a bowel movement. He has had subjective fevers, malaise, and occasional streaks of blood on the toilet tissue.
What is your diagnosis? How would you manage this in the ED?
Diagnosis: Anorectal Abscess
Anorectal conditions including abscess formation are a common presentation to the ED. Although the exact prevalence is unknown, a random phone survey found that 20 percent of respondents had some history of anorectal symptoms. (Dis Colon Rectum 1995;38:341.)
Infection typically begins with either bacterial seeding following an epithelial tear or blocked secretion of lubricants from anal glands located in the intersphincteric space. Abscess pathogens are typically gut flora and include Escherichia coli, Enterococcus species, Streptococcus species, and Bacteroides species. Sexually transmitted disease pathogens such as herpes, Chlamydia, and Gonococcus, and anal fissures are known to be inciting factors for anal abscess formation.
Once formed, abscess growth follows the path of least resistance, which typically is to the skin surface. Most anorectal abscesses are perianal (60%), lying just beneath the skin in the lowest segment of the anus. Less commonly, epithelial disruption of the internal rectal sphincter allows bacteria access to the intersphincteric space (5% of abscesses). From here, extension of bacteria through the external sphincter into the ischiorectal space (20% of cases) can result on abscess formation. If abscesses occur bilaterally in the ischiorectal space, a connection of the two via the deep postanal space can occur, also known as a “horseshoe” abscess. From the ischiorectal space, infection can travel cephalad, above the levator ani muscle, forming a supralevator infection (4%). Supralevator infections can be the result of a pelvic infectious process. Patients at risk for developing anorectal abscesses include those with immunocompromising conditions, anal sex recipients, and patients with inflammatory bowel disease.
Anorectal abscesses are more common in healthy men in their 30s and 40s. It is also a common condition in infants under a year old, mostly in males. The exact prevalence is not known. (Eur J Pediatr Surg 2010;20:35.) It is not surprising that the number of reported cases of anorectal abscesses appears to be highest in the warm months of spring and summer. A direct relationship to poor anal hygiene has not been demonstrated. Nearly 30 percent of patients with anorectal abscesses have had a similar previous infection in the past, with 75 percent occurring in the same location. (Surg Gynecol Obstet 1979; 149:884.)
Anal pain is the most common presenting symptom of patients with an anorectal abscess. The pain is typically constant and not necessarily associated with or exacerbated by a bowel movement or by sitting. Symptoms depend on the location and size of the abscess. Patients may complain of constipation, fever, malaise, localized erythema and swelling, rectal discharge, pruritus, or bleeding. Patients with deep abscesses adjacent to the urethra may complain of urinary retention. Patients with severe anorectal infection or sepsis may present with lethargy or confusion or be obtunded.
Examination of the rectal area may reveal a mass on the buttocks adjacent to the anus that is erythematous, firm, indurated, fluctuant, tender, or there may be a mass that can be palpated inside the anorectal vault during digital examination. Visualization by bedside anoscopy may help identify the area involved. Some deep space infections may be difficult to appreciate clinically. Approximately half of anal abscesses will develop into a chronic fistula with superficial wound drainage via a tract. Fistulous tracts, similar to a small cord, can sometimes be palpated. Description of the superficial perianal lesion location should use the “anal clock.” This is oriented with the patient lying in the lithotomy position, 12 o'clock points superiorly to the genitals and 3 o'clock points to the left side of the patient. (Radiographics 2000;20:623.)
Small circumscribed perianal abscesses do not require further characterization with imaging modalities. Most other anorectal abscesses do, however, to differentiate cellulitis from fluid collection, define area of tissue involvement, define location of fluid collection, and help determine the presence of a fistula. Abdominopelvic computed tomography scanning with contrast is recommended to best characterize lesions from the ED, although it may not be ideal if a fistula is present because tracts can cause streaking which mimic inflammatory changes. (Radiology 1986;161:153.) CT also is not ideal to identify small fluid collections. Magnetic resonance imaging and both transrectal and endoscopic ultrasonography are playing a larger role in identifying the extent of anorectal inflammatory disease, and are good for identifying the presence of an associated fistula, but these are not typically available to ED patients. (World J Gastroenterol 2007;13: 3153.)
The differential diagnosis of rectal abscesses is fairly circumscribed and includes other infectious etiologies (Bartholin cyst, pilonidal disease, actinomycosis), Crohn's disease, trauma, hidradenitis suppurativa, radiation therapy-induced changes, and rectal malignancies. No laboratory finding excludes the diagnosis of anorectal abscess. Leukocytosis is common, but always present in the infected infant, elderly person, and septic or immunocompromised patient. Incision and drainage is the treatment for anorectal abscess. If treatment is delayed or inadequate, sepsis and death can occur.
Antibiotic therapy alone is not recommended, but should be considered as adjunct therapy for those with immunosuppressive conditions, valvular heart disease, or coinciding cellulitis. ED management depends on the clinical condition of the patient, associated comorbid disease, abscess size, and location to the rectum or pelvis. Only superficial small perianal abscesses are appropriate for outpatient ED procedures because incomplete abscess drainage and recurrence is common, which can result in complications that include fistula formation. Operative treatment of anorectal fistulas has the known complication of anal incontinence so only superficial discrete perianal abscesses should be drained in the ED.
If there is a question about the presence of a perianal fluid collection (versus cellulitis), bedside ultrasound can be helpful instead of the historically recommended aspiration with an 18-gauge needle to identify pus. Generous local anesthetic is typically required for ED incision and drainage. Procedural sedation may be necessary in some patients. A single linear incision is made at the point of maximal fluctuance. Loculations should be opened, and all pus removed. Sitz baths should be done three to five times a day 24 hours after incision and drainage. Wounds should be reevaluated and packing removed in 48-hour intervals to verify the infection is improving until it is resolved, which typically takes four to six days. Stool softeners or a bulk fiber laxative may be recommended. Patients should be counseled to expect wound drainage. Gauze pad or other absorbable pads may be necessary to prevent soiling clothes. Post-incision and drainage wounds are painful, and oral analgesia should be given. Unfortunately, narcotics can cause constipation, which can exacerbate the pain during healing.
Patients with spontaneous rupture still require formal incision and drainage to verify that all pus is appropriately evacuated. (Clinical Procedures in Emergency Medicine. Philadelphia: Saunders; 2009.) Culture of abscess pus is not typically recommended unless there is concern for a noncoliform pathogen. Ischiorectal, supralevator, intersphincteric, deep space, and anything larger than a small perirectal abscess requires operative intervention. Abscesses with confirmed or suspected fistula formation also require operative intervention.
This patient was diagnosed with a large left perirectal abscess and right gluteal cellulitis. He was taken to the operating room for debridement.