The anorectal abscess can vary on the spectrum of complexity based on the location and involvement of surrounding tissue. A thorough understanding of the anatomical structures and their relationship to each other is important for both accurate diagnoses of the disease and to provide appropriate treatment to avoid the complications of multiple procedures and increased costs associated with delayed diagnosis.
Anorectal abscesses are typically caused by inflammation of the subcutaneous tissue usually from an obstructed crypt gland. The normal anatomy of the anus includes the presence of these glands at the dentate line. Debris overlying these glands are often the infiltrative mechanism by which the bacteria gain access to the underlying tissue and produce infection. As such, infective organisms that can cause this include Escherichia Coli, Staphylococcus aureus, Streptococcus, Enterococcus, Proteus, Prevotella, Peptostreptococcus, Porphyromonas, Fusobacteria, and Bacteroides. Risk factors that that may predispose patients to abscesses include trauma, tobacco abuse, liquid stool entering the duct, and dilated ducts which lead to poor emptying.
The incidence is 1:10,000, resulting in approximately 68,000 to 96,000 cases in the United States per year with a male prevalence of 3:1 during the third and fourth decades of life. The condition is seen more in the summer and spring months. Although often a concern of the patient, data does not support that there is an increased risk from hygiene, anal-receptive intercourse, diabetes, obesity, race, or altered bowel habits.
Although often thought of as the same, perianal abscess and perirectal abscesses differ in both complexity and care options. Except for perianal abscess which can be simply incised and drained as definitive care, all others usually require intravenous antibiotics, surgical evaluation, and drainage. A majority of abscesses are diagnosed clinically based on skin findings and palpitation of the affected area alone, but some require advanced imaging to determine the extent of infiltration. A perirectal abscess can be further divided into a category based on anatomical location: ischiorectal abscess, intersphincteric abscess, and supralevator abscess. Given the variability in location and severity of the abscess, it is important to consider the presence of fistulas or tracts which may contribute to the spread of the infection. Perianal abscesses are the most common type, followed by ischiorectal, and intersphincteric abscesses.
Alternatively, the Park’s classification system which groups the fistulas into 4 types based on the course of the fistula and the relationship to the anal sphincters.
Patients will often present to the emergency department with acute pain in the perianal or perirectal region. Other presenting symptoms include a dull or aching pain with defecation, movement, sitting, or coughing. Supralevator abscesses may be described as lower back pain or a dull ache in the pelvic region. Also, fever, malaise, rectal drainage, redness of surrounding skin, and possible urinary retention may be included in the patient history.
Most physical exams are done in the prone position, revealing erythema, induration, fluctuance, tenderness, and spontaneous drainage. Pertinent physical exam findings, often performed in the Sim position, include erythema of the surrounding skin, superficial or deep mass with tenderness to palpation, tenderness on palpation of the rectum and deep structures, or discharge. A digital rectal exam may aid in diagnosis, but variability exists among physicians ability to identify the abscess on the exam accurately. Constipation may be present in patients that have significant pain with a bowel movement.
Laboratory abnormalities may include elevated white blood cell count, increased neutrophils, the presence of bands, and elevated lactate levels. Imaging modalities such as endoanal ultrasound, transperineal sonography, computed tomography (CT), and MRI are useful to confirm the diagnosis. CT should be obtained in patients with significant comorbidities, complex suppurative anorectal conditions, and when surgical consultation may not be immediately available. Optimal imaging may require utilizing triple contrast in certain conditions and using 2.5 mm slices. Endoanal ultrasound imaging is best captured by using a 2-dimensional or 3-dimensional probe with a frequency of 5 to 16 MHz.
As with all abscess, once identified, the mainstay of treatment is incision and drainage given the significant concern of extension into nearby tissue. Simple, superficial perianal abscess and an ischiorectal abscess can be drained at the bedside. After giving the appropriate amount of anesthetic with epinephrine, the abscess can be incised and drained. Typical the incision is cruciate or elliptical form made close to the anal verge to minimize the potential long fistula formation. Given that a large number of abscesses are associated with a fistula, concomitant fistulotomy may be performed with varying results. Packing of the wound is controversial, but Perera et al. did not find significant evidence to support an advantage to packing the wound compared to incision and drainage without packing.
Physicians should perform surgery to evaluate patients with recurrent or bilateral abscesses for intraoperative drainage, including cases where internal draining may be necessary. A larger abscess may require placement of a drain for up to 3 weeks. Catheters are also recommended for patients with severe systemic illness, underlying comorbidities including diabetes and morbid obesity. The catheters can be placed after a small stab incision is made thru the skin using a mushroom tip catheter 10 to 14 Fr which is then secured to the skin with a suture. Surgeon to follow up at 2 to 3 weeks for incision and drainage patients and 7 to 10 days for patients with mushroom tip catheters. They are usually followed until completely healed. High fiber diet is recommended.
Antibiotics are recommended when there is associated cellulitis of the surrounding skin, patients that fail to improve after drainage and immunocompromised patients. Currently, no data exists to suggest that antibiotics will reduce fistula formation. Antibiotics should include coverage for the organisms listed above. We recommend obtaining wound cultures if antibiotics are prescribed, especially those who already have completed a prior course, or known resistance in the past. We recommend treating with amoxicillin-clavulanate or ciprofloxacin plus metronidazole for 10 days.
Differential diagnosis includes anal fissure, anal fistula, thrombosed hemorrhoid, pilonidal cyst, buttocks abscess, or cellulitis of the skin, Crohn’s disease, ulcerative colitis, malignancy, proctitis, HIV/ AIDS, other sexually transmitted diseases, Bartholin’s abscess, and hidradenitis suppurativa.