Snapshot A 41-year-old man presents to the emergency department with 2 days of worsening fever and severe pain in his rectum, worse with defecation. His medical history is significant for type 2 diabetes mellitus and morbid obesity. On physical exam, he has a fever of 39°C and a warm, fluctuant 2-cm mass is palpated immediately adjacent to the anus with surrounding cellulitis. Incision and drainage is performed at the bedside, and the patient is discharged with a course of oral ciprofloxacin and metronidazole. Introduction Clinical definition an abscess of the rectum, anus, or adjacent tissues Genetics not inherited increased susceptibility in inherited immunodeficiencies Associated conditions Crohn disease fistula-in-ano/perianal fistula Epidemiology Demographics 2:1 male to female middle age roughly 20-60 years of age with a mean age of 40 for both sexes occurs rarely in children Risk factors Crohn disease immunodeficiency diabetes chronic corticosteroid use ETIOLOGY Pathogenesis obstruction and infection of an anal gland may spread to contiguous areas (e.g. perianal, ischiorectal, and intersphincteric) through the extensive branching of the anal gland network Presentation Symptoms perirectal/perianal pain fever local swelling less commonly diarrhea and/or constipation Physical exam perirectal/perianal tenderness palpable mass fever surrounding cellulitis imaging Generally not required for the diagnosis of anorectal abscesses may be necessary to diagnose occult abscesses or to define the extent of large or complicated abscesses used in patients with concurrent Crohn disease No clear first-line among the following modalities endoanal ultrasound MRI with contrast CT with contrast Studies Diagnostic testing diagnostic approach diagnosis is based on history and clinical exam if clinical exam cannot be performed in the office (e.g., due to pain) examination under anesthesia (EUA) may be necessary Differential Anal fissure differentiating factors visualizable tear, bleeding, no mass, and no signs of infection Hemorrhoids differentiating factors bleeding and no signs of infection Pilonidal abscess differentiating factors location alone Treatment First-line incision and drainage early, adequate, and dependent drainage yields best results more superficial abscesses may be drained in the office deeper may require the operating room Other treatments antibiotics never indicated alone only in addition to drainage indications accompanying cellulitis systemic signs of infection immunosuppressed patients including HIV/AIDS diabetes morbid obesity typically metronidazole and a fluoroquinolone (e.g., ciprofloxacin) covers MRSA and gut flora Complications Anorectal fistula/fistula-in-ano 30-70% will present with concurrent fistula an additional 33% will eventually develop a fistula after drainage Recurrent abscess Sepsis