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Key Features

  • Infection of anal glands located at the base of the anal crypts at the dentate line, leading to abscess formation

  • Causes include

    • Anal fissure

    • Crohn disease

  • Fistula in ano arises in an anal crypt and is usually preceded by an anal abscess

  • Causes of fistulas that connect to the rectum include

    • Crohn disease

    • Lymphogranuloma venereum

    • Rectal tuberculosis

    • Cancer

Clinical Findings

  • Perianal abscess: throbbing, continuous perianal pain

    • Erythema, fluctuance, and swelling in the perianal region on external examination

    • Swelling in the ischiorectal fossa on digital rectal examination

  • Fistula in ano: purulent discharge, itching, tenderness, and pain

Treatment

  • Perianal abscess is treated by surgical incision under local anesthesia

  • Ischiorectal abscess is treated by surgical drainage in the operating room

  • Fistula in ano is treated by surgical excision under anesthesia

  • Fistulas caused by Crohn disease are frequently asymptomatic

  • Surgical fistulotomy for complex (high, transphincteric) anal fissures carries a high risk of incontinence

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