Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + Download Section PDF Listen ++ For further information, see CMDT Part 15-44: Other Anal Conditions + Key Features Download Section PDF Listen +++ ++ 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 Download Section PDF Listen +++ ++ 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 Download Section PDF Listen +++ ++ 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