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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
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Perianal abscess: throbbing, continuous perianal pain
Fistula in ano: purulent discharge, itching, tenderness, and pain
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Erythema, fluctuance, and swelling in the perianal region on external examination
Swelling in the ischiorectal fossa on digital rectal examination
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Perianal abscess is treated by surgical incision and drainage under local anesthesia
Ischiorectal abscess is treated by surgical drainage in the operating room
Simple idiopathic fistula in ano is treated by surgical incision or excision under anesthesia; care must be taken to preserve anal sphincters
Fistulas caused by Crohn disease are frequently asymptomatic
Surgical fistulotomy for complex (high, transphincteric) anal fissures carries a high risk of incontinence