: 
Hemorrhoids, abscesses, fistulas, fissures, anal itching, rectal prolapse—with so many anorectal disorders out there, it’s hard to keep track of which is which. Two of these conditions, anal abscesses and anal fistulas, are closely linked to one another but can be easily distinguished via the guidelines below.
Defining Each Disorder
Anal Abscess – This is a pus-filled, infected cavity near the opening of the anus or deep in the rectum. Most abscesses result from infection of anal glands in the lining of the anal canal near the anus opening. When bacteria from the gut passes the anal sphincter barrier and into the surrounding tissue of the rectum, an abscess of varying severity and depth forms. When an abscess fails to fully heal, an anal fistula may form.
Anal Fistula – As mentioned above, fistulas usually occur due to a previous anal abscess. A fistula is an inflamed tunnel under the skin, connecting the anal canal and the surface of the surrounding skin. The majority result from an anorectal infection, wherein the anal crypts are infected and cause pus-filled cysts to form near the anal canal.
Symptoms
Anal Abscess – The most common symptoms are pain around the anal area, swelling, redness, and fever. Rectal bleeding and urinary complications (difficult or painful urination) may also occur.
Anal Fistula – In addition to most likely having a history of anal abscesses, patients may also experience skin irritation around the anus, a throbbing pain when sitting, anal discharge, swelling and redness, and fever.
Causes
Anal Abscess – This usually occurs from infection of anal glands in the lining of the anal canal near the anus opening. Other causes include an anal fissure and sexually transmitted infections (STIs).
Anal Fistula – As previously mentioned, fistulas typically result from an abscess that did not fully heal. They may also, though less frequently, be caused by Crohn’s disease, STDs, trauma, tuberculosis, cancer or diverticulitis.
Treatments
Anal Abscess – Surgical incision and drainage should be performed ASAP, as antibiotics are ineffective at this stage of the infection. Delaying surgery can result in tissue destruction, fibrosis (scar tissue formation), and impaired anal continence. Drainage involves making a small incision above the abscess as close to the anus as possible, then removing the gauze after 24 hours. Sitz baths and stool softeners can help with post-surgery discomfort.
Anal Fistula – Surgery is generally needed to treat fistulas and involves cutting a small part of the anal sphincter muscle away. By doing so, the tunnel/fistula is opened up to form a trench that heals from the bottom outwards. After a few weeks, the trench ideally fills up with scar tissue and heals. Post-surgery discomfort is mild and can usually be addressed with painkillers.
Recurrence Rates
Anal Abscess – Nearly half of abscesses may recur, either in the form of a new abscess or as a frank fistula.
Anal Fistula – Fistulas can also potentially recur, with recurrence rates dependent upon the particular surgical technique utilized.
