Handwritten lecture Anorectal Fistula is an epithelialized tract from Rectum or anus to the Skin (perirectal skin) for USMLE

ANATOMY OF THE ANUS
The anal canal is divided by pectinate line into anal and rectal region. Embryological is much different in these two areas. Crypt of morgagni is an important location because 90% of fistulas are formed there. An abscess is formed there and then moves slowly outwards. Intersphincteric plane seperates internal and external anal sphincters.

ETIOLOGY/CAUSES
The most common cause is a chronic abscess in Crypt of Morgagni. Chron's disease is another common cause but it never presents as a rectak fistula. Radiation proctitis, LGV, rectal foreign bodies and actinomycosis can also lead to anal fistula.

TYPES OF FISTULAS
Parks classification divides the fistulas based on the route the fistula takes. Superficial fistula is not a part of park's classification. Intersphincteric fistula starts at pectinate line, then crosses the internal sphincteric and then goes along intersphinteric plane and out through the skin. Transsphinteric fistula also starts at dentate line and crosses internal and external sphincter and goes to ischiorectal fossa and goes out to buttock. Suprasphincteric fistula starts at dentate line and goes above sphincteric apparatus then proceeds upwards and then to buttock. Extrasphincteric fistula starts at the rectum. Needs to go through the levator Ani and then goes to buttock. The most common is intersphincteric and the least common is extrasphincteric. Also keep in mind that they may be branching.

SIGNS AND SYMPTOMS
Non-healing anorectal abscess with purulent abscess which is malodorous. There will also be rectal pain during defecation and pruritus. There also may be draining fluid and red perianal skni. Goodsall's Rule says that a tract in anterior will go straight back, however, a posterior fistula will have a curved shape. But an anterior fistula greater than 3 cm away also means curved.

IMAGING
CT/MRI and fistulography.

MANAGEMENT
Surgery is the management. Goal is to remove fistula and preserve continence. Simple fistulas are low transphinteric and intersphincteric fistula can be treated with primary fistulotomy and fibrin sealant. Supra and extra sphincteric or women with anterior, multiple tracts, secondary causes, and associated with incontinence are considered complex.
Fistulotomy is a procedure where a probe is sent through the tract and a scalpel cuts the tract and stitch up and done. Fibrin sealant is a device that has two plungers with calcium and fibrin. Once they mix they form a clot in the fistula. Can only be used on simple fistulas. Seton is suturing goes through the fistula and slowly tightens the suture and eventually cuts all the way through. Advancement Flaps you cut the internal opening and remove wall. Cover internal opening with the flap and prevents continued abscess and drainage. Lower recurrence, lower complication, and used in transsphincteric.

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