Anal fistula pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Manpreet Kaur, MD [2]

Anal fistula develops from infection of anal crypts gland. The initial infection occurs in the ducts of the anal glands and the spread of infection results in the formation of the abscess.If the abscess is ruptured, a fistula is formed. Anal fistulas are associated with following conditions are diverticulitis, foreign-body reactions actinomycosis, chlamydia, lymphogranuloma venereum (LGV), syphilis, tuberculosis, radiation exposure, HIV disease, Crohn’s disease, pilonidal disease, hidradenitis suppurativa, trauma, previous surgery (including ileoanal pouch surgery), presacral dermoid cysts, sacrococcygeal teratoma.

• The anal canal is a 2 to 4cm in length, starts at the anorectal junction to the end of anal verge.^[1]
• It is divided into an upper and a lower part by transition zone that is seen at the dentate line or pectinate line which is surrounded by longitudinal mucosal folds, called columns of Morgagni.^[1]
• Each of this fold contains anal crypts, each of which contains 3 to 12 anal glands, the distribution of these glands is not uniform with most of the glands present anterior to the position of the anal canal and fewer in the posterior position.

There are following steps in the formation of anal fistula:

• Anal fistula develops from infection of anal crypts gland.

• The initial infection occurs in the ducts of the anal glands and the spread of infection results in the formation of the abscess.^[2]
• The crytoglandular theory states that obstruction of anal gland duct results in a infection.
• The presence of these glands deep in relation to the anal canal and sphincter, the infection follows the path of least resistance resulting in abscess formation at the termination of the gland.^[3][4]

• If the abscess is ruptured, a fistula is formed.

Anal fistulas are associated with following conditions:^[5]

• Diverticulitis
• Foreign-body reactions
• Actinomycosis
• Chlamydia
• Lymphogranuloma venereum (LGV)
• Syphilis
• Tuberculosis
• Radiation exposure
• HIV disease
• Crohn’s disease
• Pilonidal disease
• Hidradenitis suppurativa
• Trauma
• Previous surgery (including ileoanal pouch surgery)
• Presacral dermoid cysts
• Sacrococcygeal teratoma
• Rectal duplication

On gross pathology:

• They are seen linear or completely maloriented and have the epithelial lining at one of its edges.

On microscopic histopathological analysis, following features are found:^[6]

• There is the central core of active and chronic inflammation with granulation tissue, foreign body giant cells, and surrounded by scar.
• Granulomas are seen occasionally.
• There is squamous cell extend into the fistula track which is partially epithelialized.

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