Dr. Rajendran Rajendran
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Most appropriate investigation in recurrent anal fistula-

a. EndorectalUS

b. Colonoscopy

c. MRI

d. Proctoscopy

Ans: (c)

Fistula In Ano

An anal fistula is an inflammatory tract between the anal canal and the skin. Anal fistulae are hollow tracts lined with granulation tissue connecting a primary (internal) opening inside the anal canal to a secondary (external) opening in the perianal skin.

Most anal fistulas originate in anal crypts, which become infected, with ensuing abscess formation. When the abscess is opened or when it ruptures, a fistula is formed. Fistulas are also found in patients with inflammatory bowel disease, particularly Crohn disease. Anal fistulas can also be associated with diverticulitis, foreign-body reactions, actinomycosis, chlamydia, lymphogranuloma venereum, syphilis, tuberculosis, radiation exposure, and HIV disease. A complex, recurrent, or nonhealing fistula should raise the suspicion of one of these diagnoses. Crohn disease should be ruled out in all patients with complicated or recurrent anal fistulas.

Patients present with persistent drainage from the internal and/or external openings. An indurated tract is often palpable.

Diagnosis of an anal fissure is primarily based on the history and physical examination. The external opening is usually visible as a red elevation of granulation tissue with or without concurrent drainage. The internal opening may be more difficult to identify. Injection of hydrogen peroxide or dilute methylene blue may be helpful.

Radiologic studies are not performed for routine fistula evaluation, because in most cases, the anatomy of a fistula-in-ano can be determined in the operating room. However, such studies can be helpful when the primary opening is difficult to identify or when recurrent or persistent disease is present. In the case of recurrent or multiple fistulas, MRI can be used to identify secondary tracts or missed primary openings.

MRI can be helpful in the detection and delineation of complex fistulas in ano. If the extent of the fistula is not well characterized by physical examination, MRI may be indicated to evaluate the anatomy of a complex fistula. MRI is becoming the study of choice for the evaluation of complex fistulas and recurrent fistulas. It has been shown to reduce recurrence rates by providing information on otherwise unknown extensions.

Flexible sigmoidoscopy and colonoscopy provide excellent visualization of the colon and rectum. Sigmoidoscopes measure 60 cm in length. Full depth of insertion may allow visualization as high as the splenic flexure. Colonoscopes measure 100 to 160 cm in length and are capable of examining the entire colon and terminal ileum. Both sigmoidoscopy and colonoscopy can be used diagnostically and therapeutically.

The rigid proctoscope is useful for examination of the rectum and distal sigmoid colon and is occasionally used therapeutically.

Endorectal ultrasound is primarily used to evaluate the depth of invasion of neoplastic lesions in the rectum. Ultrasound may also prove useful for early detection of local recurrence after surgery. Endoanal/endorectal ultrasonography has not been used widely for routine clinical fistula evaluation.

• Colon, Rectum, and Anus > Diagnosis
o Schwartz's Principles of Surgery, 10e, Chapter 29

• Diverticular Disease and Common Anorectal Disorders > FISTULA IN ANO
o Harrison's Principles of Internal Medicine, 19e, Chapter 3
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