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Diagnostic Modalities

Last updated on: November 16, 2020

The first, and most important, diagnostic modalities are clinical history and physical examination by the practicing gastroenterologist. The development of large anal tags (often referred to as “elephant ears”) is associated with Crohn’s disease in the perianal area. Fistulas may hide between these large folds, but the patient should either have had a rectal abscess or have pain and stricturing on physical examination. As noted earlier the diagnosis of a Bartholin abscess that has failed to heal in a patient with Crohn’s disease suggests a perivaginal fistula. The intermittent passing of air through the vagina indicates a rectovaginal fistula. This question should be asked of female patients because it is often not volunteered. Rectovaginal fistulas are usually small and derive from the distal portion of the rectovaginal septum with induration palpable on physical examination. Any patient with a suspected fistula should have a complete bowel evaluation, including colonoscopy and small bowel series.

Diagnostic ModalitiesA more precise diagnosis can be made after a colorec-tal surgeon has performed an examination under anesthesia (examination under anesthesia). This procedure has been the gold standard for assessing fistulas, but more recently rectal endoscopic ultrasonography (EUS) and pelvic magnetic resonance imaging (MRI) have been able to more definitively identify a fistula. A small study of 34 patients found that the accuracy of EUS, pelvic MRI, and surgical examination under anesthesia all exceeded 85%. However, when any2 of the diagnostic modalities were combined, the accuracy increased to 100%. All of the above modalities are very helpful in planning whether medical therapy or surgical therapy is most appropriate. The diagnosis of simple fistula by physical examination and endoscopy may be adequate when medical therapy is the initial strategy. However, it is often necessary to perform the above studies to decide whether surgical intervention is required (complex fistulas).

There have been several instruments that have been used to quantify disease activity of fistulas and to assess clinical response. These include the perianal disease activity index, as well as a more recent index used in the infliximab study, which looks at drainage and tenderness. Much has been made of the fact that the patient’s closed fistula can still be detected on MRI. I think this is important academically but of little importance clinically because the patient cares only about whether he or she is having pain and/or drainage.

Surgical therapy will be covered in another chapter and the reader can refer to a recent American Gastroenterological Association technical review of the subject. I would, however, point out that a frequent error in surgical management is the performance of diverting ostomy in the hope that the perianal fistula will heal. In my experience, this will provide only short term relief and the majority of patients will subsequently require a proctectomy Likewise many anal strictures do not require any therapy. Physicians are often surprised to find that they cannot perform a digital rectal exam and yet the patient is having relatively normal bowel movements. Retrograde passage of a finger or a scope does not always correlate with antegrade progression of stool. The same concept can be applied when colonoscopy is ineffective in entering the terminal ileum. This does not mean obstruction.

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