Perianal disease is an important and distinguishing feature of Crohn's disease (CD). The incidence of perianal disease in patients with CD varies from 3.8% to 81% in different series [1, 2]. While perianal lesions occur more often in patients with colonic disease than in patients with small intestinal disease , 5% of patients with anorectal CD do not have proximal disease. Clinical features include hypertrophic skin tags, ulceration (Fig. 1), perianal abscesses and fistulae (Figs. 2 and 3), fissures, induration and anal stenosis . A characteristic feature of perianal CD is that several abnormalities may coexist. Perianal abscesses occur in 23-62% of patients and are usually multiple and complex due to deep, cavitating ulcers that penetrate the anorectal wall . Crohn's abscesses may also arise as a result of an infection of the intersphincteric anal glands. Anorectal fistulae in CD arise in 6-34% of patients . According to their relationship with the sphincters , fistulae are classified in intersphincteric, transsphincteric, suprale-vator, extrasphincteric and submucosal. The American Gastroenterological Association recommended the division of fistulae into either simple or complex . A simple fistula is a superficial, intersphincteric or low transsphincteric fistula, without secondary tracts, and it is not associated with an abscess. Com
Fig. 2. Complex perianal sepsis in Crohn's disease with presence of multiple external fistulous openings
Fig. 3. Large perianal abscess in Crohn's disease extending to the anterior perineum plex fistulae (high transsphincteric, suprasphinc-teric, or extrasphincteric fistulae, presence of multiple external openings, secondary tracts or large abscesses) may result from active rectal disease, which form deep, cavitating ulceration and fistula-tion. Rectovaginal fistula in CD occurs in 5.2-10% of patients . In these fistulae, the internal opening may be present at the dentate line and the external opening at the fornix or low in the vagina (anovagi-nal), or the tract passes directly from the rectum to the vagina.
The diagnosis of perianal CD can be made when there is a persistent characteristic pathological lesion in association with the anal canal in a patient known to have at least two criteria for the diagnosis of the intestinal CD: clinical, radiological and histological. Perianal CD can be diagnosed in the absence of obvious clinical manifestations on intestinal CD, providing that there are typical perianal lesions showing histological evidence of granulomata in biopsies taken from ulcers or abscesses. Perianal CD is often difficult to treat, and different management modalities (surgery, medical therapy, diet) have been tried with variable results . Disease activity appears to be associated with impaired wound healing, but wounds usually heal normally when the disease is inactive. Accurate evaluation is crucial for the treatment plan. Physical examination may reveal simple fistulae with a relatively superficial position; however, it is unable to identify ischiorectal, pelvirectal and horseshoeing tracts and most of the internal openings. When disease is active, the anal lesions have a characteristic swollen, translucent pink or bluish appearance with obvious ulceration. As disease activity resolves, oedema disappears, the tissue becomes opaque and ulcers heal with a fragile layer of epithelium. Inactive lesions may remain clinically significant because of the mechanical effects of the fistula or strictures.
Due to the limitations of conventional fistulogra-phy and pelvic computed tomography (CT) scanning , endoanal ultrasonography (EAUS) [8, 9] or pelvic magnetic resonance imaging (MRI) [10, 11] have been introduced as useful investigative modalities for perianal CD. In the following chapter, equipment, technique, endosonographic anatomy of the anal canal, accuracy and reliability of EAUS in the evaluation of perianal abscesses and fistulae in CD and comparison of EAUS with MRI is discussed.
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