Endoscopic evaluation of perianal Crohn’s disease

Abbreviations

Introduction

Perianal fistulas are the most common phenotype of penetrating Crohn’s disease (CD), with a prevalence of 20%–24% in the patients with CD . The cumulative incidence was estimated to be 12% and the incidence to be 0.7 per 100 patient-years . The terms of perianal fistulizing CD and perianal CD (pCD) have been used interchangeably. pCD can be associated with strictures, abscesses, perianal skin lesions, and even malignant changes, Diagnostic evaluation of pCD has been largely relied on cross-sectional imaging [such as computed tomography (CT), magnetic resonance imaging (MRI), transanal ultrasound] or contrasted fistulography. For both diagnostic and therapeutic purposes, examination under anesthesia (EUA) is routinely performed. Based on clinical, radiographic, or operative features, various classifications have been proposed . The most commonly used is the Parks’ classification ( Table 7.1 ) , St. James Hospital classification ( Table 7.2 ) , and the American Gastroenterological Association (AGA) classification ( Table 7.3 ) , which mainly delineate characteristics of perianal fistulas (e.g., route and number of openings) in relationship to the internal and external anal sphincters. To assess patients’ quality of life (i.e., pain or restructure of physical and sexual activities) and perianal disease activity (i.e., fistula discharge, type of perianal disease, and perianal induration), investigators have proposed the Perianal Crohn’s Disease Activity Index in a graded scale . In addition, imaging-based classification of pCD has been proposed ( Table 7.4 ) . The pros and cons of the various classifications are appraised ( Table 7.5 ) .

The role of conventional endoscopy in the evaluation of pCD has been peripheral, mainly for the identification of the primary or internal opening of fistula or concurrent proctitis, distal bowel or anal strictures, or pouchitis or cuffitis (in patients with ileal pouches). An endoscopic evaluation may also help to identify pCD-associated adenocarcinoma or squamous cell cancer . However, the role of endoscopy has been evolving from a diagnostic modality to a tool of delivery of therapy. Endoscopic documentation of perianal or perineal skin lesions would provide additional “bonus.” Therefore a new Columbia Classification of Perianal Crohn’s Disease is here proposed ( Table 7.6 ). The contents of this chapter will follow the framework of this classification.

Etiologies of perianal Crohn’s disease

The pathogenesis of pCD is not entirely clear. It is believed that increased production of proinflammatory factors, such as transforming growth factor β, tumor necrosis factor, as well as interleukin-13 induce epithelial-to-mesenchymal transition and upregulation of matrix metalloproteinases, resulting in tissue remodeling and fistula formation . Although the perianal disease is a form of presentation of CD, not all pCD results solely from the underlying disease process. Perianal fistula and perianal abscess can result from surgical staple line or suture line leaks, or cryptoglandular source. The characterization of the internal opening of the fistula and the status of inflammation in the distal large bowel or anal canal are important for the differential diagnosis.

CD-associated perianal disease typically presents with inflammation of the distal rectum, ileal pouch, or anal canal. The internal opening may not be obvious to be identified, as it is often covered with granular tissue and surrounded by inflammation at the adjacent bowel ( Fig. 7.1 ). Cryptoglandular fistulae or abscesses can also occur in patients with CD, which is often short and superficial; respond favorably to medical and surgical therapy; and sometimes, maybe self-limited. A careful endoscopic examination or EUA may identify an internal opening of the fistula at the dentate line. The patients may or may not have concurrent proctitis or pouchitis or cuffitis [in patients with ileal pouch–anal anastomosis (IPAA)] ( Figs. 7.2 and 7.3 ). Cryptoglandular abscesses are common causes of anal vaginal fistulas ( Fig. 7.4C and D ).

Surgical bowel resection is an effective treatment modality for refractory CD. Currently performed bowel surgery includes resection followed by colorectal anastomosis, rectal anal anastomosis, colo-anal anastomosis, and IPAA. The lower anastomoses may be complicated with leaks, fistulas, or abscesses. The internal opening of the leak or fistula can more readily be identified than that from CD. The opening often shows a clear orifice with normal surrounding mucosa. Anastomosis leak-associated fistula or abscesses can be difficult to differentiate from that resulting from underlying CD ( Fig. 7.5 ).

Fecal diversion with an ileostomy or colostomy, which may be performed along with partial colectomy, is an effective treatment modality for refractory pCD or CD in the distal bowel. Diverted bowels, such as diverted colon, diverted rectum (i.e., Hartmann pouch), or diverted pelvic ileal pouch, often develop diversion–association inflammation or stricture. Perianal skin lesions, fistulae, or abscesses may be present before or de novo after fecal diversion ( Fig. 7.6 ).

Another form of pCD is the persistent perineal sinus or fistula after total proctocolectomy or completion proctectomy following colectomy. Patients with preproctectomy are at risk ( Fig. 7.7 ).

Associated conditions

pCD with the presence of stricture, abscess, and fistula to the adjacent organs has been classified into complex fistula, according to the AGA classification .