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Classification of Crohn’s Disease and Inflammatory Bowel Disease Surgery-Related Fistulae
List of Abbreviations
CD
Crohn's disease
CTE
Computed tomography enterography
ECF
Enterocutaneous fistula
EEF
Enteroenteric fistula
EUA
Examination under anesthesia
EUS
Endoscopic ultrasound
MRE
Magnetic resonance enterography
RVF
Rectovaginal fistula
Introduction
Fistulae occur in 14%–50% of all patients with Crohn's disease (CD). In a population-based study from Olmsted County, Minnesota, 35% of CD patients had at least one fistula. Perianal fistulae comprise at least half of all cases, enteroenteric fistula (EEF) 25%, rectal/anovaginal 10%, and others such as enterocutaneous fistula (ECF) and enterovesical account for 10%–15% of the fistulas. Over a 20-year follow-up, two-thirds of patients experience only one fistula episode whereas the remainder will have two or more related episodes. Of note, the presence of a fistula is an indicator of more aggressive disease that may require more frequent hospitalizations, higher incidence of surgery, and increased utilization of corticosteroid treatment. The diagnosis, assessment, and the treatment of fistulizing CD is complex and mandates a multidisciplinary approach involving gastroenterologists, surgeons, and radiologists at a specialized referral center.
Definitions
A fistula is defined as a pathological connection adjoining two epithelialized surfaces. They can connect a portion of the intestine to the outer surface (e.g., enteroatmospheric or anus to outer skin) or to another inner surface (e.g., enteroenteric, enterovesicular).
Pathophysiology
Despite the prevalence of fistulae in patients with CD, the pathophysiology remains largely unknown. The first step in the formation of a fistula is thought to be tissue destruction from transmural inflammation. The impaired ability of mucosal fibroblasts to migrate toward the area of tissue injury, and the inability of fibroblasts to repair mucosal defects may stimulate the migration of epithelial cells toward the defect. For faster migration, epithelial cells undergo epithelial-mesenchymal cell transition and develop a mesenchymal cell-like phenotype with loose cell to cell contacts, invasive potential, and downregulated apoptotic pathways which may penetrate into the bowel and lead to fistula formation. However, the exact mechanism has yet to be defined.
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