Fistula in Crohn's disease: classification, pathogenesis, and treatment options

Crohn's disease is a form of inflammation that affects the gastrointestinal (GI) tract. It is characterized by persistent inflammation in the gut, which can lead to the formation of abnormal connections called fistulas. These fistulas can occur between the GI tract and the abdominal cavity, adjacent organs, or the skin. The most prevalent type of fistula in Crohn's disease patients is the perianal fistula, which forms between the rectum and the skin near the anus. Although the exact cause of fistula formation is not fully understood, research suggests that factors such as epithelial to mesenchymal transition, matrix metalloproteinase, immune system dysregulation, and microbiota may contribute to their development. There is currently no definitive treatment for fistula closure, but options include surgery, endoscopic procedures, antibiotics, biologic agents, and immunosuppressive drugs. These treatments can be used alone or in combination. However, recurrence is a significant challenge that needs to be addressed in the case of fistula treatment. This review provides an overview of the common types of fistulas, their characteristics, the main factors and mechanisms of fistula formation, and available therapeutic options.