INTRODUCTION
The human appendix is similar to a diverticulum of the cecum, which is considered a vestigial organ. Previously, the biological function of the appendix was unclear; therefore, it was surgically removed on inflammation. Clinicians consider appendectomy a safe and effective technique for managing appendicitis [1]. In the United States, the lifetime appendectomy risks in men and women are 12% and 23% but the lifetime appendicitis risks are 8.6% and 6.7%, respectively [2]. In Taiwan, 10.8% of appendectomies were not related to appendicitis [3].
The submucosa of the appendix contains numerous lymphoid follicular centers. In addition, complicated immune system cells are present in the mucosa (e.g., Treg cells, M cells, and T and B cells) and submucosa (e.g., B lymphocytes, T lymphocytes, macrophages, centrocytes, and CD4+/CD8+ cells) of the appendix [4,5]. Studies have indicated that the appendix interacts with intestinal flora and balances the intestinal immune system [4,6,7]. The bacteria in the appendix may act as a biofilm inoculum of the intestinal commensal microbiome, which facilitates reinoculation of the proximal large bowel and terminal ileum. The complex immune system and a shelter for microbiome in the appendix can balance proinflammation and antiinflammation of the bowel and maintain homeostasis [4].
Inflammatory bowel diseases (IBDs) mainly consist of Crohn’s disease (CD) and ulcerative colitis (UC), which cause prolonged inflammation of the digestive tract. IBDs considerably affect health-related quality of life and markedly increase health care costs [8,9]. The incidence of IBDs has increased steadily in Taiwan [10]. The exact cause of IBDs remains unclear. In addition to genetics, the environmental composition of intestinal microbiome may play a role in uncontrolled gut inflammation [11]. However, the relationship between appendectomy and IBD development has been controversial in Western countries [12-14]. Studies on the association of appendectomy with subsequent IBD risk are scant. Therefore, we conducted a nationwide cohort study to examine whether IBD risk is higher in the appendectomy cohort than in the nonappendectomy cohort.