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.