A review of the function and evolution of the cecal appendix

Abstract

Since its initial discovery in the 1500s, the cecal appendix has been an anatomical structure of great intrigue, notorious for its inconvenient tendency to become inflamed and often require surgical intervention. Appendicitis is one of the most common indications for emergency abdominal surgery, costing healthcare systems billions of dollars globally and causing tens of thousands of deaths annually. Yet, recent studies have indicated that the appendix may serve important protective functions in fortifying the body's immune response against invading pathogens and re-inoculating the gut with commensal bacteria after periods of gastrointestinal illness. While the cecal appendix was once believed to be a synapomorphy of hominoids (humans and other great apes), recent studies suggested that it is a recurrent trait found in several other species of primates, rodents, lagomorphs, marsupials, and monotremes. Mapping appendiceal and other gastrointestinal traits across a mammalian consensus phylogeny revealed that the cecal appendix has evolved independently numerous times throughout mammalian evolution, significantly more than would be expected due to chance alone, suggesting that the appendix is adaptively advantageous. However, attempts to identify an overarching ecological, behavioral, dietary, or environmental factor driving some species to evolve an appendix have been largely unsuccessful, indicating that the cecal appendix has a complex and diverse evolutionary history. This review discusses the current understanding of the pathophysiology, evolution, and possible functions of the appendix, both within humans and broadly across the class Mammalia.

From anatomy to immunity in the gastrointestinal system

“…The article by Smith (2022) reviews the functional relevance of the cecal appendix from an evolutionary perspective, and makes a compelling case for it. The appendix, as the gallbladder, lacks a clear definition of a vital function and thus has been equally viewed as a "useless" organ.…”

“…In the United States alone, more than 500,000 cholecystectomies are performed and 400,000 cases of appendicitis are reported every year, with combined estimated health care costs of over 9 billion dollars (Davies et al, 2004; Ferris et al, 2017; NIH, 2004; Schirmer et al, 2005). This is quite something for two small organs that we do not fully understand and have branded as dispensable, even though as is the case for the appendix, managed to appear at least 29 independent times throughout mammalian evolution (Smith, 2022). Smith discusses two notable points: (i) the possible function of the appendix as a “safe house” for commensal microbial populations and the immunological response in times of intestinal emergencies and (ii) the difficulty to establish a cohesive evolutionary frame of the appendix, when the evidence suggest that there may not be one.…”

The vermiform cecal appendix, expendable or essential? A narrative review

“…The vermiform cecal appendix continues to occupy an inquisitive place in history that describes an organ with a contentious defined purpose [1 ▪ ]. When local abdominal acute inflammatory sequelae ensue, an almost immediate surgical removal of the organ may result [1 ▪ ].…”

“…The vermiform cecal appendix continues to occupy an inquisitive place in history that describes an organ with a contentious defined purpose [1 ▪ ]. When local abdominal acute inflammatory sequelae ensue, an almost immediate surgical removal of the organ may result [1 ▪ ]. Notwithstanding, a recent evidence-based report provided an updated view, with recommendations on the diagnosis, its nonsurgical and surgical management, and the use of prescribed antibiotics to resolve the local inflammation [2].…”

Comparative Study between Open and Laparoscopic Appendectomy in Acute Appendicitis

“…Appendicitis is simply defined as the vermiform appendix becoming inflamed, and the acute type is the majority intra-abdominal case that requires emergency surgery (1,2) . This condition usually begins acutely, but over time becomes chronic.…”