What is the purpose of the appendix?

The Purpose of the Appendix

The appendix is not a vestigial organ but serves important immunological functions, acting as a "safe house" for commensal bacteria that can repopulate the gut microbiome after intestinal illness and supporting immune system development.

Immunological Functions

• The appendix contains substantial lymphatic tissue that plays an important role in mammalian mucosal immune function, particularly in B-lymphocyte-mediated immune responses and extrathymically derived T-lymphocytes 1
• It serves as a component of gut-associated lymphoid tissue (GALT), contributing to the body's immune surveillance and defense mechanisms 1
• The appendix helps regulate pathogens through its lymphatic vessels, potentially producing early defenses against deadly diseases 1

Microbial Reservoir Function

• The appendix functions as a "safe house" for commensal bacteria, providing support for bacterial growth and facilitating re-inoculation of the colon after intestinal illnesses 2
• The unique architecture of the human appendix makes it well-suited to protect and support colonization by beneficial bacteria 2
• High-throughput sequencing has revealed that the human appendix contains a robust and varied microbiota distinct from other niches within the human microbiome 3
• The appendix harbors a diverse microbial community dominated by Firmicutes, with additional representation from Proteobacteria, Bacteroidetes, Actinobacteria, and Fusobacteria 3

Impact of Appendectomy on Health

• Appendectomy has been associated with significant alterations in gut bacterial and fungal populations 4
• After appendectomy, patients show decreased bacterial diversity and lower abundance of beneficial short-chain fatty acid-producing microbes like Roseburia, Barnesiella, and Butyricicoccus 4
• Long-term studies indicate that appendectomy may be associated with increased risk for developing inflammatory conditions including Crohn's disease and ulcerative colitis 5
• Appendectomy has also been linked to higher incidence of Clostridium difficile infection, sepsis, and colorectal cancer in long-term follow-up studies 5

Clinical Implications

• The removal of a normal-appearing appendix during surgery for suspected appendicitis remains controversial, with varying recommendations from surgical societies 6
• The World Society of Emergency Surgery provides a weak recommendation supporting appendix removal when it appears normal during surgery for suspected appendicitis in symptomatic patients 6
• Intra-operative macroscopic assessment of the appendix is challenging, with studies showing 19-40% of visually normal appendices are actually pathologically abnormal 6
• The decision to remove a normal-appearing appendix should weigh the risk of leaving a potentially abnormal appendix against the risk of appendectomy in each individual scenario 6

Pitfalls and Considerations

• The surgeon's macroscopic judgment of early grades of acute appendicitis is often inaccurate and highly variable 6
• Leaving an apparently normal appendix in situ carries risks of subclinical or endo-appendicitis with persisting symptoms and potential missed appendiceal malignancy 6
• Routine histopathology after appendectomy is strongly recommended to identify unexpected findings 6
• The negative appendectomy rate can be as high as 36% in some series, highlighting the diagnostic challenges in appendicitis 6