Appendix Anatomy

General

• Vermiform appendix is a blind ending tube of variable length (average 9cm) and a true diverticulum of the caecum

Structure

• Attached to the caecum 2cm below the ileocaecal valve
• Located at the coalescence of the three taeniae coli
• Made up of the same 4 layers as the colon
• Mucosa and submucosa contain B and T lymphoid follicles
• Variable locations - retrocaecal, pelvic, pre/post-ileal, sub-caecal
  • This can alter the presentation to some degree
• Mesoappendix is sail shaped and contains the blood supply and draining lymphatics

Function

• Vestigial organ harboring lymphoid masses but true function not fully understood
  • GALT - gut associated lymphatic tissue - Iga production
  • ?Maturation of thymus independent lymphocytes
  • ?Participation in secretory immune function of GIT

Blood Supply

• Appendiceal artery (posterior caecal A ← ileocolic A) = terminal branch of ileocolic A, within the free margin of the mesoappendix then close to the wall
• Lymphatics
  • Follow arterial flow to the ileocolic nodes → SMA paracolic LN

Appendix Embryology

• Midgut origin
• Caecal diverticulum appears at week 6 - precursor to caecum and appendix
• Appendix visible at 8 weeks
• Colonic elongation results in medial rotation of the caecum and appendix = descent into RLQ
• Appendix pushes ahead of the caecum resulting in variable positioning