Appendix

General

Anatomy


Editorial Board Member: Wei Chen, M.D., Ph.D.
Deputy Editor-in-Chief: Aaron R. Huber, D.O.
Maryam Kherad Pezhouh, M.D., M.Sc.

Last author update: 7 June 2023
Last staff update: 7 June 2023

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PubMed Search: Anatomy appendix

Maryam Kherad Pezhouh, M.D., M.Sc.
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Cite this page: Pezhouh MK. Anatomy. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/appendixnormalanatomy.html. Accessed April 14th, 2024.
Definition / general
  • Anatomy
    • Commonly located in retrocecal or pelvic region
    • Arises from posteriomedial cecum, usually lies posterior to cecum or ascending colon, may overlie pelvic brim and impinge on bladder; also other locations
    • Locate by following the 3 teniae coli of the large bowel, which all terminate at base of appendix
    • Same 4 layers as gut (mucosa, submucosa, muscularis externa / propria, serosa)
    • Orifice is ~2.5 cm below ileocecal valve; may be covered by small flap of mucosa
    • No known function; may have role in mucosal immunity
  • Vasculature / lymphatics / innervation
    • Vascular supply from posterior cecal branch of ileocolic artery, a branch of superior mesenteric artery
    • Drains into ileocolic vein, then superior mesenteric vein and portal circulation
    • Lymphatics drain into ileocolic lymph nodes
    • Innervation from vagus nerve and superior mesenteric plexus
  • Mesoappendix
    • Adipose tissue plus appendiceal vessels and occasionally small lymph nodes
    • Anchors appendix
  • Abnormal positions of appendix
    • Left sided appendix is associated with congenital anomalies including situs inversus and midgut malrotation; appendicitis is in the differential diagnosis of left lower quadrant pain in these patients (World J Gastroenterol 2010;16:5598)
Essential features
  • Appendix arises from posteromedial aspect of cecum, is lined by large bowel type epithelium and is variable in length from 2 - 20 cm
Diagrams / tables

Images hosted on other servers:

Cecum, appendix and arteries

View from cecum

Gross description
  • Blind vermiform structure with attached mesoappendix
Gross images

Contributed by Maryam Kherad Pezhouh, M.D., M.Sc.
Appendix

Appendix

Microscopic (histologic) description
  • Large bowel type epithelium
  • Rich lymphoid tissue in mucosa and submucosa that may disrupt the muscularis mucosa, obliterate the lumen and distort the crypt architecture (lymphoid tissue atrophies with age)
  • Epithelium contains occasional Paneth cells at crypt bases (basal nucleus, conspicuous nucleoli, abundant eosinophilic supranuclear granules)
  • Lamina propria also contains plasma cells, occasional eosinophils
  • Muscularis propria contains complete longitudinal and circular layers and prominent ganglion cells
  • Presence of neutrophils is not typical and suggests acute appendicitis
Microscopic (histologic) images

Contributed by Maryam Kherad Pezhouh, M.D., M.Sc.
Cross section of an appendix

Cross section of an appendix

Board review style question #1

Which of these features can be seen in a normal appendix?

  1. Focal lymphoid follicle
  2. Neutrophils
  3. Tubular adenoma
  4. Ulceration
Board review style answer #1
A. Focal lymphoid follicle. Focal small lymphoid follicles can normally be seen in a normal appendix. Answers B and D are incorrect because they are features of acute appendicitis. Answer C is incorrect as tubular adenoma is not a normal finding anywhere in the GI tract.

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Reference: Appendix - Anatomy
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