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Appendix

Normal anatomy


Reviewer: Jaleh Mansouri, M.D., (see Reviewers page)
Revised: 15 October 2012, last major update August 2012
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

Anatomy
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● Commonly located in retrocecal or pelvic region
● Arises from posteriomedial cecum, usually lies posterior to cecum or ascending colon, may overly 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 value; may be covered by small flap of mucosa
● No known function; may have role in mucosal immunity

Vasculature / lymphatics / innervation
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● 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
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● Adipose tissue plus appendiceal vessels and occasionally small lymph nodes
● Anchors appendix

Abnormal positions of appendix
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● 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 Gastroenterology 2010;16:5598)

Drawings
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Cecum, appendix and arteries


View from cecum

Clinical images
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Left-normal appendix in right lower quadrant versus right-appendix in left lower quadrant

Gross description
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● Wormlike (vermiform), mean 6-8 cm long in adults (range 2 cm [infants] to 15 cm)
● Mean diameter 0.7 cm
● Distal appendix may undergo fibrous obliteration in elderly but some patients have fibrous cord from birth
● Serosa smooth, glistening, transparent
● Cross section may be stellate due to lymphoid aggregates

Micro description
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● Large bowel type epithelium overlying lamina propria with irregularly distributed crypts (glands)
● 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 histiocytes, occasional eosinophils, neuroendocrine cells
● Muscularis mucosa and submucosa may be inconspicuous
● Muscularis propria contains complete longitudinal and circular layers and prominent ganglion cells

Micro images
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Various images

Virtual slides
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Normal appendix

End of Appendix > Normal anatomy


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