Vermiform appendix

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The vermiform appendix, usually just appendix, is a little thingy that is attached to the cecum. Taking it out is the bread 'n butter of general surgery.

The appendix is a vestigial structure that is thought to have arisen from a larger cecum. Larger cecae are often seen in herbivores and thought to facilitate better digestion of plant matter.[1]

Normal

Normal vermiform appendix

General

Gross

  • Shiny serosal surface.
    • No exudate.
  • Small diameter.

Microscopic

Features:

  • +/-Lymphoid hyperplasia.

Negatives:

  • No neutrophils in the muscularis propria.
  • No lesion in appendiceal tip.
  • No serosal inflammation.
  • No organisms in the appendiceal lumen, e.g. Enterobius vermicularis.

Negative appendectomy

General

Gross

See normal vermiform appendix.

Microscopic

See normal vermiform appendix.

Notes:

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VERMIFORM APPENDIX, APPENDECTOMY:
- APPENDIX NEGATIVE FOR ACUTE APPENDICITIS AND NEGATIVE FOR ACUTE PERIAPPENDICITIS. 
VERMIFORM APPENDIX, APPENDECTOMY:
- APPENDIX WITH LYMPHOID HYPERPLASIA AND FOCAL MUCOSAL EROSIONS.
- NEGATIVE FOR ACUTE APPENDICITIS.
- NEGATIVE FOR ACUTE PERIAPPENDICITIS. 

Inflammatory pathologies

Acute appendicitis

General

  • Bread 'n butter of general surgery.
  • Interesting factoid: appendicitis is considered protective against ulcerative colitis.[2][3]

Short clinical DDx:

  • GI tract:
  • Gynecologic tract:
    • Ectopic pregnancy.
    • Ruptured ovarian cyst.
    • Ovarian torsion.
      • Pelvic inflammatory disease.

Gross

Features:

  • Serosal surface dull.
  • May be perforated (best determined on gross).
  • +/-Fibrinous exudate.

Note:

  • Normal diameter of appendix (based on CT): 6.6 +/- 1.5 mm.[4]
    • Similar numbers are found in another study.[5]

Microscopic

Features:

  • Neutrophils in the muscularis propria - key feature.
  • +/- Vascular thrombosis (and necrosis) - known as gangrenous appendicitis.[6]
  • +/- Findings suggestive of etiology - usu. absent:

Images:

DDx

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VERMIFORM APPENDIX, APPENDECTOMY:
	- ACUTE APPENDICITIS.
	- ACUTE PERIAPPENDICITIS. 
VERMIFORM APPENDIX, APPENDECTOMY:
	- GANGRENOUS APPENDICITIS.
	- ACUTE PERIAPPENDICITIS. 

Micro

Gangrenous appendicitis

The sections shows appendiceal wall with marked acute transmural inflammation and necrotic appendiceal wall with large collections of neutrophils. Several medium-sized blood vessels are thrombosed. A thick layer of neutrophils cover the serosa aspect.

Adenovirus appendicitis

General

  • Rare type of appendicitis in children.
  • Presents as run-of-the-mill acute appendicitis.
  • Caused by Adenovirus.

Microscopic

Features:[8]

  • Lymphoid hyperplasia - key feature.
  • +/-Adenovirus inclusions; "smudge cells".

Notes:

  • The classic finding of appendicitis (neutrophils infiltrating into the muscularis propria) may be absent.[8]

Image:

IHC

  • Adenovirus +ve = diagnostic.

Enterobius vermicularis

General

  • May be found in the appendix.
  • The incidence is higher in normal appendices than inflamed ones.[9][10]

Microscopic

Features:

Granulomatous appendicitis

Most common cause:

  • Yersinia appendicitis.[11]

DDx:[12]

  • Yersinia appendicitis.[11]
    • Yersinia = gram negative rod (red on Gram stain).
    • "Safety pin"-like appearance[13] - approximately 0.5 micrometers diameter x 2 micrometers length.
  • Other micro-organism (TB, fungus).
  • Crohn's disease.
  • Sarcoidosis.
  • Foreign body reaction.
  • Interval (delayed) appendectomy.
    • Approximately 60% of delayed appendectomies have granulomas.[14]

Microscopic

Features:

  • Granulomas.
  • +/-"Safety pin"-like organisms (Yersinia).

Image(s):

Inflammatory bowel disease

See Inflammatory bowel disease.

Periappendicitis

General

Definition: inflammation of tissues around the (vermiform) appendix.[15]

  • May be seen in association of appendicitis or alone.
    • With appendicitis it is suggestive of perforation.
    • Without concurrent appendicitis it is suggestive of another abdominal pathology.[16][17]

Microscopic

Features:

  • Acute inflammation of the serosa.

Tumours of the appendix

Adenocarcinoma

Mucinous tumours of the appendix

General

  • Classification is controversial.
    • The controversy centres on whether to call all mucinous tumours outside of the appendix adenocarcinoma - regardless of whether they have atypia & show invasion.
  • In women - an ovarian primary must be excluded.
    • Concurrent bilateral ovarian tumours suggests the tumour originated from the appendix and spread to the ovaries.

Classification:[18]

  • Benign - low grade mucinous tumour.
  • Borderline - mucinous tumour of uncertain malignant potential or borderline mucinous tumour.
  • Malignant - mucinous adenocarcinoma.

Five year survival (in a series of 107 cases):[18]

Tumour Five year survival
LAMN 100%
LAMN extra-appendiceal spread 86%
MACA 44%
  • LAMN = low-grade appendiceal mucinous neoplasm.
  • LAMN extra-appendiceal = low-grade appendiceal mucinous neoplasm with extra-appendiceal spread.
  • MACA = mucinous adenocarcinoma of the appendix.

Microscopic

Low-grade appendiceal mucinous neoplasm

  • AKA benign mucinous tumour of the appendix.

Microscopic:

  • Epithelium forms tufts - vaguely resemble serrations, i.e. the saw-tooth pattern in hyperplastic polyps.
  • Single layer of epithelium.
  • Mucin contained (inside appendix only).

Negatives:

  • No marked nuclear atypia.
  • No invasion into the lamina propria.

Low-grade appendiceal mucinous neoplasm with extra-appendiceal spread

  • AKA mucinous borderline tumour of the appendix.

Microscopic:

  • Same as LAMN but mucin outside of the appendix.
  • Cells in mucin, i.e. cellular mucin.

Mucinous adenocarcinoma of the appendix

  • AKA malignant mucinous tumour of the appendix.

Microscopic:

  • Marked nuclear pleomorphism.
  • Invasion into the appendiceal wall.

Goblet cell carcinoid

General

  • Rare appendiceal tumour that typically has an aggressive course vis-a-vis other appendiceal carcinoids.[19]
  • Mixed (biphasic) tumour with endocrine and exocrine features.

Microscopic

Features:[20]

  • Mixed neuroendocrine-nonneuroendocrine tumour;[21] features of both carcinoid and adenocarcinoma.[20]
    • Archictecture: cells arranged in nests or clusters without a lumen.
    • Location: deep to the intestinal crypts (crypts of Lieberkühn); usually do not involve the mucosa.
    • Cytoplasm distended with mucin.
    • DNA: crescentic nucleus (similar to in signet-ring cells).
      • +/-Multinucleation.
      • +/-High mitotic rate.
      • Usually minimal nuclear atypia.

Images:

Stains

  • Mucin stains +ve:
    • Mucicarmine, perodic acid-Schiff diastase (PAS-D), alician blue.

IHC

  • Classic neuroendocrine markers:
    • Synaptophysin +ve.
    • Chromogranin +ve.
  • S100 +ve.
  • NSE +ve.
  • Serotonin +ve.

Keratins:

  • Usually CK20 +ve > CK7 +ve.
  • CEA +ve (membrane).

Notes:

  • Nice review of stains in Pahlavan and Kanthan.[20]

Neuroendocrine tumour of the appendix

  • Previously known as appendiceal carcinoid.
  • AKA appendiceal neuroendocrine tumour, abbreviated appendiceal NET.

General

  • Most common tumour of the appendix.[22]

Size matters in appendiceal NETs:[23]

  • <1.0 cm - do not metastasize.
  • 1.0-2.0 cm - rarely metastasize.

Microscopic

Features:

IHC

Features:

  • Chromogranin A -ve/+ve.
  • Synaptophysin +ve.

See: neuroendocrine tumours.

See also

References

  1. Dawkins, R. (2009). The Greatest Show on Earth: The Evidence for Evolution (1st ed.). Free Press. pp. 115. ISBN 978-1416594789.
  2. Beaugerie, L.; Sokol, H. (Aug 2009). "Appendicitis, not appendectomy, is protective against ulcerative colitis, both in the general population and first-degree relatives of patients with IBD.". Inflamm Bowel Dis. doi:10.1002/ibd.21064. PMID 19685454.
  3. Timmer, A.; Obermeier, F. (2009). "Reduced risk of ulcerative colitis after appendicectomy.". BMJ 338: b225. PMID 19273505.
  4. Charoensak, A.; Pongpornsup, S.; Suthikeeree, W. (Dec 2010). "Wall thickness and outer diameter of the normal appendix in adults using 64 slices multidetector CT.". J Med Assoc Thai 93 (12): 1437-42. PMID 21344807.
  5. Huwart, L.; El Khoury, M.; Lesavre, A.; Phan, C.; Rangheard, AS.; Bessoud, B.; Menu, Y. (Mar 2007). "[What is the thickness of the normal appendix on MDCT?].". J Radiol 88 (3 Pt 1): 385-9. PMID 17457270.
  6. URL: http://emedicine.medscape.com/article/363818-overview. Accessed on: 21 June 2010.
  7. Stangl, PC.; Herbst, F.; Birner, P.; Oberhuber, G. (Apr 2002). "Crohn's disease of the appendix.". Virchows Arch 440 (4): 397-403. doi:10.1007/s004280100532. PMID 11956821.
  8. 8.0 8.1 Grynspan D, Rabah R (2008). "Adenoviral appendicitis presenting clinically as acute appendicitis". Pediatr. Dev. Pathol. 11 (2): 138–41. doi:10.2350/07-06-0299.1. PMID 17990936.
  9. 9.0 9.1 Wiebe, BM. (Mar 1991). "Appendicitis and Enterobius vermicularis.". Scand J Gastroenterol 26 (3): 336-8. PMID 1853157.
  10. 10.0 10.1 Dahlstrom, JE.; Macarthur, EB. (Oct 1994). "Enterobius vermicularis: a possible cause of symptoms resembling appendicitis.". Aust N Z J Surg 64 (10): 692-4. PMID 7945067.
  11. 11.0 11.1 Lamps LW, Madhusudhan KT, Greenson JK, et al. (April 2001). "The role of Yersinia enterocolitica and Yersinia pseudotuberculosis in granulomatous appendicitis: a histologic and molecular study". Am. J. Surg. Pathol. 25 (4): 508–15. PMID 11257626.
  12. http://granuloma.homestead.com/appendicitis.html
  13. URL: http://www.cdc.gov/ncidod/dvbid/plague/p1.htm. Accessed on: 30 June 2011.
  14. Guo, G.; Greenson, JK. (Aug 2003). "Histopathology of interval (delayed) appendectomy specimens: strong association with granulomatous and xanthogranulomatous appendicitis.". Am J Surg Pathol 27 (8): 1147-51. PMID 12883248.
  15. URL: http://www.medilexicon.com/medicaldictionary.php?t=66889. Accessed on: 1 June 2011.
  16. Fink, AS.; Kosakowski, CA.; Hiatt, JR.; Cochran, AJ. (Jun 1990). "Periappendicitis is a significant clinical finding.". Am J Surg 159 (6): 564-8. PMID 2349982.
  17. O'Neil, MB.; Moore, DB. (Sep 1977). "Periappendicitis: Clinical reality or pathologic curiosity?". Am J Surg 134 (3): 356-7. PMID 900337.
  18. 18.0 18.1 Misdraji J, Yantiss RK, Graeme-Cook FM, Balis UJ, Young RH (August 2003). "Appendiceal mucinous neoplasms: a clinicopathologic analysis of 107 cases". Am. J. Surg. Pathol. 27 (8): 1089–103. PMID 12883241. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0147-5185&volume=27&issue=8&spage=1089.
  19. 19.0 19.1 van Eeden S, Offerhaus GJ, Hart AA, et al. (December 2007). "Goblet cell carcinoid of the appendix: a specific type of carcinoma". Histopathology 51 (6): 763–73. doi:10.1111/j.1365-2559.2007.02883.x. PMID 18042066.
  20. 20.0 20.1 20.2 Pahlavan PS, Kanthan R (June 2005). "Goblet cell carcinoid of the appendix". World J Surg Oncol 3: 36. doi:10.1186/1477-7819-3-36. PMC 1182398. PMID 15967038. http://wjso.com/content/3/1/36. Cite error: Invalid <ref> tag; name "pmid15967038" defined multiple times with different content Cite error: Invalid <ref> tag; name "pmid15967038" defined multiple times with different content
  21. Volante M, Righi L, Asioli S, Bussolati G, Papotti M (August 2007). "Goblet cell carcinoids and other mixed neuroendocrine/nonneuroendocrine neoplasms". Virchows Arch. 451 Suppl 1: S61–9. doi:10.1007/s00428-007-0447-y. PMID 17684764.
  22. Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 435. ISBN 978-1416054542.
  23. Modlin, IM.; Lye, KD.; Kidd, M. (Feb 2003). "A 5-decade analysis of 13,715 carcinoid tumors.". Cancer 97 (4): 934-59. doi:10.1002/cncr.11105. PMID 12569593.