Vermiform appendix

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.

Normal

Normal vermiform appendix

General

• Seen in right-hemicolectomies for cancer.
• May be seen in right hemicolectomies for Crohn's disease.

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

• Common.
• Use for quality control among general surgeons.^{[citation needed]}

Gross

See normal vermiform appendix.

Microscopic

See normal vermiform appendix.

Notes:

• Should be submitted in total.

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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 ACUTE PERIAPPENDICITIS. 

Inflammatory pathologies

Acute appendicitis

General

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

Short clinical DDx:

• GI tract:
  • Symptomatic Meckel diverticulum.
  • Epiploic appendagitis.
• 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.
  • Similar numbers are found in another study.

Microscopic

Features:

• Neutrophils in the muscularis propria - key feature.
• +/- Vascular thrombosis (and necrosis) - known as gangrenous appendicitis.
• +/- Findings suggestive of etiology - usu. absent:
  • +/- Fecalith.
  • +/- Viral inclusions (extremely rare)
    • See adenovirus appendicitis.

Images:

• Appendicitis - low mag. (WC).
• Appendicitis - very high mag. (WC).

DDx

• Mucinous tumour.
• Neuroendocrine tumour.
• Granulomatous appendicitis.
• Crohn's disease of the appendix.
  • Approximately of 40% colectomies for CD (that include an appendix) have involvement of the appendix.

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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:

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

Notes:

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

Image:

• Smudge cell (medpedia.com).

IHC

• Adenovirus +ve = diagnostic.

Enterobius vermicularis

Main article: Enterobius vermicularis

• AKA pinworm.

General

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

Microscopic

Features:

• Usu. the appendiceal wall has no inflammation, i.e. there is no appendicitis.
• Enterobius vermicularis organisms.

Granulomatous appendicitis

Most common cause:

• Yersinia appendicitis.

DDx:

• Yersinia appendicitis.
  • Yersinia = gram negative rod (red on Gram stain).
  • "Safety pin"-like appearance - 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.

Microscopic

Features:

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

Image(s):

• Yersinia (CDC).

Inflammatory bowel disease

See Inflammatory bowel disease.

Periappendicitis

General

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

• 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.

Microscopic

Features:

• Acute inflammation of the serosa.
  • Neutrophils in the serosa.

Tumours of the appendix

Adenocarcinoma

• Like colorectal adenocarcinoma - see colorectal tumours.

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:

• 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):

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

• AKA crypt cell carcinoma.
• AKA neuroendocrine tumour with goblet cell differentiation.

General

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

Microscopic

Features:

• Mixed neuroendocrine-nonneuroendocrine tumour; features of both carcinoid and adenocarcinoma.
  • 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:

• GCC - very high mag. (WC).
• GCC - very low mag. (WC).

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.

Neuroendocrine tumour of the appendix

Main article: Neuroendocrine tumour

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

General

• Most common tumour of the appendix.

Size matters in appendiceal NETs:

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

Microscopic

Features:

• See neuroendocrine tumours.

IHC

Features:

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

See: neuroendocrine tumours.

See also

• Colon.
• Gastrointestinal pathology.