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.
    • Colon cancer.
    • Crohn's disease.
  • Surgeries for ovarian mucinous tumours.

Gross

• Shiny serosal surface.
  • No exudate.
• Normal diameter.
  • 6.6 +/- 1.5 mm -- based on CT.

Microscopic

Features:

• +/-Lymphoid hyperplasia - mucosa or submucosa.
• Normal colorectal-type mucosa.
• Fatty submucosa.
• Benign smooth muscle.
• Serosa.

Negatives:

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

DDx:

• Adenovirus appendicitis.
• Cryptosporidiosis.
• Mild colitis.

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VERMIFORM APPENDIX WITHIN NORMAL LIMITS.

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.

DDx:

• Acute appendicitis.
• Adenovirus appendicitis.
• Appendiceal neuroendocrine tumour.
• Non-appendiceal pathology - see DDx of acute appendicitis.
  • Isolated periappendicitis.

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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. 

Micro

The sections show appendiceal wall with focal mucosa erosions and several intraluminal neutrophil clusters. Lymphoid hyperplasia is present. Fecal material is present within the lumen of the appendix.

There are no neutrophils within the muscularis propria. There is no serositis. There is no distortion of the crypt architecture. No granulomas are identified. No cryptitis is identified.

Inflammatory pathologies

Acute appendicitis

Main article: Acute appendicitis

Adenovirus appendicitis

Main article: Adenovirus appendicitis

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.
• Clinically mimics appendicitis.

Microscopic

Features:

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

Image

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  Enterobius - very low mag. (WC/Nephron)

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  Enterobius - high mag. (WC/Nephron)

• 

  Pinworm (WC/Uthman)

Granulomatous appendicitis

General

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):

• 

  Granulomatous Appendicitis (SKB)

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  Suppurating Granulomatous Appendicitis (SKB)

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  Suppurating Granulomatous Yersinia Appendicitis (SKB)

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  Suppurating Granulomatous Yersinia Appendicitis Yersinia(SKB)

• 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.

DDx:

• Acute appendicitis.

Tumours of the appendix

Adenocarcinoma

• Like colorectal adenocarcinoma - see colorectal tumours.

Mucinous tumours of the appendix

Main article: Mucinous tumours of the appendix

This grouping includes mucinous cystadenoma and mucinous cystadenocarcinoma.

Goblet cell carcinoid

Main article: Crypt cell carcinoma

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.
  • Not really common though - one is seen in approximately 300 appendectomies.

Presentation

• • Often found incidentally, may be microscopic.
  • May cause obstruction leading to mucocele or acute appendicitis.
  • May precipitate torsion.

Size matters in appendiceal NETs:

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

Gross

• Classically found in the tip of the appendix.
• Characteristic yellow cut surface (when fixed)
• Circumscribed but not encapsulated
• Firm (due to desmoplasia)
• Centred in the submucosa
• Nodules that do not usually cause erosion of the overlying mucosa.

Image:

• 

  Appendiceal neuroendocrine tumour. (WC)

Microscopic

Features:

• Classically subepithelial/mural.
• Various growth patterns:
  • Nested (insular)
  • Trabecular
  • Palisading
  • Ribbons, rosettes
• Fibrous stroma in between cell groups.
• Cytomorphology
  • Monotonous appearance with scanty mitoses.
  • Round central nuclei
  • Stippled chromatin AKA salt-and-pepper chromatin, coarse chromatin.
  • Eosinophilic granular cytoplasm

Special Types

• Tubular carcinoid
  • Neuroendocrine cells forming tubules (no cell nests)
  • Some tubules can contain mucin
  • Can be confused with adenocarcinoma
  • Features suggesting tubular carcinoid (over adenocarcinoma):
    • Arises from base of crypts, with no disruption of surface epithelium.
    • No associated epithelial precursor (no adenomatous change).
    • Neuroendocrine cytologic features, without prominent atypia
    • IHC (NE markers +ve)

• Goblet cell carcinoid aka Crypt cell carcinoma
• Signet-ring cells forming glandular structures,
• Possibly also with extra-cellular mucin

DDx:

• Colorectal adenocarcinoma.
• Adenocarcinoid.
• Crypt cell carcinoma (goblet cell carcinoid).
• Metastatic adenocarcinoma.
• Normal ganglion cells in the Meissner plexus (submucosa) and Auerbach plexus (located between the inner and outer layers of the muscularis propria).

Images

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  Appendiceal carcinoid with torsion of the appendix - 1x (SKB)

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  Appendiceal carcinoid with torsion of the appendix - low power (SKB)

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  Appendiceal carcinoid with torsion of the appendix - medium power (SKB)

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  Appendiceal carcinoid - low power (SKB)

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  Appendiceal carcinoid - high power (SKB)

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  Appendiceal carcinoid - synaptophysin (SKB)

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  Appendiceal carcinoid - low power (SKB)

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  Appendiceal carcinoid - high power (SKB)

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  Appendiceal carcinoid - low power (SKB)

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  Appendiceal carcinoid with necrosis (SKB)

www:

• Appendiceal carcinoid (humpath.com).
• Carcinoid of the appendix (brown.edu).
• Appendiceal carcinoid (flickr.com/Qiao).

IHC

Features:

• Chromogranin A -ve/+ve.
• Synaptophysin +ve.
• Keratin positive, but CK7/CK20 negative
• S100 positive for appendix

See: neuroendocrine tumours.

See also

• Colon.
• Gastrointestinal pathology.