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.
• 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 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

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.

Note:

• Eosinophils are very common.
  • Appendices with eosinophils but no apparent neutrophils probably represent the same process.

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.

Images:

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

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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

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):

• 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

Benign appendiceal mucocele and appendiceal mucocele redirect here.

General

• There are many classifications and they are controversial.
  • The controversy centres on whether to call all mucinous tumours outside of the appendix adenocarcinoma - regardless of whether they have atypia & show invasion.
• Panarelli and Yantiss created a nice summary table - that compare the classifications - see: comparison of classifications (archivesofpathology.org).
• In women - an ovarian primary must be excluded.
  • Concurrent bilateral ovarian tumours suggests the tumour originated from the appendix and spread to the ovaries.
• Onlinepathology prefers the classification of Misdraji, as it is the least complicated

Misdraji 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) as per Misdraji classification:

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.

WHO classification

WHO classification:

• Adenoma with low-grade dysplasia.
• Adenoma with high-grade dysplasia.
• Low-grade invasive mucinous adenocarcinoma
  • Confined to the appendiceal wall.
  • Outside of the appendix.
• High-grade invasive mucinous adenocarcinoma.

Comparison between Misdraji and WHO classification

Adapted from Panarelli and Yantiss:

Stage	Cytologic dysplasia	Misdraji	WHO
Confined to the mucosa	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	mucinous adenoma, negative for high-grade dysplasia
Confined to the mucosa	high-grade	non-invasive mucinous cystadenocarcinoma of the appendix	mucinous adenoma with high-grade dysplasia
At least into the submucosa, confined to the appendix	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	invasive mucinous adenocarcinoma, low-grade
At least into the submucosa, confined to the appendix	high-grade	mucinous adenocarcinoma of the appendix (MACA)	invasive mucinous adenocarcinoma, high-grade
Extra-appendiceal spread	low-grade	low-grade appendiceal mucinous neoplasm (LAMN)	invasive mucinous adenocarcinoma, low-grade
Extra-appendiceal spread	high-grade	mucinous adenocarcinoma of the appendix (MACA)	invasive mucinous adenocarcinoma, high-grade

Microscopic

Low-grade appendiceal mucinous neoplasm

• AKA benign mucinous tumour of the appendix.

Microscopic:

• Single layer of epithelium with tufts.
  • Vaguely resemble serrations, i.e. the saw-tooth pattern in hyperplastic polyps of the colon.
• Mucin contained (inside appendix only).
• No marked nuclear atypia.

Note:

• May be deceptively bland appearing from a cytologic perspective.

Images:

• LAMN - low mag. (nature.com).
• LAMN - high mag. (nature.com).
• Appendiceal mucocele (pathlabmed.typepad.com).

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.

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LAMN

VERMIFORM APPENDIX, APPENDECTOMY:
- LOW-GRADE APPENDICEAL MUCINOUS NEOPLASM.
- ACUTE APPENDICITIS.
- ACUTE PERIAPPENDICITIS. 

VERMIFORM APPENDIX AND CECUM, APPENDECTOMY WITH CECAL CUFF:
- LOW-GRADE APPENDICEAL MUCINOUS NEOPLASM (MUCINOUS CYSTADENOMA).
- MARGINS NEGATIVE FOR MUCINOUS NEOPLASM.

COMMENT:
No extra-appendiceal mucin is identified. There is no 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.