Colon

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The colon smells like poo... 'cause that's where poo comes from. This article also covers the rectum and cecum as both have a similar mucosa.

It commonly comes to pathologists because there is a suspicion of colorectal cancer or a known history of inflammatory bowel disease (IBD).

An introduction to gastrointestinal pathology is found in the gastrointestinal pathology article. The anus and ileocecal valve are dealt with in separate articles.

Technically, the rectum and cecum are not part of the colon. Thus, inflammation of the rectum should be proctitis and inflammation of the cecum should be cecitis.

Common clinical problems

Obstruction

Top three (in adults):[1]

Bleeding

Mnemonic CHAND:[2]

Infectious colitis with bleeding - causes:

  • Enterohemorrhagic Escherichia coli (EHEC) -- commonly 0157:H7.
  • Campylobacter jejuni.
  • Clostridium difficile.
  • Shigella.

Infectious colitis in the immunosuppressed:

  • Cytomegalovirus (CMV).[3]
    • May afflict patients with IBD and lead to colectomy... as IBD patients are put on immunosuppression.[4]
    • Organ transplant recipients.
    • HIV/AIDS.

Images:

Grossing

Types of specimens

Introduction to colorectal surgery:

  1. Colonic resection - remove a piece of large bowel.
  2. Total colectomy - leaves rectum and anus.[5]
  3. Subtotal colectomy - part of colon removed --or-- some of the rectum remains.
  4. Right hemicolectomy - right colon + distal ileum.
  5. Lower anterior resection (LAR) - proximal rectum +/- sigmoid (for proximal rectal malignancies).
    • Specimens have should have intact mesorectum - total mesorectal excision (TME) - reduces local recurrence.[6]
  6. Abdominoperineal resection (APR) - anus + rectum - results in a permanent stoma (for distal rectal malignancies).
  7. Stoma - these are often done emergently and then get cut-out after the patient's condition has settled.

Images

Identifying the specimen

  • Transverse colon - has omentum.
  • Ascending colon - usu. comes with ileocecal valve and a bit of ileum.
  • Descending colon - has a bare area.
  • Rectum - has adventitia.
    • Pathologists define it as starting where the adventitia starts/the serosal surface no longer completely surrounds the large intestine.[7]
    • Anatomists define it in relation to the third sacral vertebra.[8]

Images

Lymph nodes

Quirke method

  • Bowel is not opened - it is fixed... then sliced.[10][11]

Standard method

  • Bowel is prep'ed by opening it along the antimesenteric side.
  • Dimensions - length, circumference at both margins.
  • Radial margin/circumferential margin - should be painted.
    • Rectum starts/sigmoid ends @ place where serosa ends on the posterior aspect of the bowel.
      • The proximal, anterior aspect of the rectum has serosa, i.e. it is not painted.

Common non-neoplastic disease

Colorectal polyps

Polyps are the bread & butter of GI pathology. They are very common.

Main types:

  • Hyperplastic - most common, benign.
  • Adenomatous - quite common, pre-malignant.
  • Hamartomatous - rare, weird & wonderful.
  • Inflammatory, AKA inflammatory pseudopolyps - associated with IBD.

Most common (images):

Ischemic colitis

  • AKA colonic ischemia.
  • AKA ischemia of the colon.

Diverticular disease

Pseudomembranous colitis

Volvulus

General

  • Uncommonly comes to pathology.
  • It is essentially a radiologic diagnosis.
  • In the context of autopsy, it is a gross diagnosis.

Gross

  • Intestine folded over itself - typically leads to ischemia.

Images:

Microscopic

Features:

DDx - essentially anything that causes ischemia:

Sign out

RECTOSIGMOID, RESECTION:
- MURAL ISCHEMIA WITH PERFORATION, SEROSITIS, MICROABSCESS FORMATION AND POORLY FORMED PSEUDOMEMBRANES.
- SUBMUCOSAL FIBROSIS.
- NEGATIVE FOR MALIGNANCY.

COMMENT:
The findings are consistent with volvulus and the submucosal fibrosis suggests this may have been recurrent.

Inflammatory diseases

Inflammatory bowel disease

The bread 'n butter of gastroenterology. A detailed discussion of IBD is in the inflammatory bowel disease article. It comes in two main flavours (Crohn's disease, ulcerative colitis).

Microscopic

Features helpful for the diagnosis of IBD - as based on a study:[13]

  • Basal, i.e. crypt base, plasmacytosis with severe chronic inflammation,
  • Crypt architectural abnormalities, and
  • Distal Paneth cell metaplasia.
    • Paneth cells should not be in the left colon[14] - if you see 'em think of IBD and other long-standing injurious processes.
    • Some claim that (friendly right colonic) paneth cells and paneth cell metaplasia look quite different and can be distinguished.[15]

Microscopic colitis

Microscopic colitis may refer to a microscopic manifestation of an unspecified disease process that can be apparent macroscopically. This section links to a pair of diseases (lymphocytic colitis and collagenous colitis) that are considered to only have microscopic manifestations and characteristic clinical presentation.

Diversion colitis

Eosinophilic colitis

General

Clinical features:[16]

  • Abdominal pain
  • Diarrhea +/-blood.
  • +/-Weight loss.

Gross

Features - endoscopic:[16]

  • Edema.
  • Granular appearance.

Microscopic

Features:[16]

  • Abundant eosinophils - no agreed upon number.
    • "Most use 20/HPF" [17] - a definition that suffers from HPFitis.
      • There is variation along the large bowel - normal in rectum <10/HPF, normal in cecum <30/HPF (???).[17]

DDx:[16]

Image:

Sign out

DESCENDING COLON, BIOPSY:
- COLONIC MUCOSA WITH MILD EOSINOPHILIA, SEE COMMENT.
- NEGATIVE FOR DYSPLASIA.

COMMENT:
Focally, there are up to 40 eosinophils / 0.2376 mm*mm (approx. field area at 400X). This
is a non-specific finding. No eosinophilic crypt abscesses are seen. No (neutrophilic)
cryptitis is present. Clinical correlation is suggested.
DESCENDING COLON, BIOPSY:
- COLONIC MUCOSA WITH MILD EOSINOPHILIA, SEE COMMENT.
- NEGATIVE FOR ACTIVE COLITIS.
- NEGATIVE FOR DYSPLASIA.

COMMENT:
There are up to 40 eosinophils / 0.2376 mm*mm (field area at 400X). This is a 
non-specific finding.  The differential diagnosis includes inflammatory bowel 
disease, infection (especially helminths), a drug reaction, and autoimmune 
disorders (e.g. Churg-Strauss syndrome, celiac disease, scleroderma). Clinical 
correlation is required.

Infectious

Infectious colitis

This section covers non-specific colitides that appear to have an infective etiology.

General

  • Common.
  • Diarrhea - typical symptom.

Gross

  • +/-Erythema on endoscopy.

Microscopic

Features:

  • Neutrophils predominant - key feature.[18]
    • The neutrophils are often superficial - they go to were the bad guys are.
  • No architectural distortion - if acute.

DDx:

IHC

Done if the patient is immunosuppressed, or there is clinical or morphological suspicion:

Sign out

ASCENDING COLON, BIOPSY:
- MILD ACTIVE COLITIS, SEE COMMENT.

COMMENT:
There is are no granulomas.  The crypt architecture is normal.  A benign lymphoid nodule is
present.

The differential diagnosis includes infective etiologies, early inflammatory
bowel disease and ischemia.  The histomorphology is more in keeping with an infective
etiology as neutrophils are a predominant feature; however, clinical correlation is
required.

Cytomegalovirus colitis

  • Abbreviated CMV colitis.

General

  • Uncommon.
  • Immunosuppressed population at risk, e.g. transplant recipients, individuals with HIV.

Microscopic

Features:

  • Enlarged nucleus - classically in endothelial cells.

DDx:

Images

www:

IHC

  • CMV +ve.

Others:

  • HSV-1.
  • HSV-2.
  • VZV.
  • EBV.

Intestinal spirochetosis

  • AKA intestinal spirochetes; more specifically colonic spirochetes, colonic spirochetosis.

Amebiasis

  • May also be spelled amoebiasis.

General

May cause:[22]

  • Dysentery (diarrhea containing mucus and/or blood in the feces).
  • Colitis.
  • Liver abscess.

Microscopic

Features:

  • Entamoeba histolytica are round/ovoid eosinophilic bodies ~ 40-60 micrometers in maximal dimension.
    • Found in bowel lumen.
    • Ingest RBCs.

Image

Cryptosporidiosis

General

  • Usually in immune incompetent individuals, e.g. HIV/AIDS.

Microscopic

Features:

  • Uniform spherical nodules 2-4 micrometres in diameter, typical location - GI tract brush border.
    • Bluish staining of brush border key feature - low power.

Rectal pathology

Solitary rectal ulcer

  • AKA solitary ulcer syndrome of the rectum, abbreviated SUS.
  • AKA solitary rectal ulcer syndrome.
  • Mucosal prolapse syndrome may be used as a synonym; however, it encompasses other entities.[23]

General

  • Clinically may be suspected to a malignancy - biopsied routinely.
  • Mucosal ulceration.
  • "Three-lies disease":[24]
  1. May not be solitary.
  2. May not be rectal -- can be in left colon.
  3. May not be ulcerating -- non-ulcerated lesions: polypoid and/or erythematous.

Note: Each of the words in solitary rectal ulcer is a lie.

Epidemiology

  • Typically younger patients - average age of presentation ~30 years in one study.[25]
  • Rare.

Clinical presentation

  • Usually presents as BRBPR ~ 85% of cases.[25]
  • Abdominal pain present in approx. 1/3.[25]
    • May be very painful.

Treatment:

  • Usually conservative, i.e. non-surgical.
  • Resection - may be done for fear of malignancy.

Gross

  • Classically, anterior or anterolateral wall of the rectum.[24]

Microscopic

Features:[24][26]

  • Fibrosis of the lamina propria.
  • Thickened muscularis mucosa with abnormal extension to the lumen.
  • +/-Mucosa ulceration.
  • +/-Submucosal fibrosis.

DDx:

IHC

  • p53 -ve.
    • May be used to help exclude adenocarcinoma.

Rectal prolapse

Neoplastic disease

Colorectal Tumours

These are very common. The are covered in a separate article entitled colorectal tumours.

Neuroendocrine tumour

Goblet cell carcinoid

Described in detail in the appendix article.
  • AKA crypt cell carcinoma.
  • Biphasic tumour; features of carcinoid tumour and adenocarcinoma.

Other

Colonic pseudo-obstruction

Pseudomelanosis coli

  • AKA melanosis coli.

Angiodysplasia

General

  • Causes (lower) GI haemorrhage.
  • Generally, not a problem pathologists see.
  • May be associated with aortic stenosis; known as Heyde syndrome.[27]

Epidemiology:

  • Older people.

Etiology:

  • Thought to be caused by the higher wall tension of cecum (due to larger diameter) and result from (intermittent) venous occlusion/focal dilation of vessels.[28]

Gross

  • Cecum - classic location.

Note:

Microscopic

Features:[29]

  • Dilated vessels in mucosa and submucosa.

Drugs

Sodium polystyrene sulfonate

  • AKA Kayexalate.

General

  • Used to treat hyperkalemia - as may be seen in renal failure.

Microscopic

Features:[30]

Image

Graft-versus host disease

  • Abbreviated as GVHD.
  • Seen in the context of bone marrow transplants.

Bowel transplant

The histology of bowel transplant rejection is identical to GVHD - see GVHD.

Chronic constipation

This section deals with chronic constipation that has no apparent cause.

General

General differential diagnosis for constipation:

Gross

  • No changes.

Microscopic

Features:

  • Colon within normal limits.
    • Look for the Ganglion cells (submucosal plexus, myenteric plexus).
    • Look for interstitial cells of Cajal (with CD117) - typically most common around the myenteric plexus.[32]

Negatives:

  • No significant vascular disease.
  • No fibrosis.
  • No loss of muscle.

Stains & IHC

Work-up if no tumour is identified:[33][34]

  • Routine H&E.
  • Smooth muscle actin - confirm myocyte loss.
  • Gomori trichrome - examine connective tissue.
  • CD117 - to look for the interstitial cells of Cajal.
    • <50% the expected = abnormal.[34]
      • Normal numbers not defined.
  • HU - neuronal marker.[35]

Sign out

  • A long list of things to report is contained the recommendation of a working group.[34]
    • Most pathology practises do not report much.
TERMINAL ILEUM, CECUM, COLON (ASCENDING, TRANSVERSE AND SIGMOID), COLECTOMY:
- SMALL BOWEL, CECUM, AND COLON WITHIN NORMAL LIMITS.
- FOUR LYMPH NODES NEGATIVE FOR MALIGNANCY ( 0 POSITIVE / 4 ).
- NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY.

COMMENT:
Several stains were done:
 CD117: interstitial cells of Cajal present, no apparent decrease.
 SMA: no significant myocyte loss.
 Gomori trichrome: no abnormal fibrosis apparent.
 Tau: no abnormalities apparent.

See also

References

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  33. IAV. 15 December 2009.
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  35. Barami K, Iversen K, Furneaux H, Goldman SA (September 1995). "Hu protein as an early marker of neuronal phenotypic differentiation by subependymal zone cells of the adult songbird forebrain". J. Neurobiol. 28 (1): 82–101. doi:10.1002/neu.480280108. PMID 8586967.