Colon

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The colon and rectum smell like poo... 'cause that's where poo comes from. 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.

Common clinical problems

Obstruction

Top three (in adults):[1]

Bleeding

Mnemonic CHAND:[2]

  • Colitis (radiation, infectious, ischemic, IBD (UC >CD), iatrogenic (anticoagulants)).
  • Hemorrhoids.
  • Angiodysplasia.
  • Neoplastic.
  • Diverticular disease.

Infectious colitis with bleeding - causes:

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

Infectious colitis in the immunosuppressed:

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.

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. (???)

Lymph nodes

Quirke method

  • Bowel is not opened - it is fixed... then sliced.[8], [9].

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):

Bowel ischemia

General

Etiology:

Gross

Features:[10]

  • Luminal part (mucosa & submucosa) affected.
  • Splenic flexture of colon commonly affected (vascular watershed).

Note:

  • May have pseudomembranes (classically assoc. with C. difficile colitis), i.e. mimics an infectious process.
  • DDx for pseudomembranes:[11]
    • C. difficile induced pseudomembranous colitis.
    • Ischemic colitis.
    • Volvulus.
    • Necrotizing infections.
    • ... anything that causes severe mucosal injury.

Radiologic correlate

  • Bowel wall thickening.

Microscopic

Features:[12]

  • Crypt loss.
  • Lamina propria fibrosis.
  • Submucosa fibrosis.

Pseudomembranes (microscopic):[11]

  • Loss of surface epithelium.
  • PMNs in lamina propria.
  • +/-Capillary fibrin thrombi.

Note:

  • Pseudomembranes arise from the crypts.

Images:

DDx:

  • IBD.
  • Radiation.
  • Toxins/drugs.

Diverticular disease

  • AKA diverticulosis.

General

  • Very common.

Complications:

  • Diverticulitis.
  • Diverticular-associated colitis[13] - rare.

Gross

  • Corrugated - like cardboard.
  • Wall thickening (reactive).[14]

Endoscopic image: DD (WC).

Microscopic

Features:

  • Mucosa/submucosa invagination into the musuclaris propria (MP).
    • At the site the blood vessels supplying the mucosa and submucosa penetrate the MP.[15]

Image:

Pseudomembranous colitis

General

  • Pseudomembranous colitis is a histomorphologic description which has a DDx. In other words, it can be caused by a number of things.

DDx of pseudomembranous colitis:[11]

Etiology:

  • Anything that causes a severe mucosal injury.

Gross

  • Pseudomembranes.

Microscopic

Features:[11]

  • Heaped necrotic surface epithelium.
    • Described as "volanco lesions" - this is what is seen endoscopically.
  • PMNs in lamina propria.
  • +/-Capillary fibrin thrombi.

Note:

  • Pseudomembranes arise from the crypts.

Images:

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:[17]

  • 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[18] - 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.[19]

Microscopic colitis

General

Definition:

  • As the name suggests, they are microscopic, i.e. endoscopic examination is normal.

Presentation:

  • Chronic diarrhea, non-bloody.[20]

Notes:

Microscopic colitis - types

  • Lymphocytic colitis (LC).
  • Collagenous colitis (CC).

Some believe that LC and CC are different time points in the same process-- but this is unproven.[20]

Epidemiology

  • Age: a disease of adults - usually 50s.
  • Sex:
    • LC males ~= females,[20]
    • CC females:males = 20:1.[20]
  • Drugs are associated with LC and CC.
    • NSAIDs - posulated association/weak association,
    • SSRIs (used primarily for depression) - moderate association, dependent on specific drug.
  • Associated with autoimmune disorders - celiac disease, diabetes mellitus, thyroid disorders and arthritis.[21]
  • No increased risk of colorectal carcinoma.[21]

Treatment

  • Sometimes just follow-up.
  • Steroids - budesonide -- short-term treatment.[21]

Microscopic

Lymphocytic colitis

Features:

  • Lots of intraepithelial lymphocytes (>=20/100 lymphocytes/surface epithelial cells[21]) and
  • Lymphocytes in the lamina propria.
  • NEGATIVES:[22]
    • No PMNs.
    • No crypt distortion.

Collagenous colitis

Features:

  • Intraepithelial lymphocytes, and
  • lymphocytes in the lamina propria.
  • Collagenous material in the lamina propria (pink on H&E) -- key feature.
    • Can be demonstrated with a trichrome stain -- collagen = green on trichrome.
    • Subepithelial collagen needs to be >= 10 micrometres thick for Dx.[21]
      • 8 micrometres is the diameter of a RBC.
      • The normal thickness of the subepithelial collagen is 3 micrometres.[21]
    • Thickening "follows the crypts from the surface" - useful for differentiating from tangential sections of the basement membrane.[23]
    • Collagen may envelope capillaries - useful to discern from basement membrane.[24]

Images:

Notes:

  • CC is typically more prominent in the proximal colon - may reflect concentration gradient of offending causitive agents.[21]
  • Significant negative findings:[22]
    • No PMNs.
    • No crypt distortion.
  • Should not be diagnosed in the cecum - as it (normally) has a thickened subepithelial collagen band. (???)

Diversion colitis

General

  • Segment of de-functioned bowel due to surgical diversion, i.e. ileostomy or stoma.

Microscopic

Features:[25]

  • Lymphoid follicular hyperplasia.
  • Lymphocytes.
  • Plasma cells.

Notes:

  • May show IBD-like changes.[26]
    • IBD should not be diagnosed on a diverted segment of bowel.

Infectious

Intestinal spirochetosis

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

General

  • Caused by spirochetes[27][28] - specifically Brachyspira piloicoli[29] (previously Serpulina pilosicoli[30]) and Brachyspira aalborgi.
  • Very rare cause of diarrhea, associated with male homosexual behaviour.

Symptoms:[28]

  • Watery diarrhea, abdominal pain, +/-blood per rectum.

Treatment:[31]

  • Metronidazole.

Microscopic

Features:

  • Hyperchromatic fuzz on luminal aspect of epithelial cells; at brush border.

Images:

Special stains

  • Silver stains highlight 'em (e.g. Warthin-Starry stain).

Amebiasis

General

  • Infection with Entamoeba histolytica.[32]
  • May also be spelling amoebiasis.
  • May mimic colon cancer.[33]

May cause:[34]

  • 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

General

  • Clinically may be suspected to a malignancy - biopsied routinuely.
  • Mucosal ulceration.
  • "Three-lies disease":[35]
  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.[36]
  • Rare.

Clinical presentation

  • Usually presents as BRBPR ~ 85% of cases.[36]
  • Abdominal pain present in approx. 1/3.[36]
    • May be very painful.

Treatment:

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

Microscopic

Features:[35]

  • Fibrosis of the lamina propria - should be obliterated.
  • Thickened muscularis mucosa - abnormally extends to the lumen.

Histologic DDx:

Rectal prolapse

Generally

  • Usually close to the anal verge.
  • Rare forms can occasionally be confused with cancer.[37]

Microscopic

Features:[38]

  • "Fibromuscular hyperplasia" - key feature:
    • Fibrosis (submucosa, lamina propria).
    • Muscularis mucosae is "too superficial" (muscle in the lamina propria).
  • Surface ulceration + inflammation (neutrophils).
  • +/-Serration of epithelium at the surface.

Notes:

  • Important NEGATIVE: no nuclear atypia.

Images:

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

Pseudomelanosis coli

  • AKA melanosis coli.[39]

General

  • Not melanin as the name melanosis coli suggests; it is actually lipofuscin (in macrophages).[40]
  • Endoscopist may see brown pigmentation of mucosa and suspect the diagnosis.

Epidemiology

  • Classically associated with anthracene containing laxative (e.g. Senokot) use and herbal remedies.[40]

Gross

  • Brown pigmentation of the mucosa.

Image:

Microscopic

Features:

  • Brown granular pigment - in the lamina propria.
    • Typically more prominent in the cecum and proximal colon.[40]

Images:

Notes:

  • DDx of brown pigment:
    • Lipofuscin - comes with age (can be demonstrated with a PAS stain[41] or Kluver-Barrera stain[42]).
      • Melanosis coli.
    • Old haemorrhage, i.e. hemosiderin-laden macrophages (may be demonstrated with Prussian blue stain[43]).
    • Melanin (from melanocytes) - rare in colon (may be demonstrated with a Fontana-Masson stain[44] -- though not so useful in the GI tract).
    • Foreign material (e.g. tattoo pigment) - not seen in GI tract.

Stains

Angiodysplasia

General

  • Causes (lower) GI haemorrhage.
  • Generally, not a problem pathologists see.
  • May be associated with aortic stenosis; known as Heyde syndrome.[46]

Classic location:

  • Cecum.

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.[47]

Microscopic

Features:[48]

  • Dilated vessels in mucosa and submucosa.

Drugs

Kayexalate (sodium polystyrene sulfonate):[49]

Image: Sodium polystyrene crystals (WC).

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 is occasionally an indication for colectomy.

Causes:

  • Tumour.
  • Adhesions - due to previous surgery.
  • Neuropathy.
  • Congenital defect (Hirschsprung's disease).
  • Medications/substance use.
  • Idiopathic.

Work-up if no tumour is identified:[50]

  • Routine H&E.
  • Pan-actin.
  • Gomori trichrome.
  • CD117 - to look for the interstitial cells of Cajal.
  • HU - neuronal marker.[51]

See also

References

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