Colon

The colon smell 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 is dealt with in a separate article.

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):

• Neoplasia.
• Volvulus (cecal, sigmoid).
• Diverticular disease + stricture formation.

Bleeding

Mnemonic CHAND:

• 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:

• Cytomegalovirus (CMV).
  • May afflict patients with IBD and lead to colectomy... as IBD patients are put on immunosuppression.
  • Organ transplant recipients.
  • HIV/AIDS.
    • Images:
      • CMV colitis - high. mag. (WC).
      • CMV colitis - intermed. mag. (WC).

Grossing

Types of specimens

Introduction to colorectal surgery:

1. Colonic resection - remove a piece of large bowel.
2. Total colectomy - leaves rectum and anus.
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. 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:

• Rectal specimen - anterior (wikia.com).
• Rectal specimen - lateral (wikia.com).
• Rectal specimen - inked (wikia.com).

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.
  • Anatomists define it in relation to the third sacral vertebra.

Image:

• Rectum and sigmoid colon (wikia.com).

Lymph nodes

• One should get at least 12 lymph nodes if it is cancer.

Quirke method

• Bowel is not opened - it is fixed... then sliced.

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

Main article: Intestinal 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):

• Hyperplastic polyp image - intermed. mag. (WC).
• Hyperplastic polyp image - low mag. (WC).

Ischemic colitis

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

General

• May occur together with ischemic enteritis, in which case it is known as ischemic enterocolitis.

Etiology - anything that leads to vascular occlusion:

• Atherosclerosis.
• Vasculitis.
• Embolization, e.g. thrombotic, foreign body.

Possible associated pathology:

• Necrotizing enteritis - necrosis of the small bowel only.
• Necrotizing enterocolitis - necrosis of the small and large bowel.

Closely related:

• Radiation colitis.
• Infective colitis.

Note:

• Ischemia = compromised blood supply.

Gross

Features - location:

• Luminal part (mucosa & submucosa) affected - edema.
• 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:
  • C. difficile induced pseudomembranous colitis.
  • Ischemic colitis.
  • Volvulus.
  • Necrotizing infections.
  • ... anything that causes severe mucosal injury.
• Radiologic correlate = bowel wall thickening.

Microscopic

Features:

• Crypt loss/drop-out.
  • Less intestinal crypts present.
• Withering crypts.
  • Colonic epithelium has decreased cytoplasm - NC ratio increased.
• Lamina propria hyalinization.
  • Dense pink material replaces loose connective tissue.
• Submucosa hyalinization.
• +/-Pseudomembranes (microscopic):
  • Loss of surface epithelium.
  • PMNs in lamina propria.
  • +/-Capillary fibrin thrombi.

Note:

• Pseudomembranes arise from the crypts - considered acute.

DDx:

• Inflammatory bowel disease.
• Radiation.
• Toxins/drugs.
• Infection.

Images:

• WC:
  • Ischemic colitis - low mag. (WC).
  • Ischemic colitis - high mag. (WC).
  • Ischemic colitis - very high mag. (WC).
  • Colonic pseudomembranes - low mag. (WC).
  • Colonic pseudomembranes - intermed. mag. (WC).
• www:
  • Ischemic colitis (flickr.com/euthman).
  • Ischemic colitis (uchc.edu).

Sign out

LEFT COLON AND SIGMOID COLON, RESECTION:
- PSEUDOMEMBRANOUS COLITIS, SEE COMMENT.
- ONE LYMPH NODE NEGATIVE FOR MALIGNANCY ( 0 POSITIVE / 1 ).
- NEGATIVE FOR DYSPLASIA AND NEGATIVE FOR MALIGNANCY.

COMMENT:
Pseudomembrane formation is a non-specific finding.  It is consistent with ischemia;
however, it may be seen in other contexts, including infection. Clinical correlation is
required.

Diverticular disease

• AKA diverticulosis.

General

• Very common.

Complications:

• Diverticulitis.
• Diverticular-associated colitis - rare.
  • Rectal biopsy to differentiate from ulcerative colitis.

Gross

• Corrugated - like cardboard.
• Wall thickening (reactive).

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.

Image:

• DD (wikispaces.com).

Sign out

RECTO-SIGMOID, LARGE BOWEL RESECTION:
- PERFORATED DIVERTICULITIS WITH SEROSITIS AND ABSCESS FORMATION.
- SUBMUCOSAL FIBROSIS.
- ONE LYMPH NODE NEGATIVE FOR MALIGNANCY ( 0 POSITIVE / 1 ).
- NEGATIVE FOR MALIGNANCY.

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:

• C. difficile.
  • Known as C. difficile colitis.
• Ischemic colitis.
  • Volvulus.
• Other infections.

Etiology:

• Anything that causes a severe mucosal injury.

Gross

Features:

• Pseudomembranes:
  • Pale yellow (or white) irregular, raised mucosal lesions.
  • Early lesions: typical <10 mm.
• Interlesional mucosa often near normal grossly.

Images:

• Pseudomembranous colitis - endoscopic image (WP/Samir).
• Pseudomembranous colitis (WC).

Microscopic

Features:

• 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:

• WC:
  • Micrograph of pseudomembranes - low mag. (wikimedia.org).
  • Micrograph of pseudomembranes - intermed. mag. (wikimedia.org).
• www:
  • Pseudomembranous colitis (upmc.edu).

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:

• Cecal volvulus (utah.edu).
• Volvulus (uic.edu).

Microscopic

Features:

• +/-Ischemic changes and/or necrosis.

DDx - essentially anything that causes ischemia:

• Embolus.
• Thrombosis.
• Vasculitis.

Inflammatory diseases

Inflammatory bowel disease

Main article: 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:

• 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 - 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.

Microscopic colitis

General

Definition:

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

Presentation:

• Chronic diarrhea, non-bloody.

Notes:

• Clinical DDx includes irritable bowel syndrome - which has no or subtle histopathologic changes.

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.

Epidemiology

• Age: a disease of adults - usually 50s.
• Sex:
  • LC males ~= females,
  • CC females:males = 20:1.
• 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.
• No increased risk of colorectal carcinoma.

Treatment

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

Microscopic

Lymphocytic colitis

Features:

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

Image:

• LC (nih.gov).

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.
    • 8 micrometres is the diameter of a RBC.
    • The normal thickness of the subepithelial collagen is 3 micrometres.
  • Thickening "follows the crypts from the surface" - useful for differentiating from tangential sections of the basement membrane.
  • Collagen may envelope capillaries - useful to discern from basement membrane.

Images:

• Collagenous colitis - intermed mag. (WC).
• Collagenous colitis - high mag. (WC).

Notes:

• CC is typically more prominent in the proximal colon - may reflect concentration gradient of offending causitive agents.
• Significant negative findings:
  • 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.
• Diagnosis dependent on history - key point.

Microscopic

Features:

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

Notes:

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

Eosinophilic colitis

General

• Rare.
• May be a component of eosinophilic gastroenteritis.

Clinical features:

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

Gross

Features - endoscopic:

• Edema.
• Granular appearance.

Microscopic

Features:

• Abundant eosinophils - no agreed number.

DDx:

• Inflammatory bowel disease:
  • Crohn's disease.
  • Ulcerative colitis.
• Infection:
  • Pinworm.
  • Strongyloidiasis.
• Autoimmune disease:
  • Scleroderma.
  • Churg-Strauss syndrome.
  • Celiac disease.
• Drug reactions.

Sign out

DESCENDING COLON, BIOPSY:
- COLONIC MUCOSA WITH ABUNDANT EOSINOPHILS, 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), drug reaction, autoimmune disorders 
(e.g. Churg-Strauss syndrome, celiac disease, scleroderma). Clinical correlation 
is required.

Infectious

Cytomegalovirus colitis

Main article: CMV

• Abbreviated CMV colitis.

General

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

Microscopic

Features:

• Enlarged nucleus - classically in endothelial cells.

Images:

• CMV colitis - intermed. mag. (WC).
• CMV colitis - high mag. (WC).

IHC

• CMV +ve.

Others:

• HSV-1.
• HSV-2.
• VZV.
• EBV.

Intestinal spirochetosis

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

General

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

Symptoms:

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

Treatment:

• Metronidazole.

Microscopic

Features:

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

Images:

• WC:
  • Intestinal spirochetes - cropped - very high mag. (WC).
  • Intestinal spirochetes - very high mag. (WC).
  • Intestinal spirochetes - intermed. mag. (WC).
• www:
  • Intestinal spirochetosis & CMV colitis - several images (upmc.edu).

Special stains

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

Amebiasis

• May also be spelling amoebiasis.

General

• Infection with Entamoeba histolytica.
• May mimic colon cancer.

May cause:

• 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:

• Amebiasis - very high mag. (WC).
• Amebiasis (WC).

Cryptosporidiosis

Main article: 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.

General

• Clinically may be suspected to a malignancy - biopsied routinuely.
• Mucosal ulceration.
• "Three-lies disease":

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.
• Rare.

Clinical presentation

• Usually presents as BRBPR ~ 85% of cases.
• Abdominal pain present in approx. 1/3.
  • 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.

Microscopic

Features:

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

DDx:

• Inflammatory pseudopolyp (inflammatory polyp).
  • Associated with inflammatory bowel disease.
• Rectal prolapse.^{[citation needed]}

Rectal prolapse

General

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

Microscopic

Features:

• "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:

• Rectal prolapse - low mag. (WC).
• Rectal prolapse - intermed. mag. (WC).

Neoplastic disease

Colorectal Tumours

Main article: Colorectal tumours

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

Neuroendocrine tumour

Main article: Neuroendocrine neoplasms#GI tract

• AKA carcinoid.

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.

General

• Not melanin as the name melanosis coli suggests; it is actually lipofuscin (in macrophages).
• Endoscopist may see brown pigmentation of mucosa and suspect the diagnosis.
• Presence may lead to endoscopic misinterpretation of colitis severity.

Epidemiology

• Classically associated with anthracene containing laxative (e.g. Senokot) use and herbal remedies.
  • May be seen in individuals not using laxatives.
• Seen in (long-standing) inflammatory bowel disease, especially ulcerative colitis.

Gross

• Brown pigmentation of the mucosa, esp. cecum and proximal colon.

Image:

• Melanosis coli - endoscopic image (WC).

Microscopic

Features:

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

Images:

• Melanosis coli - high mag. (WC).
• Melanosis coli - low mag. (WC).

Notes:

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

Stains

• Can be demonstrated with a PAS stain.

Angiodysplasia

General

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

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.

Gross

• Cecum - classic location.

Note:

• Crohn's disease - may mimic angiodysplasia radiographically.

Microscopic

Features:

• Dilated vessels in mucosa and submucosa.

Drugs

Main article: Drug toxicity

Sodium polystyrene sulfonate

• AKA Kayexalate.

General

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

Microscopic

Features:

• Purple blobs on H&E stain - look somewhat like calcium phosphate.
• Can cause focal necrosis.

Image:

• Sodium polystyrene crystals (WC).

Graft-versus host disease

Main article: 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:

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

See also

• GIST.
• Gastrointestinal pathology.
• Intestinal polyps.
• Small bowel.