Pathology of the colon, rectum and anus Flashcards
What is the pathogenesis of adenocarcinoma of the large intestine
Adenoma:
- Mutations of APC gene
- LEft colon
Mismatch repair pathway:
- Loss of mismatch repair genes
- Microsatelite instability
- Right colon
Increased CpG island methylation in the absence of microsatelite instability
- Similar to group 2 but without microsatellite instability
- Right colon
What is the morphology of rectosigmoid colon (left) and caecum (right)
Rectosigmoid colon:
- Annular, napkin-ring lesions causing constriction of the bowel
- Lumen narrowed and the proximal bowel distended
- Infiltartive growth pattern, widely invasive
Caecum:
- Polypoid, exophytic masses
- Seldom produce obstruction
- Less invasive
Explain the histology of cancers of the large intestine
Microscopic characteristics of both proximal and distal cancers are similar
Adenocarcinomas:
- Resemble dysplastic glandular structures
- May produce mucin
- May contain signet ring cells
- Desmoplastic stromal response
What are the different types of neoplastic lesions of the large bowel
Carcinoma
Neuroendocrine tumours
Lymphoma
Mesenchymal tumours (GIST)
Metastatic lesions
What are the different staging modalities for tumours of the large bowel
Lymphnode metasteses
Distant metasteses
TNM - clinical
Astler-Coller - histological
What are the different types of non-neoplastic polyps
Hyperplastic polyp
- 90% of all epithelial polyps
- Sigmoid
Hamartomatous
- Retention polyps
- Peutz Jeghers polyps
Inflammatory polyps (IBD)
Lymphoid polyps
What are the different adenomas
Tubular adenomas
Vilous adenomas
Tubulovillous adenomas
What are the different inflammatory bowel diseases and what is the triad associated with it
Crohn’s disease
Ulcerative colitis
Triad:
- Genetics
- Role of intestinal flora
- Abnormal T-cell response
Explain the abnormal CD4 T-cell response in Crohns disease and ulcerative collitis
Crohns disease:
- Delayed type hypersensitivity reaction
- Th 1 response
Ulceratice collitis
- Th2 response
What are the clinical features for IBD
Non-specific abdominal pain
Diarrhoea and fever
Bloody diarrhoea (UC)
First attack preceded by a stressor
Replase
Increased risk of malignancy in UC
Explain the pathophysiology of UC
It starts at rectum and extends proximally to involve the entire colon (pancolitis)
Continues into the ileum resulting in ileitis
Only affects the mucosal surfaces and results in pseudopolyps (due to regeneration) and toxic megacolon.
Along with mucosal ulceration and acute on chronic inflammation in the lamina propria with crypt abscesses
Explain Crohns disease
It affects the terminal ileum and results in skip lesions along with transmural fissures and fistulas with mucosal inflammation and ulceration, non-caseating granulomas with fibrosis and strictures
What are the extra-intestinal manifestations of IBD
Polyarthritis
Sacroiliitis
Ankylosing spondylitis
Erythema nodosum
Primary sclerosing cholangitis
Uceitis
Amyloid deposition
Explain what is melanosis coli
It is a deposition of dark melanin-like pigment in colonic macrophages after ingestion of laxatives
May also be seen in any condition that acuses colonic epithelial apoptosis
Not associated with malignancy
Explain what is pseudomembranous colitis
It is antibiotics associated colitis
It is and adherent layer of inflammatory cells and debris overlying a site of mucosal injury
Clostridium difficile
Results in chronic diarrhoea
