disorders of colon and rectum Flashcards
what are the two types of polyps?
neoplastic or non-neoplastic: hamartomas, metaplastic polyps, inflammatory polyps
may be single or multiple
what is the incidence of colorectal adenomas?
extremely common in western world and prevalence rises with age
50% of people over 60 have adenomas, half these polyps are multiple
where are the colorectal adenomas located mostly?
more common in rectum and distal colon and either peduculated or sessile
how are colorectal adenomas classified histologically?
either tubular, villous, tubulovillous according to glandular architecture
what is the most common trajectory to colorectal carcinoma?
nearly all forms develop from adenomatous polyps over 5-10 years
not all polyps carry same degree of risk
what are the symptoms of colorectal adenomas?
usually asymptomatic
discovered incidientlly
occasionally cause bleeding and anaemia
villous adenomas sometimes secrete large amounts of mucus causing diarrhoea and hypokalaemia
when are colonoscopys required to assess adenoma?
discovery of polyp usually at sigmoidoscopy is indicator for colonscopy because proximal polyps present in 40-50% such patients
colonscopic polypectomy carried out to reduce subsequent colorectal cancer risk
how to remove polyps safely?
very large or sessile polyps sometimes removed safely by endoscopic mucosal resection otherwise require surgery
once all polyps removed, patients should undergo surveillance colonscopy at 3-5 year intervals as new polyps develop in 50% patients
patients over 75 do not require repeated colonscopies as subsequent lifetime cancer risk is low
when is segmental colonic resection recommended??
between 10-20% polyps show histological evidence of malignancy
when cancer cells found within 2mm of resection margin of polyp
when polyp cancer poorly differentiated
lymphatic invasion present
without these, followed up by surveillance colonscopy
what are the risk factors for malignant change in colonic polyps?
large size >2mm
villous architecture
multiple polyps
dysplasia §
what is FAP?
familial adenomatous polyposis
autosomal dominant disorder
affects 1 in 13000 of population
accounts for 1% of all colorectal cancer
what causes FAP?
germline mutation of tumour suppressor APC gene followed by acquired mutation of remaining allele
APC large gene and over 1400 different mutations reported
most result in truncated protein
what are the functions of the APC protein?
regulation of colonic epithelial turnover
normally binds to and sequesters B-catenin and unable to do so when mutated allowing beta-catenin to translocate to the nucleus where it upregulates the expression of many genes
what is the pathophysiology of colorectal cancer?
environmental and genetic factors
environmental factors account for 70% of all sporadic colorectal cancers
dietary factors most important risk
results from accumulation of multiple genetic mutations arising from two major pathways: chromosomal instability and microsatellite instability
what are the dietary risk factors for colorectal cancer?
red meat: high saturated fat and protein content- carcinogenic amines formed during cooking
saturated animal fat: high faecal bile acid and fatty acid levels, may affect colonic prostaglandin turnover
