mechanical vascular and neoplastic abnormalities of the gut
TRANSCRIPT
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Mechanical vascular and neoplastic abnormalities of the gut
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Intestinal obstruction
Hernia – protrusion of all or part of an organ from the cavity normally containing it. Trapping leads to oedema and obstruction of vascular supply
Volvulus – twisting of a loop of bowel about its mesentery. Commonest in sigmoid colon. Very common in Africa (associated with high fibre diet). Can be associated with worms. Leads to ischaemia/infarction
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Intestinal obstruction
Adhesions – fibrous bans representing organised inflammation (after peritonitis, surgery) – internal hernias
Intussusception – telescoping of one segment of bowel into a more
distal one
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Intussusception
Occurs in infants and children (often associated with infection and lymphoid hyperplasia
In adults usually associated with a tumour
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Vascular disorders
Ischaemic bowel disease The bowel has a good collateral
circulation but Occlusion of a major vessel will lead to
extensive infarction Gradual loss of supply may be tolerated
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Causes
Arterial occlusion – atherosclerosis, embolism, vasculitis
Venous occlusion – thrombotic states (malignancy, sepsis, dehydration)
Non-occlusive ischaemia – severe drop in blood pressure (cardiac failure, shock)
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Extent and effects of injury
Mucosal necrosis only – can recover
Deeper necrosis leads to fibrosis and stricture
Transmural necrosis (gangrene) - perforation
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Ischaemia
Chronic ischaemia can lead to ulceration, fibrosis and obstruction mimicking inflammatory disease
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Intestinal neoplasms
Small intestine accounts for 75% of length of GI tract but is not a common site for tumours
Large bowel tumours are more common – particularly in the developed world
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Small intestine
Carcinoid tumours are as common as adenocarcinomas
Other tumours include lymphoma, GIST
Carcinoid with node metastases
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Colon and rectum
Polyps (mass lesion protruding from a mucosal surface) are common: Hyperplastic Inflammatory Adenomas (benign tumours of glandular
epithelium) – important as precursors of cancer
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Important Points
The adenoma-carcinoma sequence Colorectal cancer as a model of
multistage carcinogenesis in the human Pathological determinants of patient
prognosis
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The adenoma-carcinoma sequence
Adenomatous polyps are common. How do we know that they predispose to cancer?…….and how do we assess the risk for a particular individual with a polyp(s).
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Polyposis coli
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Adenoma-carcinoma sequence 2
Familial Adenomatous Polyposis Coli (hundreds of adenomas, certainty of cancer at an early age)
Anatomical distribution of adenomas and cancers is the same
Epidemiology is similar
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Tubular adenoma
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Biology (a well studied system!)
A number of gene and chromosomal abnormalities have been identified (APC, p53, K-ras, loss of 18q, gain of 13q, 20)
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Dukes’ Staging
A - confined to bowel wall
B - local spread beyond bowel wall
C - lymph node metastases
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Dukes’ Staging and Prognosis
A 90% 5yr survival B 70% 5yr survival C 30% 5yr survival
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Other colonic neoplasms
Lymphoma Carcinoid GIST