The small & large intestines
Tumors of the small intestine:
Account for 10% of GIT neoplasms and the
majority are benign.
Pathology:
A. Benign:
1. Adenoma 2. Hemangioma 3. Lipoma
4.Neurogenic tumors 5.GIST
Presentation: 1. Asymptomatic 2. Bleeding 3.
Obstruction 4.Intussusception
Peutz- Jeghers Syndrome:
Related to STK-11 mutation on chromosome 19.
Autosomal dominant and characterized by:
1. Melanosis of the mouth and lips
2. Multiple hammartomas of the bowel and colon
3. Melanin spots on the digits and peri-anal skin
Screening relatives is needed for cancer of the :
1. Colon 2.Cervix 3.Breast
Malignant transformation of the polyps rarely occurs and
they can be managed conservatively while surgery is
preserved for bleeding, obstruction and intussusception.
B. Malignant:
1. Adenocarcinoma: Predisposing factors include Crohn’s
disease, FAP, Peutz- Jeghers Syndrome, HNPCC and coeliac
disease.
2. Carcinoid
3. Lymphoma:
May be primary or secondary to generalized body
lymphoma. Classified into:
a. Western type: B cell Non-Hodgkin
b. T cell: Related to coeliac disease.
c. Mediterranean lymphoma.
Lymphoma is treated by chemotherapy and surgery only
used for the complications.
4. GIST:
Occur most commonly in the stomach but can occur
anywhere in the GIT.
Treatment: Mainly surgery. They are radio-resitant and
Glivec( Imatinib) which is tyrosine kinase inhibitor can also
be used.
.
Tumors of the large intestine:
Polyp types:
1. Inflammatory
2. Metaplastic
3. Hammartomatous: Peutz- Jeghers
Juvenile rectal polyps
4. Neoplastic: a. Adenoma:
Tubular
Villous: Causes hypokalemia and hypoproteinemia
Tubulo-villous
b. Adenocarcinoma
c. Carcinoid
Familial Adenomatous Polyposis ( FAP):
Presence of > 100 colorectal and also duodenal adenomas.
80% have previous family history and 20% occur as a new mutation.
Mutations occur in the apc gene on chromosome 5. Autosomal dominant and
cancer risk is 100%. May be associated with mesodermal tumors eg. osteoma
and desmoid tumors. When associated with epidermoid cyst, it is called
Gardner syndrome. 50% are associated with CHRPE( congenital hypertrophy
of retinal pigment epithelium). Polyps are usually present at the age of 15yrs
and always at the age of 30yrs. Carcinoma of the large intestine occurs
10-20yrs after the onset of polyposis.
Screening:
1. At risk family members are offered genetic testing in the early teens.
2. At risk family members should have colonoscopy at 10-12yrs and repeated
annually.
3. If no polyps at 20yrs, continue with five yearly colonoscopy till the age of
50yrs.
Treatment: The aim is to prevent the development of colorectal cancer.
Options:
1. Colectomy and ileo-rectal anastomosis.
2. Restorative proctocolectomy with ileal pouch- anal anastomosis.
3. Panproctocolectomy with permanent ileostomy.
Human non-polyposis colorectal cancer( HNPCC): Lynch syndrome
Increased risk of colorectal, small intestine, endometrial and ovarian
cancer. Affected genes are MLH1 and MSH2. Inheritance is autosomal
dominant. Life time risk is 80% and 30-50% for colorectal and endometrial
cancer respectively.
Colorectal cancer:
Etiology:
1. Adenoma- carcinoma sequence: Evidence:
a. The prevalence of adenomas and carcinoma is very similar with carcinoma patients
about 5yrs older.
b. Distribution of carcinoma and adenoma is similar( 70% in the left colon).
C. When small cancers are studied, they almost always have adjacent adenomas.
d. Adenomas are found in a 1/3 of the specimens resected for colorectal cancers.
e. Sporadic adenomas are identical to FAP adenomas which is associated with 100%
colorectal cancer risk unless treated.
f. Large adenomas are more likely to be dysplastic.
g. Incidence of colorectal cancer falls within a screening program that involves
colonoscopy and polypectomy.
2. Genetics: Mutations of apc, K-ras, HNPCC and P 53.
3. Diet: Red meat is carcinogenic due to the effect of its components( hem and N
nitroso) on the DNA of colorectal mucosa. Dietary fibers have a protective role due to
the reduced transit time which reduces the exposure of the mucosa to carcinogens.
Increased cancer risk is associated with alcohol and smoking.
4. Ulcerative colitis and Crohn’s disease.
5. Cholecystecyomy is associated with increased right side colorectal cancer risk due
to increased exposure to bile salts.
6. Ureterosigmoidostomy.
Pathology:
Macroscopic:
Annular 2. Tubular 3.Cauliflower 4. Ulcerative
Microscopic: Adenocarcinoma
Spread:
1. Direct: Transverse and longitudinal
2. Lymphatic
3. Hematogenous
4. Trans-coelomic
Staging:
1. Dukes:
A Confined to colorectal wall
B Involves adjacent tissues
C Lymph nodes involvement
D Distant metastasis ‘ not described by Dukes but added later on’
2. TNM
Clinical features:
Typically occurs above 50yrs and most common in the 8
th
decade
but it is not uncommon in early adult life.
Tumors of the left colon, which are far more common, present with
a change of bowel habit and rectal bleeding while more proximal
lesions present later with a mass and iron deficiency anemia.
Screening for colorectal carcinoma:
To do FOBT for people aged 60-69yrs every year and to do
colonoscopy for the positive patients. Guaiac- based test is used to
detect peroxidase activity of hematin.
Investigations:
1. Endoscopy:
a. Sigmoidoscopy: Up to the splenic flexure. 70% of all cancers
occur in this segment and almost all bleeding cancers.
b. Colonoscopy: Has the advantage of discovering synchronous
and multiple cancers and polyps.
2. Radiology:
a. Double contrast barium enema to show apple-core
appearance.
b. CT abdomen and chest which are important for staging.
c. Chest X ray. For staging.
.
Treatment: Is mostly surgical:
Pre-operative preparation:
1. Mechanical by enema or purgative.
2. Chemical preparation by antibiotics at induction of anesthesia to reduce
wound infection.
3. Thrombo-prophylaxis by mechanical method ( compressive stockings) or
chemical ( low molecular weight heparin).
4. Stoma counseling
Options:
1. Right hemicolectomy: For cecal and ascending colon cancer. Resection
incudes the last 20 cm of the ileum and the proximal 1/3 of the transverse
colon. Injury might happen to:
a. Duodenum b. Gonadal vessels c. Ureter
2. Extended right hemicolectomy for cancer involving the transverse colon
and the hepatic flexure.
3. Left hemicolectomy for cancer involving the descending and sigmoid
colon.
4. Laparoscopic surgery
Adjuvant chemotherapy by 5 FU may be used.
Metastatic disease: Isolated hepatic and lung metastasis can be resected.