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necessary for barium enema).

A Diet

Solid food should be avoided for at least 24 hours and preferably 48 hours before the anticipated procedure.

1.Clear liquids should be ingested to maintain adequate hydration.

2.Intravenous fluids are occasionally required for patients with cardiac or renal disease.

B

Cathartics or laxatives are almost always required. Preferences are quite variable.

1.Mannitol, a nonabsorbable sugar, is an osmotic agent that attracts water into the bowel lumen and thus purges the gut. It is pleasant tasting but has disadvantages.

a.Colonic bacteria metabolize the sugar and produce hydrogen and methane, which are gases that may explode if electrocautery is used.

b.Wound infections are increased in patients prepared with mannitol. Apparently, mannitol promotes growth of E. coli.

2.Polyethylene glycol (PEG) is an isotonic lavage solution that acts as an osmotic purgative but is not fermented by bacteria. Approximately 4 L of PEG must be ingested within 4 hours for adequate cleansing.

3.Castor oil (2 oz) and magnesium citrate (10 oz) ingested 24 hours before the planned procedure have equivalent efficacy.

4.Bisacodyl tablets are often used as an element of the bowel preparation. They are taken 36 hours before the anticipated procedure.

C

Enemas are at least as important as laxatives and cathartics to cleanse the colon. Either saline enemas or commercial phosphasoda enemas should be administered the night before the procedure until returns are clear.

D

Antibiotics are important to reduce concentrations of colonic bacteria, with the goal of preventing postoperative infections.

1.Antibiotics must be given preoperatively. Postoperative antibiotics have no effect in the reduction of postoperative infections.

2.Oral antibiotics often recommended before surgery are neomycin and erythromycin base. These antibiotics achieve high concentrations in the colonic lumen and are administered the day before surgery, along with the purgative.

3.A broad-spectrum intravenous antibiotic is usually administered immediately before the start of a surgical procedure and is given again in the immediate postoperative period. Prophylactic antibiotics should not be continued after the day of operation.

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IV Benign and Malignant Colorectal Tumors

A Polyps

A polyp may be defined as any projection from the surface of the intestinal mucosa.

1. Gross appearance

a.Pedunculated polyps are attached to the bowel wall by a stalk.

b.Sessile polyps are flat growths with no stalk.

2.Histologic types

a.Hyperplastic polyps are small (usually 5 mm) lesions of thickened mucosa without cellular atypia. They are present in 50% of adults, which makes them the most common type of polyp. There is no malignant potential, and treatment is usually unnecessary.

b.Hamartomatous polyps are non-neoplastic growths that consist of an abnormal mixture of normal tissue. Juvenile polyps are hamartomas that occur most frequently in children and may cause gastrointestinal bleeding or intussusception.

c.Inflammatory polyps are growths resulting from tissue reaction to inflammation, such as pseudopolyps in ulcerative colitis (UC) or benign lymphoid polyps. They have no neoplastic potential.

d.Neoplastic polyps are by definition benign, but they have the potential to develop into cancer. These polyps are classified by histology into three types:

1.Tubular adenomas (75% of adenomas) have a smooth, firm surface and are often on a stalk.

2.Villous adenomas (10% of adenomas) are soft, sessile lesions with frondlike projections. Large villous adenomas may cause watery diarrhea and potassium loss.

3.Tubulovillous adenomas (15% of adenomas) have elements of both tubular and villous adenomas.

3.The adenoma-carcinoma sequence. Cumulative evidence suggests a progression from benign neoplasia to malignancy in colorectal polyps. Supporting observations include:

a.Patients with colorectal cancer often have synchronous adenomatous polyps.

b.Histopathologic studies have shown a transition from adenoma to carcinoma in polyps. The peak incidence for discovery of colon polyps is 50 years of age; the peak incidence for development of cancer is 60 years of age. This fact suggests a 10-year span for adenomas to transform to cancer.

c.Patients with familial adenomatous polyposis (FAP) invariably develop colon cancer if not treated.

d.Polypectomy has been shown to reduce the risk of colorectal cancer.

e.Molecular genetic studies have detected four main genetic alterations in colorectal adenomas and carcinomas (ras mutations and deletions from chromosomes 5, 17, and 18).

4.Malignant potential. Probably more than 95% of colorectal cancers arise from neoplastic polyps. At least three characteristics of polyps are associated with malignancy:

a.Size

1.Polyps <1 cm: 1% malignant

2.Polyps 1–2 cm in size: 10% malignant

3.Polyps >2 cm in size: 50% malignant

b.Histologic type

1.Tubular: 5% malignant

2.Tubulovillous: 20% malignant

3.Villous: 40% malignant

c.Grade of atypia

1.Mild: 5% malignant

2.Moderate: 20% malignant

3.Severe: 35% malignant

5.Treatment of polyps. Neoplastic polyps should be removed because of their malignant potential.

a.Endoscopic polypectomy (excision with a colonoscope or sigmoidoscope) is ideal for pedunculated polyps. Small, superficial, sessile polyps are often amenable to piecemeal removal by this technique.

b.Transanal polypectomy. Rectal polyps may be removed surgically through the anus.

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c.Segmental colectomy is required both for sessile polyps that cannot be excised with an endoscope and for most polyps that are malignant. Removal of the polyp through a colotomy, or a surgically made opening in the colon, is a historical procedure that has no place in treatment of polyp disease.

d.A malignant polyp may be treated by endoscopic polypectomy if all of these characteristics are present:

1.The polyp is pedunculated.

2.The cancer is confined to the head (i.e., does not invade the stalk).

3.There is no venous or lymphatic invasion.

4.The polyp is moderately differentiated or well differentiated histologically.

B Polyposis syndromes

1.Peutz-Jeghers syndrome is an autosomal dominant disorder characterized by hyperpigmented spots on the lips, buccal mucosa, face, and digits and hamartomas throughout the gastrointestinal tract.

a.Complications. The polyps may cause gastrointestinal bleeding and intussusception.

b.Cancer risk. There is an increased risk of malignancy of the intestine and other organ systems.

c.Treatment. Symptomatic polyps should be removed, with a goal of preservation of intestine.

2.Diffuse juvenile polyposis is an autosomal dominant disease characterized by a heterogeneous population of polyps, both hamartomas and adenomas.

a.Complications. Intussusception, diarrhea, and protein loss may occur.

b.Cancer risk. There is at least a 10% risk of developing colon cancer.

c.Treatment is most commonly subtotal colectomy and ileorectal anastomosis.

1.Proctoscopy of the remaining rectum should be done every 6 months, and any new rectal polyps should be excised.

2.If there are diffuse rectal polyps, total protocolectomy with either an ileostomy or preferably an ileal pouch—anal anastomosis is indicated.

3.Cowden's syndrome is an autosomal dominant disorder characterized by hamartomas throughout the gastrointestinal tract; mucocutaneous abnormalities (e.g., facial and oral papules, keratotic growths on the hands and feet); and breast, thyroid, or uterine cancer. Treatment is not usually required for the polyps but is directed toward the extraintestinal malignancies.

4.Cronkhite-Canada syndrome is a noninherited syndrome characterized by generalized intestinal hamartomas in association with alopecia, cutaneous pigmentation, and atrophy of the fingernails and toenails.

a.Symptoms include vomiting, diarrhea, malabsorption, and protein-losing enteropathy.

b.The cause is unclear. Mortality is usual; most patients die within a short time after diagnosis, but there have been reports of spontaneous remission.

c.Treatment is reserved for complications such as intestinal obstruction.

5.FAP is characterized by more than 100 adenomatous polyps throughout the colon and rectum. If untreated, almost 100% of patients develop colon cancer by the fifth decade of life.

a.Genetic transmission

1.FAP is an autosomal dominant syndrome with high penetrance. Fifty percent of offspring of affected patients develop the disease.

2.Almost all cases caused by germline mutations of adenomatous polyposis coli (APC) gene located on chromosome 5.

3.One third of patients with FAP have no family history of the disease: They represent spontaneous mutations.

b.Clinical presentation. Although the disease is inherited, polyps are not present at birth, and they rarely appear before puberty. Fifty percent of FAP patients develop adenomas by age 15 and 95% by age 35.

1.Complications. The polyps may cause bleeding or, rarely, intussusception.

2.Extraintestinal expressions are common and include:

a.Epidermoid cysts

b.Osteomas

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c.Cutaneous fibromas

d.Desmoid tumors of the abdomen and mesentery

e.Gastrointestinal polyps

f.Retinal pigmentation

g.Periampullary carcinoma

h.Thyroid carcinoma

c.Screening. First-degree relatives of FAP patients should undergo screening for FAP at age 10–12 years. Screening test of choice is testing for mutation of the APC gene. If genetic testing cannot be done, patients are advised to pursue yearly endoscopy beginning at age 12.

d.Diagnosis is made by confirming the numerous polyps by endoscopy and obtaining a biopsy to ensure the adenomatous nature of the polyps.

e.Treatment: If untreated, virtually all patients will develop colon cancer with the average age of onset between 34 and 43 years. Treatment is aimed at colectomy and includes:

1.Total proctocolectomy with ileostomy. This procedure removes all colorectal mucosa, and the patient must wear an appliance.

2.Total proctocolectomy and continent ileostomy. A reservoir is fashioned from the ileum to prevent outflow; the ileostomy must be intubated several times a day for elimination. The patient does not have to wear an appliance, but the operation is technically difficult and has a high incidence of complications.

3.Colectomy with ileorectal anastomosis. The colon is excised, and the ileum is anastomosed to the rectum, which leaves only 15 cm of bowel at risk for cancer.

a.Patients must be examined by proctoscopy every 6 months, and all rectal polyps are destroyed when they appear.

b.Celecoxib, a selective cyclooxygenase-2 inhibitor, has been reported to cause regression of polyps in some patients with FAP. This feature may be advantageous for patients treated by this operation.

4.Total protocolectomy with ileal pouch–anal anastomosis. This operation is especially attractive for patients with “carpeting” of the rectum by polyps too numerous to remove.

a.Advantages

i.Removes all colorectal mucosa at risk for cancer

ii.Frequent proctoscopic examinations not required

b.Disadvantages

i.Some complications, including sepsis, impotence, and fistula are more likely with this procedure.

ii.More frequent stools

iii.Higher incidence of anal incontinence and nocturnal seepage

6.Gardner's syndrome is FAP with osteomatosis, epidermoid cysts, and skin fibromas.

7.Turcot's syndrome is FAP associated with central nervous system malignancies (e.g., medulloblastoma of the spinal cord, glioblastoma of the cerebrum).

C Carcinoma of the colon and rectum

1.Incidence. Colorectal cancer is the most common malignancy of the gastrointestinal tract.

a.It is the third most lethal cancer in women (after lung and breast).

b.It is the third most lethal cancer in men (after lung and prostate).

c.An American has approximately a 5% probability of developing colorectal cancer during a 70-year life span.

d.Most cancers are detected after the age of 50; incidence rises with age.

2.Site. During the past 50 years, there has been a shift in the location of carcinomas from the rectum and left colon toward the right colon. This fact suggests that methods for detecting early large bowel cancer should be directed at the entire colon, rather than the rectosigmoid.

3.Etiology. Neither the cause nor the pathogenesis is well understood. A number of factors are considered important in the development of colorectal cancer.

a.The polyp–cancer sequence has been discussed previously (Chapter 13, IV B).

b.Inflammatory bowel disease

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1.Patients with UC have an increased risk of colorectal cancer, estimated to be more than 40% at 25 years after the onset of pancolitis.

2.Patients with Crohn's colitis have a lower risk of cancer than those with UC but a higher risk than the general population.

c.Genetics. The importance of genetic causes of colon cancer is becoming increasingly obvious.

1.There is an increased incidence of first-degree relatives of patients with colorectal cancer.

2.The genetic transmission in FAP was described previously (Chapter 13, IV B).

3.Hereditary nonpolyposis colorectal carcinoma (HNPCC). HNPCC, unlike FAP, cancer arises from a single colorectal lesion in the absence of polyposis.

a.Characteristics include:

i.Accounts for 3%–5% of all colorectal cancers

ii.Autosomal dominant inheritance

iii.Predominance of proximal colon cancers

iv.Increased synchronous colon cancers

v.Early age of onset (average age is 44 years)

vi.Increased risk of metachronous cancers

vii.Increased incidence of mucinous or poorly differentiated carcinomas