Atlas of pathophysiology, 2 Edition

Part II - Disorders

Gastrointestinal Disorders

Colorectal Cancer

Colorectal cancer is the second most common visceral malignant neoplasm in the United States and Europe. It tends to progress slowly and remains localized for a long time. Incidence is equally distributed between men and women. It's potentially curable in about 90% of patients if early diagnosis allows resection before nodal involvement.

Causes

Unknown

Risk factors

·   Intake of excessive saturated animal fat

·   Low-fiber diet

·   Other diseases of the digestive tract

·   History of ulcerative colitis (average interval before onset of cancer is 11 to 17 years)

·   Familial polyposis (cancer usually develops by age 50)

Age Alert

Age over 40 is a risk factor for colorectal cancer.

Pathophysiology

Most lesions of the large bowel are moderately differentiated adenocarcinomas. These tumors tend to grow slowly and remain asymptomatic for long periods. Tumors in the sigmoid and descending colon grow circumferentially and constrict the intestinal lumen. At diagnosis, tumors in the ascending colon are usually large and are palpable on physical examination.

Signs and symptoms

·   Changes in bowel habits, such as bleeding, pain, anemia, and anorexia

·   Symptoms of local obstruction

·   Symptoms of direct extension to adjacent organs (bladder, prostate, ureters, vagina, sacrum)

·   Symptoms from distant metastasis (usually liver).

Signs specific to site of obstruction

·   Right colon:

§  Black, tarry stools; anemia

§  Abdominal aching or pressure; dull cramps

§  Weakness, fatigue, exertional dyspnea

§  Vomiting

·   Left colon:

§  Rectal bleeding; dark or bright red blood or mucus in stools

§  Abdominal fullness or cramping

§  Rectal pressure

§  Constipation

§  Diarrhea

§  Ribbon- or pencil-shaped stools

§  Pain relieved by flatus or bowel movement

Diagnostic test results

·   Digital rectal examination detects almost 15% of colorectal cancers; specifically, it detects suspicious rectal and perianal lesions.

·   Fecal occult blood test possibly shows blood in stool.

·   Barium enema studies can determine the location of lesions that aren't normally detected manually or visually.

Clinical Tip

Barium examination shouldn't precede colonoscopy or excretory urography because barium sulfate interferes with these tests.

·   Computed tomography scan allows better visualization if a barium enema yields inconclusive results or if metastasis to the pelvic lymph nodes is suspected.

·   Proctoscopy or sigmoidoscopy permits visualization of the lower GI tract, which can detect up to 66% of colorectal cancers. Colonoscopy permits visual inspection and photography of the colon up to the ileocecal valve and provides access for polypectomies and biopsies of suspected lesions.

·   Carcinoembryonic antigen permits patient monitoring before and after treatment to detect metastasis or recurrence.

·   Excretory urography verifies bilateral renal function and allows inspection for displacement of the kidneys, ureters, or bladder from a tumor pressing against these structures.

Treatment

·   Surgery to remove tumor plus adjacent tissues and any lymph nodes that may contain cancer cells

·   Chemotherapy for patients with metastasis, residual disease, or a recurrent inoperable tumor

·   Radiation therapy for tumor mass reduction, done before or after surgery or combined with chemotherapy

·   High-fiber diet

P.169

TYPES OF COLORECTAL CANCER

image

image