C h a p t e r 2 9
Disorders of Gastrointestinal Function
721
Diagnosis andTreatment.
Cancer of the colon may be
detected with a high degree of reliability with barium
enema or colonoscopy. Colonoscopy permits biopsy
for pathologic confirmation. CT scans, pelvic magnetic
resonance imaging (MRI), and ultrasonography may be
used to determine the extent of the lesions and whether
metastasis has occurred.
The only recognized treatment for cancer of the colon
and rectum is surgical removal.
65
Preoperative radiation
therapy may be used and has in some cases demonstrated
increased 5-year survival rates. Postoperative adjuvant
chemotherapy may be used. Radiation therapy and che-
motherapy are used as palliative treatment methods.
The prognosis for persons with colorectal cancer
depends largely on the stage of the cancer. Colorectal can-
cer commonly is classified into four TNM (tumor, node,
and metastasis) stages.
6,7
In this system, a stage I tumor is
limited to invasion of the mucosal and submucosal lay-
ers of the colon and has a 5-year survival rate of 90% to
100%. Stage IV (metastatic) tumors penetrate the serosa
or adjacent organs and have a much poorer prognosis.
Screening.
The single most important prognostic indi-
cator of colorectal cancer is the extent (stage) of the
tumor at the time of diagnosis. The challenge, therefore,
is to discover the tumors at their earliest stages. Among
the methods used for early detection of colorectal can-
cers are the digital rectal examination and the fecal
occult blood test, usually done during routine physical
examinations; x-ray studies using barium (e.g., barium
enema); and flexible sigmoidoscopy and colonoscopy.
58,59
Almost all cancers of the colon and rectum bleed
intermittently, although the amount of blood is small
and usually not apparent in the stools. It therefore is
feasible to screen for colorectal cancers using com-
mercially prepared tests for occult blood in the stool.
The sensitivity of fecal occult blood tests is improved
by performing stool tests on three different occasions.
Digital rectal examinations are most helpful in detecting
neoplasms of the rectum. Rectal examination should be
considered a routine part of a good physical examina-
tion. Flexible sigmoidoscopy involves examination of
the rectum and sigmoid colon with a hollow, lighted
tube that is inserted through the rectum. The procedure
is performed without sedation and is well tolerated.
Approximately 40% of cancers and polyps are out of
the reach of the sigmoidoscope, emphasizing the need
for fecal occult blood tests. Polyps can be removed or
tissue can be obtained for biopsy during the procedure.
Colonoscopy provides a means for direct visualiza-
tion of the rectum and colon. The colonoscope con-
sists of a flexible, 4-cm–diameter glass fiber bundle that
contains approximately 250,000 glass fibers and has a
lens at either end to focus and magnify the image. Light
from an external source is transmitted by the fiber-optic
viewing bundle. Instruments are available that afford
direct examination of the sigmoid colon or the entire
colon. This method is used for screening persons at high
risk for development of cancer of the colon (e.g., those
with ulcerative colitis) and for those with symptoms.
Colonoscopy also is useful for obtaining a biopsy and
SUMMARY CONCEPTS
■■
Disorders of the small and large intestines
include inflammatory bowel disease, infectious
enterocolitis, diverticular disease, appendicitis,
disorders of motility, peritonitis, alterations in
intestinal absorption, and colorectal cancer.
■■
The term inflammatory bowel disease is used to
designate two inflammatory conditions: Crohn
disease, which affects the small and large bowel,
and ulcerative colitis, which affects the colon and
rectum. Both are chronic diseases characterized
by remissions and exacerbations of diarrhea,
weight loss, fluid and electrolyte disorders, and
systemic signs of inflammation.
■■
Enterocolitis includes viral (e.g., rotavirus) and
bacterial (e.g., C. difficile and E. coli O157:H7)
infections.
■■
Diverticular disease is a condition in which the
mucosa and submucosa of the colon herniate
through the muscularis layer, and diverticulitis,
in which there is inflammation and gross or
microscopic perforation of the diverticulum.
■■
Diarrhea, constipation, and irritable bowel
syndrome represent disorders of intestinal
motility. Diarrhea or excessively frequent passage
of stools can be caused by infectious organisms,
food intolerance, drugs, or intestinal disease.
Constipation or the infrequent passage of stools
is commonly caused by failure to respond to
the urge to defecate, inadequate fiber or fluid
intake, weakness of the abdominal muscles,
inactivity and bed rest, or pregnancy. Irritable
bowel syndrome is characterized by a variable
combination of chronic and recurrent intestinal
symptoms, that are not related to a structural or
biochemical abnormality.
for removing polyps. Although this method is one of the
most accurate for detecting early colorectal cancers, it is
not suitable for mass screening because it is expensive
and time consuming and must be done by a person who
is highly trained in the use of the instrument.
It is recommended that persons at average risk for
colonic adenomatous polyps or cancer should undergo
colonoscopy every 10 years or alternative screening
tests at periodically prescribed intervals beginning at
age 50.
59
Persons who are members of high-risk groups,
such as those with a family history of adenomatous pol-
yps or disorders that predispose to colon cancer (e.g.,
ulcerative colitis), should undergo periodic surveillance
more frequently.
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