300
UNIT 3
Organ Systems
Figure 15-18A.
Colon Polyps.
H&E,
3
97; inset (
upper
)
3
1.3
Colon polyps
are tissue masses that grow on the inner
mucosal surface and protrude into the lumen of the colon.
Polyps may contain a
stalk
or may be
sessile
, without a stalk.
There are several types of polyps, the most common of which
are
adenomatous
and
hyperplastic
. Adenomatous polyps are
benign neoplasms, subdivided based on morphologic fea-
tures into
tubular adenomas
,
tubulovillous adenomas
, and
villous adenomas
. Although adenomatous polyps are them-
selves benign, they should be considered as having malignant
potential, because adenocarcinoma may arise in these
polyps.
Hyperplastic polyps
, which are common in the descending
colon and rectum, are considered benign with minimal risk for
progression to cancer.
Pseudopolyps
may be seen in infl am-
matory bowel disease, particularly ulcerative colitis. Polyps
may be removed during colonoscopy by endoscopic mucosal
resection and sent for pathologic evaluation. These images
show a large,
pedunculated tubular adenoma
(
inset
) and a
higher power view of the
adenomatous epithelium
featuring
pseudostratif
cation
of the crypt cells.
Figure 15-18B.
Colorectal Cancer.
H&E,
3
97
Colorectal cancer
is a
malignant neoplasm
of the colon or the
rectum. Risk factors include genetics, infl ammatory bowel
disease—especially ulcerative colitis—adenomatous polyps,
high-fat and low-F ber diets, and excessive red meat consump-
tion.
Adenocarcinoma
is the most common type of colon cancer
(98% of cases), arising from the
mucosal glandular
epithelium
,
often in adenomatous polyps. Colorectal carcinomas invade
through the layers of the intestinal wall and metastasize pre-
dominantly through the lymphatic system. Depending on the
location, colorectal cancers may be asymptomatic for years.
Presenting symptoms may be a change in bowel habits due to
bowel obstruction, blood in the stool, or iron deF ciency ane-
mia. Surgical resection is the F rst choice for early-stage cancer,
although chemotherapy may be considered. This photomicro-
graph shows a moderately differentiated
adenocarcinoma
of
the colon inF ltrating the muscularis propria.
Figure 15-18C.
Meckel Diverticulum.
H&E, ×19
Meckel diverticulum
is a congenital abnormality
characterized
by an outpouching in the small bowel due to failure of the
vitelline duct to close or
involute
. As a true diverticulum, it
contains all three layers (mucosa, submucosa, and muscu-
laris propria) of the normal bowel wall and is found on the
antimesenteric aspect of the bowel.
Meckel diverticula
occur
in 2% of the population, are usually located within 2 ft of
the ileocecal valve, and are about 2 in length. Some Meckel
diverticula contain
heterotopic rests
of
pancreatic
or
gastric
mucosa
. Most people with a Meckel diverticulum are asymp-
tomatic. Bleeding, infl ammation, and peptic ulceration and
perforation can occur, producing signs and symptoms simi-
lar to appendicitis. Surgery is the appropriate treatment for
symptomatic patients. This image shows a section of a Meckel
diverticulum showing normal ileal mucosa with goblet cells
on the left side and
ectopic gastric mucosa
on the right side.
This gastric mucosa increases the risk of
perforation because
of the elaboration of acid.
CLINICAL CORRELATIONS
Pseudostratified
columnar epithelium
Stalk
Colon
polyp
A
Adenocarcinoma
(malignant glands)
B
Ectopic
gastric
mucosa
Meckel
diverticulum
Ileal
mucosa
C
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