cell reproduction, for cells in the mucous mem-
brane lining of the COLONand RECTUM. Having the
GENE mutations for HNPCC increases the likeli-
hood that a person will develop colorectal CANCER
before the age of 50 years. HNPCC accounts for
about 5 percent of colorectal cancer in the United
States as well as increased risk for GASTRIC CANCER,
ENDOMETRIAL CANCER, andOVARIAN CANCER.
Cancer experts recommend annual
COLONOSCOPY(examination of the colon with a
flexible, lighted scope) to screen for colorectal can-
cer when HNPCC mutations are present, begin-
ning at age 20 or upon identification of the
mutations. Such screening permits the early
detection and removal of the intestinal polyps that
are the preliminary foundation for colorectal can-
cer. Polyps tend to progress to malignancy much
faster in people who have genetic predisposition
to colorectal cancer. Such aggressive screening has
good potential for preventing colorectal cancer.
GENETIC TESTINGis important as well.
See also ADENOMA-TO-ADENOCARCINOMA TRANSI-
TION; CANCER PREVENTION; CANCER RISK FACTORS; CELL
STRUCTURE AND FUNCTION; FAMILIAL ADENOMATOUS
POLYPOSIS(FAP); GENETIC DISORDERS; GENETIC TESTING;
INHERITANCE PATTERNS; INTESTINAL POLYP.
hiatal hernia A weakening in the DIAPHRAGM, the
muscular wall that separates the thoracic cavity
(chest) from the abdominal cavity, that allows part
of the upper STOMACHto slide upward into the
chest. The weakening develops in the natural
lapse in the diaphragm’s continuity, called the hia-
tus, that allows the ESOPHAGUSto join the stomach.
Hiatal hernia becomes more common with
increasing age and often coexists with GASTROE-
SOPHAGEAL REFLUX DISORDER(GERD). Most hiatal her-
nias do not present symptoms, though the GERD
does. The hiatal hernia can worsen the symptoms
of GERD by forming a pocket that traps the
refluxed gastric contents, intensifying the duration
of exposure the esophageal mucosa experiences.
Risk factors for hiatal hernia include PREGNANCY
(which pressures the diaphragm) and OBESITY.
BARIUM SWALLOWor esophagoscopy (endoscopic
examination of the esophagus) can detect the
presence of hiatal hernia. Unless there is risk for
gastric or esophageal strangulation, in which a
portion of the esophagus or stomach becomes
pinched off on the thoracic side of the diaphragm,
lifestyle modifications such as weight loss and
medications to treat associated GERD can success-
fully manage hiatal hernia. When there is a sub-
stantial risk for strangulation, such as with a large
hernia, the gastroenterologist may recommend
surgery to repair the hernia and prevent strangu-
lation. Gastric or esophageal strangulation, though
rare, requires emergency surgery.
See also ACHALASIA; BARRETT’S ESOPHAGUS;
ENDOSCOPY; ESOPHAGITIS.Hirschsprung’s disease A CONGENITAL ANOMALY,
also called congenital megacolon, in which the
nerves that supply the lower COLON, typically the
sigmoid colon and RECTUM, are missing. Nerves to
the ANUSand anal sphincter are generally intact.
The absence of nerves maintains the muscular
wall of the lower colon in a state of perpetual con-
traction, bringing PERISTALSISto a halt and causing
digestive waste to accumulate. These events create
pressure in the preceding segments of the colon,
causing it to greatly dilate (megacolon).
Untreated, this dilation results in TOXIC MEGACOLON,
a massive dilation of the colon. Toxic megacolon is
a life-threatening emergency that requires imme-
diate surgery.
Symptoms include failure to pass MECONIUM(a
newborn’s first stool) within 48 hours of birth and
ABDOMINAL DISTENTION. Hirschsprung’s disease that
involves only a short segment of the colon may
remain undetected into childhood and even early
adulthood, producing primarily symptoms of
chronic CONSTIPATIONand intermittent abdominal
distress. The diagnostic path may include DIGITAL
RECTAL EXAMINATION (DRE), abdominal X-rays,
ULTRASOUND, or BARIUM ENEMA. Biopsy of the rectal
wall confirms the absence of NERVEganglia.
Treatment is surgery to remove the defective
segments of bowel, connecting the ends of healthy
bowel to maintain the integrity of the lower intes-
tinal tract. The surgery restores normal bowel
motility and function, allowing normal bowel
movements. Sometimes the surgery takes place in
two operations, the first to remove the defective
bowel and the second to reconstruct the colon. A
temporary COLOSTOMY allows digestive waste to
leave the body during the interim HEALINGphase.
Most infants who undergo surgical repair before58 The Gastrointestinal System