IUHS Student-2-Student USMLE Step 1 Recall
GI Tract
Esophagus
Normal Esophagus
the mucosa is composed of a nonkeratinizing
stratified squamous epithelial layer that
overlies a lamina propria...a small number of specialized cell types, such as melanocytes, endocrine cells, and langerhans
cells are present in the deeper portion of the epithelial layer...
the submucosa consists of loose connective
tissue containing blood vessels, a rich network of lymphatics,
a sprinkling of leukocytes with occasional lymphoid follicles, nerve fibers (including the ganglia of Meissner
plexus), and submucosal glands...
Achalasia
achalasia
is characterized by three major abnormalities: (1) aperistalsis,
(2) partial or incomplete relaxation of the LES
with swallowing, and (3) increased resting tone of the LES...
the
pathogenesis of primary achalasia is poorly
understood but is thought to involve degenerative changes in neural innervation, either intrinsic to the esophagus or in the extraesophageal vagus nerves and
the dorsal motor nucleus of the vagus...
secondary achalasia may arise in Chagas disease, in which Trypanosoma
Cruzi causes destruction of the myenteric
plexus of the esophagus, duodenum, colon, and ureter,
with resultant dilation of these viscera...
diseases
of the dorsal motor nuclei, particularly polio or surgical ablation, can cause
an achalasia-like illness, as can diabetic autonomic
neuropathy, and infiltrative disorders, such as malignancy, amyloidosis,
and sarcoidosis...
"birds beak"...
in most
instances, however, achalasia occurs as a primary
disorder of uncertain cause...
achlasia shows a high pressure nonrelaxing LES
with absent motility in the body of the esophagus...
in
primary achalasia, there is progressive dilation of the esophagus above the level of the
LES...
the wall
of the esophagus may be of normal thickness, thicker than normal owing to
hypertrophy of the muscularis, or markedly thinned
out by dilation...
the myenteric ganglia are usually absent from the body of the esophagus
but may or may not be reduced in number in the region of the lower sphincter...
the
mucosal lining may be unaffected, but sometimes inflammation, ulceration, or fibrotic thickening may be evident just above the lower
sphincter...
"birds beak"...
myenteric
ganglia are in the muscularis externa...
the most
serious aspect of this condition is the hazard of developing
esophageal squamous cell carcinoma, said
to occur in about 5% of patients...
there
is a sensation of "food stickin
in my throat"....
do an endoscopy to inject botulinum toxin into the lower esophageal sphincter, and it
would provide a direct view of the dilation...
patients with achalasia most commonly complain of
dysphagia (difficulty swallowing), chest pain, and
regurgitation...
Hiatal Hernia
hiatal
hernia is characterized by separation of the diaphragmatic crura
and widening of the space between the muscular crura
and the esophageal wall...two anatomic patterns are recognized: the axial, or sliding hernia, and the nonaxial,
or paraesophageal hiatal hernia...
the sliding hernia constitutes 95% of cases;
protrusion of the somach above the diaphragmatic
narrowing...
in paraesophageal hernias, a separate
portion of the stomach, usually along the greater curvature, enters the thorax
through the widened foramen...
the
cause of hiatal hernia is unknown...reflux esophagitis is frequently
seen in association with sliding hernias, but compromise of the LES with
regurgitation of peptic juices into the esophagus is probably the result of,
rather than the cause of, a sliding hernia...the uncommon paraesophageal
hernias may be caused by previous surgery, including operations of resliding hernia...
based
on barographic studies, hiatal
hernias are reported in 1-20% of adult subjects, increasing in incidence with
age...hiatal hernias, however, are well recognized in
infants and children...only about 9% of adults with a sliding hernia suffer
from heartburn or regurgitation of gastric juices into the mouth...these
symptoms are attributed to incompetence of the LES and are accentuated by
positions favoring reflux (bending forward, lying supine) and obesity...
complications
of hiatal hernias are numerous...both types may
ulcerate, causing bleeding and perforation...paraesophageal
hernias can become strangulated or obstructed, and early surgical repair has
been advocated...
Diverticulum of the Esophagus
a diverticulum is an outpouching of
the alimentary tract that contains all visceral layrs;
a false diveticulum denotes an outpouching
of mucosa and submucosa only...
true diveticula are usually discovered in later life and may
develop in three regions of the esophagus:
zenker diverticulum
immediately above the upper esophageal sphincter...traction diverticulum near
the midpoint of the esophagus...epiphrenic diverticulum immediately above the LES...
disordered
cricopharyngeal motor dysfunction is implicated in
the genesis of zenker diverticulum...scarring
resulting from medistinal lymphadenitis (as from
tuberculosis) was a presumed cause of traction on the esophagus, giving rise to
midesophageal diverticula...arguments,
however, have been advanced in favor of traction diverticula
actually arising from motor dysfunction or being a congenital erosion...dyscordination of peristalsis and LES relaxation are the
proposed cause of epiphrenic diverticula...
zenker
diverticula may reach several centimeters in size and
accumulate significant amounts of food...typical symptoms
are food regurgitation in the absence of dysphagia
and a mass in the neck; aspiration with resultant pneumonia is a
significant risk...while midesophageal diverticula are generally
asymptomatic, epiphrenic diverticula
can give rise to nocturnal regurgitation of massive amounts of fluid...
Lacerations (Mallory-Weiss Syndrome) of the
Esophagus
linear and longitudinal tears in the
esophagus at the esophagogastric
junction are termed Mallory-Weiss tears and are believed to be the consequence of severe retching...
they are
encountered most commonly in alcoholics, attributed to
episodes of excessive vomiting and reflux in of gastric contents in the setting
of an alcoholic stupor...
since
these tears may occur in persons who have no history of vomiting or alcholism, other mechanisms must exist; underlying inapparent hiatal hernias have been implicated...
tearing of lower esophageal mucosa which causes
massive bleeding...
the linear and longitudinal irregular lacerations are
oriented in the axis of the esophageal lumen and are several millimeters to
several centimeters in length...
they are
usually found astride the esophagogastric junction or in the proximal gastric mucosa...
the tears may involve only the mucosa or may penetrate deeply enough
to perforate the wall...
the
histology is not distinctive and reflects trauma accompanied by fresh
hemorrhage and a nonspecific inflammatory response...
infection
of the mucosal defect may lead to an inflammatory ulcer or to mediastinitis...
esophageal lacerations account for 5-10% of upper GI bleeding episodes...
most often,
bleeding is not profuse and ceases without surgical intervention, although massive hematemesis may occur...
supportive
therapy, such as vasoconstrictive medications and
transfusions and sometimes ballon tamponade,
is usually all that is required....
healing
tends to be prompt, with minimal to no residua...the rare instance of
esophageal rupture is known as Boerhaave syndrome and
may be a catastrophic event...
Boerhaave Syndrome - lateral tears through esophagus into mediastinum...
Reflux Esophagitis
reflux of gastric contents into the lower esophagus is the first and
foremost cause of esophagitis...many
causative factors are involved, less well characterized than the name
implies...
decreased
efficacy of esophageal antireflux mechanisms,
particularly LES tone...CNS depressants, hypothyroidism, pregnancy, systemic sclerosing disorders alcohol or tobacco exposure, or the
presence of a nasogastric tube may be contributing
causes...in most instances, no antecedent cause is identified...
simple hyperemia (redness) may be the
only alteration...in uncomplicated reflux esophagitis,
three histologic features are characteristic...
1)
the presence of inflammatory cells, including eosinophils, neutrophils, and
excessive numbers of lymphocytes, in the epitheilial
layer...
2)
basal zone hyperplasia exceeding 20% of the epithelial
thickness...
3)
elongation of lamina propria
papillae with congestion, extending into the top third of the epithelial
layer...
infiltrates of intrepithelial eosinophils
are believed to be a nearly histologic
abnormality, since they occur even in the absence of basal zone hyperplasias...
intraepithelial neutrophils
are markers of more severe injury, such as ulceration, rather than reflux esophagitis per se...
the
clinical manifestations consist principally of dysphagia;
heartburn; and sometimes regurgitation of a sour brash, hematemesis,
or melena...
the
severity of symptoms is not related closely to the presence of degree of histologic esophagitis; most
people experience reflux symptoms without damage to the distal esophageal
mucosa, owing to the short duration of the reflux....
anatomic
damage appears best correlated with prolonged
exposure of the lower esophagus to refluxed material...
Barret Esophagus
in barrett esophagus, the distal squamous
mucosa is replaced by metaplastic
columnar epithelium, as a response to
prolonged injury...
barrett
esophgus patients tend to have a long history of
heartburn and other reflux symptoms and appear to have more massive reflux with
more and longer reflux episodes than most reflux patients...it is unknown why
the columnar epithelium develops in some patients with reflux and not in
others...
the
pathogenesis of barrett esophagus is not
clear...inflammation and ulceration followed by in growth of pluripotent stem cells had been proposed; these cells would
then differentiate into a columnar epithelium that
is more resistant to acid peptic injury...
more recent
studies suggest that true metaplasia
of the esophageal mucosa occurs b/c the
columnar cells of barrett esophagus can exhibit ultrastructural and cytochemical
features of both a squamous and a columnar epithelial
phenotype...
barrett
esophagus seen grossly, or better still on endoscopy,
is apparent as a red, velvety mucosa located
between the smooth, pale esophageal squamous mucosa
and the more lush light brown-pink gastric mucosa...
microscopically
the esophageal squamous epithelium is replaced by metaplastic columnar epithelium complete
with mucosal glands...
dysplasia
is recognized by the presence of cytologic and
architectural abnormalities extending to the luminal surface of the columnar
epithelium...these abnormalities consist of enlarged,
crowded, and stratified hyperchromatic nuclei and
loss of interveinng stroma
between adjacent glandular structures...
of
greatest importance is the development of adenocarcinoma, which, in
patients with greater than 2 cm of barrett mucosa,
occurs at an estimated 30-40 fold increased rate over the general population...
Esophageal Varices
regardless
of cause, portal hypertension,
when sufficently prolonged or severe, induces the formation of collateral bypass channels wherever
the portal and caval systems communicate...
collaterals
develop in the region of the lower esophagus when portal blood flow is diverted
through the coronary veins of the stomach into the plexus of esophageal mucosal
and submucosal veins, thence into the azygos veins, and eventually into the systemic
circulation...
the
increased pressure in the esophageal plexus produces dilated tortuous vessels called varices...varices develop in 90% of cirrhotic patients and are most
often associated with alcoholic cirrhosis...
worldwide, hepatic schistosomiasis is the second
most common cause of variceal bleeding...
vessels
affected in esophageal varices include the
left gastric and azygous veins...
varices
appear as tortuous dilated veins lying primarily
within the submucosa of the distal esophagus and
proximal stomach; mucosal venous channels directly beneath the
esophageal epithelium may also become massively dilated...
varices
produce no symptosm until they rupture, when massive hematemesis ensues...among
patients with advanced cirrhosis of the liver, half the deaths result from
rupture of a varix...
Squamous Cell Carcinoma of the Esophagus
presents
as dysphagia...often in middle
third of esophagus and often extends into adjacent tissue (lung
tissue)...
biopsy
would most likely reveal infiltrating sheets of cells forming keratin...
most likely due to smoking and alcohol...
Tracheoesophageal Fistula
esophageal
atresia occurs in 1 in 3,000/4500 live births; 30% of
infected infants are born prematurely...
in more
than 85% of cases, a fistula between the trachea
and distal esophagus accompanies the atresia
mom has polyhydraminos...
disorders
in the formation and movement of the paired cranial and single caudal folds in
the primitive foregut explain the variation in atresia
and fistula formation...
approximately 50% of infants with esophael atresia have associated anomalies...tracheal esophaeal malformations associated with Vertebral, Anorectal, Cardiac, Renal, Radial, and Limb abnormalities
make up the VATER (or VACTERAL) syndrome...