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...