Abdominal Pain Case 5

A 17-year-old boy is taken to the emergency department because he has developed severe abdominal pain. The pain began abruptly several hours previously, and was felt initially in the periumbilical region, but later shifted to the right lower quadrant. The boy had initially felt somewhat nauseous, but this has passed. On physical examination, he is noted to have localized pain on cough and to be running a low-grade fever.

Q 1

Examination of the abdomen demonstrates right lower quadrant tenderness at the junction of the middle and outer thirds of the line joining the umbilicus to the anterior superior spine of the iliac. This location is known as which of the following?

/ A. Gubernaculum

/ B. Langer's line

/ C. Linea alba

/ D. McBurney's point

/ E. Tunica albuginea

Q 2

Which of the following is the most likely diagnosis?

/ A. Appendicitis

/ B. Diverticulitis

/ C. Gallstones

/ D. Rectal ulcer

/ E. Renal colic

Q 3

The patient also exhibits an increase in pain in the right lower quadrant from the passive extension of the right hip joint. This finding suggests that the inflammation also involves which of the following?

/ A. BIadder

/ B. External oblique muscle

/ C. Femur

/ D. IIiopsoas muscle

/ E. Transverse abdominal muscle

Q 4

The patient is prepared for immediate surgery. Cefotaxime is administered before, during, and after surgery. The specimen, once removed, is sent to the laboratory for pathology and bacteriologic culture. A malodorous pus surrounds the serosa of the surgical specimen, and a mixed gram-negative flora is cultured. Rapid enzyme tests for beta-Iactamase production are positive. Which of the following drugs should be added to the initial cefotaxime regimen?

/ A. Bacitracin

/ B. CIavulanic acid

/ C. CIindamycin

/ D. Isoniazid

/ E. Vancomycin

Q 5

The patient's postoperative recovery is uneventfuI, but 10 days after discharge, he returns to his physician complaining of continuous low-grade fever. An abscess is drained transrectally, and organisms are cultured from the pus. Which of the following is an attribute of this organism that makes it an important abscess former?

/ A. It is an anaerobe

/ B. It is an intracellular pathogen

/ C. Its endotoxin lacks 2,3-ketodeoxyoctonate

/ D. Mycolic acid

/ E. Prodigious capsule

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Abdominal Pain Case 5 Answers

A1

The correct answer is D. The point described is McBurney's point, which overlies the location of the appendix in most individuals.

The gubernaculum (choice A) is the fibrous cord that connects the primordial testis or ovary to the anterolateral abdominal wall.

Langer's lines (choice B) are the cleavage lines of the skin.

The linea alba (choice C) is a sheet-like aponeurosis that covers the anterior abdominal wall.

The tunica albuginea (choice E) is a tough fibrous coat that covers the testis.

A2

The correct answer is A. This patient has a typical presentation for appendicitis, and the diagnosis is confirmed by the presence of localized tenderness at McBurney's point.

Diverticulitis (choice B) is usually a disease of middle-aged or older individuals and most commonly affects the left-lower quadrant.

Symptomatic gallstone disease (choice C) causes pain and tenderness in the right upper quadrant.

Rectal ulcer (choice D) causes pain with stool movement, but does not usually produce tenderness identifiable on abdominal examination.

Renal colic (choice E) usually produces flank or lower back pain.

A3

The correct answer is D. This patient has a "positive psoas sign," which is an increase in pain from passive extension of the right hip joint. This maneuver stretches the iliopsoas muscle, which lies behind the appendix and can become secondarily inflamed when the appendiceal inflammation extends through the serosa. The psoas sign is clinically useful in both confirming the appendix as the probable origin of the patient's pain, and indicating that the inflammation is transmural and that the risk of rupture and peritonitis is increased.

The bladder (choice A) is located more medially, and is usually not affected by appendicitis.

The external oblique (choice B) and transverse abdominal (choice E) muscles are in the anterior and lateral abdominal walls, and do not usually become inflamed with appendicitis.

The femur (choice C) is moved during the extension of the right hip joint, but is not the source of the pain.

A4

The correct answer is B. Clavulanic acid is a beta-lactamase inhibitor, which when administered with beta lactam agents, irreversibly binds and inactivates bacterial beta-lactamases, thereby permitting the companion drug to disrupt bacterial cell wall synthesis. Suspected appendicitis is usually treated with prompt appendectomy, since delay is associated with increased risk of potentially life-threatening peritonitis and sepsis.

Bacitracin (choice A) is not correct, since this drug inhibits bacterial cell wall synthesis by binding to and inhibiting the dephosphorylation of a membrane-bound lipid pyrophosphate. Gram-negative bacteria are resistant to this agent, and it would not have a synergistic effect if administered with a third generation cephalosporin.

Clindamycin (choice C) is not correct, because this drug blocks protein elongation by binding to the 50S ribosome. Although it is effective against anaerobic gram-negative bacilli, it would not have a complementary effect when administered with a third generation cephalosporin.

Isoniazid (choice D) is not correct because it inhibits the synthesis of mycolic acids for the cell wall of actively dividing Mycobacteria. It would not be effective in the flora of this patient's gut, nor would it act synergistically with third generation cephalosporins.

Vancomycin (choice E) is not correct because it disrupts cell wall synthesis in growing gram-positive bacteria. It would not be effective against the flora of this patient's gut, nor would it act synergistically with third generation cephalosporins.

A5

The correct answer is E. Prevotella (Bacteroides) is a frequent cause of abscesses in the intestinal tract because it is a normal flora organism and produces a large capsule, which impedes phagocytosis.

Although the genus is anaerobic (choice A), it is not this attribute which causes its formation of abscesses.

Prevotella is extracellular, not an intracellular pathogen (choice B).

Although Prevotella does indeed have this type of endotoxin (choice C), the absence of this molecule decreases the toxicity of the toxin, and does not contribute to its proclivity toward abscess formation.

Mycobacteria, and not other genera such as Prevotella, are known for their long-chain fatty acids (mycolic acids; choice D).

Gastrointestinal Bleeding case 2

A 9-day-old baby is noted to be lethargic and has been feeding poorly. Over the next day, the baby develops bilious vomiting, a distended tender abdomen, and bloody stools.

Q 1

Which of the following diseases would most likely cause gastrointestinal bleeding in a neonate?

/ A. Crohn disease

/ B. Cystic fibrosis

/ C. Diverticulitis

/ D. Necrotizing enterocolitis

/ E. UIcerative colitis

Q 2

Which of the following is considered the most important risk factor for this patient's disease?

/ A. Perinatal asphyxia

/ B. Polycythemia

/ C. Prematurity

/ D. Respiratory distress syndrome

/ E. Shock

Q 3

A plain radiograph of the abdomen demonstrates gas within the bowel walI (pneumatosis). Which of the following would most likely be

associated with this finding?

/ A. Air in the biliary tract

/ B. BIood in the biliary tract

/ C. Gas in the hepatic veins

/ D. Gas in the mediastinum

/ E. Gas in the portal vein

Q 4

The baby's condition continues to deteriorate, and the decision is made to surgically resect the affected GI segment. Resection of which of the

following areas of the gastrointestinal tract would most likely produce severe long-term malabsorption?

/ A. Ascending colon

/ B. Duodenum

/ C. Jejunum

/ D. Stomach

/ E. Terminal ileum

Q 5

The baby's resected gastrointestinal segment would be most likely to show which of the following on pathologic examination?

/ A. Distended macrophages with PAS-positive granules in the submucosa

/ B. Gangrenous intestinal wall

/ C. Granuloma formation

/ D. Neoplastic epithelial proliferation

/ E. Outpouching of intestinal mucosa through the muscular layer

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Gastrointestinal Bleeding case 2 answers

A1

The correct answer is D. Necrotizing enterocolitis is a feared complication of infancy. It has an incidence of 1 to 5% in neonatal intensive care unit admissions. The condition is a necrotizing disease of the small intestine, and sometimes, the colon. The pathogenesis is still not clear, but may involve an ischemic insult leaving the bowel susceptible to bacterial overgrowth. Necrotizing enterocolitis may develop suddenly, with features suggesting neonatal sepsis, or more slowly, over a period of one or two days. The case description illustrates typical features.

Crohn disease (choice A) and ulcerative colitis (choice E) may present as early as in the teenage years, but not usually in infancy.

Cystic fibrosis (choice B) is a cause of meconium ileus and later malabsorption, but does not typically present with gastrointestinal bleeding.

Diverticulitis (choice C) is usually a disease of middle-aged to older adults.

A2

The correct answer is C. Prematurity is the most important risk factor for necrotizing enterocolitis, although term infants also sometimes develop the condition. Clinical series have reported that between 60 and 95% of affected babies are premature, and the incidence is markedly increased in babies born at lower gestational ages.

Many other purported risk factors have also been cited but seem to have a lesser effect, including perinatal asphyxia (choice A), respiratory distress syndrome (choice D), umbilical catheterization, hypothermia, shock (choice E), patent ductus arteriosus, cyanotic congenital heart disease, polycythemia (choice B), thrombocytosis, anemia, exchange transfusion, congenital GI anomalies, chronic diarrhea, non-breast milk formula, nasojejunal feedings, hypertonic formula, and colonization with necrogenic bacteria. It may simply be that any already fragile baby, particularly if premature, who has other significant underlying disease, is at increased risk for developing necrotizing enterocolitis.

A3

The correct answer is E. Portal venous gas is seen in association with pneumatosis intestinalis, most commonly with necrotizing enterocolitis. The physiology of this is that the portal vein, via the mesenteric veins, drains nutrient-rich blood from the gut to the liver. In the case of necrosis with air in the bowel wall, air migrates into the portal venous system and to the liver. On CT, this has the characteristic appearance of peripheral lucencies following the portal venous system intrahepatically. In cases of more severe pneumatosis, the bowel may rupture and lead to pneumoperitoneum.

Note: Although this item may have seemed difficult, it was, in essence, a straightforward pathophysiology question, i.e., "Where would gas in the wall of the intestine go?" The distracter explanations give additional information concerning the radiographic appearance of the other conditions (the following will most likely NOT be tested on Step I of the USMLE).

Pneumobilia, or air in the biliary tract (choice A), would be seen after instrumentation of the biliary system, such as after an endoscopic retrograde cholangiopancreatogram (ERCP). Other causes include a gas-forming infection within the biliary tree or previous sphincterotomy (endoscopic opening of the sphincter of Oddi). Pneumobilia has a distinct appearance on CT: there is gas located centrally in the liver within the ducts.

Hemobilia, or blood in the biliary tract (choice B), would be seen after instrumentation of the biliary system, such as after an endoscopic retrograde cholangiopancreatogram (ERCP), from a biliary or hepatic tumor, or secondary to a hypocoagulable state. Hemobilia is found at endoscopy, and is generally not visible on plain radiographs. High attenuation material may be seen within the bile ducts on a CT scan, suggesting hemobilia.

Hepatic venous gas (choice C) would not be seen with pneumatosis because the hepatic veins drain the liver into the inferior vena cava (IVC). Gas from the bowel wall gets trapped in the portal veins and does not traverse the liver to get into the hepatic veins.

Pneumomediastinum (choice D) is usually from thoracic trauma causing rupture of the esophagus or pneumothorax. Gas within the soft tissues of the head and neck may dissect to the mediastinum. Rarely, pneumoperitoneum may lead to secondary pneumomediastinum. Pneumatosis without pneumoperitoneum would not lead to pneumomediastinum.

A4

The correct answer is E. Babies with early necrotizing enterocolitis are sometimes successfully managed medically with fluids, bowel rest, and correction of anemia and thrombocytopenia that may have developed secondary to the gastrointestinal bleeding. Surgical resection may be necessary in more severe cases of necrotizing enterocolitis, but may have a mortality of 30-40% in these deathly ill infants. Unfortunately, necrotizing enterocolitis most often affects the terminal ileum, which is also the site most necessary to prevent long-term malnutrition. In practice, more than 50% of the bowel must usually be removed before substantial malabsorption occurs. The ileum is the site that is most active in nutrient (particularly fats) absorption, vitamin B12 absorption, and conjugated bile salt absorption.

The ascending colon (choice A) is good at absorbing water and has a small capacity for absorbing carbohydrates.

The duodenum (choice B) and jejunum (choice C) are also important absorptive sites, but are less of a long-term problem because the ileum appears to usually have the capacity to replace their absorptive function after proximal small intestine resection.

Nutrient absorption does not usually occur in the stomach (choice D).

A5

The correct answer is B. The intestinal wall in early necrotizing enterocolitis shows edema, hemorrhage, and necrosis. In more advanced disease, gangrenous necrosis of the full bowel thickness is seen, and necrotic inflammatory debris may adhere to the mucosal surface. Some cases show evidence of reparative change, such as epithelial regeneration and granulation tissue formation, suggesting that the lesion may have evolved over several days before becoming clinically obvious.

Choice A is a feature of Whipple disease.

Choice C is a feature of Crohn disease.

Choice D is a feature of colonic polyps and cancers.

Choice E is a feature of diverticulitis.

Gastrointestinal Bleeding case 1

A 60-year-old man comes to the emergency department complaining of bright red blood per rectum. The bleeding began abruptly several hours prior to his visit. He has light-headedness when he stands up rapidly, but has no abdominal pain, cramping, fever, nausea, or vomiting. He has no history of previous episodes of bleeding or abdominal pain, but has a history of coronary artery disease and takes aspirin as a "blood thinner." He is afebrile, slightly hypotensive and tachycardic, but stable. On examination, he has decreased skin turgor, and dry mucous membranes. He has no abdominal tenderness. Rectal examination is positive for gross blood.

Q 1

Which of the following is the most likely diagnosis?

/ A. Arteriovenous malformation

/ B. Diverticulitis

/ C. Infectious colitis

/ D. Ischemic colitis

/ E. UIcerative colitis

Q 2

After the patient has stabilized, a colonoscopy is performed to elucidate the origin of the bleeding. Several star-shaped branching vessels

measuring 0.2 to 1.0 cm are seen in the colonic submucosa. BIeeding is stopped by electrocoagulation. A diagnosis of lower gastrointestinal

bleeding is given. Which anatomic landmark demarcates upper gastrointestinal bleeding from lower gastrointestinal bleeding?

/ A. IIeocecal valve

/ B. Ligament of Treitz

/ C. Papilla of Vater

/ D. Pylorus

/ E. Splenic flexure of the colon

Q 3

The aspirin taken by this patient represents a contributor to his condition. Which of the following best describes the mechanism of action of

aspirin?

/ A. Aspirin decreases the serum level of factor VIII

/ B. Aspirin decreases the serum level of factor IX

/ C. Aspirin irreversibly inhibits platelets

/ D. Aspirin irreversibly inhibits thrombin

/ E. Aspirin reversibly inhibits platelets

/ F. Aspirin reversibly inhibits thrombin

Q 4

Which of the following is an important mechanism in short-term blood pressure maintenance?

/ A. BIood pressure regulation occurs slowly by endocrine mechanisms only

/ B. Decreased stretch in the carotid bodies decreases sympathetic and increases parasympathetic discharge to the heart

/ C. Decreased stretch in the carotid bodies increases sympathetic and decreases parasympathetic discharge to the heart

/ D. Decreased stretch in the carotid sinus decreases sympathetic and increases parasympathetic discharge to the heart

/ E. Decreased stretch in the carotid sinus increases sympathetic and decreases parasympathetic discharge to the heart

Q 5

Normal saline is administered to this patient and his blood pressure and heart rate normalize. One of the goals in fluid resuscitation is to

optimize cardiac parameters according to Starling's Law. Starling's Law describes which of the following?

/ A. The relationship between end diastolic volume and contractility

/ B. The relationship between heart rate and stroke volume

/ C. The relationship between preload and afterload

/ D. The relationship between stroke volume and end systolic volume

/ E. The relationship between systemic vascular resistance and cardiac output

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Gastrointestinal Bleeding case 1 answers

A1

The correct answer is A. Painless hematochezia or bright red lower GI bleeding can come from many sources. While bright red lower GI bleeding tends to indicate lower GI bleeding (bleeding distal to the ligament of Treitz), brisk upper GI bleeding can also be the source. The clinical manifestations of such bleeding range from negligible to hemodynamic instability, depending upon the rate of bleeding. The differential diagnosis for painless hematochezia includes AV malformations, gastric erosions, esophageal varices, esophagitis, duodenal or gastric ulcer, hemorrhoids, diverticulosis, and colonic neoplasm.

Diverticulitis (choice B) occurs when a colonic outpouching or diverticulum becomes inflamed. Patients tend to be elderly and present with fever, abdominal pain, and abdominal tenderness on examination. While painful, these lesions do not bleed significantly (unlike their uninflamed counterparts in diverticulosis).

Infectious colitis (choice C) may present as rectal bleeding, but this bleeding is typically accompanied by pain, cramping, and fever. Causative organisms may include Salmonella, Shigella, Campylobacter jejuni, E. coli, and Entamoeba histolytica.

Ischemic colitis (choice D) may have rectal bleeding, but the hallmark of ischemic colitis is severe abdominal pain out of proportion to examination findings.

Ulcerative colitis (choice E) presents as abdominal pain and diarrhea, which may be bloody or nonbloody. In addition, the onset of the disease tends to be earlier, so this patient would likely have had previous episodes of pain

A2

The correct answer is B. The ligament of Treitz, or the peritoneal ligament, which separates the third (retroperitoneal) portion of the duodenum from the fourth (peritoneal) portion of the duodenum, traditionally demarcates upper GI bleeding from lower GI bleeding. Bleeding proximal to this landmark tends to produce melena or black tarry stools. Bleeding distal to this landmark tends to produce hematochezia or red blood per rectum.

The ileocecal valve (choice A) separates the terminal ileum from the cecum.

The papilla of Vater (choice C) is where the pancreatic duct and common bile duct empty into the duodenum.

The pylorus (choice D) is the sphincter separating the stomach from the duodenum.

The splenic flexure of the colon (choice E) marks the transition from transverse colon to the descending colon.

A3

The correct answer is C. Patients with gastrointestinal bleeding must be assessed for anatomic as well as physiologic and pharmacologic sources of bleeding. Aspirin acts as an anticoagulant by irreversibly inhibiting platelets, preventing the formation of a clot by blocking platelet adhesion and aggregation. Since this platelet mass acts as a matrix for fibrin clot formation, blocking platelets prevents clot formation. This mechanism has been utilized in patients with atherosclerotic disease to prevent intravascular clot formation, but may aggravate bleeding conditions such as this.

Aspirin does not decrease the serum level of factor VIII (choice A). Factor VIII deficiency is the pathophysiology behind hemophilia A.

Factor IX deficiency (choice B) is associated with hemophilia.

Aspirin does not inhibit thrombin (choices D and F). Thrombin is the enzyme responsible for cleaving fibrinogen to fibrin.

Aspirin's effects on platelets are not reversible (choice E), and a new population of functional platelets must replace the inhibited platelets before coagulation is fully restored.

A4

The correct answer is E. As blood pressure falls in this patient with hypovolemia, many short term and long term mechanisms work to raise the falling pressure. In the short term, the baroreceptors found in the carotid sinus and aortic arch regulate blood pressure by modulating the autonomic nervous system. As pressure falls in this patient, the baroreceptors sense this change as a decrease in stretch in the vessel walls. Afferent fibers from the baroreceptors then "report" this change to the medullary cardiovascular center. This center responds by increasing sympathetic discharge and decreasing parasympathetic discharge to the heart and resistance vessels. This acts to restore the blood pressure by increasing heart rate, stroke volume, and vascular resistance.

While endocrine mechanisms (choice A) restore mean arterial pressure for the long term, the sympathetic mechanisms outlined above restore pressure toward baseline much more rapidly.

Choices B and C are incorrect. The carotid bodies contain chemoreceptors (not stretch receptors) that detect changes in PO₂, PCO₂, and pH. They restore these parameters to normal by acting through the medullary centers to change heart rate, stroke volume, vascular resistance, and ventilatory parameters.

The decrease in pressure triggers an increase in sympathetic discharge and decrease in parasympathetic discharge (compare with choice D).

A5

The correct answer is A. Starling's law of the heart describes the relationship between end diastolic volume or preload and cardiac contractility. It states that cardiac contractility is maximized at a particular preload. It also states that cardiac contractility declines as the preload is increased or decreased from this optimum. The basis for this principle is that at a particular preload, the myocardium is "stretched" to a point that maximizes the number of actin and myosin units that may interact in a given contraction.

Choice B is incorrect. Heart rate x stroke volume = cardiac output

Choice C is incorrect. Preload is related to end diastolic volume and passive wall tension exerted on the diastolic ventricle.

Choice D is incorrect. End diastolic volume - end systolic volume = stroke volume

Choice E is incorrect. Mean arterial pressure = cardiac output x total peripheral resistance.