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.