Small Intestine and Colon Pathology

Question 1

What is Ileus?

Answer 1

Loss of the normal propulsive function of the bowel in the absence of mechanical obstruction (intestinal pseudo-obstruction).

Question 2

What can Ileus be associated with?

Answer 2

A variety of conditions such as a complication of abdominal surgery, abdominal trauma, peritonitis, mesenteric ischemia or infarction, use of medications (e.g. narcotics), intra-abdominal infection, and as a complication of gastroenteritis (not a complete list).

Question 3

What is a hernia?

Answer 3

Defect in the wall of the peritoneal cavity, permitting protrusion of a serial lined pouch of peritoneum called a hernia sac.

Question 4

What is the most common location for acquired hernias?

Answer 4

Inguinal or femoral canal, umbilicus, or at sites of abdominal surgical scars.

Question 5

How can external herniation lead to infarction of the bowel?

Answer 5

Visceral protrusion (external herniation) of the bowel can lead to venous outflow obstruction, resulting in stasis of blood, edema, and entrapment (incarceration). This can be followed by arterial and venous insufficiency (strangulation) leading to infarction.

Question 6

What are Adhesions?

Answer 6

Fibrous bands of scar tissue between bowel segments, the abdominal wall, or operative sites.

Question 7

What can Adhesions lead to?

Answer 7

Fibrous bands can lead to obstruction, as well as the formation of closed loops through which the bowel can slide through and become entrapped (internal herniation). Fibrous adhesions are usually secondary to previous surgical procedures, abdominal infection or other cases of peritoneal injury/inflammation such as endometriosis. Rarely, fibrous adhesions can be congenital.

Question 8

What is Volvulus?

Answer 8

Complete twisting of a loop of bowel about its mesenteric base. This can lead to obstruction and vascular compromise with the potential for bowel infarction. Developmental anomalies of embryologic gut rotation (such as malrotation) can lead to volvulus in children as well as adults.

Question 9

Where does Volvulus most often occur?

Answer 9

Volvulus most often occurs in the sigmoid colon, followed by the cecum, and can involve the small bowel, stomach and transverse colon.

Question 10

What is Intussusception?

Answer 10

Occurs when a segment of bowel, constricted by a wave of peristalsis, telescopes into the immediately distal segment. This involved segment is then further propelled by peristalsis, leading to intestinal obstruction, compromise of mesenteric blood vessels, and infarction.

Question 11

What does age have to do with Intussusception?

Answer 11

In infants and young children, intussusception is usually associated with some type of underlying anatomical defect, whereas in older children and adults intussusception is associated with an intraluminal tumor or mass.

Question 12

What is Stenosis?

Answer 12

A form of atresia in which the lumen is markedly decreased in caliber, usually associated with fibrous thickening of the wall. Any site can be involved, more commonly the esophagus, small bowel or anus (imperforate anus)

Question 13

What is Omphalocele?

Answer 13

Closure of ventral abdominal musculature is incomplete, and abdominal viscera herniate into the ventral membranous (peritoneal) sac.

Question 14

What is Meckel’s Diverticulum and what causes it?

Answer 14

A true diverticulum of the small bowel, composed of all three layers (mucosa, submucosa, and muscularis propria). Occurs as a result of failed involution of the vitelline duct, which connects the developing gut to the yolk sac.

Question 15

What is the rule of 2s with Meckel’s Diverticulum?

Answer 15

Located on the anti mesenteric side of the ileum in 2percent of the population, they are usually within 2 feet of the ileocecal valve, generally 2 inches long, twice as common in males as females, if symptomatic symptoms occur by age two (only 4percent of patients with Meckel diverticulum develop symptoms)

Question 16

What are complications of Meckel’s Diverticulum?

Answer 16

Ulceration (may have ectopic gastric mucosa with acid production and peptic ulcers in adjacent ileum), perforation, hemorrhage, fistula formation to the bladder, and intussusception.

Question 17

What causes Hirchsprung’s disease?

Answer 17

Results when the normal migration of neural crest cells from cecum to rectum is arrested prematurely or when the ganglion cells undergo premature death.

Question 18

What is the incidence and genetic link in Hirchsprung’s Disease?

Answer 18

1 of 5000 live births, mostly males (M:F ratio 4:1). Etiologic mechanism is unknown, but appears to be genetic. Many patients have heterozygous loss-of-function mutations of the receptor tyrosine kinase RET. Some cases are familial as opposed to sporadic and some are associated with other congenital anomalies (10% of cases occur in patients with Down Syndrome)

Question 19

What is the Pathophysiology behind Hirchsprung’s Disease?

Answer 19

Most common form (75 percent) involves the distal sigmoid colon and rectum (classic short-segment disease). The affected segment lacks ganglion cells in both the submucosal (Meissner) and myenteric (Auerbach) plexus. Coordinated peristaltic contractions are absent, leading to function obstruction and dilation proximally.

Question 20

How do patients with Hirschsprung’s Disease present?

Answer 20

Failure to pass meconium in the neonatal period; infants and older children present with obstructive constipation, abdominal distention, and vomiting.

Question 21

How do you diagnose Hirschsprung’s Disease?

Answer 21

Imaging studies, rectal manometry, and biopsy to demonstrate loss of ganglion cells.

Question 22

What are some complications of Hirschsprung’s Disease?

Answer 22

Enterocolitis, perforation, peritonitis.

Question 23

What is the treatment for Hirschsprung’s Disease?

Answer 23

Removal of the aganglionic segment with anastomosis.

Question 24

What is Malabsorption?

Answer 24

Refers to the impaired absorption of nutrients (fats, proteins, carbohydrates, vitamins, electrolytes and minerals, water)

Question 25

What are mechanisms of malabsorption?

Answer 25

These mechanisms include disturbance in at least one of the phases of nutrient absorption as listed below:
Intraluminal digestion and brush border digestion
Transepithelial transport (absorption) into the small intestinal epithelium with intraepithelial processing
Lymphatic transport of absorbed lipids

Question 26

What is Global Malabsorption?

Answer 26

Results from diseases associated with either diffuse mucosal involvement or a reduced absorptive surface (e.g. celiac disease). These patents can present with diarrhea, steatorrhea (excessive fecal fat with bulky, frothy, greasy, and foul-smelling stools), flatulence, borborygmi, abdominal distention, abdominal pain, and weight loss. However many people may only exhibit a few of these symptoms or may be asymptomatic.

Question 27

What is Partial or isolated malabsorption?

Answer 27

Results from diseases that interfere with the absorption of specific nutrients (e.g. VB12 deficiency from pernicious anemia or diseases (or resection) of the terminal ileum as in Crohn’s disease)

Question 28

What are the most common causes of malabsorption in the USA?

Answer 28

Pancreatic insufficiency due to chronic pancreatitis, celiac disease, and Crohn’s disease.

Question 29

What is Diarrhea?

Answer 29

Defined as excessive increase in stool mass, frequency, or fluidity, typically greater than 200 g/day. In clinical practice, diarrhea is defined as more than 3 loose stools per day.

Question 30

What is Acute Diarrhea?

Answer 30

Diarrhea lasting less than 14 days.

Question 31

What is Chronic Diarrhea?

Answer 31

Diarrhea lasting more than 4 weeks.

Question 32

What are four mechanisms for Diarrhea?

Answer 32

1. Secretory diarrhea, characterized by isotonic stools
2. Osmotic diarrhea, due ot excessive osmotic forces from unabsorbed luminal solutes (e.g. lactase deficiency).
3. Malabsorptive diarrhea, due to failure of global nutrient absorption with steatorrhea

Question 33

What is Celiac Disease or Sprue?

Answer 33

An immune mediated enteropathy triggered by the ingestion of gluten-containing grains such as wheat, barley, or rye in genetically predisposed individuals. Incidence in European or Caucasian populations is 0.5 to 1 percent.

Question 34

What does gluten sensitivity do pathologically?

Answer 34

Sensitivity to gluten and the alcohol soluble fraction of gluten, gliadin, results in an immune reaction which damages the surface epithelium of the small bowel (intraepithelial lymphocytes and villous atrophy)

Question 35

What host genetic factors are involved in Celiac disease?

Answer 35

Almost all individuals with celiac disease carry HLA allele HLA-DQ2 or HLA-DQ8 (but not all people who have these have celiac disease). There is also an association of celiac disease with other autoimmune diseases such as type I diabetes, thyroidosis, sjogren syndrome, RA, and immune mediated liver diseases. Incidence of selective IgA deficiency is also increased in celiac sprue.

Question 36

What is Tropical Sprue?

Answer 36

It’s a malabsorption disease that mimics celiac disease occurring in the tropics. Patients have inflammatory bowel changes with milder degree of villous atrophy than celiac disease.

Question 37

What can patients with Tropical Sprue develop?

Answer 37

It typically affects the distal small bowel, so patients can have vitamin B12 deficiency.

Question 38

What are two very rare conditions that Dr. Nelsen has never seen?

Answer 38

Abetalipoproteinemia and Whipple disease

Question 39

What is Abetalipoproteinemia?

Answer 39

Rare autosomal recessive disorder caused by a mutation in the microsomal triglyceride transfer protein (MTP) that catalyzes the transport of triglycerides, cholesterol esters, and phospholipids from the enterocyte. Monoglycerides are not assembled into chylomicrons and triglycerides accumulate within the cytoplasm, which can be seen microscopically.

Question 40

What is an example of a disorder of transepithelial transport?

Answer 40

Abetalipoproteinemia

Question 41

When do patients with Abetalipoproteinemia and what do they present with?

Answer 41

Present in infancy with failure to thrive, diarrhea, and steatorrhea. Plasma apolipoprotein B (Apo B) is absent. Failure to absorb essential fatty acids leads to deficiencies of fat soluble vitamin (e.g. Vita E deficiency). Lipid membrane defects in RBCs produces burr cells (acanthocytes) in peripheral blood.

Question 42

What is Whipple disease?

Answer 42

Systemic infection caused by a gram-positive actinomycete, Tropheryma whippelii.

Question 43

What is the pathogenesis behind Whipple disease?

Answer 43

Organism-laden macrophages accumulate within the lamina propria of the small bowel and within mesenteric lymph nodes, leading to lymphatic obstruction. The bacteria laden-macrophages can also accumulate in synovial membranes, cardiac valves, brain and other organs.

Question 44

What is the clinical presentation of Whipple disease?

Answer 44

Diarrhea, weight loss, malabsorption, and abdominal pain. Extra intestinal symptoms, which can occur before malabsorption becomes evident, include arthritis, arthralgia, fever, lymphadenopathy, and neurologic, cardiac (endocarditis) or pulmonary disease

Question 45

How can you make a definitive diagnosis of Whipple disease?

Answer 45

By performing PCR on tissue biopsy.

Question 46

How do you treat Whipple disease?

Answer 46

Antibiotics

Question 47

What are disaccharidases?

Answer 47

Enzymes that break down complex sugars (e.g. lactose) into simple sugars (e.g. glucose) so that the intestine can absorb the nutrients. The main enzymes are lactase, maltase, and sucrase-isomaltase complex. Disaccharidase deficiency may be congenital or acquired.

Question 48

What is the most common type of disaccharidase deficiency?

Answer 48

Acquired lactase deficiency

Question 49

What is congenital lactase deficiency?

Answer 49

A rare autosomal recessive disorder caused by mutations in the gene encoding lactase. Upon ingestion of milk, the infant will develop diarrhea with abdominal distention (the unabsorbed lactose produces an osmotic diarrhea). Symptoms abate when exposure to milk and diary products is eliminated.

Question 50

What is Acquired lactase deficiency?

Answer 50

Caused by down-regulation of lactase gene expression. A common finding in most of the world’s population. It is almost a normal physiologic change. It reflects the lack of a need to digest lactose once a child has stopped ingestion of mother’s milk, prior to the farming of diary animals.

Question 51

Activity of what enzyme declines with age? What populations is this associated with?

Answer 51

Lactase. By adulthood the loss of the enzyme leads to lactose intolerance. Highly prevalent among Asian, African, Native-American and Mediterranean populations.

Question 52

What do patients with adult-onset lactase deficiency present with?

Answer 52

After consuming dairy products, they experience diarrhea, flatulence, and abdominal distention.

Question 53

What is Pancreatic Insufficiency?

Answer 53

Most often due to alcoholic induced chronic pancreatitis in adults, and cystic fibrosis in children. Dec. luminal lipase and trypsin result in undigested fats and protein in the stool. Carbohydrate absorption not affected.