25 Pathology of the Small Bowel

Question 1

Anatomy

• The small intestine
  
  • length
• The duodenum is divided into parts:
• After the duodenum, the small intestine becomes
  
  • the jejunum
  • the ileum
• The small intestine is entirely supplied with/

Answer 1

• The small intestine
  
  • about 6 meters long in humans, the first 25 cm of which is the duodenum, which is retroperitoneal.
• The duodenum is divided into parts:
  
  • first (superior),
  • second (descending),
  • third (horizontal)
  • fourth (ascending).
• After the duodenum, the small intestine becomes peritoneal;
  
  • the jejunum is the first third (defined arbitrarily) of the peritoneal small intestine,
  • the ileum is the remainder (down to the cecum).
• The small intestine is entirely supplied with blood by the superior mesenteric artery, which also supplies the colon to the level of the hepatic flexure.

Question 2

Histology:
The small intestinal wall has several layers

• Inside to outside, they are
• The mucosa
  
  • villi
  • epithelial cells
  • lamina propria
  • intestinal crypts
  • villi vs. crypts
  • epithelium
  • microvilli
  • endocrine cells and Paneth cells

Answer 2

• Inside to outside, they are: mucosa, submucosa, muscularis propria, subserosa and serosa.
• The mucosa
  
  • has innumerable villi, which are finger-like projections into the lumen.
  • lined by epithelial cells and serve to increase the absorptive surface area of the intestine.
  • At their core is lamina propria, a loose connective tissue matrix with inflammatory cells, lymphatics and capillaries.
  • Between the villi are the intestinal crypts, also lined by epithelium and serving as a source of reserve/replacement epithelium.
  • Normally, the villi are at least three times as long as the crypts are deep.
  • The epithelium is composed of columnar absorptive cells and goblet cells, which produce mucus.
  • The absorptive cells have microvilli on their surface (seen as the brush border by microscopy), which further increase the absorptive area.
  • There are also scattered endocrine cells and Paneth cells.

Question 3

Histology

• muscularis mucosa
• muscularis propria
• myenteric plexus
  
  • submucosal plexus
  • muscular plexus
• subserosa and serosa
• Brunner’s glands
• lymphocytes
• Peyer’s patches

Answer 3

• At the base of the mucosa is the muscularis mucosa, which divides the mucosa from the submucosa, where larger blood vessels and lymphatics reside.
• Next is the muscularis propria, divided into inner (circular) and outer (longitudinal) layers.
  
  • These smooth muscle layers serve in peristalsis.
• Two nerve networks make up the myenteric plexus:
  
  • the submucosal plexus is located where the name suggests
  • the muscular plexus is between the layers of the muscularis propria.
• Outside the muscularis is another layer of loose connective tissue (subserosa) with the serosa on the outside (visceral peritoneum, made up of mesothelial cells).
• The duodenum has Brunner’s glands within the submucosa (mucus-producing).
• There are always a few lymphocytes within the surface epithelium (normally fewer than 20 for every 100 epithelial cells).
• The terminal ileum (right before the cecum) has Peyer’s patches (collections of lymphocytes with germinal centers involved in immunity).

Question 4

Congenital problems (p.3-4)

• Due to improper lumen formation, there may be segments of/
• Failure of the gut to rotate in utero may lead to/
• Omphalocoele results when/
• Gastroschisis occurs when/
• Another result of improper lumen formation and/or in utero insults/
  
  • These conditions may result in
• Failure of the vitelline duct to involute results in the formation of/
  
  • These usually follow a unique pattern known as/
  • They are often completely/
  • They may result in/

Answer 4

• Due to improper lumen formation, there may be segments of duplication (typically seen as long, cystic structures).
• Failure of the gut to rotate in utero may lead to things being misplaced (the most severe form of this is situs inversus).
• Omphalocoele results when the anterior abdominal wall fails to form correctly, and the intestine herniates into a ventral sac.
• Gastroschisis occurs when the abdominal wall fails to form at all, leading to catastrophic protrusion of the (uncovered) gut.
• Another result of improper lumen formation and/or in utero insults is intestinal stenosis (narrowing) and/or atresia (complete blockage).
  
  • These conditions may result in small intestinal obstruction soon after birth.
• Failure of the vitelline duct to involute results in the formation of a Meckel’s diverticulum, a blind pouch located on the anti-mesenteric side of the bowel.
  
  • These usually follow a unique pattern known as the “rule of twos” and may contain areas of ectopic tissue, such as gastric and/or pancreatic tissue.
  • They are often completely asymptomatic,
  • They may result in abdominal pain, bleeding, or other problems.

Question 5

Other anatomic conditions (p.7)

• Each of these may result in/
• Serosal adhesions
• A herniation occurs when/
• Intussusception
  
  • ?
  • This usually happens when/
• volvulus occurs when/

Answer 5

• Each of these may result in the dreaded small bowel obstruction (“SBO” in surgical parlance), as well as loss of blood supply and potential bowel infarction
• Serosal adhesions are fibrous bands inappropriately connecting the outside of bowel loops;
  
  • these may result from a variety of injuries, like prior surgery (“surgeon tracks”), infections and so on.
• A herniation occurs when the bowel protrudes through some opening where it shouldn’t (like the inguinal canal or the umbilicus).
• Intussusception
  
  • the protrusion of one segment of bowel into the lumen of the next more distal segment;
  • This usually happens when there is something for the bowel to grab onto, like a Meckel’s diverticulum or a tumor; peristalsis then pulls the piece of bowel along.
• volvulus occurs when a loop of bowel twists on its mesentery, potentially cutting off the blood supply.

Question 6

Diarrheal illness—Enterocolitis

• Diarrhea
• dysentery
• Enterocolitis
• Infectious organisms cause one type of enterocolitis;
  
  • viruses
  • Bacterial
• Some bacteria make toxins that cause/
• Some organisms, however, can actually/

Answer 6

• Diarrhea is defined as a stool volume greater than 250g/day (normal is <200g/day), accompanied by a sense of increased frequency, urgency, and stool fluidity.
• Low-volume, bloody diarrhea is termed dysentery.
• Enterocolitis is a general inflammatory condition of the small intestine and/or colon, often resulting in diarrhea.
• Infectious organisms cause one type of enterocolitis;
  
  • most commonly, these are viruses (which are discussed elsewhere).
  • Bacterial enterocolitis is less common, but has more characteristic pathologic features.
• Some bacteria make toxins that cause tissue damage and diarrhea;
• Some organisms, however, can actually invade the intestinal mucosa and cause diarrhea that way.

Question 7

Infectious enterocolitis (p.11-15)

• Yersinia
  
  • organism
  • can infect/
  • typically, this occurs/
  • resutls in/
  • if it invades through the mucosa, it may involve/
• Salmonella
  
  • may cause/
  • organism
  • invade/
  • may involve/
  • Ulcers/
  • Some types of Salmonella may disseminate widely to/
• Campylobacter jejuni
  
  • frequency
  • outbreaks may occur from/
  • Sporadic infection can come from/
  • can invade/

Answer 7

• Yersinia
  
  • a gram-negative coccobacillus,
  • can infect the small bowel and colon.
  • Typically, this occurs in the distal ileum, cecum and appendix, resulting in “right lower quadrant” symptoms that can mimic acute appendicitis or other conditions.
  • results in mucosal hemorrhage, ulceration and bowel wall thickening.
  • If it invades through the mucosa, it may involve the Peyer’s patches and even spread systemically.
• Salmonella
  
  • may cause self-limited food poisoning, or life-threatening systemic disease (typhoid fever).
  • gram-negative bacteria
  • invade epithelial cells and tissue macrophages
  • may involve Peyer’s patches as with Yersinia.
    
    • When Peyer’s patches are involved, they become hypertrophic and protrude into the bowel lumen like mesas in the desert.
  • Ulcers form in the damaged mucosa, causing bloody diarrhea.
  • Some types of Salmonella may disseminate widely to the liver, spleen and gallbladder.
• Campylobacter jejuni
  
  • more common than with Salmonella,
  • outbreaks may occur from unpasteurized milk or water contamination.
  • Sporadic infection can come from undercooked chicken.
  • can invade the bowel mucosa, leading to ulceration and dysentery.

Question 8

Infectious enterocolitis (p.16-20)

• Parasites may also lead to enterocolitis.
  
  • frequency
  • include/
  • Parasitic amoebae may involve/
  • more common in
• Giardiasis
  
  • frequency
  • Cyst forms are ingested, most commonly from/
  • The organisms excyst in the/
  • These irritate/
  • the trophozoites may be seen/
• Cryptosporidiosis
  
  • affects/
  • is spread by/
  • attach to/
  • lead to/
  • Usually, this is/
    
    • However, the condition may be/

Answer 8

• Parasites may also lead to enterocolitis.
  
  • Fairly common small intestinal parasites
  • include Giardia lamblia and Cryptosporidium parvum.
  • Parasitic amoebae may involve the small intestine,
  • more common in the colon.
• Giardiasis
  
  • the most common parasitic infestation in humans.
  • Cyst forms are ingested, most commonly from contaminated water—perhaps while camping (hence, “beaver fever”).
  • The organisms excyst in the small intestine, releasing trophozoites, which then proliferate.
  • These irritate the small mucosa and interfere with absorption, leading to copious, foul-smelling stools (steatorrhea).
  • the trophozoites may be seen on duodenal biopsy, where they cause an increase in inflammation as well as shortened (“blunted”) villi.
• Cryptosporidiosis
  
  • affects the small and large intestines
  • is spread by the fecal-oral route.
  • attach to the surface epithelium
  • lead to diarrhea.
  • Usually, this is self-limited as long as the patient is immunocompetent.
    
    • However, the condition may be life threatening in immunosuppressed patients.

Question 9

Necrotizing enterocolitis (p.21)

• ?
• can occur at any age, but is most common in/
• usually occurs around the time of/
• results in/
• Most often, it involves/
• Its pathogenesis may involve/

Answer 9

• acute, necrotizing condition of the small and/or large intestine
• can occur at any age, but is most common in neonates, especially those born prematurely.
• usually occurs around the time of first oral intake (postnatal day 2-4)
• results in copious, bloody stools, gangrenous necrosis of the intestine, shock and possible bowel perforation.
• Most often, it involves some combination of the right colon and/or terminal ileum.
• Its pathogenesis may involve some type of bacterial insult, which results in bowel ischemia.

Question 10

Other diarrheal illnesses (p.22-23)

• HIV/AIDS enteropathy
  
  • Most patients with AIDS that develop diarrhea do so as a result of/
  • HIV itself may lead to/
• Drug-induced injury
  
  • drugs may lead to/
  • Most commonly, this is caused by/
  • the rapid turnover of the intestinal mucosa leaves it prone to/
  • Occasionally, the injury and resulting inflammation may be/
• Radiation enterocolitis
  
  • may damage/
  • results in/

Answer 10

• HIV/AIDS enteropathy
  
  • Most patients with AIDS that develop diarrhea do so as a result of opportunistic infections,
  • HIV itself may lead to intestinal injury and diarrhea.
• Drug-induced injury
  
  • drugs may lead to intestinal injury.
  • Most commonly, this is caused by NSAIDs, which may lead to ulceration of the mucosa.
  • the rapid turnover of the intestinal mucosa leaves it prone to injury by other types of drugs as well, such as chemotherapy agents.
  • Occasionally, the injury and resulting inflammation may be more widespread.
• Radiation enterocolitis
  
  • Like chemotherapy agents, radiation therapy for various neoplasms may damage the intestine.
    
    • The more tissue falling within the radiation field, the more damage may occur.
  • Such damage results in a characteristic appearance under the microscope, including an amorphous, pink lamina propria, thick-walled blood vessels, and atypical-appearing stromal and endothelial cells.

Question 11

Malabsorption syndromes

• Digestion and absorption is a tremendously complex process, involving /
• Problems may
  
  • occur
  • involve
• Small bowel biopsies are often performed during

Answer 11

• Digestion and absorption is a tremendously complex process, involving
  
  • _​_intraluminal processes (like mixing, exposure to acid, etc.),
  • terminal digestion (like hydrolysis of carbohydrates and peptides),
  • transepithelial transport of fluid, ions and nutrients across the intestine and into the bloodstream.
• Problems may
  
  • occur principally in one phase of digestion
  • involve different sites and processes.
• Small bowel biopsies are often performed during the diagnostic work-up of malabsorption.

Question 12

Malabsorption syndromes:
Celiac disease (p.9+26-28)

• frequency
• genetic component and/or predisposition,
• Fundamentally, the problem is with/
• There is an inappropriate cell mediated immune response to/
  
  • what suffers the most intense damage
• The clinical portion of this clinicopathologic diagnosis comes in the form of

Answer 12

• This disease is fairly common cause of malabsorption, especially in Western Caucasians
• genetic component and/or predisposition,
  
  • association with certain major histocompatibility complex haplotypes, namely HLA-DQ2 and –DQ8.
• Fundamentally, the problem is with a hypersensitivity to gluten, a protein found in various grains, including wheat, rye and barley.
• There is an inappropriate cell mediated immune response to an alcohol-soluble fraction of gluten called gliadin, which leads to tissue damage, since there is also an autoimmune component to the response.
  
  • Because the proximal small intestine is where much of the gliadin is encountered, it suffers the most intense damage.
• The clinical portion of this clinicopathologic diagnosis comes in the form of
  
  • several antibodies in the serum (both to gliadin and to several autoantigens),
  • a clinical response when gluten is removed from the patient’s diet.

Question 13

Malabsorption syndromes:
Celiac disease (p.9+26-28)

• Clinically, celiac disease patients suffer/
  
  • especially true when the disease presents in/
• Histopathologically,
  
  • most often performed to aid in diagnosis
  • The primary lesion in celiac disease
  • There is also an increase in/
• Once gluten is removed from the diet, the mucosa may/
• Unfortunately, celiac disease patients are at an increased risk for/

Answer 13

• Clinically, celiac disease patients suffer weight loss, diarrhea and general “failure to thrive”.
  
  • especially true when the disease presents in the young, often around the time of solid food introduction.
  • older patients may first present with celiac disease in the 4th or 5th decade of life and suffer similar symptoms.
• Histopathologically,
  
  • duodenal biopsies are most often performed to aid in diagnosis.
  • The primary lesion in celiac disease is an increase in cytotoxic T-lymphocytes within the epithelium itself, reflecting the ongoing mucosal damage.
    
    • The majority of these T-cells have a cytotoxic phenotype.
  • There is also an increase in lamina propria inflammation and, to a greater or lesser degree, blunting of the duodenal villi.
    
    • However, these findings are, strictly, nonspecific and may occur in a variety of conditions—hence, the need for clinicopathologic correlation.
• Once gluten is removed from the diet, the mucosa may return nearly to normal.
• Unfortunately, celiac disease patients are at an increased risk for several malignancies, most notably certain T-cell lymphomas.

Question 14

Other malabsorption syndromes (p.29-30)

• Tropical sprue
  
  • affects/
  • The clinical and histological findings/
  • may be the result of/
  • may respond to/
• Whipple’s disease
  
  • ?
  • the result of/
  • typically affects/
  • distinctive GI findings.
  • These can be highlighted with/

Answer 14

• Tropical sprue
  
  • This malabsorptive disease affects those who live in or visit tropical locations.
  • The clinical and histological findings are similar to those of celiac disease, but without any connection to dietary gluten.
  • may be the result of some type of infection
  • may respond to broad-spectrum antibiotics, however.
• Whipple’s disease
  
  • malabsorptive, diarrheal disease + systemic infection
  • the result of a gram-positive organism (an actinomycete) called Tropheryma whipplei.
  • typically affects middle-aged men
  • distinctive GI findings.
    
    • lymphatic obstruction with dilation of the superficial lymphatics,
    • characteristic inclusions within mucosal macrophages.
  • These can be highlighted with a special stain (periodic acid-Schiff), which turns them bright pink.

Question 15

Inflammatory bowel disease (IBD)

• encompasses two different diseases:
  
  • ulcerative colitis (UC)
    
    • mostly affects/
  • Crohn’s disease (CD).
    
    • may affect
• The etiology
• CD has several features that distinguish it from ulcerative colitis.
  
  • where they affect
  • inflammation pattern
  • involvement of the intestinal wall

Answer 15

• encompasses two different diseases:
  
  • ulcerative colitis (UC)
    
    • mostly affects the colon
  • Crohn’s disease (CD).
    
    • may affect the GI tract anywhere along its length, from mouth to anus, but most commonly has small intestinal involvement.
• The etiology
  
  • may relate to an inappropriate immune response to organisms normally found in the gut.
  • may be a genetic predisposition.
• CD has several features that distinguish it from ulcerative colitis.
  
  • CD can affect the GI tract anywhere along its length, while UC typically involves only the colon.
  • CD tends to “skip around” leaving areas unaffected, while UC most often shows continuous inflammation, often from the rectum to a point more proximal in the colon (possibly all the way to the cecum).
  • CD tends to involve the full thickness of the intestinal wall with inflammation, whereas UC is pretty much a mucosal disease.

Question 16

Inflammatory bowel disease (IBD)

• Clinically,
  
  • diarrhea
  • systemic
  • inflammation can lead to/
• Grossly, CD
  
  • causes
  • the mese/nteric fat/
  • Inside, the mucosa is/

Answer 16

• Clinically,
  
  • intermittent, relapsing attacks of diarrhea, which may be bloody, as well as abdominal pain (“IBD flare”).
  • These are systemic diseases, and there may also be arthralgias, fever, and other gastrointestinal manifestations.
  • The chronic inflammation can lead to adhesions, strictures, fistulae (abnormal connections between loops of bowel and/or other organs, including skin), and even cancer.
• Grossly, CD
  
  • causes a thick-walled intestine, with serosal adhesions on its surface.
  • the mesenteric fat will encroach on the portions of the bowel wall that are normally devoid of fat, a process called “creeping fat” or “fat wrapping”.
  • Inside, the mucosa is ulcerated, usually in a patchy fashion with areas of uninvolved mucosa between.
    
    • There are deep, linear ulcers running along the mucosa.
    • Numerous patches of preserved mucosa may protrude between the ulcers, reminiscent of a cobblestone street.

Question 17

Inflammatory bowel disease (IBD):
Under the microscope (p.32-41)

• the ulcers
• There may be
• The submucosa
• Attempts to heal
• In areas affected by chronic ulcer
• there may (or may not) be

Answer 17

• the ulcers can be seen to extend deeply into the bowel wall.
• There may be perforations and/or fistulae.
• The submucosa is obliterated by scar, and nodules of lymphocytic inflammation extend through the entire intestinal wall, all the way out to the serosa.
• Attempts to heal are always ongoing, and the previously involved mucosa can show intense distortion of the intestinal crypts, with dilated, bizarre outlines replacing the normal orderly pattern.
• In areas affected by chronic ulcer, the normal intestinal crypts may be replaced by structures lined by epithelium most like that found in the distal part of the stomach—so-called pyloric gland metaplasia.
• there may (or may not) be collections of macrophages and lymphocytes (epithelioid granulomas) found in the mucosa.

Question 18

Vascular disorders:
Ischemia (p.42-44)

• Lack of blood supply to the intestine
  
  • may be caused by/
  • No matter the cause, the hypoxia that results may lead relatively quickly to/
  • If hypoxia persists/
  • If and when blood flow is restored/
  • The end result may be/
• Grossly,
  
  • the ischemic segment appears/
  • Depending on the vessel involved, the area of necrosis/
  • The mucosa has/
• The histological picture reflects this, with/

Answer 18

• Lack of blood supply to the intestine
  
  • may be caused by arterial thrombosis and thromboembolism, venous thrombosis and general “low-flow” states, like shock.
  • No matter the cause, the hypoxia that results may lead relatively quickly to mucosal necrosis.
  • If hypoxia persists, the entire bowel wall may become necrotic.
  • If and when blood flow is restored, the rush of cytokines and oxygen free radicals can enhance the tissue injury.
  • The end result may be loss of the normal intestinal barrier to microbial entry, with circulatory collapse and death in 50-70% of patients.
    
    • The bowel may perforate as well.
• Grossly,
  
  • the ischemic segment appears “dusky” with loss of the normal glistening serosal appearance.
  • Depending on the vessel involved, the area of necrosis can be quite sharply demarcated.
  • The mucosa has ulcers, hemorrhage, and areas of sloughing.
• The histological picture reflects this, with hemorrhagic and coagulative necrosis, ulcers and inflammation.

Question 19

Vascular disorders:
Angiodysplasia (p.45)

• ?
• most often found/
• The pathogenesis may relate to/
• these lesions can be the source of/
• They appear as/

Answer 19

• a focal vascular malformation,
• most often found in the right colon in older patients.
• The pathogenesis may relate to local mechanical factors combined with some congenital predisposition.
• While rare, these lesions can be the source of significant GI bleeding.
• They appear as disorganized collections of different-sized blood vessels, often with large vascular spaces right beneath or within the mucosa—leading to the risk of blood loss.

Question 20

Peptic ulcer disease and Neoplasia (p.46)

• Peptic ulcer disease
  
  • Most common in/
  • related to/
  • may result in/
  • Melenic bleeding
• Neoplasia
  
  • the small bowel gives rise to/
  • the most common type of tumor in the small bowel
  • Primary small bowel tumors may be/

Answer 20

• Peptic ulcer disease
  
  • Most common in the stomach,
  • related to infection with Helicobacter pylori, ulcers may also affect the duodenum.
  • Like gastric ulcers, these may result in blood loss from the GI tract.
  • Melenic bleeding is loss of blood that has been exposed to gastric acid, which turns it a dark black color with a tarry consistency.
• Neoplasia
  
  • While primary tumors are quite common in the large intestine, the small bowel (75% of the length of the human intestines) gives rise to only 3-6% of the primary tumors.
  • the most common type of tumor in the small bowel is metastatic, usually breast or lung carcinoma, or melanoma.
  • Primary small bowel tumors may be adenomas, adenocarcinomas, tumors of the mesenchymal (“soft tissue”) component of the bowel, or endocrine tumors (carcinoid).

Question 21

Adenoma/Carcinoma (p.48-52)

• account for/
• most arise/
• They are composed of/
• These changes reflect/
• As more and more mutations and damages to the DNA are accumulated, the cells may/
• DNA mutations and damage may be acquired in a variety of ways, such as/
• when invasive carcinoma develops, one finds/

Answer 21

• Adenomas account for about 25% of benign small bowel tumors.
• most arise near the ampulla of Vater in the duodenum.
• They are composed of dysplastic cells, which proliferate abnormally, and have a characteristic appearance under the microscope (dark, crowded, elongated nuclei; an increased number of mitotic figures; a decrease in the normal goblet cell number).
• These changes reflect an accumulation of DNA defects/mutations in the neoplastic cells.
• As more and more mutations and damages to the DNA are accumulated, the cells may lose their normal respect for the mucosal boundary, and may acquire the ability to invade the surrounding tissue as they proliferate—invasive adenocarcinoma.
• DNA mutations and damage may be acquired in a variety of ways, such as
  
  • environmental exposures
  • increased turnover and proliferation associated with chronic injury (perhaps from Crohn’s disease or other inflammatory conditions).
• when invasive carcinoma develops, one finds epithelial cells where they don’t belong, such as in the submucosa or muscularis propria.

Question 22

Carcinoid (p.53-55)

• This term refers to/
• These account for/
• considered/
• Degree of aggressiveness correlates with/
• Macroscopically/
• Microscopically/

Answer 22

• This term refers to a neoplasm arising from mucosal endocrine cells, which normally function in the control of digestion.
• These account for nearly half of all small bowel tumors, and are potentially malignant;
• considered the “well-differentiated” end of a spectrum of neuroendocrine carcinomas.
• Degree of aggressiveness correlates with larger tumor size, depth of infiltration into the underlying bowel, and tumor site.
• Macroscopically, these tumors are fairly well-circumscribed, but often have “fingers” spreading into the surrounding tissue (e.g., the muscularis propria).
  
  • They often “pucker” the overlying mucosa or serosa, and may cause ulcers in the mucosa.
• Microscopically, they are composed of monotonous, small, blue cells with scant cytoplasm, arranged in small “nests” or cords with surrounding connective tissue.
  
  • Immunostains to neuroendocrine antigens are positive.

Question 23

Carcinoid (p.53-55)

• the cells that make up these tumors may be/
  
  • Some may produce/
  • The resultant syndrome
• Other patients may have signs and symptoms of increased serotonin, which has a variety of effects, including/
  
  • This is the so-called/
  • patients usually do not exhibit this syndrome unless/
  • The classic example

Answer 23

• Because of their normal endocrine and paracrine function, the cells that make up these tumors may be biologically “active”, releasing a variety of substances.
  
  • Some may produce gastrin, which functions to increase gastric acid production by parietal cells.
  • The resultant syndrome of hyperacidity and ulcers is termed “Zollinger-Ellison” syndrome.
• Other patients may have signs and symptoms of increased serotonin, which has a variety of effects, including intestinal hypermotility, flushing, diarrhea and others.
  
  • This is the so-called “carcinoid syndrome”.
  • Because the liver degrades serotonin (5-hydroxytryptamine; 5-HT) to 5-hydroxyindoleacetic acid (5-HIAA), patients usually do not exhibit this syndrome unless there are tumors whose 5-HT will not be subject to hepatic degradation (i.e., which will be released into the systemic circulation instead of the portal circulation).
  • The classic example is an intestinal carcinoid with metastases to the liver.

Question 24

Lymphoma

• Gastrointestinal lymphoma
• primary GI lymphoma
  
  • frequency
  • some lymphomas characteristically affect/
  • These can be composed of/
  • MALT lymphoma (for Mucosa-Associated Lymphoid Tissue)
    
    • most often thought of in association with/
    • often seen as a result of/
    • This is yet another example of/
  • enteropathy-associated T-cell lymphoma
• grossly
• Microscopically
• In the small intestine, the expanding lymphomatous infiltrate may cause/

Answer 24

• Gastrointestinal lymphoma
  
  • lymphoma may involve the gastrointestinal tract secondarily.
• primary GI lymphoma
  
  • much more rare,
  • some lymphomas characteristically affect the GI tract.
  • These can be composed of either B- or T-lymphocytes.
    
    • B-cell lymphomas are more common,
  • a type of B-cell lymphoma termed MALT lymphoma (for Mucosa-Associated Lymphoid Tissue)
    
    • most often thought of in association with the GI tract.
    • This particular type is often seen as a result of infection with the ulcer-causing organism Helicobacter pylori in the stomach.
    • This is yet another example of inflammatory processes becoming “unleashed” and leading to neoplasia;
  • Similarly, one type of T-cell lymphoma can be seen as a result of chronic celiac disease and is called “enteropathy-associated T-cell lymphoma”.
• lymphomas cause a homogeneous expansion of the tissue grossly,
  
  • characteristic tan, glistening appearance (termed “fish-flesh”).
• Microscopically, the neoplastic lymphocytes are seen to infiltrate throughout the tissue, destroying the normal architecture, and generally wreaking havoc.
• In the small intestine, the expanding lymphomatous infiltrate may cause ulcers, perforation, obstruction, and so on.