Gastrointestinal and Abdominal: Small Intestine Flashcards
Anatomy and Physiology
- comprises the duodenum, jejunum, and ileum and extends from the pylorus proximally to the cecum distally
- is to digest and absorb nutrients
- Absorption is achieved by the large surface area of the small intestine, secondary to its long length and extensive mucosal projections of villi and microvilli.
- A broad-based mesentery suspends the small intestine from the posterior abdominal wall once the retroperitoneal duodenum emerges at the ligament of Treitz and becomes the jejunum.
- Arterial blood is supplied from branches of the superior mesenteric artery, and venous drainage is via the superior mesenteric vein (Fig. 4-1).
- The mucosa has sequential circular folds, called plicae circulares.
- are more numerous in the proximal bowel than in the distal bowel.
- The mucosal villi and microvilli create the surface through which carbohydrates, fats, proteins, and electrolytes are absorbed (Figs. 4-2 and 4-3).
Small Bowel Obstruction
- causes progressive proximal accumulation of intraluminal fluids and gas.
- Peristalsis continues to transport swallowed air and secreted intestinal fluid through the bowel proximal to the obstruction, resulting in small bowel dilation and eventual abdominal distention.
- Depending on the location of the obstruction, vomiting occurs early in proximal obstruction and later in more distal blockage (Fig. 4-4).
- Crampy abdominal pain initially occurs as active proximal peristalsis exacerbates bowel dilation.
- With progressive bowel wall edema and luminal dilation, however, peristaltic activity decreases and abdominal pain lessens.
- exhibit abdominal distention and complain of mild diffuse abdominal pain
Small Bowel Obstruction: Etiology
- first and second most common causes:adhesions and hernias, respectively (Table 4-1).
- adhesions are caused by postoperative internal scar formation.
- Discovering the actual mechanism of obstruction is important for therapeutic planning, because the mechanism of obstruction relates to the possibility of vascular compromise and bowel ischemia.
- a closed-loop obstruction caused by volvulus with torsion is at higher risk for vascular compromise than an SBO from a simple adhesive band (Fig. 4-5).
- incarceration in a fixed space
- Incarceration and subsequent strangulation impedes venous return, causing edema and eventual bowel infarction.
- intraluminal obstruction by a gallstone or bezoar and intussusception caused by an intramural or mucosal lesion at the leading edge
Small Bowel Obstruction: History
- complaints of intermittent crampy abdominal pain, abdominal distention, obstipation, nausea, and vomiting. Vomiting of feculent material usually occurs later in the course of obstruction
- Constant localized pain or pain out of proportion to physical findings may indicate ischemic bowel and is a clear indication for urgent surgical exploration
Small Bowel Obstruction: Physical Examination
- A distended abdomen with diffuse midabdominal tenderness to palpation
- Typically, there are no signs of peritonitis.
- If constant localized tenderness is apparent, indicating localized peritonitis, then ischemia and gangrene must be suspected.
- An essential aspect of the physical examination is to check for abdominal wall hernias, especially in postsurgical patients.
- Elevation in temperature should not be present in uncomplicated cases.
- Tachycardia may be present from hypovolemia secondary to persistent vomiting or from toxemia caused by intestinal gangrene.
Small Bowel Obstruction: Diagnostic Evaluation
- Upright radiographs classically demonstrate distended loops of small bowel with multiple air–fluid interfaces.
- Occasionally, the radiograph shows the etiology of the obstruction, the site of obstruction, and whether the obstruction is partial or complete.
- Dilated small bowel in the presence of a dilated colon suggests the diagnosis of paralytic ileus, not SBO.
- A small bowel contrast study may be necessary to demonstrate transit of contrast into the colon, thereby ruling out SBO.
- Free air indicates perforation of the intra-abdominal gastrointestinal tract, whereas biliary gas and an opacity near the ileocecal valve indicate gallstone ileus.
- Abdominal computed tomography (CT) scans can often demonstrate the transition point, where the dilated bowel proximal to the point of obstruction transitions to the decompressed bowel more distally.
- Also, in cases where the bowel has twisted on its mesentery, a “swirl sign” can be seen as the mesenteric vasculature twists on itself, creating a distinctive swirling radiographic pattern.
- Laboratory examination often reveals a hypokalemic alkalosis owing to dehydration from repeated emesis.
- White blood cell count and amylase may be mildly elevated.
- Lactic acidosis is cause for concern and may indicate intestinal necrosis.
Small Bowel Obstruction: Treatment
- In decades past, most patients were taken directly to the operating room for exploration to rule out intestinal necrosis
- over the past few decades it became apparent that most patients can be safely managed medically in the absence of peritonitis or other worrisome clinical findings
- Supportive therapy allows for spontaneous resolution of the obstruction and return of normal bowel function.
- For patients who are candidates for a trial of nonsurgical therapy, initial treatment consists of nasogastric decompression to relieve proximal gastrointestinal distention and associated nausea and vomiting.
- Fluid resuscitation and supportive hydration is necessary because patients are typically intravascularly depleted from diminished oral fluid intake and vomiting.
- The decision to operate is based on the nature of the obstruction and the patient’s clinical condition.
- On initial presentation, if ischemia or perforation is suspected, immediate operation is necessary. Otherwise, patients can be observed with serial physical examinations, serum tests, and abdominal radiographs for evidence of resolution. If the patient’s condition worsens or fails to improve with supportive therapy, operative intervention is indicated.
Crohn’s Disease
- a transmural inflammatory disease that may affect any part of the gastrointestinal tract, from the mouth to the anus.
- Ileal involvement is most common.
- characterized by skip lesions that involve discontinuous segments of abnormal mucosa.
- Granulomata are usually seen microscopically, but not always.
- Areas of inflammation are often associated with fibrotic strictures, enterocutaneous fistulae, and intra-abdominal abscesses, all of which usually require surgical intervention.
Crohn’s Disease: Epidemiology
- occurs throughout the world,
- The incidence in the United States is approximately 10 times that of Japan. Ashkenazi Jews have a far higher incidence of disease than do African Americans.
Crohn’s Disease: Etiology
- cause remains unknown
- Because of the presence of granulomata, mycobacterial infection has been postulated as the causative agent
- An immunologic basis for the disease has also been advanced; however, although humoral and cellular immune responses are involved in disease pathogenesis, no specific immunologic disturbance has been identified.
Crohn’s Disease: Pathology
- small intestine is affected in at least 70% of all patients with Crohn’s disease
- ileum is typically diseased, with frequent right colon involvement.
- On gross inspection, the serosal surface of the bowel is hypervascular, and the mesentery characteristically shows signs of “creeping fat.”
- The bowel walls are edematous and fibrotic. The mucosa has a cobblestone appearance, with varying degrees of associated mucosal ulceration (see Color Plates 2 and 3).
- Histologically, a chronic lymphocytic infiltrate in an inflamed mucosa and submucosa is seen.
- Fissure ulcers penetrate deep into the mucosa and are often associated with granulomata and multinucleated giant cells.
- Granulomata are seen more frequently in distal tissues, which explains why granulomata are seen more often in colonic disease than in ileal disease.
Crohn’s Disease: History
- complaining of diarrhea, abdominal pain, anorexia, nausea, and weight loss.
- diarrhea is usually loose and watery, without frank blood
- Dull abdominal pain is usually in the right iliac fossa or periumbilical region.
- Children often present with symptoms of malaise and have noticeable growth failure.
- Strictures may cause partial SBO, resulting in bacterial overgrowth and subsequent steatorrhea, flatus, and bloating.
Crohn’s Disease: Physical Examination
- appear to be either generally healthy or may have significant cachexia.
- Abdominal examination may reveal right iliac fossa tenderness.
- In acutely ill patients, a palpable abdominal mass may be present, indicating abscess formation.
- Enterocutaneous fistulae may be present.
- Oral examination may reveal evidence of mucosal ulceration, whereas perianal inspection may show skin tags, fissures, or fistulae.
- Extraintestinal manifestations include erythema nodosum, pyoderma gangrenosum, ankylosing spondylitis, and uveitis.
Crohn’s Disease: Diagnostic Evaluation
Blood studies often show a mild iron-deficiency ane-
mia and a depressed albumin level. If hypoalbumine-
mia is severe, peripheral edema may be present.
Small intestine Crohn’s disease is diagnosed by
bariumcontrast enteroclysis. This small intestine enema
technique provides better mucosal definition than stan-
dard small bowel follow-through studies. This tech-
nique illustrates aphthoid ulcers, strictures, fissures,
bowel wall thickening, and fistulae. Fistulograms are
helpful to define existing fistula tracks, and CT can
localize abscesses. Once radiographic evidence of
disease is found, colonoscopy should be performed to
evaluate the colonic mucosa and to obtain biopsies of
the terminal ileum
Crohn’s Disease: Differential Diagnosis
In addition to the diagnosis of Crohn’s disease, one
should consider the possibility of acute appendicitis,
Yersinia infection, lymphoma, intestinal tuberculosis,
and Behçet disease.
Crohn’s Disease: Complications
Crohn’s disease carries a high morbidity and low mor-
tality. Small bowel strictures secondary to inflam-
mation and fibrosis are common complications that
present as obstructions. Fistulae from small bowel to
adjacent loops of small bowel, large bowel, bladder,
vagina, or skin also occur. Ileal Crohn’s disease can
result in gallstone formation because of the interrup-
tion of the enterohepatic circulation of bile salts.
Kidney stones may also form because of hyperox-
aluria. Normally, calcium and oxalate bind in the
intestine and are excreted in the feces. With ileal
Crohn’s disease, steatorrhea causes ingested fat to bind
intraluminal calcium, thus allowing free oxalate to be
absorbed. Finally, adenocarcinoma is a rare complica-
tion that usually arises in the ileum.
Crohn’s Disease: Treatment
Mild disease can be controlled with a 4- to 6-week
course of sulfasalazine or mesalazine. Alternatively, oral
corticosteroids can be used with equivalent results.
Metronidazole may also be useful. Patients with bile
salt–induced diarrhea after ileal resection may benefit
from cholestyramine.
Severe disease is treated with hospitalization, bowel
rest, hydration, intravenous nutrition, corticosteroids,
and metronidazole. Patients with chronic active disease
may benefit from a course of mercaptopurine.
Surgery for Crohn’s disease should only be per-
formed for complications of the disease (Table 4-2).
Operation should be conservative and should address
only the presenting indication, using gentle surgical
technique. Resections should be avoided, as overly
aggressive intervention can produce surgically induced
short bowel syndrome and malnutrition. Some com-
mon surgical problems encountered in Crohn’s disease
and its treatments include ileocolic disease, which is
managed by conservative ileocecal resection to
grossly normal margins (Fig. 4-6); stricture, managed
by stricturoplasty, which entails incising the antime-
senteric border of the stricture along the intestinal
long axis and then closing the enterotomy trans-
versely (Fig. 4-7); and abscess/fistula, which is man-
aged by open or percutaneous drainage of the abscess
and resection of the small bowel segment responsible
for initiating the fistula with primary anastomosis
(Fig. 4-8)
Crohn’s Disease: Treatment: Picture
Crohn’s Disease: Treatment: Picture
Meckel’s Diverticulum
This most common congenital anomaly of the small
intestine is an antimesenteric remnant arising from a
failure of vitelline duct obliteration during embryonic
development. Meckel’s diverticula are true diverticula
affecting all three intestinal muscle layers. Diverticula
are usually 12 cm in length and are found within
100 cm of the ileocecal valve.
Associated abnormalities of the vitelline duct
depend on the degree of duct obliteration that occurs
during development. Complete ductal obliteration
leaves a thin fibrous band connecting ileum to umbili-
cus, whereas complete duct persistence results in a
patent ileoumbilical fistula. Partial obstruction results
in cyst or blind sinus formation (Fig. 4-9). Heterotopic
tissue (gastric, pancreatic) is found in 30% to 50% of
diverticula.
In the United States, Meckel’s diverticulum is
associated with the “Rule of 2s”: it occurs in 2% of the
population, is located within 2 ft of the ileocecal
valve, is usually 2 in long, contains two types of het-
erotopic tissue (gastric, pancreatic, duodenal, or intes-
tinal), and is the most common cause of rectal
bleeding in infants younger than 2 years.
Meckel’s Diverticulum: Complications
Bleeding within the diverticulum may occur from pep-
tic ulceration arising from heterotopic gastric mucosa.
In infants, Meckel’s diverticulum is the most common
cause of major lower gastrointestinal bleeding.
Bowel obstruction may result from one of two mech-
anisms. Intussusception can occur when an inverted
diverticulum functions as a lead point, or small bowel
volvulus can occur around a fixed obliterated vitelline
duct extending from the ileum to the umbilicus.
Meckel’s Diverticulum: Diagnostic Evaluation
For Meckel’s diverticula containing heterotopic gastric
mucosa, the technetium 99 (99Tc) scan is helpful for
diagnosis: pertechnetate anions are taken up by ectopic
gastric parietal cells and indicate diverticulum loca-
tion. Diverticula that do not contain heterotopic gas-
tric tissue can occasionally be visualized using standard
barium-contrast studies.
Meckel’s Diverticulum: Treatment
Definitive treatment for Meckel’s diverticulum compli-
cations is surgical resection. In adult patients inci
dentally found to have an asymptomatic Meckel’s diverticu-
lum during laparotomy, the diverticulum should be
left in situ, as the chance of producing surgical mor-
bidity and mortality are respectively 23 and five times
higher for resection than when only symptomatic
diverticula are removed.
Small Bowel Tumors
Tumors of the small bowel are rare, accounting for 1%
to 5% of all gastrointestinal tumors. Most tumors are
benign. Common benign neoplasms of the small bowel
include tubular and villous adenomas, lipomas, leiomy-
omas, and hemangiomas. Telangiectasias of R
endu-Osler-Weber syndrome, neurofibromas of neurofibro-
matosis, hamartomatous polyps of Peutz-Jeghers
syndrome, and heterotopic tissue as in Meckel’s diver-
ticulum are also found. Possible explanations for this
lack of malignancy include short exposure to ingested
carcinogens secondary to rapid transit time, low bac-
terial counts resulting in fewer endogenously pro-
duced carcinogens, and the intraluminal secretion of
IgA by small bowel mucosa.
Benign lesions are usually asymptomatic and are
incidental findings. Of symptomatic lesions, obstruc-
tion is the most common presentation, followed by
hemorrhage. In the workup of gastrointestinal bleed-
ing, however, unless other evidence exists, small bowel
lesions should be low on the list of differential diag-
noses, because >90% of bleeding lesions occur between
the esophagus and distal duodenum and between the
ileocecal valve and anus. Small bowel lesions should
be suspected if careful skin examination reveals café-
au-lait spots (neurofibromatosis), telangiectasia (Rendu-
Osler-Weber syndrome), or mucocutaneous
pigmentation (Peutz-Jeghers syndrome).
Malignant tumors of the small bowel typically
present with obstruction or bleeding. The four major
malignant tumors are adenocarcinoma, gastrointesti-
nal stromal tumors, carcinoid, and lymphoma.
Small Bowel Tumors: Diagnostic Evaluation
Visual endoscopic identification of small bowel
tumors is usually possible for lesions of the proximal
duodenum and terminal ileum. The remainder of the
small bowel requires examination by barium-contrast
studies. For larger lesions, CT may be helpful.
In situations involving active hemorrhage,
99 Tc sulfur colloid or 99 Tc-labeled red blood cell studies may
show the bleeding site. However, a bleeding rate of
1 mL/min is required for accurate localization.
When available diagnostic modalities are insuffi-
cient, exploratory laparotomy may be necessary. In
addition to external inspection at laparotomy, operative
endoscopy can be used for intraluminal evaluation.
