Intestinal Pathology 1 Flashcards
Congenital Malformations
Meckel diverticulum (failure of the vitelline duct to involute) - Ileum
Hirschsprung Disease
- Large Bowel
Meckel DiverticulumRule of 2s
Occur in approximately 2% of the population
Are generally present within 2 feet (60 cm) of the ileocecal valve
Are approximately 2 inches (5 cm) long
Are twice as common in males
Are most often symptomatic by age 2 (only approximately 4% are ever symptomatic)
Hirschsprung Disease
Occurs in approximately 1 of 5000 live births
10% of all cases occur in children with Down syndrome, serious neurologic abnormalities are present in another 5%.
Normal migration of neural crest cells from cecum to rectum is arrested prematurely or the ganglion cells undergo premature death.
typically presents with a failure to pass meconium in the immediate postnatal period.
Obstruction or constipation, often with visible, ineffective peristalsis, that may progress to abdominal distention
Primary mode of treatment is surgical resection of the aganglionic segment followed by anastomosis of the normal proximal colon to the rectum
Signs and Symptoms
of Gastrointestinal Obstruction
Crampy abdominal pain that comes and goes.
Nausea.
Vomiting.
Diarrhea.
Constipation.
Inability to have a bowel movement or pass gas.
Swelling of the abdomen (distention
signs of strangulation
Clinical criteria such asfever, tachycardia, localized tenderness, and leukocytosismay be used as sign of strangulation.
Mechanical Causes of Obstruction
Intussusception
Volvulus
Hernia
Adhesions
*** air fluid levels are sign on x-ray of obstruction!!!
chagas disease associated with
megacolon
wipes out the ganglion cells in the colon
Instussusception
defined:
as the invagination of one bowel segment into another (telescoping into a distal segment).
Most common cause of intestinal obstruction in children younger than two years of age
Most commonly between 5-9 months
Twice as frequent in males than females
intussusception etiology
90% are idiopathic. 10% involve a discrete lead point
Associated with viral illness and rotavirus vaccine, possibly related to Peyer patch lymphoid hyperplasia
The telescoping can produce obstruction, ischemia, and eventual strangulation of the bowel
Common lead points include Meckel’s diverticulum, intestinal polyps, appendicitis, neoplastic lesions, and foreign bodies.
Volvulus
Radiographic
“coffee bean” sign
Volvulus is most common in adults occuring with equal frequency in small intestine (around a twisted mesentery) and colon (in either sigmoid or cecum.
In very young children, volvulus almost always happens in the small intestine.
External Inguinal Hernia
Protrusion of a serosa-lined pouch of peritoneum called a hernia sac.
Acquired hernias typically occur anteriorly, via the inguinal and femoral canals, umbilicus, or at sites of surgical scars
Obstruction usually occurs because of visceral protrusion into hernia sac.
Small bowel loops are typically involved.
With prolonged incarceration, get ischemia and obstruction and danger of perforation
most common cause of intestinal obstruction in the United States.
adhesions
- Postoperative adhesions
- Inflammation
- Endometriosis
Lower Gastrointestinal Bleeding
Lower GI tract bleedingrefers this to bleeding distal to the ligament of Treitz.
Colorectal causes are more prevalent than small intestinal causes.
Most common in the seventh decade
Chronic low-grade bleeding is often not visible to the patient
** (iron deficiency anemia)
Common Causes of Lower Gastrointestinal Bleeding
Diverticulosis accounts for 30% to 40% of cases of significant lower GI hemorrhage
Angiodysplasia is a common cause of lower GI bleeding in elderly patients (acquired lesions associated with aging)
Other Causes of Lower Gastrointestinal Bleeding
Inflammatory Bowel Disease
Anal fissure
Ischemia *** (watershed zones) > 70 yo
Infectious enteritis
Intestinal polyps
Cancer
Hemorrhoids
Intestinal Vascular Disorders
Angiodysplasia
Non-neoplastic vascular lesion. Usually cecum or proximal right colon
Pathogenesis unknown
Tortuous dilatation of malformed submucosal and mucosal blood vessels
Accounts for * 20% of significant lower intestinal bleeding
Ischemic Bowel Disease
Patients with acute mesenteric ischemia commonly present with * abdominal pain and hematochezia.
Paradoxically, elderly patients (who are the most prone to ischemia from arterial insufficiency) * often experience little or no pain until the disease is far advanced
- Watershed areas:
Splenic flexure
Recto-sigmoid junction
Lower Gastrointestinal Ischemia: Arterial Insufficiency
vast majority
Nonocclusive mesenteric ischemia (* inadequate arterial blood flow)
- Systemic hypotension
- Shock
- Hypoxemia
- Dehydration
Occlusive ischemia (~70%) (obstruction to arterial blood flow)** - Atheromatous emboli (50%) - Thrombus (10%) - Atherosclerosis (mesenteric origin) - Arteritis - Dissecting aneurysm
Lower Gastrointestinal Ischemia: venous insufficiency
Abdominal pain Younger patients External venous compression Mesenteric venous thrombosis Hypercoagulable states (genetic and acquired)
Mechanical causes of ischemia
External compression
(volvulus, incarceration, adhesions)
Normal Bowel
Vasculature
Extensive anastomosing arterial blood supply to the bowel make it more difficult to infarct
Ischemic Bowel Disease
Small intestine and colon tolerate slowly progressive loss of blood supply
- Acute compromise of any major vessel can lead to infarction of several meters of intestine.
- Superficial mucosal infarction extending no deeper than the muscularis mucosae
- Transmural infarction involving all three wall layers
Pathogenesis of Intestinal Ischemia
The initialhypoxic injuryoccurs at the onset of vascular compromise.
The second phase,reperfusion injury, is initiated by restoration of the blood supply and it is at this time that the greatest damage occurs.
Mechanisms of reperfusion injury:
- leakage of gut lumen bacterial products- lipopolysaccharide into the systemic circulation
- free radical production and neutrophil infiltration
most common cause of intravascular occlusion.
Thrombi and emboli
Outcome of obstruction is
determined by size of affected artery and degree of collateral circulation.
Diarrhea.
Normally, absorption and secretion take place simultaneously, but * absorption is quantitatively greater.
Either a decrease in absorption or an increase in secretion leads to additional fluid within the lumen and thus Diarrhea.
Disruption of epithelial electrolyte transport or its regulatory system by toxins, drugs, hormones, and cytokines is a major cause of diarrhea.
Diarrhea
Classification
Increase of fecal water excretion of 100mL is the upper limit of normal
- Watery diarrhea implies either * secretory or osmotic diarrhea.
- Fatty diarrhea implies * defective absorption of fat and perhaps other nutrients in the small intestine.
- Inflammatory diarrhea implies the presence of one of a limited number of inflammatory or neoplastic diseases involving the GI tract. * (purulent or bloody stools)
