7. Disorders of the Intestines

Disorders of the Intestines

• Objectives for the unit include matching symptoms to intestinal disorder categories, describing lactose intolerance, comparing diagnostic tests for intestinal disorders, and understanding surgical and non-surgical treatment approaches.

Intestinal Obstruction and Ischemic Bowel Disease

• Obstruction of the gastrointestinal (GI) tract frequently involves the small intestine due to its narrow lumen.
• Mechanical obstructions, accounting for 80%, include hernias, adhesions, intussusception, and volvulus.
• Other causes include tumors and infarctions.
• Surgical intervention is often necessary for mechanical obstruction and bowel infarction.

Clinical Manifestations

• Common clinical manifestations include abdominal pain, distention, vomiting, and constipation.
• Figure 17.23 displays the four major causes of intestinal obstruction: herniation, adhesions, volvulus, and intussusception.

Hernias

• Hernias occur due to weaknesses or defects in the abdominal wall that allow a serosa-lined pouch (hernia sac) to protrude.
• Acquired hernias commonly occur in the inguinal and femoral canals, and umbilicus or at surgical sites.
• They are the most frequent cause of intestinal obstruction globally and the third most common in the US.
• Obstruction often occurs with inguinal hernias due to narrow orifices and large sacs.

Adhesions

• Adhesions (scar tissue) can form after surgery, infection, or peritoneal inflammation (e.g., endometriosis).
• These fibrous bridges can create closed loops that trap other abdominal organs, resulting in internal herniation.
• Complications can include obstructions and strangulations, similar to external hernias.

Volvulus

• Volvulus occurs when a loop of bowel twists around its mesenteric attachment, causing luminal and vascular compromise.
• It commonly affects the sigmoid colon, cecum, or small bowel, and less often, the transverse colon.
• Volvulus can lead to both obstruction and infarction.

Intussusception

• Intussusception is characterized by a segment of intestine telescoping into an adjacent segment.
• This can lead to intestinal obstruction, vessel compression, and infarction.
• Intussusception is frequently observed in children under 2 years of age, often linked to unknown causes or an intraluminal mass.
• One treatment approach includes contrast enemas or, if appropriate, surgical intervention.

Ischemic Bowel Disease

• Damage can range from mucosal, limited to the mucosa and submucosa, to transmural, affecting all three layers of the bowel wall.
• Causes of ischemic bowel disease include chronic or acute hypoperfusion and, acutely, vascular obstruction.
• The severity, duration, and affected blood vessels determine the extent of the damage.
• Watershed zones are susceptible to ischemia, including the splenic flexure and the rectosigmoid colon.

Pathogenesis

• Initial injury, hypoxic injury, occurs with vascular compromise.
• Reperfusion injury, subsequent to restoration of blood supply, further damages the tissues, potentially because of gut lumen bacterial byproducts' entry into systemic circulation, free radicals, and inflammatory response.

Intestinal Capillary Arrangement

• Intestinal capillaries run from the intestinal crypts to the surface, turning to return to the venules.
• Surface epithelium is more at risk for ischemic injuries due to this arrangement.
• Crypt protection refers to the capillaries' ability to preserve stem cells in the crypts for epithelium regeneration following injury.

Morphology

• Acute ischemia damage extends to the submucosal and muscularis propria, and frequently involves substantial portions of the bowel wall.
• Chronic ischemia results in fibrous scarring of the lamina propria, and occasionally, stricture formation.
• Bacterial invasion can lead to pseudomembranous colitis-like symptoms in both acute and chronic ischemia.

Affected Bowel and Wall Changes

• Affected portions of the bowel appear sharply demarcated, congested, and discolored.
• Wall changes are characterized by edema, thickening, and necrosis.
• Microscopically, epithelial atrophy and inflammation are present after reperfusion.

Clinical Features

• Acute colonic ischemia presents with abrupt cramping-associated pain, left lower quadrant abdominal pain, blood in stool or bloody diarrhea, and a desire to defecate.
• Chronic ischemia frequently involves limited mucosal and mural infarctions that could progress to substantial infarction without collateral circulation restoration.
• CMV infection causes localized vascular obstruction due to viral tropism.
• Radiation injury to the GI tract may lead to radiation enterocolitis.

Angiodysplasia

• Angiodysplasia consists of dilated and thin-walled submucosal and mucosal vessels.
• It is commonly observed in the cecum or right colon after individuals reach 60 years of age.
• It is a less prevalent but significant cause of lower gastrointestinal bleeding among older adults (about 20% of cases).

Malabsorption

• Malabsorption is defined as impaired absorption of fats, fat-soluble vitamins, proteins, carbohydrates, electrolytes, minerals, and water.
• A key feature is steatorrhea (excessive fat in the stool), characterized by excessive, bulky, frothy, greasy, and pale or clay-colored stools.
• Common causes in the US include pancreatic insufficiency, celiac disease, Crohn's disease, and graft-versus-host disease following allogeneic hematopoietic stem cell transplantation.
• Malabsorption arises from disturbances in one or more of the four phases of nutrient absorption.

Phases of Nutrient Absorption

• Intraluminal digestion: Breaking down nutrients into absorbable forms.
• Terminal digestion: Hydrolyzing carbohydrates and peptides in the intestinal mucosa.
• Transepithelial transport: Transporting absorbed nutrients and fluids.
• Lymphatic transport: Transporting lipids through the lymphatic system.

Diarrhea

• Diarrhea is defined as an increase in stool mass, frequency, or fluidity (typically greater than 200 g/day).
• Causes include nutrient malabsorption and increased fluid secretion by the intestines.
• Severity can be mild to extreme, potentially life-threatening in cases with excessive fluid loss.
• Types include secretory, osmotic, malabsorptive, and exudative diarrhea. (A classification system is described).

Celiac Disease

• Celiac disease is triggered by gluten ingestion.
• The disease is an immune-mediated disorder affecting genetically-prone individuals.
• Pathologic findings include villous atrophy, increased intraepithelial lymphocytes, and crypt hyperplasia.
• Common symptoms include diarrhea, bloating, and fatigue, and can also manifest as anemia, dermatitis herpetiformis, and other extra-intestinal conditions.
• Gluten-free diet is the primary treatment approach.
  • It typically resolves symptoms, reduces antibody titers, and restores healthy intestinal histology.
  • Future therapies aim to help manage exposure to gluten.

Environmental Enteric Dysfunction (EED)

• EED is associated with repeated bouts of diarrhea that can negatively affect growth, height and weight, development, and lead to potential cognitive impairments.
• Chronic exposure to intestinal pathogens and other microbial, environmental contaminants contributes to this persistent diarrhea.
• Mucosal immune abnormalities and inflammation are factors involved in this persistent damage to the gut.

Autoimmune Enteropathy

• Autoimmune enteropathy involves a persistent, severe diarrhea with autoimmune symptoms involving the intestinal mucosa.
• This condition is an X-linked disorder and a rarer, severe form (IPEX) associated with FOXP3 gene mutations.
• Treatment strategies often focus on immunosuppression or hematopoietic stem cell transplantation.