Disorders of the Small and Large Intestines

Gastrointestinal bleeding indicates underlying pathology in either the upper or lower gastrointestinal (GI) tract. Hematemesis (vomiting red blood or “coffee-ground” material) and melena (black, tarry stool) usually indicate upper GI bleeding proximal to the suspensory ligament of the duodenum, also called the ligament of Treitz. Peptic ulcer disease (PUD) is the most common cause of upper GI bleeding. Hematochezia (red blood in the stool) is most often associated with lower GI bleeding (although it infrequently occurs with massive upper GI bleeding that is typically associated with hypotension). Lower GI bleeding can be from diverticular disease, angiodysplasia, polyps or tumors, inflammatory bowel disease, or internal hemorrhoids. Diagnosis is made by clinical history and physical exam, followed by upper and/or lower GI endoscopy. The source of the bleeding can usually be identified and treated with endoscopy.

Intestinal ischemia occurs when perfusion fails to meet the demands of the intestines, resulting in ischemic tissue injury that can be life-threatening if bowel necrosis and/or perforation occurs. Symptoms can range from mild indigestion or diarrhea to severe abdominal pain. Imaging techniques including CT and angiography are used to detect stenosis or occlusion. The chronic form of intestinal ischemia benefits from medical therapies and revascularization procedures (stents, bypass surgery) while acute forms require urgent interventions to restore blood flow and remove any dead bowel tissue. Delay in the diagnosis and management of acute intestinal ischemia results in high mortality and severe complications, including intestinal perforation and sepsis.

Pseudomembranous colitis is inflammation of the colon caused by an overgrowth of the bacterium Clostridioides difficile. This condition is associated with antibiotic use and the consequent disruption of the normal colonic microbiota. It is one of the most common healthcare-associated infections and a significant cause of morbidity and mortality, especially in hospitalized older adults. Clinical manifestations of C. difficile infection (CDI) include asymptomatic colonization, diarrheal illness, and fulminant colitis with sepsis in severe cases. The diagnosis is established based on stool studies. Most patients can be treated with antibiotics. Fecal transplantation is considered in a few cases, whereas surgical intervention may be required in severe cases.

Peptic ulcers are mucosal defects > 5 mm in diameter that penetrate the muscularis mucosae in the wall of the stomach or duodenum. Peptic ulcer disease (PUD) results when exposure to acid and digestive enzymes overcomes mucosal defense mechanisms. The most common etiologies are Helicobacter pylori (H. pylori) infection and prolonged use of nonsteroidal antiinflammatory drugs (NSAIDs). Patients may be asymptomatic or present with abdominal pain, nausea, and early satiety. PUD typically responds well to medical treatment with risk factor modification, H. pylori eradication, and acid reduction. If left untreated, PUD can lead to bleeding, perforation, gastric outlet obstruction, and gastric cancer.

Colorectal cancer (CRC) is the 2nd-leading cause of cancer-related death in the United States. Almost all cases of CRC are adenocarcinoma and the majority of lesions come from the malignant transformation of an adenomatous polyp. As most CRCs are asymptomatic, screening is essential in detecting early disease. Screening is recommended to start at the age of 45 years, utilizing various screening tools available with colonoscopy, flexible sigmoidoscopy, and fecal tests among them. For high-risk individuals, earlier and more frequent screening is recommended. Other stool-based strategies and visualization tests are also available for CRC screening.

Imaging of the intestines is typically performed utilizing a multimodal approach, with clinical suspicion being the primary indicator for which study should be completed and in what order. There are also many differences between outpatient imaging versus emergency or inpatient imaging of the intestines. Imaging varies widely based on the patient's history, symptoms, and physical exam findings. The patient's age will also play a factor in the modality chosen. For example, appendicitis is typically 1st evaluated via ultrasound in the pediatric population versus CT in adults.

Pseudomembranous colitis is a bacterial disease of the colon caused by Clostridium difficile. Pseudomembranous colitis is characterized by mucosal inflammation and is acquired due to antimicrobial use and the consequent disruption of the normal colonic microbiota. C. difficile infections account for the most commonly diagnosed hospital-acquired diarrheal illnesses. C. difficile infections can range from asymptomatic colonization to diarrhea and progress to fulminant colitis with systemic sepsis in severe cases. The diagnosis is established based on stool studies. Management of pseudomembranous colitis is mainly using antibiotics. Fecal transplant is considered in a few cases, whereas surgical intervention is required in severe cases.

Colorectal cancer (CRC) is the 2nd-leading cause of cancer-related death in the United States. Almost all cases of CRC are adenocarcinoma and the majority of lesions come from the malignant transformation of an adenomatous polyp. As most CRCs are asymptomatic, screening is essential in detecting early disease. Screening is recommended to start at the age of 45 years, utilizing various screening tools available with colonoscopy, flexible sigmoidoscopy, and fecal tests among them. For high-risk individuals, earlier and more frequent screening is recommended. Other stool-based strategies and visualization tests are also available for CRC screening.

Short bowel syndrome is a malabsorptive condition most commonly associated with extensive intestinal resection for etiologies such as Crohn's disease, bowel obstruction, trauma, radiation therapy, and vascular insufficiency. The short length of bowel results in insufficient surface area for fluid and electrolyte absorption. Patients typically present with diarrhea, electrolyte abnormalities, and dehydration. Management options include antimotility agents, antisecretory agents, and total parenteral nutrition for patients who cannot maintain themselves with oral intake. Last-resort options include surgical intestinal lengthening procedures and small bowel transplant.

Intestinal ischemia occurs when perfusion fails to meet the demands of the intestines, resulting in ischemic tissue injury that can be life-threatening if bowel necrosis and/or perforation occurs. Symptoms can range from mild indigestion or diarrhea to severe abdominal pain. Imaging techniques including CT and angiography are used to detect stenosis or occlusion. The chronic form of intestinal ischemia benefits from medical therapies and revascularization procedures (stents, bypass surgery) while acute forms require urgent interventions to restore blood flow and remove any dead bowel tissue. Delay in the diagnosis and management of acute intestinal ischemia results in high mortality and severe complications, including intestinal perforation and sepsis.

Colon polyps are growths of mucosal tissue in the colon, the most common site of polyps in the GI tract. Polyps can be classified as neoplastic or nonneoplastic and may be associated with genetic syndromes. Hyperplastic polyps are nonneoplastic and are the most common type overall, whereas adenomas are the most common type of neoplastic polyp and have the potential to progress to cancer. For most people without hereditary syndromes, colon cancer screening should begin at age 50 (at age 45 for Black individuals) and in adolescence for those with the rare familial adenomatous polyposis (FAP) syndrome. Diagnosis is by biopsy, and management includes frequent surveillance in people with adenomatous polyps or screening every 10 years in the general population until age 75.

Colorectal cancer (CRC) is the 2nd leading cause of cancer-related deaths in the United States. Colorectal cancer is a heterogeneous disease that arises from genetic and epigenetic abnormalities, with influence from environmental factors. Almost all cases of CRC are adenocarcinoma, and the majority of lesions come from the malignant transformation of an adenomatous polyp. Since most CRC cases are asymptomatic, screening colonoscopy or stool tests are generally recommended in patients ≥ 50 years of age. Along with screening, diagnosis is reached by colonoscopy, which allows visualization as well as tissue sampling. Treatment is primarily surgical, with chemotherapy reserved for advanced disease.

Diverticula are protrusions of the bowel wall occurring most commonly in the colon. The condition of having diverticula (called diverticulosis) is mostly asymptomatic. These diverticula can become symptomatic, however, when associated with diseases. Diverticulitis is the inflammation of diverticula, often presenting with lower abdominal pain and changes in bowel habits. The condition may be further complicated by abscess, perforation, fistula, and bowel obstruction. Management consists of antibiotics, fluid resuscitation, and bowel rest. Surgery is required for complications, failure of medical management, and recurrent disease. In most cases of diverticular bleeding, spontaneous cessation occurs. Invasive intervention will be needed for persistent or recurrent bleeding.

Peptic ulcer disease (PUD) refers to the full-thickness ulcerations of duodenal or gastric mucosa. The ulcerations form when exposure to acid and digestive enzymes overcomes mucosal defense mechanisms. The most common etiologies include Helicobacter pylori (H. pylori) infection and prolonged use of non-steroidal anti-inflammatory drugs (NSAIDs). Patients may be asymptomatic or may present with abdominal pain, nausea, and early satiety. Peptic ulcer disease typically responds well to medical treatment consisting of H. pylori eradication, eliminating risk factors, and proton pump inhibitors (PPIs). If left untreated, it can lead to bleeding, perforation, gastric outlet obstruction, and gastric cancer.

Gastrointestinal bleeding (GIB) is a symptom of multiple diseases within the gastrointestinal (GI) tract. Gastrointestinal bleeding is designated as upper or lower based on the etiology’s location to the ligament of Treitz. It is more common to have bleeding in the upper GI tract, with peptic ulcer disease being the most frequent cause. Depending on the location of the bleeding, the patient may present with hematemesis (vomiting blood), melena (black, tarry stool), or hematochezia (fresh blood in stools). Some patients presenting with GIB can be hemodynamically unstable and require emergent stabilization and evaluation. The source of the bleed can often be located and treated with endoscopy.