Pathophysiology
Summary
The large bowel and appendix are associated with a variety of disorders ranging from structural abnormalities to inflammatory conditions.
Disorders of the large bowel include diverticulosis, which features false diverticula found primarily along the mesenteric border. These diverticula primarily affect the sigmoid colon, and are associated with chronic constipation due to the chronically elevated intraluminal pressure. Clinically, diverticulosis often manifests as painless hematochezia due to vasa recta injury and rupture. Diverticulitis results when a diverticulum perforates and often manifests as fever, nausea, vomiting, and LLQ pain (due to frequent occurrence in the sigmoid colon). Complications include abscess formation and fistulas.
Large bowel volvulus involves twisting of the bowel around its mesenteric root, which can result in ischemia and necrosis. The cecum and sigmoid colon are most commonly affected in children and adults respectively. Chronic constipation serves as the main risk factor. Large bowel obstruction is most frequently caused by malignancy and presents with symptoms such as abdominal distension, nausea, vomiting, and colicky abdominal pain. Physical examination may reveal high-pitched ‘tinkling’ bowel sounds and hyperresonance to percussion, while X-rays display dilated loops of bowel and air-fluid levels.
Irritable bowel syndrome (IBS) typically presents with vague abdominal pain that is relieved by defecation. Patients with IBS may experience varying bowel movement frequency.
Appendicitis is the most prevalent appendiceal disorder and is usually caused by obstruction. In adults, inspissated fecaliths are the most common etiology, while lymphoid tissue hyperplasia following an infection is the most prevalent cause in children. The resultant increased intraluminal pressure compresses the blood vessels and lymphatics in the appendix, leading to ischemia and necrosis. Initially, it presents with vague periumbilical pain, which later localizes to the RLQ, particularly at McBurney's point. Appendicitis causes inflammation and bacterial overgrowth, which can result in abscess formation and potentially lead to perforation of the appendix.
Lesson Outline
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FAQs
Diverticulosis refers to the presence of false diverticula that involve only the mucosa and submucosa, most commonly found in the sigmoid colon. Risk factors include chronic constipation, as straining creates pressure within the colon, facilitating diverticulum formation. The condition may result in painless hematochezia due to injury to the vasa recta arteries. Diverticulitis, in contrast, is a complication arising from diverticulosis. It occurs when a diverticulum perforates, leading to symptoms such as fever, nausea, vomiting, and lower left quadrant pain. Complications can include abscess and fistula formation.
Appendicitis in adults is most commonly associated with obstruction from an inspissated fecalith, fibrosis, malignancy, or carcinoid tumor. In children, the primary cause is usually lymphoid tissue hyperplasia following an infection. Obstruction leads to increased intraluminal pressure, causing compression of vessels and lymphatics in the appendiceal wall. This can result in ischemia, necrosis, and inflammation. Initial symptoms include vague periumbilical pain, which later localizes to the right lower quadrant, particularly at McBurney's point. Additional symptoms may include nausea, vomiting, and fever, usually appearing later in the course of the illness.
Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by episodic abdominal pain, often relieved by defecation. Patients may experience varying bowel movement frequency and consistency, including diarrhea, constipation, or alternating between the two. The symptoms can vary widely among individuals and may be influenced by dietary and psychological factors.
A large bowel volvulus occurs when a portion of the bowel twists around its mesentery, potentially causing strangulation, which in turn can lead to ischemia and necrosis. In children, the condition most commonly affects the cecum, while it is more frequently seen in the sigmoid colon in adults. The most common risk factor for developing a large bowel volvulus is chronic constipation.
A large bowel obstruction is most often caused by malignancy. Clinical presentation includes symptoms such as abdominal pain and distention, nausea, vomiting (which may include feculent vomiting), and colicky abdominal pain. On physical examination, high-pitched ‘tinkling' bowel sounds and hyperresonance to percussion may be noted due to gas-filled bowel. Diagnosis is commonly confirmed through X-ray, which can reveal dilated loops of bowel appearing as dark pockets of gas, and air-fluid levels seen as horizontal contrast lines.
