Appendicitis is inflammation of the appendix, a narrow tubular structure attached to the caecum at the beginning of the large intestine. It is a common cause of acute abdominal pain and can become a surgical emergency when inflammation progresses to perforation, abscess formation or widespread peritonitis. Appendicitis often begins when the appendix lumen becomes obstructed, although the precise initiating mechanism can vary. Obstruction can promote bacterial proliferation, increased intraluminal pressure, impaired blood flow and progressive inflammation. Because symptoms can overlap with many gastrointestinal and urinary conditions, diagnosis requires clinical assessment rather than reliance on one symptom.
The classical progression of Appendicitis involves pain that initially develops around the central abdomen and subsequently becomes more prominent in the right lower quadrant as inflammation extends to the adjacent parietal peritoneum. Nausea, vomiting, loss of appetite and fever are common but not universal. Some patients develop diarrhoea or constipation, particularly when the inflamed appendix irritates nearby bowel. Pain often worsens with movement, coughing or physical activity. The classical pattern is not present in every patient because anatomical position of the appendix varies and symptoms can differ according to age, pregnancy and the extent of inflammation.
Diagnosis of Appendicitis involves history, examination and, when appropriate, laboratory and imaging investigations. Clinicians may look for localised tenderness and signs of peritoneal irritation while also assessing temperature, heart rate and general appearance. Blood tests can demonstrate inflammatory changes but cannot by themselves confirm appendicitis. Ultrasound can be useful, particularly in children and pregnancy, while computed tomography provides high diagnostic accuracy in many adults when the diagnosis remains uncertain. Clinical scoring systems can support assessment but do not replace clinical judgement or imaging when indicated.
Untreated Appendicitis can progress through increasing inflammation to tissue necrosis and perforation. Once the appendix perforates, intestinal contents and bacteria can enter the abdominal cavity and cause peritonitis. A localised perforation may instead become walled off, producing an abscess or inflammatory mass. These complications can require prolonged antibiotic treatment, drainage or surgery and are associated with greater morbidity than uncomplicated appendicitis. The risk of complications generally increases with delayed diagnosis, although disease progression varies between individuals and not every inflamed appendix follows the same timeline.
Treatment of Appendicitis depends on the clinical presentation and local protocols. Appendectomy remains a standard definitive treatment for many patients and can be performed through open or minimally invasive approaches. Antibiotics are also an important component of treatment, particularly around surgery and in selected patients. For some forms of uncomplicated appendicitis, antibiotic-first management can be considered, but recurrence and the possibility of later surgery remain relevant. Complicated disease involving perforation or abscess may require antibiotics, drainage and delayed or immediate surgery depending on the circumstances.
Appendicitis can occur at any age but is particularly common in adolescents and young adults. Diagnosis may be more difficult in very young children, older adults and pregnant patients because symptoms can be atypical or pain may be displaced by anatomical changes. The appendix can occupy pelvic, retrocaecal or other positions, altering where pain is perceived and which neighbouring structures become irritated. In pregnancy, for example, anatomical displacement can change the location of tenderness. These variations are important because absence of textbook right-lower-quadrant pain does not exclude the disease.
Differential diagnosis of Appendicitis includes gastroenteritis, constipation, inflammatory bowel disease, urinary infection, kidney stones and, where relevant, gynaecological or reproductive conditions. Gastroenteritis often produces more prominent diarrhoea and vomiting, whereas appendicitis may produce progressive localised pain, but substantial overlap exists. In reproductive-age patients, ectopic pregnancy and ovarian pathology can produce acute abdominal pain and require appropriate assessment. Urinalysis can sometimes show abnormalities in appendicitis because of adjacent inflammation, so urinary findings do not necessarily exclude an appendiceal cause.
Appendicitis is an important example of how acute abdominal disease evolves from a localised process to a potentially life-threatening intra-abdominal infection. The appendix itself is part of the immune-associated lymphoid tissue of the gastrointestinal tract, but its precise physiological role is not essential for normal digestion. Removal generally does not cause a clinically important digestive deficit. Modern management has become more nuanced because some uncomplicated cases can be treated non-operatively, but patient selection and recurrence risk remain important. Prompt assessment remains essential when symptoms are compatible with acute appendicitis because delay can increase the likelihood of complications.
