Acute Appendicitis

The appendix is a small, finger sized and shaped hollow pouch that branches off the cecum in the right lower portion of the abdomen. It arises embryologically from the midgut and is lined with intestinal cells and specialized lymphoid tissue.   While historically viewed as an evolutionary leftover with no vital purpose, modern science suspects that the appendix plays an active role in mucosal immunity. In addition, it may function as a protected reservoir of normal, healthy intestinal bacteria. When diarrheal illnesses or gastrointestinal infections flush out the gut, the appendix can help safely recolonize and restore normal colonic bacteria. Despite these proposed functions, the appendix is not an essential organ. Vast experience demonstrates that removing it causes no long-term digestive deficits, nutritional problems, or chronic immune deficiencies.

Appendicitis develops through a classic chain reaction of obstruction, bacterial proliferation, and blood flow compromise:

• Initial Blockage: The hollow center of the appendix (its lumen) becomes plugged,  either by luminal debris (such as a calcified poop ball called an appedicolith) or from swollen lymphoid tissue from recent illness. Rare causes include foreign bodies, thick mucus, or appendiceal tumors.

• Pressure Build-Up: The lining of the appendix continues to secrete mucus even though the exit into the colon is blocked. Normal intestinal bacteria multiply rapidly inside the closed space, inciting an inflammatory response and causing lumenal pressures to spike.

• Wall Ischemia and Bacterial Invasion: As pressure climbs, it occludes the veins that drain blood from the appendix. Deprived of normal circulation and oxygen, the tissues of the appendiceal wall weaken. Bacteria then invade directly through the compromised wall, setting off intense, full-thickness inflammation.

• Potential for Perforation: If the blockage and pressure remain unrelieved, segments of the wall can lose blood supply entirely die, eventually tearing or rupturing (perforating). 

The presentation of appendicitis depends on time elapsed since onset and the anatomical position of the appendiceal tip. Pain typically begins as a dull, crampy, poorly localized ache around the navel (belly button). This represents early visceral pain from stretching of the organ wall. Loss of appetite and mild nausea almost universally accompany this early phase. Vomiting, if present, typically starts after the pain begins (vomiting that precedes abdominal pain is unusual for appendicitis). Over 12 to 24 hours, as inflammation spreads to the outer lining of the abdominal cavity (parietal peritoneum), the pain shifts and sharpens, focusing directly in the right lower abdomen. Movement or pressing the area will aggravate the discomfort.

Because the tip of the appendix can rest in multiple positions, symptoms can differ significantly. For instance, if the appendix is tucked behind the colon, Abdominal wall tenderness may be minimal, presenting instead as dull flank or lower back discomfort. Or if it is hanging into the pelvis, patients may experience urinary urgency, diarrhea, or the urge to pass stool due to irritation of the bladder or rectum.

Very young children (<4 years old) often cannot articulate their symptoms. They often present atypically with lethargy, irritability, or abdominal distension, leading to higher rates of rupture before presentation. Older adults often show blunted inflammatory responses, experiencing more subtle pain and little to no fever.

Diagnosis relies on combining the story of symptoms, clinical examination, laboratory testing, and targeted imaging. A doctor checks for focal tenderness. Labs are checked and most often show a mild-to-moderate elevation in their white blood cell count, signaling active infection. A urinalysis helps rule out urinary tract infections or kidney stones.   A pregnancy test is crucial in females of childbearing age to rule out ectopic pregnancy or ovarian emergencies.  Then diagnostic imaging is usually ordered. A CT scan is the most common test in adolescents and adults. Ultrasound is preferred in children, and MRI is preferred in most pregnant women when it is available. On imaging, the appendix will be found to be swollen with thickened walls and edema surrounding it. An appendicolith may be seen, and a perforation or abscess may be seen if present. 

Clinicians categorize acute appendicitis into two primary clinical categories to determine the safest treatment plan.

 Uncomplicated Appendicitis: The infection and inflammatory process are entirely confined within the appendix itself. The organ wall remains physically intact, and no bacterial spillage or pus has leaked into the surrounding abdominal space.  

 Complicated Appendicitis: The appendix wall has lost structural integrity, allowing bacteria to escape into the abdomen. This can present as a phlegmon: A solid, inflamed mass of adhered bowel and fatty tissue that walls off the infected appendix without an organized fluid pocket; an abscess: A localized, walled-off cavity filled with pus; or (much more rarely) diffuse peritonitis: bacteria and intestinal contents spread across the peritoneal cavity, producing severe, generalized abdominal pain and systemic illness

Treatment is guided by whether the appendicitis is uncomplicated or complicated, as well as individual patient factors. Uncomplicated appendicitis can be treated medically (with strong antibiotics) or surgically. Surgial treatment is definitive, though associated with small surgical risk. Antibiotic only treatment avoids surgical risks at the cost of assuming risk of recurrnece. At the bottom of this page is more information about choosing between surgical and non-surgical management of uncomplicated appendicitis.

When patients present overnight and elect for surgery, it is most often delayed until business hours. The risk of an uncomplicated appendix suddenly rupturing during a brief in-hospital delay is low (<2%). Ensuring an accurate, well-verified diagnosis and a well staffed OR team is safer than rushing into an operation prematurely. 

The managment of complicated appendicitis is nuanced. Operating immediately in the presence of severe, dense inflammation or abscess carries higher risks of unintended injury to adjacent bowel. In such cases we often delay appendix removal, opting instead for intravenous antibiotics, percutaneous or laparoscopic drainage of abscesses, and patience. In modern practice the appendix is never actually removed in such cases, though follow-up tests are performed to rule out the rare case of an underlying tumor. For diffuse peritonitis, urgent surgery is performed to eliminate the source of infection and thoroughly wash out the abdominal cavity.   

The overall prognosis for acute appendicitis is excellent with modern clinical care.  Whether treated surgically or medically, the vast majority of patients achieve complete resolution of their infection and return to normal daily life with no long-term dietary restrictions, digestive alterations, or nutritional issues.  Most of the time patients can be diagnosed, treated, and discharged within one day and rarely more than 2-3 days.  Follow up rarely consist of more than a 2 week postop visit in clinic.  For patients over 40 who are managed without surgery or who present with complicated appendicitis, follow-up colonoscopy and cross-sectional imaging may be recommended to rule out uncommon underlying growths or neoplasms.