Appendicitis is an inflammation of the appendix, a small, finger-like outpouching from the large intestine in the lower-right area of the abdomen. The most common symptom is abdominal pain that often begins near the belly button and moves to the lower-right side, becoming sharper and more severe over time. Other symptoms may include loss of appetite, nausea, vomiting, fever, and swelling in the abdomen. Some people may also experience constipation, diarrhea, or difficulty passing gas.

In the United States, appendicitis is the most common cause of sudden abdominal pain requiring surgery, affecting about 5% to 9% of people at some point in their lives. It is slightly more common in males than in females, and most often occurs in teens and young adults, though it can develop at any age.

Appendicitis can be managed effectively, and with prompt diagnosis and treatment, most people recover fully.

The appendix is a narrow, finger-shaped tube located in the lower-right part of the abdomen, near the spot where the small intestine meets the large intestine. For a long time, its role in the body was unclear, but research now suggests the appendix may offer some immune function. However, it is not essential for health.

When appendicitis develops, the appendix becomes inflamed and infected, which can cause it to swell. As the inflammation worsens, pressure builds up inside the appendix, and the blood supply to its wall can become diminished. This can lead to tissue damage, infection, and, if untreated, the appendix can rupture, permitting the spread of infection throughout the abdomen.

Appendicitis can occur at any age but is most common in children, teenagers, and young adults. The condition often develops suddenly, with symptoms typically appearing within 24 hours. If not treated promptly, appendicitis can lead to serious complications, including infection of the abdominal cavity (peritonitis), formation of an abscess (a pus-filled pocket that may form when the appendix ruptures), and, in rare cases, sepsis or death.

The exact cause of appendicitis is not always clear, but most cases are thought to begin when the inside of the appendix becomes blocked. This blockage can be caused by hardened stool (also called a fecalith), a small growth, a foreign object, swelling of tissue in the appendix wall (often due to infection elsewhere in the body), or, less commonly, a tumor or intestinal parasites. In children and young adults, lymphoid tissue (specialized tissue that helps the body fight infection) in the appendix may become enlarged after an infection and block the opening. In older adults, blockage is more likely to be caused by a growth or mass.

When the appendix is blocked, bacteria that normally live in the intestine can multiply inside the appendix, leading to inflammation, swelling, and infection. As the blockage and inflammation progress, pressure builds up inside the appendix, which can reduce blood flow and cause tissue damage. If the inflammation continues without treatment, the appendix can rupture, spreading infection into the abdomen and leading to serious complications.

Risk factors for appendicitis include:

• Age (most common in children, teenagers, and young adults)
• Male sex
• Family history of appendicitis
• Obstruction of the appendix by hardened stool, growths, or foreign objects
• Infections in the digestive tract or elsewhere in the body
• Presence of tumors or intestinal parasites

Symptoms of appendicitis may include:

• Abdominal pain, often starting near the belly button and moving to the lower-right side
• Pain that worsens with movement, coughing, deep breathing, or walking
• Loss of appetite
• Nausea or vomiting
• Low-grade fever
• Swelling in the abdomen
• Constipation or diarrhea
• Inability to pass gas
• Chills and shaking
• Pain that may interrupt sleep
• Pain that gets worse within a few hours

Young children, older adults, and pregnant women may not have typical symptoms. In children, the pain may be generalized throughout the abdomen, rather than localized to the lower-right side of the abdomen. Older adults and pregnant women may have less severe pain than others.

To diagnose appendicitis, a doctor will review the individual’s medical history, conduct a physical exam, and may order one or more diagnostic tests.

The doctor may ask about symptoms, including when the abdominal pain began, how severe it is, where the pain is located, and whether other symptoms are present, such as nausea, vomiting, fever, or changes in bowel habits. They may also ask about medical history, recent illnesses, and any risk factors for appendicitis.

During the physical exam, the doctor will check for pain or tenderness in the lower-right side of the abdomen and may gently press or move the legs to see if this causes pain. They may also listen to the abdomen, perform a digital rectal exam, or, for women, a pelvic exam.

Additional tests that may be necessary to make a diagnosis include:

• Blood tests: Used to check for a high white blood cell count or other markers of infection or inflammation (such as C-reactive protein).
• Urinalysis: Helps rule out urinary tract infections (UTIs) or kidney stones as the cause of symptoms.
• Pregnancy test: For women of childbearing age, to rule out pregnancy-related causes of abdominal pain.
• Abdominal ultrasound: Uses sound waves to create images of the appendix and surrounding organs; often the first imaging test in children, young adults, and pregnant women.
• Magnetic resonance imaging (MRI): Provides detailed images of the abdomen; may be used if ultrasound results are unclear or to avoid radiation exposure.
• Computed tomography (CT) scan: Combines X-rays and computer technology to create detailed images.

In some cases in which the diagnosis remains uncertain after these tests, doctors may recommend observation in the hospital or a diagnostic laparoscopy (a minimally invasive surgical procedure to look inside the abdomen).

Appendicitis is a medical emergency that requires prompt treatment. The main treatments for appendicitis include:

• Surgery (appendectomy): The most common and definitive treatment for appendicitis is surgical removal of the appendix (known as an appendectomy). This can be done through laparoscopic surgery, which uses small incisions and a camera for a faster recovery and fewer complications, or through open surgery, which uses a larger incision and may be necessary in certain cases. Laparoscopic surgery is generally preferred when possible because it leads to less pain and a quicker recovery.
• Antibiotics: Antibiotics are given before surgery to treat infection and reduce the risk of complications. In some cases of mild or uncomplicated appendicitis—especially if surgery is not immediately possible or if a person is not a good candidate for surgery—antibiotics alone may be used as the initial treatment. However, there is a risk that appendicitis may return or that surgery will be needed later.
• Drainage of an abscess: If an abscess (a pocket of pus) has formed around the appendix, doctors may drain it using a needle or tube guided by imaging. This is usually followed by antibiotics and, in some cases, delayed surgery to remove the appendix after the infection has resolved.
  

People with appendicitis may be at increased risk for certain complications, including:

• Perforated (ruptured) appendix: If the appendix ruptures, infection can spread throughout the abdomen, leading to serious illness.
• Peritonitis: A life-threatening infection and inflammation of the lining of the abdominal cavity, which can occur if the appendix ruptures.
• Abscess: A pus-filled pocket of infection that forms in the abdomen, often requiring drainage and antibiotics.
• Sepsis: A severe, body-wide response to infection that can be life-threatening.
• Intestinal blockage: Scar tissue or infection can cause the intestines to become blocked.
• Wound infection: Infection at the site of surgery after an appendectomy.
• Ileus: A condition in which the bowel temporarily stops working properly.
• Fistula: An abnormal connection that can form between the intestine or stomach and the skin.
• Adhesions: Bands of scar-like tissue that can form inside the abdomen after surgery, sometimes leading to bowel obstruction.
• Stump appendicitis: In rare cases, inflammation can occur in a small piece of the appendix left after surgery.
• Infertility (in women): Infection and scarring from a ruptured appendix can affect the fallopian tubes and ovaries, potentially leading to infertility.

People who receive prompt treatment—especially before the appendix ruptures—usually recover quickly and completely, often returning to normal activities within a few days after surgery.

If the appendix ruptures or complications such as abscess, peritonitis, or sepsis occur, recovery may take longer, and the risk of further health problems increases. Older adults and people with other health conditions may also face a longer recovery.

“Appendicitis is a common surgical disease that requires specialized care from several providers working in different departments,” says Yale Medicine pediatric surgeon Robert A. Cowles, MD. “Our highly trained emergency physicians are trained to suspect appendicitis and perform initial evaluations for this condition. Our radiologists use modern imaging technologies to aid in diagnosis while minimizing the use of radiation. Finally, our surgeons use advanced techniques to treat appendicitis in a minimally invasive manner using a data-driven approach. The seamless collaboration between our emergency physicians, radiologists, and surgeons ensures the best outcome for patients who present to Yale with appendicitis.”