Acute appendicitis is a sudden inflammation of the appendix, a small finger-shaped pouch attached to the large intestine on the lower right side of the abdomen. It’s the most common reason for emergency abdominal surgery, and the lifetime risk falls somewhere around 7 to 8 percent. The condition develops when the opening of the appendix becomes blocked, trapping bacteria inside and triggering a rapid inflammatory response that can progress to a surgical emergency within hours.
What Causes It
The process starts with a blockage at the narrow opening where the appendix connects to the large intestine. Once blocked, bacteria that normally live in the gut multiply inside the sealed-off space. Pressure builds, blood flow gets cut off, and the appendix wall begins to break down. Without treatment, it can eventually rupture and spill infected contents into the abdominal cavity.
The type of blockage varies by age. In children, the most common culprit is an overgrowth of immune tissue (lymphoid hyperplasia) inside the appendix, often triggered by a viral infection. In adults, hardened pieces of stool called fecaliths are a frequent cause. Less commonly, the blockage comes from tumors, intestinal parasites, or swollen lymph tissue from a nearby infection.
How the Pain Typically Progresses
Appendicitis follows a recognizable pattern, though not everyone experiences every stage. The classic sequence starts with vague pain around the belly button, followed by loss of appetite, nausea, or mild vomiting, then migration of the pain to the right lower abdomen, and finally a low-grade fever. About 50 to 60 percent of patients notice the pain shift from the belly button area to the lower right side within the first 24 hours.
That migration happens because of how the body processes pain signals. Early on, the inflammation irritates nerve fibers inside the appendix itself, which the brain interprets as a dull ache near the center of the abdomen. As the inflammation spreads to the lining of the abdominal wall, localized nerve endings kick in, and the pain sharpens and settles over the appendix in the lower right quadrant. Walking, coughing, or hitting a bump in the car often makes the pain noticeably worse at this stage.
What Doctors Look For on Exam
The most important physical finding is tenderness at McBurney’s point, located about one-third of the way from the hip bone to the belly button on the right side. This spot represents where the pain is greatest on the abdominal wall, not necessarily where the appendix sits. Significant tenderness here is a strong indicator of appendicitis with inflammation reaching the abdominal lining.
Doctors also use a few specific tests during the exam. Rovsing’s sign involves pressing on the left side of the abdomen and checking whether it causes pain on the right, a clue that the right-sided inflammation is real. The psoas sign tests whether straightening the right hip while lying on the left side causes pain, which suggests the inflamed appendix is sitting against the psoas muscle in the back of the abdomen. Rebound tenderness, where releasing pressure on the abdomen hurts more than pressing down, is another red flag.
How It’s Diagnosed
No single test confirms appendicitis with certainty, so diagnosis relies on combining symptoms, exam findings, blood work, and imaging. A scoring system called the Alvarado score helps doctors weigh the evidence. It assigns points for symptoms like pain migration (1 point), nausea or vomiting (1 point), and loss of appetite (1 point), along with physical signs like right lower quadrant tenderness (2 points), rebound tenderness (1 point), and fever (1 point). Lab findings showing elevated white blood cells add up to 3 more points. A high total score pushes toward surgery, while a low score may prompt watching and waiting.
CT scanning is the most accurate imaging tool, with sensitivity and specificity both around 94 percent. For children and pregnant women, ultrasound is the preferred first step because it avoids radiation exposure. If ultrasound is inconclusive, MRI offers similar accuracy to CT. Contrast-enhanced MRI matches CT’s performance at about 94 percent sensitivity and specificity, making it an excellent alternative when radiation is a concern.
Appendicitis During Pregnancy
Pregnant women present a diagnostic challenge. The pain usually still starts near McBurney’s point in the lower right abdomen, but as the uterus grows, the appendix can shift upward. In later pregnancy, the pain may appear in the right flank or even the upper right abdomen. Ultrasound is the first imaging choice, followed by MRI if results are unclear. CT is reserved for situations where MRI isn’t available, since reducing radiation exposure during pregnancy is a priority.
Risk of Rupture
The fear with appendicitis is perforation, where the appendix bursts and releases bacteria into the abdominal cavity, causing a potentially life-threatening infection called peritonitis. Timing matters: the risk of rupture stays at 2 percent or lower during the first 36 hours of symptoms. After 36 hours without treatment, the rupture risk climbs to about 5 percent for every additional 12-hour window and holds steady at that rate.
This is why appendicitis is treated as urgent rather than a true seconds-count emergency. There’s a reasonable window for diagnosis and preparation, but unnecessary delays beyond a day and a half meaningfully increase the danger.
Surgery: What to Expect
Appendectomy, the surgical removal of the appendix, remains the standard treatment. Most operations today are done laparoscopically, using a few small incisions and a camera to guide the surgery. Compared to the traditional open approach with a larger incision, laparoscopic surgery results in shorter hospital stays (about 2 days versus nearly 3 days on average), less postoperative pain, and a faster return to normal activities.
For uncomplicated cases done laparoscopically, many patients go home within one to two days. The small incisions heal relatively quickly, and most people return to light daily activities within a week or two. Open surgery, which may be necessary if the appendix has already ruptured or if there are complications, involves a longer recovery.
Antibiotics Instead of Surgery
For uncomplicated appendicitis, meaning the appendix hasn’t ruptured and there’s no abscess, treating with antibiotics alone has become a legitimate option. This approach can resolve the immediate episode in most patients and allows some to avoid surgery entirely. However, the long-term picture is important to understand.
The APPAC trial, one of the most rigorous studies on the question, followed antibiotic-treated patients for 10 years. The true recurrence rate was 37.8 percent, meaning roughly 4 in 10 patients eventually had another bout of appendicitis confirmed after surgery. The cumulative rate of eventually needing an appendectomy reached 44.3 percent over a decade. So antibiotics work well as an initial treatment, but there’s close to a coin-flip chance you’ll end up having surgery down the road anyway. This makes antibiotics a reasonable choice for people who want to avoid or delay surgery, as long as they understand the tradeoff.
Who Gets It and When to Worry
Appendicitis peaks between the ages of 10 and 30, though it can happen at any age. It’s slightly more common in males. Young children and older adults tend to have less typical symptoms, which can delay diagnosis and increase the risk of perforation. In elderly patients, the pain may be mild or diffuse rather than sharply localized, and fever may be absent.
The symptoms that matter most are steady abdominal pain that worsens over 12 to 24 hours, especially if it starts near the belly button and moves to the lower right side. Loss of appetite paired with that pain pattern is a particularly telling combination. If you’re experiencing this progression, getting evaluated promptly keeps you well within the safe window before rupture risk begins to climb.