Acute appendicitis is one of the most familiar diagnoses in emergency medicine, affecting an estimated 7% to 10% of people worldwide. The workup is well worn: right lower abdominal pain, elevated white cells, an inflamed appendix on ultrasound or CT, then surgery.
A 53-year-old man followed that script exactly. He arrived with right lower abdominal pain and tenderness, no rebound tenderness or guarding, elevated white cells and a raised C-reactive protein. Ultrasound of the region where the small and large intestine meet suggested acute appendicitis, and he was taken for laparoscopy.
What the surgeons saw when the camera went in was not a plain inflamed appendix. Running along its surface were multiple cylindrical, red, swollen outpouchings, each up to about 4 millimeters. His case anchors a case report and systematic review published in 2025 in Clinics and Practice.
Diverticula Where They Are Not Supposed to Be
Diverticula are small pouches that push out through weak points in the wall of the digestive tract. In the colon, they are so common that a large share of older adults have them.
In the appendix, they are rare. Reported prevalence in appendectomy specimens ranges from 0.004% to 2.1%, and a pooled meta-analysis of more than 17,000 patients put the figure at about 1.74%. The pathologist T. H. Kelynack first described the entity in 1893, and it has been studied only sporadically since.
They come in two forms. True or congenital diverticula involve all layers of the appendix wall. Acquired or false diverticula, which are the large majority, occur when the inner lining herniates through the muscular layer, generally driven by raised pressure inside the appendix from a hardened stool fragment, scarring, or a tumor.
When one of these pouches becomes inflamed, the result is appendiceal diverticulitis. It produces right lower quadrant pain, nausea, and a raised white cell count, which is to say it produces acute appendicitis. Across 112 published cases, roughly two-thirds of patients were men, and the median age was 49.
Imaging Almost Never Catches It
The reason this condition keeps being discovered in the operating room is that scans usually cannot distinguish it.
In a case published in the Journal of Surgical Case Reports, a 35-year-old man arrived with right lower quadrant pain, nausea, vomiting, and diarrhea. Imaging suggested uncomplicated acute appendicitis. Surgery instead revealed a large mass at the tip of the appendix with nodules across its surface, which the team handled carefully on the assumption it was a carcinoid tumor. Pathology returned appendicular diverticulosis complicated by acute appendicitis and an organizing abscess.
The systematic review found that among published cases, diagnosis was established by pathology 86.9% of the time, by CT in only 4.1%, and by ultrasound in just 1.6%. In other words, in the overwhelming majority of cases, nobody knew until the pathologist looked. A report in the International Journal of Surgery Case Reports noted the same pattern, describing most cases as diagnosed incidentally on histopathology.
The Numbers That Change How Surgeons Act
Two findings explain why this obscure entity receives attention disproportionate to its rarity.
The first is perforation. Appendiceal diverticulitis appears to rupture far more readily than ordinary appendicitis. The systematic review cites reported rates of up to 70%, against roughly 10% to 20% for acute appendicitis, with a correspondingly higher risk of sepsis. Other series report the rate at around 66%, four times the rate seen in ordinary appendicitis, and the figures vary widely across reports.
The second is tumors. A systematic review and meta-analysis published in the ANZ Journal of Surgery pooled 11 studies, covering 17,147 patients, and found neoplasia in 26.94% of appendix specimens containing diverticula, compared with 1.28% of specimens without them.
That is roughly a twentyfold difference. The tumors involved are typically mucinous neoplasms and neuroendocrine carcinoids rather than aggressive cancers, and mucinous tumors carry their own particular concern because rupture can spread cells through the abdominal cavity. The 2025 review’s own analysis identified neoplasms in 4.1% of its cases, a much lower figure that shows how widely these estimates swing between series.
The practical consequence is a standing recommendation across the literature: when appendiceal diverticula are found, whether during surgery for another reason or on subsequent pathology, removal of the appendix is advised, and the specimen requires careful examination.
What Patients Should Actually Take From This
Almost nothing here changes what an individual should do when their side hurts. Appendicitis symptoms, emergency evaluation, and operation are the same.
What it does change is the value of the pathology report. Patients who have had an appendectomy receive a histopathology result, and that document is where a diverticulum or an incidental tumor would be recorded. It is worth asking for and worth keeping. A review in the Bratislava Medical Journal suggests that when diverticula are found incidentally, particularly in older men or patients with recurrent symptoms, further evaluation may be warranted to rule out other bowel disease.
For anyone told incidentally that they have appendiceal diverticula, the association with tumors is a reason to follow the surgical advice they are given, not a reason to assume cancer. Association is not diagnosis, and these findings come from specimens already removed because of symptoms, which likely inflates the numbers relative to the general population.
Anyone with persistent or recurrent right lower abdominal pain should be evaluated rather than self-managing, and should mention any prior episodes of similar pain.
Key Questions Answered
What is appendiceal diverticulitis? It is inflammation of small pouches in the wall of the appendix. It causes right lower abdominal pain, nausea, and elevated white blood cell counts, closely mimicking typical acute appendicitis.
How common is it? Diverticula are found in roughly 1.74% of appendectomy specimens in pooled analyses, with individual series reporting anywhere from 0.004% to 2.1%.
Why is it so hard to diagnose before surgery? Symptoms and imaging closely resemble acute appendicitis. In published cases, diagnosis was made by pathology about 87% of the time and by CT only about 4% of the time.
How strong is the tumor link? A meta-analysis of more than 17,000 patients found tumors in about 27% of appendix specimens containing diverticula, versus about 1% of those without. Most were mucinous neoplasms or carcinoid tumors.
Does this change how appendicitis should be treated? No. Removing the appendix remains the treatment for both. The difference is that specimens require careful pathological examination, and incidentally found diverticula are generally an indication for appendectomy.
