Your pathology report for acute appendicitis

by Madeline Fitzpatrick MD and Stephanie Reid, MD FRCPC
September 23, 2025

Acute appendicitis means sudden inflammation of the appendix, a small, finger-shaped pouch attached to the first part of the large intestine (colon). In most people, the appendix is located in the lower right side of the abdomen, just above the hip bone.

Acute appendicitis is a common condition and can affect people of all ages, although it is most often seen in adolescents and young adults. It is not a type of cancer.

What causes acute appendicitis?

The most common cause of acute appendicitis is blockage of the small opening that connects the appendix to the large intestine. The blockage is often caused by a piece of hardened stool called a fecalith. Once the opening is blocked, bacteria multiply inside the appendix, and the immune system responds by sending white blood cells called neutrophils. This leads to swelling, pus, and inflammation.

Although much less common, other causes of appendicitis include:

  • Tumors: Both benign (non-cancerous) and malignant (cancerous) tumors of the appendix can block the opening and cause inflammation. Well differentiated neuroendocrine tumor is one of the most common types of cancer associated with acute appendicitis.

  • Parasites: In rare cases, intestinal parasites such as pinworms can block the appendix.

  • Inflammatory bowel disease: Conditions such as Crohn’s disease can affect the appendix and lead to appendicitis.

These causes are rare compared to fecaliths, which are by far the most common reason for appendicitis.

What are the symptoms of acute appendicitis?

The most common symptom is abdominal pain that often begins near the belly button and then moves to the lower right side of the abdomen. The pain usually becomes steady and more severe over time.

Other possible symptoms include:

  • Nausea and vomiting.

  • Loss of appetite.

  • Fever.

  • Diarrhea or constipation.

  • Tenderness in the lower right abdomen.

If left untreated, appendicitis can become very serious and even life-threatening.

How is acute appendicitis diagnosed?

Doctors often suspect appendicitis based on symptoms and physical examination. Additional tests are usually performed, such as:

  • Bloodwork: A high white blood cell count may suggest infection or inflammation.

  • Imaging: An ultrasound or CT scan may show an enlarged or swollen appendix.

The final diagnosis is made after the appendix is surgically removed in a procedure called an appendectomy. The appendix is sent to a pathologist, who examines it under a microscope to confirm the diagnosis.

What does acute appendicitis look like under the microscope?

When a pathologist examines the appendix, they look for neutrophils (a type of white blood cell) within the wall of the appendix. These cells often cluster with bacteria to form pus or an abscess. Neutrophils may also be seen on the outside surface of the appendix, a finding called peri-appendicitis.

The inflammation usually begins inside the appendix but can spread through the wall and onto the outer surface. In some cases, the swelling blocks blood flow, causing parts of the appendix to die in a process called necrosis.

What does perforated appendicitis mean?

If appendicitis is not treated, a hole (perforation) can form in the appendix wall. When this happens, pus and bacteria leak into the abdominal cavity. This can cause a serious infection or an abscess (a pocket of pus) to form around the appendix.

What does peri-appendicitis mean?

Peri-appendicitis means inflammation on the outside surface of the appendix. This is a common finding in appendicitis and usually happens when the inflammation spreads outward from inside the appendix.

What is the difference between acute and chronic appendicitis?

Acute appendicitis develops quickly and causes sudden, severe symptoms that usually require surgery.

Chronic appendicitis is much less common. In this condition, inflammation develops slowly over time and may come and go. The symptoms are usually milder and can last for weeks or even months. Chronic appendicitis is also treated with surgery, but because the symptoms are less dramatic, it can sometimes take longer to diagnose.

What is the prognosis for a person with acute appendicitis?

For most people, the prognosis after an appendectomy is excellent. Once the appendix is removed, the problem is usually cured, and people can return to normal activities within a few weeks.

If the appendix perforates before surgery, recovery may take longer, and there is a higher risk of complications such as infection or abscess formation. Rare causes of appendicitis, such as tumors, may require additional treatment depending on the specific diagnosis.

In general, once the appendix has been removed and the infection has cleared, most people do not experience long-term health problems.

Questions to ask your doctor

If your appendix has been removed and your pathology report shows acute appendicitis, you may find it helpful to ask your doctor the following questions:

  • Does my pathology report describe perforation, necrosis, or an abscess?

  • Was peri-appendicitis found?

  • Did the report mention a fecalith, tumor, parasite, or another unusual cause?

  • Does my report rule out other conditions in the appendix, such as cancer?

  • How long will it take me to fully recover after surgery?

  • Do I need any follow-up care or additional treatment?

A+ A A-