When “Appendicitis” Is Endometriosis in Disguise

If your right-sided pain keeps getting dismissed... you’re not imagining it

Right-lower-abdominal pain (the classic “appendicitis area”) can be terrifying—especially when it comes on suddenly, sends you to urgent care or an emergency department, or shows something alarming on a CT scan. If you live with endometriosis or adenomyosis, that fear can be mixed with frustration: “Is this just my usual pain, or is something actually wrong?”

Here’s an important—and practical—truth: endometriosis can grow on the appendix and can look exactly like acute appendicitis or even an appendiceal mass on imaging. A recent case report in Cureus highlights how easily this can be missed, and why you deserve a care team that keeps endometriosis on the table as a possibility.

What “appendix endometriosis” can feel like in real life

When endometriosis affects the appendix, your symptoms may overlap with common GI and appendix problems. Some people describe:

• • Sharp or cramping pain in the right lower abdomen
  • Pain that flares with your period (or began that way and later became more constant)
  • Nausea, bloating, bowel changes, or pain with bowel movements
  • Pain that doesn’t fit neatly into “GI” or “gynecologic” boxes

In the case described, the person’s right-sided pain started with menses and then became persistent, which is a pattern many patients recognize: cyclical pain that gradually becomes more frequent or continuous.

Why scans and bloodwork can still miss it

One of the most frustrating parts: imaging often can’t reliably tell appendiceal endometriosis apart from appendicitis or even a tumor.

In the case report, a CT scan showed an enlarged right-lower-quadrant structure that looked suspicious for acute appendicitis, and there was also concern about a possible malignant appendiceal mass. That is a common nightmare scenario for patients—being told, “We’re worried this could be cancer,” and then waiting for answers.

The key patient-centered point is this: there may be no distinctive radiology features that scream “this is endometriosis.” Even if you’ve already been diagnosed with endometriosis elsewhere, the appendix may not be the first thing clinicians think about.

Blood tests don’t necessarily clear things up either. In this report, CA-125 was elevated, but CA-125 is nonspecific—it can rise for many reasons (including endometriosis or any inflammatory process), and it cannot confirm what an appendiceal mass is.

How the diagnosis is actually confirmed

If imaging can’t reliably distinguish appendiceal endometriosis, what can?

Pathology. In the case report, the definitive answer came only after surgery, when the appendix tissue was examined: the pathology showed a 2.8 cm endometriotic mass involving the appendix wall, and importantly, it was negative for dysplasia and malignancy.

This matters for your decision-making because it explains why some situations move quickly to surgery: when imaging suggests appendicitis, a complicated infection, or a mass that could be malignant, clinicians often can’t “watch and wait” safely.

If this happens to you, it’s not “just random”—it can be a clue

A big takeaway from this case is that appendiceal endometriosis may be a sign of more widespread disease, especially if you have symptoms beyond the appendix area. If not suspected, the surgeons operating for what they think is appendicitis may not even look in the pelvis and certainly not the deep pelvis.

After the appendiceal surgery, pelvic MRI in this patient showed multiple other issues that commonly travel together:

• • Adenomyosis
  • Uterine fibroids (leiomyomas)
  • An ovarian endometrioma (a cyst associated with endometriosis)

If you’ve had unexplained right-sided abdominal pain plus heavy bleeding, cramping, deep pelvic aching, painful sex, infertility concerns, or bladder/bowel pain—this combination can be a signal to step back and reassess the whole picture, not just the appendix.

What treatment typically looks like (and what “success” may mean)

For appendiceal endometriosis that presents like appendicitis or a concerning mass, treatment often ends up being surgical removal of the appendix (appendectomy), because:

• • it treats the immediate problem (appendicitis-like symptoms or mass concern)
  • it provides tissue for diagnosis (pathology)
  • it can remove a pain generator

In the case report, surgical exploration and histology were consistent with advanced (stage IV) endometriosis, and the patient later reported resolution of pain after subsequent surgery.

A reality check that protects you: this is one person’s experience. It doesn’t guarantee that surgery will fully resolve pain for everyone, and it doesn’t tell us how long relief lasted. But it does support something many patients already learn the hard way—when endometriosis is outside the uterus/ovaries, it can drive symptoms that won’t be fixed by “IBS treatment” alone.

Practical takeaways you can use immediately

If you have right-lower-quadrant pain (especially if it’s cyclical, recurrent, or unexplained), you’re not being dramatic to ask whether endometriosis could be involved—even if the pain feels “too high” or “too GI” to be pelvic.

Bring these questions to your clinician (ER, primary care, GI, or gynecologist—whoever is in front of you):

• • “Could this be appendiceal or bowel-related endometriosis, especially since my pain is cyclical or I have known endometriosis/adenomyosis?”
  • “If the CT shows an appendiceal mass, what diagnoses are you considering besides cancer and appendicitis?”
  • “What is the plan to confirm the diagnosis—will pathology be done if surgery happens?”
  • “If my appendix is removed, do I need follow-up with an endometriosis-experienced gynecologist to look for additional disease?”
  • “If I still have pelvic pain afterward, what’s the next step—pelvic MRI, referral to an endometriosis specialist, or both?”

Red flags: when you should seek urgent care

Right-lower-quadrant pain can still be true appendicitis or other urgent conditions. Don’t self-diagnose. Seek urgent care if you have worsening localized pain, fever, vomiting, fainting, rigid abdomen, or pain that escalates quickly—especially if clinicians are worried about appendicitis or a complicated infection. A possible differentiating symptom is that in classic acute appendicitis periumbilical pain and nausea can acutely precede right lower quadrant pain.

Reality check: what we still don’t know (and why your case may differ)

This evidence comes from a single case report, which is useful for recognizing patterns but can’t tell you how common appendiceal endometriosis is, who is most at risk, or whether surgery is always the “best” option.

It also highlights a frustrating truth: even good imaging may not give a clear answer. Sometimes the only way to know what’s happening is through surgery and pathology—particularly when there’s concern for malignancy or complicated appendicitis.

What you can do is make sure your symptoms are interpreted in context: your menstrual cycle pattern, your endometriosis/adenomyosis history, and whether you have other pelvic pain features that suggest a broader endometriosis picture.