Adenomyosis Basics: What Is It and Why Is It Overlooked?

Adenomyosis is one of those diagnoses many people hear only after years of painful periods, heavy bleeding, or sub-fertility stress—often after being told their symptoms are “normal” or “just part of getting older.” If you’ve recently come across the term and feel confused (or dismissed), you’re not alone.

So, how common is it? Most information published seems to indicate that adenomyosis it is less common than endometriosis. In fact, it is often stated that it is only present in about 1% of women. The problem is that imaging is only about 70% sensitive in finding adenomyosis and the only way to know for sure is after the pathologist finds it on hysterectomy specimen evaluation. In most published papers adenomyosis is found in 20-25% of uteri, and as high in 60% in other studies. This means it is entirely plausible that adenomyosis is at least as common as—if not more far more common than—endometriosis in the general population.

Recent research across imaging, inflammation, and uterine muscle biology helps explain two things at once: what adenomyosis is inside the body, and why it’s so often missed. This article draws on multiple recent studies and reviews to give you a clear starting point—so you can recognize the condition, understand how it overlaps with endometriosis, and know what to ask for next.

What is adenomyosis, in plain language?

Adenomyosis happens when tissue similar to the uterine lining (endometrium) is found within the muscular wall of the uterus (the myometrium). Instead of staying where it normally belongs, this tissue can contribute to swelling, irritation, and—over time—changes in the uterine muscle itself.

A useful way to think about it is: adenomyosis isn’t only a “lesion problem.” It can become a whole-uterus environment problem, involving hormones, inflammation, how the normal endometrial uterine lining behaves, and the way the uterine muscle contracts.

Large overviews describe adenomyosis (and endometriosis) as chronic, hormone-dependent inflammatory diseases, with a major role for estrogen and a reduced ability of progesterone to “calm” the tissue (often called progesterone resistance). That hormone/inflammation mix helps explain why symptoms can be persistent and why long-term management is often needed rather than a one-time fix through some of the interventions available like surgery or microwave or freezing and so on.

Why adenomyosis can hurt: more than “just cramps”

Many people are simply told adenomyosis triggers “bad cramps,” but newer mechanistic research gives a much clearer explanation: adenomyosis may change how the uterine muscle behaves as a whole.

A 2026 study examining human uterine muscle tissue (and a mouse model) found patterns consistent with more fibrosis (scar-like stiffening) in adenomyosis, especially close to adenomyosis areas. Importantly, pain severity tracked with these tissue changes. The study linked worse period pain (dysmenorrhea) with:

• More fibrosis and higher oxytocin receptor signaling (signals that can promote stronger contractions)
• Lower activity in a pathway that supports muscle relaxation via nitric oxide (NO)

In simple terms, this line of sceintific evidence supports an idea many patients recognize: the pain may come from a uterus that is not only inflamed, but also more “irritable” and hypercontractile—contracting more strongly or irregularly. This doesn’t change today’s standard diagnosis, but it helps validate that adenomyosis pain can have a real, physical driver beyond a generic “sensitivity” explanation.

Common symptoms—and why symptoms don’t always “match” the scans

Adenomyosis is often associated with:

• Heavy menstrual bleeding
• Severe period pain
• Pelvic pressure or bloating
• Painful sex in some cases
• Bowel/bladder discomfort for some people
• Fertility challenges for some people

But symptoms vary widely. One reason adenomyosis is overlooked is that symptoms overlap with multiple conditions—fibroids, endometriosis, pelvic floor pain, irritable bowel syndrome, bladder pain syndrome—and sometimes multiple issues exist at the same time.

Research also suggests that coexisting adenomyosis and endometriosis is common, and that having both can worsen symptoms and complicate fertility. In one small 2026 pilot study of people with endometriosis, a large proportion also had imaging-diagnosed adenomyosis, and adenomyosis clustered strongly with another inflammatory condition (more on that below). While that study is too small to set rules, it reinforces a practical point: if you have persistent symptoms, it may not be “either/or.”

Why adenomyosis is often missed

1) The diagnosis used to depend on hysterectomy pathology

As mentioned already, adenomyosis is often “confirmed” only after hysterectomy, because the diagnosis was historically based on what a pathologist saw in the uterine muscle. That automatically biased understanding toward people with severe symptoms who ended up with a hysterectomy or those who were done with childbearing.

Modern reviews emphasize that prevalence is still uncertain partly because criteria have not always been standardized and many older studies relied on hysterectomy specimens. When imaging-based criteria are used, it appears that adenomyosis maybe far more common than many people were taught—on the order of around one in five in some ultrasound cohorts, and even higher in specific selected groups. That doesn’t mean one in five people will have severe symptoms; it means adenomyosis-like changes may be present more often than previously recognized.

2) Imaging quality and expertise matter a lot

Transvaginal ultrasound (TVUS) and MRI can be very helpful, but adenomyosis diagnosis is not just “did you get an ultrasound.” It’s also: was it done and interpreted by someone trained to look for adenomyosis features? There are different variations like central and diffuse, among other categories.

A 2025 review highlights that skilled imaging can diagnose endometriosis without surgery in many cases and discusses imaging as central for adenomyosis as well—reflecting a broader shift away from “you need surgery to know.” But in real life, access to expert ultrasound or adenomyosis-focused MRI protocols can be uneven, which contributes to delays.

3) Symptoms are normalized—especially painful periods

Research on endometriosis repeatedly documents long diagnostic delays (often years). While adenomyosis-specific delays aren’t always measured the same way, many patients experience a similar pattern: symptoms begin earlier, but the diagnosis comes later—sometimes after fertility evaluation, worsening bleeding, or repeated “normal” tests.

The underlying issue is not that patients failed to report symptoms; it’s that the healthcare system often underestimates pelvic pain and heavy bleeding, and adenomyosis hasn’t been emphasized in general training as much as other conditions. It is less often considered than endometriosis, which already lacks awareness in the general medical community.

4) Adenomyosis can be diffuse and subtle

Unlike a single visible fibroid, adenomyosis can be diffuse, blending into the muscle and changing the junction between the lining and the muscle (often called the junctional zone). That makes it harder to spot, harder to describe consistently, and easier to miss unless someone is looking for the pattern.

Is adenomyosis caused by hormones? inflammation? something you’re born with?

Most experts now describe adenomyosis as multifactorial—not one single cause. Several research themes help explain why:

• Hormones and inflammation: Reviews consistently frame adenomyosis as estrogen-influenced with inflammatory signaling. This helps explain why hormonal treatments often help symptoms, even if they don’t “erase” the condition.
• Uterine muscle changes over time: Tissue studies suggest a cycle where inflammation and micro-injury may contribute to fibrosis and abnormal contractions, which may then worsen pain.
• Possible developmental influences: A 2026 case–control study explored whether a specific body measurement called anogenital distance (AGD) differed in people with adenomyosis. One AGD measurement was, on average, shorter in the adenomyosis group, and the measurement reliability was strong. However, the ability to distinguish individuals with and without adenomyosis was only fair—meaning there was substantial overlap and it’s not useful as a stand-alone screen. Still, it contributes to a broader hypothesis that early-life developmental factors might influence risk in some people.

The most important patient takeaway: adenomyosis is not something you “caused” by doing the wrong workout, using tampons, or missing a supplement. The biology being studied points toward complex interactions between hormones, immune signaling, tissue repair, and possibly genetic predisposition.

Adenomyosis vs. endometriosis: what’s the difference (and why it matters)?

They’re related, and they can coexist, but they are not the same condition.

• Adenomyosis: lining-like tissue within the uterine muscle; tends to be tied to heavy bleeding and a globally “angry” uterus.
• Endometriosis: endometrial-like tissue outside the uterus (pelvis and sometimes beyond); often tied to pelvic pain, bowel/bladder pain, and infertility, depending on location.

Both are described in modern reviews as chronic inflammatory and estrogen-influenced, and both may involve progesterone resistance. The reason this matters is practical: if you only treat one condition (or only look for one), symptoms may persist.

Fertility: why adenomyosis can affect implantation and miscarriage risk

Adenomyosis is not just a “pain condition.” Multiple lines of evidence summarized in a 2026 review link adenomyosis to lower pregnancy rates and higher miscarriage risk, including in IVF/ICSI settings.

One key concept is the junctional zone, the interface between the lining and the muscle. The review describes this zone as important for both coordinated uterine contractions and immune regulation. When it becomes thickened or inflamed, the uterus may develop abnormal peristalsis (movement) and a less receptive environment for implantation. Inflammation-related molecules (cytokines such as IL‑6 and others) are repeatedly implicated as part of this environment, which also results in an inflamed endometrium. This inflammation means a more hostile environment for durable embryo implantation, resulting in no pregnancy or early miscarriages.

A practical nuance: not everyone with adenomyosis has infertility. But the evidence suggests that severity and the number of imaging features may matter, meaning “mild features” and “more extensive disease” can have different implications. This is exactly the kind of detail worth asking your clinician to interpret with you.

A “newer” overlap to know about: chronic endometritis (CE)

Chronic endometritis (CE) is a specific kind of inflammation inside the uterine lining diagnosed by biopsy and specialized staining (often looking for plasma cells with a marker called CD138). It’s not the same thing as adenomyosis, and it can’t be diagnosed from symptoms alone.

In a small 2026 pilot study in people with endometriosis, CE was common—and notably, adenomyosis was strongly clustered among those with CE. That doesn’t prove CE causes adenomyosis (or vice versa), and it doesn’t mean everyone with adenomyosis needs a biopsy. But it raises a patient-relevant possibility: for some people—especially those with infertility, recurrent implantation failure, or persistent symptoms—providers may increasingly consider whether an additional, treatable inflammatory factor is present.

Of note, BCL6 (via Receptiva testing) is a biomarker for endometriosis, not endometritis, though recent evidence shows it may also be elevated in adenomyosis. These are distinct diagnostic tests for different conditions. However, especially since endometriosis and adenomyosis often coexist, this is another pathway for sub-fertility and should be explored with your doctor. To be complete, the science behind testing and impact on fertility is imprecise. So, some reproductive endocrinologists (REI) advocate for this type of testing and others do not.

Practical takeaways: how to advocate for yourself now

• If you suspect adenomyosis, consider asking for adenomyosis-focused imaging (TVUS by an experienced sonographer and/or MRI when appropriate), not just “any ultrasound.”
• If you have endometriosis—or symptoms suggestive of it—ask whether your clinician has considered both endometriosis and adenomyosis, since coexistence is common.
• If fertility is a concern, ask your specialist to describe how extensive adenomyosis looks on imaging (e.g., diffuse vs focal patterns, junctional zone findings), because severity may influence expectations and planning.

Questions to ask your doctor

• “Do my symptoms and imaging suggest adenomyosis, endometriosis, or both?”
• “Was my ultrasound/MRI interpreted using standardized adenomyosis criteria and by someone experienced in it?”
• “Do my imaging features suggest mild vs more extensive adenomyosis and is it central or diffuse—and what does that mean for pain, bleeding, or fertility?”
• “Given my goals (pain control, bleeding control, pregnancy), what are the next steps to confirm the diagnosis and start treatment?”
• “In my situation, is there any reason to evaluate for other contributors like fibroids, pelvic floor dysfunction, or (in select fertility cases) chronic endometritis?”

What we still don’t know

Even with better imaging and stronger biological models, adenomyosis research still has gaps:

• No single cause explains all cases. Hormones, immune factors, tissue repair/fibrosis, and possibly developmental influences may all play roles.
• Not all imaging features predict symptoms perfectly. Some people have significant symptoms with subtle imaging, and others have imaging features with fewer symptoms.
• Many proposed biomarkers aren’t ready for clinic yet. Reviews discuss inflammatory cytokines as potential tests and even future anti-cytokine therapies, but these are not validated, routine tools right now.
• Smaller studies can hint at important overlaps (like CE), but larger, diverse studies are needed to know who benefits from added testing or targeted treatment.

Adenomyosis basics—what it is and why it’s overlooked—often come down to this: it’s common, real, and biologically complex, yet historically under-recognized. The good news is that presumptive diagnosis is increasingly possible without surgery, and understanding is rapidly improving. In the next posts in this series, we’ll build from this foundation into symptoms, diagnosis pathways, and the full range of treatment options (including what to consider if pregnancy is a goal).