Adenomyosis
Adenomyosis is a condition in which endometrial tissue—the lining that normally sits inside the uterine cavity—becomes embedded within the muscular wall of the uterus. That misplaced tissue responds to hormonal cycles like normal lining does, bleeding and inflaming within the muscle, which thickens and enlarges in response. The result is typically heavy, painful periods and a bulky, tender uterus. For most of the last century it could only be confirmed after hysterectomy, which meant it was underdiagnosed and often dismissed. Modern ultrasound and MRI now identify it reliably in women who still have their uterus, and that shift has made earlier recognition and a much wider range of treatment options possible.
What is it?
The uterus has three layers: an inner lining called the endometrium, which thickens and sheds with each menstrual cycle; a thick muscular wall called the myometrium; and an outer serosal covering. Between the endometrium and the bulk of the myometrium lies a transitional layer known as the junctional zone, which has a distinct structure and appearance on imaging and plays an important role in this condition.
In adenomyosis, endometrial glands and their surrounding supporting tissue are found within the myometrium, where they do not belong. This ectopic tissue remains hormonally responsive, so it proliferates and bleeds in response to the same cycle that governs the normal lining. Because the blood has nowhere to escape, it accumulates within the muscle, causing inflammation, and the surrounding muscle responds by thickening and increasing in bulk. The uterus becomes enlarged, globular, and often tender, and its ability to contract in a coordinated way is disrupted.
That last point explains much of the symptom picture. Normal menstruation involves organised contractions of the uterine muscle that help control bleeding. In adenomyosis, the disordered muscle contracts abnormally, contributing to both the heavy bleeding and the deep cramping pain that characterise the condition.
How the tissue gets there is not fully settled, and more than one mechanism may operate. The most widely held explanation is that the boundary between endometrium and myometrium becomes disrupted, allowing endometrial tissue to invade downward into the muscle—which fits with the association between adenomyosis and previous uterine surgery such as caesarean section or curettage. Other proposed mechanisms include the development of adenomyosis from embryonic tissue remnants within the myometrium, and the involvement of stem cells. Oestrogen drives the process, and local oestrogen production within the lesions themselves appears to sustain it.
Adenomyosis takes several forms, and the distinction affects treatment options.
Diffuse adenomyosis involves widespread scattered tissue throughout much of the uterine wall, producing generalised enlargement. This is the more common pattern.
Focal adenomyosis is confined to one area, and when it forms a discrete mass it is called an adenomyoma. This can resemble a fibroid on imaging, though the two behave differently and are managed differently.
Cystic adenomyosis is uncommon and features a distinct blood-filled cavity within the muscle. Adenomyosis can also be classified as superficial or deep depending on how far into the muscle it extends.
An important relationship exists with two other conditions. Endometriosis, in which endometrial-type tissue grows outside the uterus altogether, coexists with adenomyosis in a substantial proportion of women, and the two share features while being distinct. Fibroids also frequently coexist, and because both cause heavy bleeding and an enlarged uterus, distinguishing which is responsible for a woman’s symptoms is a common clinical challenge—and one where imaging is genuinely decisive.
The symptoms of adenomyosis are the reason it matters, and they are frequently underestimated.
Heavy menstrual bleeding is the most common. Periods may be prolonged, with clots, and heavy enough to interfere with work, exercise, and daily activity. Chronic blood loss commonly causes iron deficiency anaemia, producing fatigue, breathlessness on exertion, and reduced concentration, and this is sometimes the presenting problem.
Painful periods are the other hallmark. The pain is characteristically deep, cramping, and dragging, often begins before bleeding starts, and tends to worsen progressively over years—a pattern women frequently describe as their periods having become steadily worse rather than always having been bad.
Chronic pelvic pain outside menstruation affects a proportion of women, as does pain during or after intercourse, particularly with deep penetration.
A sense of pelvic pressure, bloating, or fullness arises from the enlarged uterus, and some women notice a change in abdominal shape.
Fertility and pregnancy are affected in ways that are increasingly recognised. Adenomyosis is associated with reduced implantation and pregnancy rates, higher miscarriage rates, and increased risk of certain pregnancy complications including preterm birth, pre-eclampsia, abnormal placentation, and postpartum haemorrhage. The effect is not absolute—many women with adenomyosis conceive and have uncomplicated pregnancies—but it is a recognised consideration in fertility care.
A meaningful proportion of women have adenomyosis without symptoms, and it is identified incidentally on a scan performed for another reason. In this situation it generally requires no treatment.
One aspect of this condition deserves direct acknowledgement. Because adenomyosis could historically only be confirmed after hysterectomy, and because heavy painful periods are common and often normalised, many women experienced years of symptoms being minimised before a diagnosis was reached. Delays measured in years are well documented. The shift to imaging-based diagnosis has changed this considerably, but it remains worth stating that severe period pain and bleeding heavy enough to disrupt life are not something to be endured without explanation.
Diagnosis is now imaging-based rather than surgical.
Transvaginal ultrasound is the first-line investigation and performs well in experienced hands. Recognised features include a uterus that is enlarged and globular rather than pear-shaped; asymmetric thickening, with the front and back walls differing noticeably; small cystic spaces within the muscle representing pockets of trapped blood; echogenic islands and short lines or buds extending from beneath the endometrium into the muscle; fan-shaped shadowing, in which alternating light and dark striations radiate through the muscle; increased blood flow passing through the affected area rather than around it, which distinguishes it from a fibroid; and an irregular, interrupted, or poorly defined junctional zone. A consensus set of standardised reporting criteria has improved consistency between examinations and is increasingly used.
The distinction from fibroids is one of the most practically important tasks. A fibroid is typically well-circumscribed and round with a clear boundary and blood vessels running around its edge, and it can usually be separated from surrounding muscle. Adenomyosis is ill-defined, blends into the surrounding muscle without a clear border, and has vessels passing through it. Recognising which is present matters because treatment differs substantially.
MRI of the pelvis is the reference standard and is particularly valuable when ultrasound is inconclusive, when multiple fibroids obscure assessment, when the uterus is very enlarged, or when planning surgery or a uterus-preserving procedure. Thickening of the junctional zone beyond approximately 12 millimetres is a key criterion, along with the ratio of junctional zone to total myometrial thickness and the presence of small bright foci within the muscle representing trapped blood.
Examination may reveal a diffusely enlarged, softened, and tender uterus, though this is neither sensitive nor specific.
Blood tests do not diagnose adenomyosis but assess its consequences: a full blood count and ferritin identify iron deficiency anaemia, which is common and frequently undertreated.
Endometrial sampling is not required to diagnose adenomyosis but is performed when there is a need to exclude other causes of abnormal bleeding, particularly in women over 45, those with risk factors for endometrial pathology, or where bleeding is irregular rather than simply heavy.
Important to Know
Treatment is directed at symptoms rather than at eliminating the condition, since only hysterectomy removes adenomyosis entirely. The right approach depends heavily on how troublesome symptoms are, a woman’s age, and whether she wishes to have children, and there is no single correct answer. Care is typically coordinated by gynaecologists, with fertility specialists involved where relevant.
Asymptomatic adenomyosis found incidentally requires no treatment and no routine follow-up. This is worth stating clearly, since the term can sound alarming on a report.
Medical treatment is the starting point for most women with symptoms.
The levonorgestrel-releasing intrauterine system is often the preferred first-line option. It delivers progestogen directly to the uterus, substantially reduces menstrual bleeding, improves pain, and treats the condition and provides contraception simultaneously. Evidence supports its effectiveness in adenomyosis specifically, and many women achieve very light periods or none at all. It can be less reliable in a substantially enlarged uterus, where expulsion is more likely.
Tranexamic acid reduces menstrual blood loss and is taken only during bleeding. Non-steroidal anti-inflammatory drugs reduce both bleeding and pain and are most effective when started as periods begin.
Combined hormonal contraceptives, used continuously to reduce or eliminate withdrawal bleeds, help many women. Progestogens including dienogest have good evidence for pain reduction in adenomyosis and related conditions.
GnRH agonists and antagonists suppress ovarian hormone production and produce marked improvement, but they induce a temporary menopausal state with hot flushes and bone density loss. They are therefore generally used for limited periods, before surgery, or with add-back hormone therapy allowing longer use.
Iron deficiency deserves specific attention. It is extremely common in this condition and is frequently under-recognised and undertreated. Ferritin should be checked rather than relying on haemoglobin alone, since iron stores deplete well before anaemia appears, and fatigue from low iron is often attributed to other causes. Oral iron is usually sufficient, with intravenous iron used where absorption is poor or depletion severe.
Uterus-preserving procedures offer options between medication and hysterectomy. Uterine artery embolisation reduces blood supply to the affected tissue and provides meaningful symptom improvement in a substantial proportion of women, with a lower success rate in adenomyosis than in fibroids and some loss of benefit over time. High-intensity focused ultrasound uses focused energy to destroy affected tissue without incisions and is available at a limited number of centres. Surgical excision of a focal adenomyoma is possible where disease is localised, though it is technically demanding and the uterus is generally weakened, which has implications for future pregnancy and delivery.
Hysterectomy is the only definitive cure and is highly effective, eliminating both bleeding and pain in almost all cases. It is a reasonable choice for women with severe symptoms who have completed their families and for whom other treatments have failed, and it should be presented as a legitimate option rather than a last resort—many women report substantial improvement in quality of life afterwards. Endometrial ablation is generally less effective in adenomyosis than in other causes of heavy bleeding, because the affected tissue extends deeper than ablation reaches.
For women trying to conceive, management requires particular care. Most medical treatments are contraceptive and therefore unsuitable. A period of GnRH agonist treatment before embryo transfer improves outcomes in some studies and is used in selected cases. Adenomyosis is associated with increased risks in pregnancy, so care is generally provided with awareness of these, including monitoring for growth restriction, preterm birth, and postpartum bleeding. This is a field where evidence is still developing and individualised specialist input is valuable.
Symptoms improve after menopause, since the condition is oestrogen-dependent and the tissue becomes inactive once ovarian hormone production ceases. For women approaching menopause with manageable symptoms, this can reasonably influence the decision to persist with medical treatment rather than pursue surgery.
Adenomyosis is a benign condition and does not develop into cancer. Coexisting endometriosis should be considered where pain is prominent, since treating one without recognising the other can leave symptoms unexplained.
Care is typically coordinated by gynaecology, with fertility, pain management, radiology, and haematology input as needed. Imaging, laboratory, and clinical findings are interpreted alongside symptoms, reproductive plans, and preferences rather than in isolation.
Patient education plays an important role. Understanding that adenomyosis is a real and identifiable condition rather than an unexplained set of symptoms, that heavy painful periods are not something to simply tolerate, that several effective treatments exist short of surgery, that iron deficiency should be actively looked for, and that symptoms resolve after menopause all contribute to appropriate care.
Red flag symptoms include bleeding heavy enough to soak through protection hourly, pass large clots repeatedly, or cause dizziness, fainting, breathlessness, or a racing heart; bleeding between periods or after intercourse; any bleeding after menopause; severe pelvic pain that is sudden, different from usual period pain, or accompanied by fever; a rapidly enlarging uterus or abdominal swelling; pain unrelieved by usual measures; and persistent fatigue, pallor, or breathlessness suggesting significant anaemia. These warrant prompt medical evaluation, urgently where bleeding is heavy or symptoms of significant blood loss are present.