Adenomyosis is a benign uterine condition in which endometrial-type glands and stroma are present within the muscular wall of the uterus, known as the myometrium. The abnormal tissue is associated with surrounding muscular hypertrophy, inflammation and structural changes within the uterine wall. Adenomyosis can cause heavy or prolonged menstrual bleeding, painful menstruation, chronic pelvic pain and an enlarged or tender uterus, although some people have few or no symptoms.
It is distinct from Endometriosis, where endometrial-like tissue occurs outside the uterus, although the two conditions can coexist. The condition can occur during the reproductive years and is increasingly recognised through modern imaging, particularly transvaginal ultrasound and magnetic resonance imaging. Historically, definitive diagnosis was often made after hysterectomy through pathological examination, but imaging now allows many cases to be diagnosed or strongly suspected without removing the uterus.
The precise cause of Adenomyosis is not fully established. Proposed mechanisms include inward growth or displacement of endometrial tissue into the myometrium, tissue injury and repair processes at the boundary between endometrium and myometrium, metaplastic changes and developmental factors. Local hormonal signalling, inflammation and altered uterine muscle function contribute to the disease environment. Adenomyotic tissue can respond to ovarian hormones and undergo cyclical changes, producing local inflammation and stimulating changes in the surrounding myometrium.
Increased uterine vascularity and abnormal contractility may contribute to heavy bleeding and pain. The disease can therefore be understood as both a structural and hormonally responsive disorder. Because several mechanisms may contribute, Adenomyosis is unlikely to have one universal initiating event in every affected person.
Symptoms of Adenomyosis commonly include heavy menstrual bleeding and dysmenorrhoea, particularly when symptoms develop or worsen during the reproductive years. Some people experience pelvic pressure, chronic pelvic discomfort or pain during sexual activity. The uterus may become diffusely enlarged and tender, although these findings are not present in every case. Heavy bleeding can lead to iron-deficiency anaemia, producing fatigue, reduced exercise tolerance or other systemic consequences.
Symptoms may overlap substantially with Endometriosis, fibroids and other causes of abnormal uterine bleeding, which can make clinical differentiation difficult. Some people have incidental imaging findings without major symptoms, emphasising that radiological disease and clinical burden are not identical. Assessment should therefore consider both anatomical findings and the person's actual symptoms and functional impact.
Imaging has transformed recognition of Adenomyosis. Transvaginal ultrasound can show features such as an enlarged or globular uterus, heterogeneous myometrial texture, asymmetry of the uterine walls, small myometrial cysts and changes in the boundary between the endometrium and myometrium. Magnetic resonance imaging can provide additional anatomical detail and may be particularly useful when ultrasound findings are uncertain or when treatment planning requires precise mapping.
No imaging feature is perfectly specific in every patient, and interpretation depends on operator expertise and the presence of coexisting conditions. Histological examination of the uterus after hysterectomy remains a definitive pathological method, but it is not a prerequisite for diagnosis in every clinical situation. Modern management increasingly aims to diagnose and treat symptomatic disease without requiring definitive surgery solely to establish the diagnosis.
Adenomyosis has important relationships with fertility and pregnancy, although the precise magnitude of reproductive effects varies between studies. Changes in uterine architecture, inflammation, abnormal contractility and altered implantation conditions may contribute to reduced fertility in some patients. The condition can coexist with Endometriosis and other reproductive disorders, making it difficult to isolate its independent effect on conception. During pregnancy, adenomyosis has been associated in research with several adverse outcomes, although individual risk depends on disease characteristics and other maternal factors. Fertility counselling therefore needs to consider the person's age, reproductive history, symptoms, imaging findings and other causes of infertility rather than assuming that Adenomyosis alone determines reproductive outcome. Research continues to clarify which imaging patterns are most clinically meaningful.
Treatment depends on symptom severity, reproductive goals, age and whether preservation of the uterus is desired. Anti-inflammatory medicines can reduce pain, while hormonal treatments can reduce menstrual bleeding and suppress cyclical endometrial stimulation. Progestogen-releasing intrauterine systems can be effective for heavy bleeding in suitable patients, while other hormonal options may be used according to individual circumstances. Uterine-sparing procedures have been investigated and can be appropriate for selected patients, but their availability and effectiveness depend on disease distribution and local expertise. Hysterectomy is definitive treatment because it removes the uterus containing the adenomyotic tissue, but it is major surgery and eliminates the possibility of carrying a future pregnancy. Management therefore requires careful discussion of symptom control, fertility and the person's treatment priorities.
The natural history of Adenomyosis is incompletely defined because historical diagnosis depended heavily on pathological examination after hysterectomy, which biased research populations towards people with severe symptoms. Modern imaging has identified milder and asymptomatic forms, broadening understanding of the condition. It is sometimes described as more common in later reproductive years, but it can occur in younger patients as well.
Previous uterine procedures, childbirth and other factors have been associated with the condition in observational research, although associations do not establish a single cause. Improved imaging has also revealed that Adenomyosis can be focal or diffuse, with focal disease concentrated in particular regions and diffuse disease affecting a broader portion of the myometrium. These patterns can influence symptoms and treatment planning.
A common misconception is that Adenomyosis and Endometriosis are simply two names for the same condition. Both involve endometrial-type tissue and can produce pelvic pain, but their principal anatomical locations differ. Adenomyosis involves the muscular wall of the uterus, whereas Endometriosis involves tissue outside the uterine cavity. Another misconception is that an enlarged uterus always indicates Adenomyosis; fibroids, pregnancy and other conditions can also enlarge the uterus.
The presence of Adenomyosis on imaging likewise does not automatically explain every pelvic symptom. Its importance lies in recognising a distinct structural and hormonally responsive uterine disorder that can cause substantial bleeding and pain, overlap with other gynaecological conditions and require long-term management tailored to reproductive goals.
