What are the key differences between adenomyosis and endometriosis in terms of epidemiology, clinical presentation, diagnostic approach, and management?

Adenomyosis vs Endometriosis: Key Differences

Adenomyosis and endometriosis are distinct diseases that differ fundamentally in anatomical location: adenomyosis involves ectopic endometrial tissue within the myometrium itself, while endometriosis consists of endometrial-like tissue located outside the uterus entirely. 1, 2

Fundamental Pathologic Distinction

Location defines the disease:

• Adenomyosis: Endometrial glands and stroma invade into and reside within the myometrial wall of the uterus 1, 2, 3
• Endometriosis: Endometrial-like tissue exists outside the endometrial cavity—on peritoneal surfaces, ovaries, bowel, bladder, ureter, or other pelvic/extrapelvic locations 4, 5

Despite sharing estrogen-dependent growth patterns and some overlapping symptoms, these are considered two separate clinical entities 1, 6

Epidemiology & Demographics

Adenomyosis:

• Historically thought to affect primarily multiparous women over age 40, but now increasingly diagnosed in younger reproductive-age women and infertile patients using modern imaging 2, 3
• Often coexists with endometriosis and uterine fibroids 2

Endometriosis:

• Affects approximately 10% of women of reproductive age 4, 5
• Impacts an estimated 176 million women worldwide 5
• Approximately 50% of patients with endometriosis experience infertility 4, 5

Clinical Presentation

Adenomyosis presents with:

• Abnormal uterine bleeding and heavy menstrual bleeding 2, 3
• Pelvic pain, dysmenorrhea, and dyspareunia 2, 3
• Infertility (negative impact on IVF outcomes documented) 1, 2
• Diffusely enlarged, tender uterus on examination 3

Endometriosis presents with:

• Pelvic pain as the most common symptom: dysmenorrhea (pain commencing before menses), deep dyspareunia (exaggerated during menses), or sacral backache with menses 4, 5
• Dysuria, dyschezia, or menorrhagia depending on lesion location 4
• Infertility in approximately 50% of cases 4, 5
• Variable presentation ranging from asymptomatic to severe symptoms interfering with daily activity 4, 5

Critical pitfall: Pain severity correlates poorly with anatomical extent in endometriosis—the r-ASRM staging system shows very poor correlation with pain symptoms and quality of life 4, 5. However, depth of endometriosis lesions does correlate with pain severity 4

Diagnostic Approach

Adenomyosis diagnosis:

• Transvaginal ultrasound is the primary imaging modality, showing features such as myometrial thickening, heterogeneous myometrial echogenicity, and subendometrial linear striations 4, 3, 7
• MRI has sensitivity of approximately 78% and specificity of nearly 93% for adenomyosis diagnosis 4
• MRI can differentiate adenomyosis from leiomyomas when ultrasound findings are indeterminate 4
• Historically diagnosed only on hysterectomy specimens, but modern imaging now allows non-invasive diagnosis 1, 2, 3

Endometriosis diagnosis:

• Expanded protocol transvaginal ultrasound performed by specialists trained in endometriosis imaging can identify and "map" deep endometriosis, evaluating uterosacral ligaments, anterior rectosigmoid wall, appendix, and performing dynamic sliding maneuvers 4, 5
• These specialized ultrasounds require at least 40 examinations to achieve competency 4
• MRI serves as an alternative when ultrasound is incomplete or indeterminate 4
• Historically required diagnostic laparoscopy with histologic confirmation, but preoperative imaging is now strongly supported to reduce surgical morbidity and incomplete surgeries 4, 5
• Histologic examination should confirm endometrial lesions, especially those with nonclassical appearance 4
• CA-125 serum levels have limited utility, particularly for minimal or mild disease 4

Deep endometriosis is specifically defined as lesions extending deeper than 5 mm under the peritoneal surface or involving/distorting bowel, bladder, ureter, or vagina 4, 5

Classification Systems

Adenomyosis:

• Multiple classification systems exist based on imaging features and anatomical distribution (internal vs external myometrium involvement) 3, 7
• No standardized consensus classification due to heterogeneity in imaging techniques and clinical spectrum 7
• Different phenotypes may have distinct epidemiological and clinical characteristics 3

Endometriosis:

• r-ASRM classification is the longest-established system but has severe limitations: very poor correlation with pain/quality of life, poor correlation with fertility outcomes, and inadequate description of deep endometriosis 4, 5
• Enzian classification should be used alongside r-ASRM when deep endometriosis is present to provide complete operative description 4, 5
• Endometriosis Fertility Index (EFI) is validated specifically for predicting fertility outcomes post-surgery 5
• The American Society for Reproductive Medicine recommends a "classification toolbox" combining r-ASRM, Enzian, and EFI 5

Management Considerations

Adenomyosis:

• Requires lifelong management plan including pain control, bleeding control, fertility preservation, and monitoring for pregnancy complications 2
• Medical options include hormonal treatments (GnRH agonists, danazol, steroid-releasing IUDs) 6
• Surgical management ranges from conservative procedures to hysterectomy 2

Endometriosis:

• Medical therapy (progestins, danazol, oral contraceptives, NSAIDs, GnRH agonists) reduces lesion size and provides pain relief but does not eradicate lesions 4
• GnRH agonist therapy for at least 3 months or danazol for at least 6 months provides equivalent pain relief 4
• Add-back therapy with GnRH agonists reduces bone mineral loss without compromising pain relief efficacy 4
• Surgical excision by a specialist is considered definitive treatment 4
• Up to 44% of patients experience symptom recurrence within one year after surgery 4
• No evidence that medical or surgical therapy improves future fertility outcomes 4
• Annual economic burden estimated at $69.4 billion, comparable to other chronic diseases 4, 5

Critical caveat: Both conditions are estrogen-dependent and hormone-responsive, with adenomyosis and endometriosis showing altered estrogen metabolism including aromatase expression patterns 6