What are the criteria for diagnosing endometriosis?

Diagnostic Criteria for Endometriosis

Endometriosis is diagnosed clinically based on characteristic symptoms and imaging findings, without requiring surgical confirmation before initiating treatment. 1

Clinical Diagnostic Framework

The modern approach to endometriosis diagnosis has shifted away from mandatory surgical confirmation toward a clinical diagnosis model that prioritizes earlier intervention and reduced morbidity. 1, 2

Key Clinical Features

Symptom patterns that establish clinical diagnosis include:

• Dysmenorrhea (painful menstruation) 3, 1
• Dyspareunia (painful intercourse) 3, 1
• Dyschezia (painful bowel movements) 3, 1
• Dysuria (painful urination) 3, 1
• Chronic pelvic pain 1
• Infertility (present in approximately 50% of cases) 3, 1

Physical examination findings suggestive of endometriosis:

• Nodularity on pelvic examination 1
• Fixed retroverted uterus 1
• Tender uterosacral ligaments 1
• Adnexal masses 4

Imaging Criteria (First-Line Diagnostic Approach)

Transvaginal ultrasound (TVUS) is the recommended initial imaging modality, with expanded protocol TVUS being superior to standard pelvic ultrasound. 1

Expanded Protocol TVUS Requirements

The expanded protocol differs substantially from routine pelvic ultrasound and requires specialized training (minimum 40 examinations learning curve): 3

• Evaluation of uterosacral ligaments 3
• Assessment of anterior rectosigmoid wall 3
• Dynamic sliding maneuvers to evaluate organ mobility 3
• Bowel preparation or enema for detection of bowel lesions 3
• Evaluation of appendix and diaphragm 3

Critical pitfall: Standard TVUS has significantly lower sensitivity than expanded protocol TVUS for detecting deep endometriosis. 3, 1

MRI Criteria

MRI pelvis without IV contrast is sufficient for detecting deep endometriosis, though MRI with IV contrast is highly recommended to differentiate endometriomas from ovarian malignancies. 1

MRI diagnostic features:

• Endometriomas: High signal on T1-weighted images with low signal on T2-weighted images (T2 shading) 3
• T2 dark spot sign: 93% specificity for differentiating endometriomas from hemorrhagic cysts 3
• Deep infiltrating endometriosis: Low signal intensity regions with or without hyperintense foci on T2- and/or T1-weighted images 3
• Adhesions/cul-de-sac obliteration: Fixed retroverted uterus, low-signal intensity bands, obliteration of organ interfaces 3

MRI performance by location:

• Intestinal endometriosis: 92.4% sensitivity, 94.6% specificity 3
• Deep infiltrating endometriosis (posterior locations): 88% sensitivity, 83.3% specificity 3
• Bladder wall endometriosis: 50% sensitivity, 97.3% specificity 3

MRI protocol recommendations:

• Moderate bladder distention 3
• Vaginal contrast to improve lesion conspicuity 3

When to Use MRI vs. TVUS

Use MRI when:

• TVUS findings are inconclusive 5, 1
• Coexisting pathologies like leiomyomas are present (TVUS sensitivity drops to 33.3%) 5
• Assessment for deep infiltrating endometriosis is required prior to fertility-sparing surgery 3
• Differentiating endometriomas from ovarian malignancies 1

Transabdominal ultrasound can be added to widen the field of view for urinary tract and bowel involvement beyond the pelvis. 1

Laboratory Testing

CA-125 has no clinical utility for diagnosis. 1

• May be helpful for monitoring clinical response in patients with confirmed extrauterine disease 1
• Can be falsely elevated due to peritoneal inflammation/infection 1

Surgical Diagnosis (Historical Gold Standard)

Laparoscopy with histologic confirmation was historically considered the gold standard but is no longer required before initiating empiric treatment. 3, 1, 2

Current role of surgery:

• Preoperative imaging reduces morbidity and mortality by decreasing incomplete surgeries requiring reoperation 3, 1
• Surgery is reserved for definitive treatment (surgical excision by a specialist) rather than diagnosis 3
• Imaging helps inform patient decision-making, surgical planning, and management 3, 1

Important limitation: Correlation between laparoscopic observations and histological findings is often low. 4

Critical Diagnostic Pitfalls

Do not assume negative imaging excludes endometriosis: Superficial peritoneal disease is poorly detected by all imaging modalities. 1

Do not use CT pelvis for initial imaging: CT has no role in standard endometriosis diagnosis. 3, 1

Do not delay treatment waiting for surgical confirmation: The diagnostic delay from symptom onset to surgical diagnosis averages 4-11 years, contributing to significant morbidity. 2

Do not rely on symptom severity to predict disease stage: Correlation between symptoms and stage of endometriosis is poor. 4

Diagnostic Algorithm

1. Clinical assessment: Identify characteristic pain patterns (dysmenorrhea, dyspareunia, dyschezia, dysuria) and/or infertility 1
2. Physical examination: Assess for nodularity, fixed retroverted uterus, tender uterosacral ligaments 1
3. Initial imaging: Expanded protocol TVUS (if available) or standard TVUS plus transabdominal ultrasound 1
4. Second-line imaging: MRI pelvis if TVUS inconclusive or when assessing for deep infiltrating disease 1
5. Initiate empiric treatment based on clinical diagnosis without requiring surgical confirmation 1, 2
6. Reserve surgery for definitive treatment or when medical management fails 3