Normal Endometrial Thickness in Postmenopausal Women
In postmenopausal women, the endometrial lining should measure ≤4 mm by transvaginal ultrasound, which provides a nearly 100% negative predictive value for endometrial cancer. 1
Established Thresholds
The American College of Radiology has established clear cutoffs for endometrial thickness assessment in postmenopausal women:
- ≤4 mm is considered normal and requires no further evaluation in asymptomatic postmenopausal women 1, 2
- ≥5 mm warrants endometrial tissue sampling to rule out malignancy 1, 2
- The European Society for Medical Oncology uses a slightly more conservative threshold of ≤3 mm, though this is less commonly applied in practice 1, 2
Variation by Symptom Status
The threshold differs based on whether the patient has symptoms:
- Asymptomatic women: An endometrial thickness ≤11 mm may be acceptable without immediate biopsy, though this carries a higher baseline cancer risk of 6.7% if >11 mm 3
- Symptomatic women with postmenopausal bleeding: The ≤4-5 mm threshold should be strictly applied, as any measurement >5 mm requires investigation 1, 2
Time Since Menopause Considerations
Endometrial thickness naturally varies with years since menopause (YSM):
- First 5 years postmenopause: Mean thickness is 2.3 mm, decreasing by 0.03 mm/year 4
- 5-13 years postmenopause: Thickness stabilizes at approximately 1.8 mm 4
- Beyond 13 years: Minimal increase of 0.01 mm/year 4
Diagnostic Approach
Transvaginal ultrasound (TVUS) combined with transabdominal ultrasound should be the initial imaging modality for complete pelvic assessment 1, 2:
- TVUS is the first-line screening test for endometrial cancer in postmenopausal women 1, 2
- Measurement of endometrial thickness should be the first step in the diagnostic pathway 1
When to Proceed with Tissue Sampling
Endometrial biopsy is indicated when:
- Thickness ≥5 mm in any postmenopausal woman with bleeding 1, 2
- Thickness >11 mm in asymptomatic women, as this carries a 6.7% cancer risk 3
- Abnormal echogenicity or texture even with normal thickness, as this may indicate underlying pathology 1, 2
Critical Pitfalls to Avoid
- Do not rely solely on thickness measurement - TVUS cannot determine the etiology of endometrial thickening, only detect its presence 1, 2
- Negative office-based biopsy is not definitive when significant thickening is present; consider hysteroscopy with directed biopsy if clinical suspicion remains high 2
- Intracavity fluid can falsely elevate measurements - ensure proper technique to distinguish fluid from true endometrial thickening 5
- Body mass index affects measurements - higher BMI correlates with increased endometrial thickness in asymptomatic women 6
Sampling Techniques
When tissue sampling is required:
- Pipelle or Vabra devices have high sensitivity (99.6% and 97.1% respectively) for detecting endometrial carcinoma 1, 2
- Hysteroscopy with directed biopsy is preferred over blind sampling for focal lesions 1, 2
- Sonohysterography can distinguish focal from diffuse pathology when initial TVUS is inconclusive 1, 2