What is the ideal thickness of the endometrial lining in a postmenopausal woman?

Endometrial Thickness in Postmenopausal Women

In postmenopausal women, the endometrial lining should be 4 mm or less in thickness, as measured by transvaginal ultrasound. 1

Normal Endometrial Thickness and Clinical Significance

• An endometrial thickness of 4 mm or less in a postmenopausal woman conveys a negative predictive value for endometrial cancer of nearly 100% 1
• When the endometrium measures ≥5 mm in a postmenopausal woman, endometrial tissue sampling is generally recommended 1
• If repeat imaging shows the endometrium remains <4 mm in a postmenopausal woman, the negative predictive value for cancer remains nearly 100% 1

Evaluation Algorithm for Postmenopausal Women

Initial Assessment:

• Transvaginal ultrasound (TVUS) should be combined with transabdominal ultrasound whenever possible for complete assessment of pelvic structures 1
• TVUS is considered the first-line screening test for endometrial cancer in women with postmenopausal bleeding 1
• The measurement of endometrial thickness should be the first step in the diagnostic pathway 1

Follow-up Based on Endometrial Thickness:

• ≤4 mm: No further evaluation needed if asymptomatic 1
• ≥5 mm: Endometrial tissue sampling recommended 1
• 4.1-8 mm: Studies show significant prevalence of endometrial hyperplasia and cancer, warranting histological assessment 2

Special Considerations

• For postmenopausal women without vaginal bleeding but with incidentally found thickened endometrium:

  • Thickness <15 mm might not warrant endometrial biopsy sampling 3
  • However, this is controversial as other studies suggest evaluation of any thickness >4 mm 1, 2

• Echogenic fluid in the endometrial cavity is a significant risk factor for pathology:

  • Postmenopausal women with echogenic endometrial fluid collection should undergo endometrial sampling regardless of endometrial thickness 4
  • Clear fluid with endometrial lining ≤3 mm may not require endometrial sampling, but endocervical sampling is recommended 4

Diagnostic Techniques

• Endometrial sampling techniques like Pipelle or Vabra devices are highly sensitive for detecting endometrial carcinoma (99.6% and 97.1% respectively) 1
• If endometrial sampling is negative but endometrial thickness is ≥10 mm, hysteroscopic evaluation with directed biopsy is strongly recommended 5
• Sonohysterography can help distinguish between focal and diffuse pathology when initial TVUS demonstrates a focal endometrial abnormality 1

Pitfalls and Caveats

• TVUS is sensitive for evaluating endometrial thickness but cannot reliably determine the etiology of endometrial thickening 1
• Pipelle sampling has limitations with a sensitivity of about 87.65% 5
• Women with lower BMI may be more likely to have false-negative Pipelle results requiring hysteroscopy for diagnosis 5
• Abnormal echogenicity and texture of the endometrium correlate with significant underlying uterine pathology even when thickness is normal 1
• The European Society for Medical Oncology (ESMO) guidelines recommend using a cut-off level of ≤3 mm for postmenopausal women 1, which is slightly more conservative than the 4 mm threshold in other guidelines 1