Normal Endometrium Thickness on Ultrasound and MRI
The endometrium is the inner mucosal lining of the uterus, undergoing cyclical changes under hormonal influence throughout a woman’s reproductive life. Accurate measurement of endometrial thickness is a cornerstone of gynecologic imaging, used to screen for hyperplasia and malignancy, evaluate abnormal uterine bleeding, and assess treatment response. Establishing whether a measurement falls within normal limits requires knowledge of the patient’s menopausal status and hormonal therapy use.
Normal Reference Values
| Location | Measurement |
|---|---|
| Premenopausal | <16 mm |
| Postmenopausal, Symptomatic And Without Hormonotherapy | <5 mm |
| Postmenopausal, Symptomatic And With Hormonotherapy | <8 mm |
| Postmenopausal And Asymptomatic | <11 mm |
| Post-Abortion | <8 mm |
Clinical Significance
Endometrial thickness thresholds vary significantly by clinical context. In premenopausal women, a thickness up to 16 mm is considered within normal limits, reflecting physiological variation across the menstrual cycle. In postmenopausal women with symptomatic bleeding and without hormone therapy, the accepted upper limit is 5 mm; exceeding this threshold warrants further evaluation for endometrial carcinoma or hyperplasia. Women on hormone therapy have a higher normal ceiling of 8 mm, as exogenous estrogen and progesterone stimulate endometrial proliferation.
Asymptomatic postmenopausal women have a broader normal range up to 11 mm, reflecting lower pre-test probability of malignancy. Post-abortion, residual endometrial thickness should measure less than 8 mm; values above this threshold may indicate retained products of conception.
- Endometrial carcinoma — most common concern in postmenopausal bleeding with thickened endometrium
- Endometrial hyperplasia — often associated with unopposed estrogen; precursor to type I carcinoma
- Endometrial polyp — focal thickening, often with a feeding vessel on Doppler
- Retained products of conception — post-abortion thickening with or without internal vascularity
- Submucosal leiomyoma — can mimic focal endometrial thickening on greyscale imaging
Reference: Nalaboff KM, Pellerito JS, Ben-levi E. Imaging the endometrium: disease and normal variants. Radiographics. 21 (6): 1409-24.
Imaging Notes
On transvaginal ultrasound (TVUS), the endometrium is measured in the sagittal plane as the maximum double-layer thickness (anterior plus posterior), excluding any intracavitary fluid. TVUS remains the first-line modality given its accessibility, real-time capability, and high resolution for the endometrial stripe. Doppler interrogation can help characterize vascularity within focal thickening.
On MRI, the endometrium appears as a high T2-signal stripe surrounded by the low-signal junctional zone. Measurement is performed on sagittal T2-weighted sequences at the point of maximum thickness. MRI is preferred for further characterization of suspected malignancy, local staging, and when ultrasound is technically limited. Contrast-enhanced sequences improve delineation of tumor extent and myometrial invasion.