MRI to diagnose endometriosis


A review of magnetic resonance imaging (MRI) for diagnosing endometriosis and related diseases in the Korean Journal of Radiology has found that the medical imaging technique can help in the early and accurate diagnosis of ovarian endometriotic cysts and deep infiltrating endometriosis (DIE), while avoiding the need for invasive procedures and radiation exposure, due to MRI’s high contrast and objectivity.

“Furthermore, MRI plays a role in evaluating severity, leading to optimal treatment selection and preoperative planning,” wrote the authors, noting that ovarian endometriotic cysts can present with an atypical appearance like a decidual change or polypoid endometriosis.1

Laparoscopy with histological confirmation of ectopic endometrial tissue is the gold standard for the diagnosis of endometriosis, whereas ultrasonography is the first-line imaging modality for assessing pelvic endometriosis because of its easy accessibility, low degree of invasiveness and cost-effectiveness.

But ultrasonography has a limited field of view and is operator dependent, according to the authors. Conversely, MRI is more expensive and time-consuming. Still, MRI is more objective than ultrasonography and the images can cover a large field-of-view with multiple directions.

In 2017, the European Society of Urogenital Radiology (ESUR) published in the journal European Radiology recommendations on the optimal MRI protocol and guidelines for diagnosing pelvic endometriosis, based on literature evidence and the consensus of expert opinion.2

For patient preparation, 3 to 6 hours of fasting is recommended, as well as bladder emptying 1 hour before the examination.

A moderately distended bladder is preferable because an overly distended bladder may not allow for the detection of small endometriosis of the bladder.

An anti-peristaltic agent is also advised to prevent bowel motion artifacts, unless contraindicated.

Vaginal or rectal opacification by a gel is optional, although distention of the vagina or rectum by a gel might make pelvic endometriosis easier to detect, especially for Douglas pouch or rectosigmoid colon endometriosis.

The review mentioned that complications such as rupture, abscess and endometriosis-related tumors should be observed during a MRI.

For the diagnosis of DIE and secondary adhesion in pelvic organs, looking for ‘fibrosis’ with T2 hypointense nodules or thickened structures is recommended.

Hemorrhagic foci on T1-weighted images can also be helpful, although they are infrequent.

In addition, indirect imaging findings of adhesion, such as kissing ovaries or intestinal tethering, are significant.

Early detection of endometriosis-associated ovarian carcinoma (EAOC) is important because clear cell carcinoma is chemotherapy resistant. The most sensitive of the three key MRI findings for EAOC diagnosis is the emergence of enhanced mural nodules within the ovarian endometriotic cyst.

There is no significant difference between menstruating and non-menstruating MRI scans to evaluate the extent or severity of endometriosis, according to a study published in the European Journal of Radiology in 2015.3

“Radiologists should be familiar with both common and uncommon locations of endometriosis, their characteristic imaging findings, and their relationship to disease severity and treatment selection,” wrote the authors of the current review.


  1. Kido A, Himoto Y, Moribata Y, et al. MRI in the diagnosis of endometriosis and related diseases. Korean J Radiol. 2022 Apr; 23(4):426-445.
  2. Bazot M, Bharwani N, Huchon C, et al. European society of urogenital radiology (ESUR) guidelines: MR imaging of pelvic endometriosis. Eur Radiol. 2017;27:2765–2775.
  3. Botterill EM, Esler SJ, McIlwaine KT, et al. Endometriosis: does the menstrual cycle affect magnetic resonance (MR) imaging evaluation? Eur J Radiol. 2015;84:2071–2079.
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