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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Transvaginal ultrasound and magnetic resonance imaging (MRI) scans are both accurate ways to diagnose the most severe form of deep endometriosis affecting the bowel. By using both transvaginal ultrasound and MRI, the chance of non-invasively and accurately diagnosing endometriosis of the lower bowel rises to nearly 100%.

This review and meta-analysis looked at eight studies where both transvaginal ultrasound and MRI had been used to diagnose endometriosis in a total of 1,132 women. In each individual the investigation findings were compared with the reference standard, which was histological confirmation of endometriosis at surgery.

The quality of the studies was mostly high. Although none of these was a UK study, the results broadly support current UK practice. Also, they suggest that clinicians could consider using either of these examinations to non-invasively achieve an accurate diagnosis

Why was this study needed?

Endometriosis, where tissue similar to the lining of the womb starts to grow in other places, affects around 10% of all women, and 20-50% of infertile women. In up to a third of cases, the bowel is affected, mostly the lower or recto-sigmoid portion of the intestine. Symptoms such as pelvic pain, painful sex and pain when urinating or passing stools persist for years before a diagnosis is made. The impact on women’s lives, and the economic burden on healthcare systems, is very significant.

Transvaginal ultrasound and MRI have been shown to be effective at detecting endometriosis. They are less invasive than surgical methods and don’t require sedation. While MRI is more complex and more expensive, transvaginal ultrasound is slightly more invasive as an ultrasound sensor is inserted vaginally and is operator-dependent.

This review aimed to compare their accuracy in the diagnosis of recto-sigmoid endometriosis.

What did this study do?

This systematic review and meta-analysis included eight studies with a total of 1,132 women, published between 2007 and 2018. Three studies were from Italy, the rest from Spain, France, Brazil and Iran.

All the women in the studies had both transvaginal ultrasound and MRI for suspected deep endometriosis, based on clinical history and/or physical examination. Diagnosis was confirmed at surgery with a biopsy.

The main outcome measure was accuracy: the combination of sensitivity (how good is this test at picking up people who have bowel endometriosis?) and specificity (how good is the test at excluding it in those who don’t have it?).

Overall, the quality of the studies was high. The results should be reliable, though there was a small risk of bias. Bowel preparation, which has been shown to increase the accuracy of intestinal lesion detection, was not taken into consideration.

What did it find?

  • MRI correctly identified 90% of cases (95% confidence interval (CI) 87 to 92%) in those who had endometriosis and correctly excluded bowel endometriosis in those without it for 96% of people (95% CI 94 to 97%).
  • Transvaginal ultrasound correctly identified 90% of cases (95% CI 87 to 92%) in those who had endometriosis and correctly excluded bowel endometriosis in those without it for 96% of people (95% CI 94 to 97%).
  • On average, prevalence was high: 47% of women in the studies had lower bowel endometriosis. So for individual women tested the chance of a positive test meaning that they indeed had endometriosis (the positive “post-test probability” or predictive value) was 94.8% for MRI and 93.9% for transvaginal ultrasound. The combined use of them yielded an even better post-test probability of 99.6%.

What does current guidance say on this issue?

The NICE 2017 guideline recommends transvaginal ultrasound as a first choice where endometriosis is suspected, or to identify deep endometriosis involving the bowel, bladder or ureter. If this is refused or not appropriate, they suggest trying a trans-abdominal ultrasound scan of the pelvis.

NICE does not recommend MRI as a first line choice but suggest using MRI to assess the extent of deep endometriosis involving the bowel, bladder or ureter. MRI scans should be interpreted by a specialist gynaecological radiologist.

Where endometriosis is suspected, NICE suggests that surgical investigation (laparoscopy) is considered even when an ultrasound is normal.

What are the implications?

The results of this useful update support UK current practice concerning a condition that can be difficult to diagnose.

The finding that when both MRI and transvaginal ultrasound are used together, positive predictive value increases to nearly 100% is worth consideration by clinicians, as it effectively makes the diagnosis. The authors suggest that both can be performed on the same day, requiring a single bowel preparation.

In terms of resource, ultrasound is a safe, low-cost and widely-used technique – but accuracy is more dependent on the operator’s experience. MRI is more expensive, but can be interpreted by a specialist remotely – potentially increasing accuracy.

Citation and Funding

Moura A, Ribeiro H, Bernardo W et al. Accuracy of transvaginal sonography versus magnetic resonance imaging in the diagnosis of rectosigmoid endometriosis: Systematic review and meta-analysis. PLoS One. 2019;14(4):e0214842.

No funding information was provided for this study.



European Society of Human Reproduction and Embryology (ESHRE). Management of women with endometriosis. Grimbergen, Belgium; 2013.

NHS website. Endometriosis. London: Department for Health and Social Care; updated 2019.

NICE. Endometriosis: diagnosis and management. NG73. London: National Institute for Health and Care Excellence; 2017.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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Endometriosis is defined as the presence of endometrial-like tissue outside the uterine cavity. Superficial endometriosis (also called ‘peritoneal endometriosis’): peritoneal infiltration is less than 5mm in depth. Ovarian endometriosis: includes superficial ovarian implant and endometriomas. Deep endometriosis: foci of depth greater than 5mm affecting the retrocervix, paracervix, recto-vaginal septum, digestive tract (e.g. recto-sigmoid), ureter, bladder. Exceptionally affects more distant sites, such as the lungs, liver, diaphragm and operative scars.  
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