This is a plain English summary of an original research article
MRI scans are not sufficiently accurate to find the cause of chronic pelvic pain in women and should not replace laparoscopy (keyhole surgery), which can be used for diagnosis and often treatment. MRI only correctly ruled out a gynaecological condition in half of women judged to have no obvious cause and missed half of women who did have a treatable gynaecological condition.
Pinpointing the origin of chronic pelvic pain is often difficult due to the number of possible causes. If initial tests and examinations, including ultrasound, don’t identify the cause, a laparoscopy under anaesthesia is often the next step. This NIHR-funded study aimed to see whether MRI could reliably rule out disease and thereby avoid laparoscopy.
The findings suggest MRI does not have a routine place in the diagnosis of most chronic pelvic pain.
Why was this study needed?
Pelvic pain is defined as chronic when it has been present for more than six months. There are many possible causes, but mostly these from are gynaecological, urinary tract or bowel problems. It is reported that 38 in every 1,000 adult women consult their GP with chronic pelvic pain every year. It accounts for 1 in 5 of all gynaecology referrals. No definite cause is found in as many as half of women even after investigations.
If examination and initial investigations do not indicate the cause, laparoscopy is often considered to diagnose and possibly treat the condition. However, the invasive nature of the procedure, the need for anaesthesia, high cost and frequent failure to establish a diagnosis highlight the need to look for alternatives.
This study aimed to see whether MRI was reliable enough to use after initial investigations, so avoiding the need for laparoscopy.
What did this study do?
The MEDAL study involved 291 women (average 31.6 years) with chronic pelvic pain recruited from 26 UK gynaecology outpatient clinics.
Following clinical history taking, physical examination and ultrasound, the women received an MRI scan followed by diagnostic laparoscopy. Both investigations were interpreted without awareness of the findings of the other. The accuracy of MRI to make the diagnosis was compared against findings of the diagnostic laparoscopy in combination with consensus of an expert panel (the “reference standard”).
Patients were followed up for six months, which may not be a long enough period of capture the success of diagnosis and treatment. As there are diverse gynaecological causes for pelvic pain, the sample size may not be able to give accurate data on the performance of MRI for each individual condition.
What did it find?
- The most common diagnosis (affecting 54% of women) was unknown or “idiopathic” chronic pelvic pain, meaning a structural gynaecological cause for pain could not be found.
- The negative predictive value (NPV) measures the decision faced by clinicians, using the MRI scan results, to recommend not to proceed to a therapeutic laparoscopy. The result, NPV 58.1% (95% confidence interval [CI] 47.4% to 68.2%) suggests a “no laparoscopy” decision is correct in 58% of women, whereas 42% of women not receiving a therapeutic laparoscopy would have benefited from it.
- In theory, if MRI findings were used to decide the need for laparoscopic treatment, then for every 1,000 women with chronic pelvic pain, 369 women would have the laparoscopy procedure unnecessarily. Conversely, 136 women who could benefit from laparoscopy would not receive one because the MRI scan missed the treatable cause.
- MRI was unreliable for detecting the majority of conditions (sensitivity was low). For example, it detected 18.7% of women who were found to have adhesions at laparoscopy (sensitivity 18.7%, 95% CI 11.8 to 27.4) and 19.6% of women with ovarian cysts at laparoscopy (sensitivity 19.6%, 95% CI 10.2 to 32.4%).
- It had higher sensitivity for fibroids (sensitivity 87.5%, 95% CI 67.6 to 97.3%). As laparoscopy only views outside of the uterus MRI was therefore confirmed as a reasonable investigation for this condition.
- There were few false positives for these conditions (those reported on MRI scans but not found at laparoscopy). Specificity was between 93 and 99%.
- Laparoscopy resulted in higher gain in quality years of life and is more cost-effective than MRI. None of the economic analyses showed MRI to be a cost-effective option at usual NHS thresholds.
What does current guidance say on this issue?
Guidance from the Royal College of Obstetricians and Gynaecologists on the management of chronic pelvic pain recommends that initial assessment includes history taking, physical examination and screening for sexually transmitted infections. Transvaginal ultrasound scanning is said to be appropriate to assess masses. Diagnostic laparoscopy is described as the “gold standard” to consider if other investigations don’t find a cause. The potential drawbacks of laparoscopy are highlighted, including the negative consequences from failure to identify the cause of pain.
NICE specifically advises against the use of MRI in the diagnosis of endometriosis.
What are the implications?
The findings support current guideline recommendations and suggest that MRI does not have a routine place in the diagnosis of chronic pelvic pain.
However, it cannot be overlooked that laparoscopy will fail to produce a diagnosis for around half of women. This suggests there is still a need to find better tests in the diagnostic pathway for chronic pelvic pain.
Citation and Funding
Khan KS, Tryposkiadis K, Tirlapur SA, et al. MRI versus laparoscopy to diagnose the main causes of chronic pelvic pain in women: a test-accuracy study and economic evaluation. Health Technol Assess. 2018;22(40):1-92.
This project was funded by the National Institute for Health Research Health Technology Assessment programme (project number 09/22/50).
NHS website. Pelvic pain. London: Department of Health and Social Care; updated 2016.
NICE. Endometriosis: diagnosis and management. NG73. London: National Institute for Health and Care Excellence; 2017.
RCOG. Chronic pelvic pain, initial management (green-top guideline No. 41). London: Royal College of Obstetricians and Gynaecologists; 2012.
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