This study aims to determine whether the investigators can predict who will get benefit in terms of their pain from surgery for more severe forms of endometriosis. The investigators will use brain imaging to explore this, as it allows meaningful results from a smaller sample of people than if questionnaires alone were relied on.

Endometriosis is a chronic gynaecological condition that affects around 10% of women of reproductive age. This condition can cause debilitating pain, infertility, and poor quality of life. Endometriosis is a condition where tissue resembling the womb lining is present outside of the womb and is associated with an inflammatory pelvic environment. Symptoms of endometriosis can consist of pain during periods, chronic (non-cyclical) pelvic pain, pain during sex, pain when urinating, pain when defecating, and fatigue. Current treatments for endometriosis consist of hormonal, anti-inflammatory and / or analgesic medications and surgery, which is usually laparoscopic ("key-hole"). However, surgery does not always result in a reduction in pain for patients with endometriosis, therefore, it is important to try and understand which patients are most likely to benefit from surgery for their pain management.

Endometriosis is categorized into 4 stages (I - IV), ranging from small areas of tissue that do not extend deeply (stage I) to deep lesions associated with significant scarring of the pelvis and ovarian cysts (endometriomas). Interestingly, symptoms do not correlate with stage of disease. An NIHR funded clinical trial is currently investigating whether surgical treatment of superficial peritoneal endometriosis is of clinical benefit (ESPriT2) and is expected to report early in 2026 (recruitment and baseline data collection are complete). However, women with more severe forms of the disease are excluded from this trial. Surgery is commonly recommended for those with more extensive disease (stages III and IV), however, the risks of surgery are considerably greater for these patients including risk of bladder and bowel damage (sometimes requiring stoma formation) and a negative impact on future fertility. Therefore it is important to better understand who will benefit from this type of surgery. Rather than performing a full clinical trial, the investigators will use a set of experimental tests that allow pain to be understood in more detail meaning less people need to be included in the study and results will be available sooner.

In the present study, patients with pelvic endometriosis at stage III or IV with planned surgical treatment scheduled will be recruited to the project. Participants taking part will provide data at 5 different time points: Time point 1 will consist of several baseline questionnaires, an experimental sensory assessment, and a brain functional magnetic resonance imaging (fMRI) scan. Time point 2 will be the date of their endometriosis surgery, where a questionnaire will be taken, the surgery will be completed, and several biological samples (e.g. blood and small amounts of pelvic fluid and tissue) will be taken. Time points 3 (3 months post-surgery), 4 (6 months post-surgery), and 5 (12 months post-surgery) will consist of completing online questionnaires. All data collected within this project will be used to investigate pain outcome following endometriosis surgery. This research is funded by NIHR BRC.

Inclusion Criteria:

• willing and able to give informed consent
• aged between 18 and 50 years of age
• female or born female
• diagnosed with stage III or IV endometriosis by scan (MRI or USS) or previous surgery
• surgical treatment of severe endometriosis planned (surgical procedure at discretion of operating surgeon)
• reports pelvic pain of ≥4/10 (measured using a 0 - 10 numerical rating scale asking about the participant's worst pelvic pain associated with their endometriosis)
• reasonably fluent in English
• in the Investigator's opinion, is able and willing to comply with all study requirements
• willing to allow his or her General Practitioner and consultant to be notified of participation in the study

Exclusion Criteria:

• pregnant, lactating or planning pregnancy during the course of the study
• contraindication to MRI

Patients on the waiting list for surgery for severe endometriosis at the Oxford University Hospitals NHS Trust

Once data analysis is complete all data will be deposited in appropriate publicly accessible repositories as required by the funders. No personal data will be included in these datasets.

After publication of all manuscripts from the study

Data will be publicly accessible