When endometriosis burrows into the bowel wall, the treatment options have long been stark. Bowel endometriosis is estimated to affect roughly 5% to 12% of women with endometriosis, a subset that often faces the most difficult decisions about care. A woman can try hormonal medications that suppress the disease but often fail to control deep pelvic pain. Or she can undergo major surgery, typically a segmental bowel resection or disc excision, to cut out the affected segment of rectum. That surgery remains the current standard of care at most specialized centers, but it carries real risks: infection, bowel perforation, and in some cases a temporary colostomy bag while the gut heals. Now, a series of clinical trials conducted in France over the past decade is testing a third option that requires no incision at all.
The technique, called high-intensity focused ultrasound (HIFU), uses a probe inserted through the rectum to deliver concentrated sound waves directly into endometriosis nodules embedded in the bowel wall. The energy heats and destroys the diseased tissue from the inside, sparing the surrounding structures. Across studies enrolling patients from 2015 through 2022, researchers report that the approach reduces pain and causes fewer complications than conventional operations in the short term. But as of May 2026, definitive proof from a randomized trial has not yet arrived, and critical questions about whether the benefits last remain unanswered.
What the studies show so far
The most substantial evidence comes from a prospective multicenter study that enrolled 60 women with symptomatic rectal endometriosis at several French hospitals between 2020 and 2022. Investigators used the Focal One device, a platform originally developed to treat prostate cancer and later adapted for gynecologic use. According to the open-access report published in PMC, the team increased the ultrasound power by 30% compared to earlier protocols and reported meaningful reductions in pelvic pain along with acceptable short-term safety. Because the study was conducted across multiple centers rather than a single expert clinic, it offered stronger evidence that the procedure can be reliably reproduced.
The study did not include a comparison group, however, which makes it difficult to separate the effects of HIFU from natural symptom fluctuation, concurrent hormonal therapy, or the placebo response that often accompanies high-tech procedures.
A separate retrospective multicenter study, recently published in 2025, addressed that gap by directly comparing outcomes in women who received HIFU against those who underwent surgery for rectal endometriosis. According to findings in the Journal of Minimally Invasive Gynecology, patients in the HIFU group experienced lower rates of moderate and severe complications at six months, as measured by the Clavien-Dindo classification, a standard grading system used across surgical specialties. Those complication grades capture events that matter enormously to patients: infections requiring antibiotics, unplanned return trips to the operating room, or admissions to intensive care.
The comparison is the clearest head-to-head data available, but it was not randomized. Surgeons decided which patients received which treatment, raising the possibility that women with smaller or less complex lesions were more likely to be offered HIFU, skewing the results in its favor.
Both of these studies built on earlier groundwork. Between 2015 and 2018, a Phase I trial tested the feasibility and immediate safety of transrectal HIFU using the same Focal One platform in a small group of women with deep infiltrating endometriosis of the rectosigmoid. That initial study, indexed on PubMed, confirmed that the probe could be positioned accurately and that focused energy could be delivered to bowel wall nodules without causing perforation or uncontrolled bleeding. It was never designed to measure long-term symptom relief, but it proved the concept was viable enough to justify larger trials.
Taken together, these three studies trace a logical arc: from proof of concept, to broader safety evaluation, to early comparative effectiveness research. Across all of them, HIFU appears technically achievable in most patients with rectal lesions and is associated with low rates of immediate serious harm.
The trial that could settle the debate
The missing piece is a randomized, blinded trial, and one is underway. Registered on ClinicalTrials.gov under the identifier NCT05755958 and titled ENDO-HIFU-R2, the study assigns women with rectal endometriosis to receive either active HIFU or a sham procedure. Neither the patients nor the clinicians evaluating their outcomes know which treatment was delivered. The primary endpoint is pelvic pain at three months.
This design matters because chronic pain conditions are notoriously susceptible to placebo effects. Patients who believe they have undergone a cutting-edge procedure often report feeling better regardless of whether the treatment itself did anything. A sham-controlled trial is the only reliable way to separate genuine tissue destruction from expectation and regression to the mean. As of the latest registry update, no results from ENDO-HIFU-R2 have been posted.
Where the gaps are widest
Even if the randomized trial confirms that HIFU reduces pain more than a sham procedure, several large questions will remain open.
Durability is the most pressing. Endometriosis is a chronic, relapsing disease that can affect women throughout their reproductive years. In the available HIFU studies, follow-up extends to six months, with the retrospective surgical comparison (PMID 40842102) providing the longest reported outcome window. That timeframe is far too short to know whether symptom relief holds, whether treated nodules regrow, or whether new lesions appear elsewhere in the pelvis. Without multi-year data, clinicians cannot tell patients how often they might need repeat sessions or whether they could eventually end up in the operating room anyway.
Functional outcomes beyond pain are underreported. For women with rectal endometriosis, subtle changes in bowel habits, continence, urgency, or pain during sex can be just as disruptive as deep pelvic pain. Published HIFU studies focus heavily on pain scores and complication rates but provide little detail on these everyday quality-of-life measures. There is also no published data on fertility after rectal HIFU, an important gap given that many patients with endometriosis are of reproductive age and may be trying to conceive.
Cost-effectiveness has not been formally studied. Bowel surgery for deep endometriosis often means several days in the hospital, specialized nursing if a temporary colostomy is created, and weeks away from work. HIFU, being incisionless, could plausibly shorten hospital stays and speed recovery. But the Focal One device is expensive, the procedure still requires anesthesia and operating room time, and specialized training is needed to perform it safely. Without formal economic analyses comparing direct medical costs, lost productivity, and long-term outcomes, insurers and health systems have little basis for coverage decisions.
Imaging follow-up is a blind spot. Magnetic resonance imaging (MRI) is the standard tool for mapping deep endometriosis in the bowel wall, yet none of the published HIFU studies report systematic MRI assessments after treatment. Without before-and-after imaging, clinicians cannot confirm whether HIFU completely destroys the targeted nodule, merely shrinks it, or leaves behind pockets of viable disease. Correlating imaging changes with symptom trajectories would help distinguish persistent pain caused by residual endometriosis from pain driven by nerve sensitization or unrelated pelvic conditions.
How HIFU fits into current treatment decisions
For women currently facing a recommendation for bowel surgery, the HIFU research offers a reason for cautious hope but not yet a reason to delay proven treatment while waiting for a procedure that remains experimental.
On solid ground: transrectal HIFU using the Focal One device is technically feasible in many women with rectal endometriosis, carries low short-term complication rates in the studies published so far, and appears less morbid than segmental bowel resection over the first six months. These findings suggest that, in experienced hands at specialized centers, HIFU could eventually become a less invasive alternative for carefully selected patients.
On uncertain ground: there is not yet rigorous evidence that HIFU provides lasting relief measured in years rather than months, preserves or improves fertility, or outperforms optimized medical therapy. The technique has been tested almost exclusively at French academic centers, and it is unclear how quickly training, equipment access, and institutional expertise could expand to other countries. The Focal One device does not have regulatory clearance for gynecologic use in the United States, adding another barrier to near-term availability outside Europe.
The most honest framing is that HIFU for bowel endometriosis sits at a familiar inflection point in medicine: promising enough to justify continued investment and rigorous testing, but too early in its evidence arc to replace established treatments. When the ENDO-HIFU-R2 randomized trial reports its findings, and when longer follow-up data from existing cohorts become available, the picture will sharpen considerably. Until then, any decision about pursuing HIFU should be a shared one between patient and clinician, grounded in a clear-eyed view of both what the early data suggest and what they cannot yet prove.
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*This article was researched with the help of AI, with human editors creating the final content.
