The procedure itself is elegantly simple in concept. Under real-time ultrasound guidance, a needle is passed, usually transvaginally, into the endometrioma, the thick dark fluid is aspirated, and a sclerosing agent, most commonly absolute ethanol, is instilled into the cavity. The ethanol destroys the endometrial lining that secretes the cyst’s contents, effectively gluing the walls together and dramatically lowering the chance that the lesion refills. Because the ovarian cortex and its follicles are never incised, the technique has attracted growing interest among fertility specialists who worry that repeated cystectomies can measurably deplete anti-Müllerian hormone levels and antral follicle counts, the two laboratory and imaging markers of ovarian reserve. Yet sclerotherapy has never achieved the clinical standing of laparoscopic surgery, and the new review makes clear why: the evidence base is fragmented, with studies differing wildly in who gets treated, how the procedure is performed, how much sclerosant is used, and how success and recurrence are even defined.

What the Chinese team proposes is a standardized framework in which ultrasound is not merely a guidance tool for the moment of needle insertion but an active decision-making partner across the entire care pathway. The review, which synthesized English-language literature up to May 2026 from PubMed, Embase, Web of Science, and Scopus, organizes the ultrasound contribution into distinct phases: diagnosis, risk stratification, patient selection, procedural planning, treatment guidance, and post-treatment surveillance. This staging matters because each phase demands different information from the same imaging modality, and because errors made early in the pathway, such as mistaking a malignant tumor for an endometrioma, can be catastrophic if a clinician proceeds to puncture and sclerose the wrong lesion.

Diagnosis is where transvaginal ultrasound already reigns supreme. The characteristic appearance of an endometrioma, a well-defined cyst with homogeneous low-level internal echoes, so-called ground-glass echogenicity, and no internal vascular flow, is recognizable to any trained sonographer. But the review emphasizes that the real diagnostic task is exclusion. Endometriomas have a notorious gallery of mimickers, including hemorrhagic corpus luteum cysts, dermoid cysts, fibromas, and, most dangerously, malignant ovarian tumors that can present with atypical cystic features. Structured approaches such as the International Ovarian Tumor Analysis simple rules and the IOTA ADNEX model allow clinicians to classify adnexal masses with high accuracy and to flag red features, solid components, papillary projections, ascites, or increased color Doppler flow, that mandate referral for magnetic resonance imaging or oncological assessment rather than any intervention. Only after malignancy is excluded can the conversation about sclerotherapy responsibly begin.

Once the diagnosis is secure, ultrasound shifts to a second, less celebrated role: risk stratification and patient selection. Here the review draws on the International Deep Endometriosis Analysis framework, which uses ultrasound to map not just the cyst itself but the entire pelvic environment. Is the ovary mobile or fixed to the uterosacral ligament? Is there deep endometriosis infiltrating the rectovaginal septum? Are there signs of hydrosalpinx, tubo-ovarian abscess, or dense adhesions that would make a transvaginal puncture hazardous or futile? These findings directly determine candidacy. An ideal candidate for sclerotherapy is typically a woman with a unilateral or bilateral endometrioma of sufficient size, a mobile ovary that can be safely reached by the needle, no suspicious features, and a clinical priority of preserving ovarian reserve, whether because she is pursuing assisted reproduction or because she has already lost ovarian function on the contralateral side. Conversely, ultrasound evidence of deep infiltrating disease, frozen pelvis, or an ovary inaccessible without traversing bowel or vessels steers the patient back toward laparoscopy or medical management.

The procedural planning phase is where the review’s technical depth becomes most apparent. Ultrasound provides the measurements that dictate the mechanics of the intervention: cyst diameter determines needle gauge and the volume of aspirated fluid, which in turn informs the volume and dwell time of the ethanol instillation. Most published protocols rinse the cavity with ethanol for a fixed number of minutes, on the logic that contact time between the sclerosant and the cyst lining governs the completeness of epithelial destruction. Too brief an exposure invites recurrence; too prolonged an exposure risks ethanol leaking past the needle tract and injuring surrounding tissue. Real-time imaging allows the operator to confirm that the needle tip remains intracystic throughout, that the cyst wall does not collapse prematurely, and that the sclerosant is fully recovered before withdrawal. Doppler imaging adds a further safety check, ensuring the puncture path avoids the ovarian hilar vessels and the iliac vasculature that lie in harm’s way during a transvaginal approach.

For women pursuing in vitro fertilization or intracytoplasmic sperm injection, the timing question is especially delicate. Aspiration and sclerotherapy performed too close to ovarian stimulation can theoretically impair the response of the treated ovary, while an untreated endometrioma can complicate egg retrieval by contaminating follicular fluid or becoming infected. The review suggests that ultrasound-based assessment of the lesion’s size, accessibility, and behavior over serial scans can help clinicians individualize the sequencing of sclerotherapy relative to assisted reproductive technology cycles, although it candidly acknowledges that the literature does not yet provide definitive answers on optimal timing. This honesty is a recurring theme: the authors repeatedly note that heterogeneity in patient selection criteria, sclerosant exposure protocols, response definitions, and follow-up intervals makes head-to-head comparison of published studies treacherous.

Surveillance after treatment is the final and arguably most underdeveloped link in the chain. Here ultrasound again carries the load, with serial transvaginal scans tracking whether the treated cyst remains collapsed, refills, or regrows. Recurrence definitions vary across studies, from any re-accumulation of fluid to symptomatic recurrence requiring re-intervention, and follow-up windows range from a few months to several years. The review argues that a standardized ultrasound surveillance schedule, combined with laboratory markers such as anti-Müllerian hormone to monitor whether ovarian reserve is genuinely preserved, would allow the field to finally generate comparable outcome data. It also points out that ultrasound can detect the rare but serious complications of the procedure, including pelvic infection, bleeding, and, in theory, iatrogenic endometriosis dissemination along the needle tract, early enough for effective management.

The bigger picture painted by the review is one of cautious optimism. Ultrasound-guided sclerotherapy appears feasible and attractive for selected women, particularly when preservation of ovarian reserve is the overriding priority, and it can be performed on an outpatient basis without general anesthesia, at a fraction of the cost of laparoscopic surgery. But the authors stop well short of declaring it ready to displace surgery. Instead, they issue a call to action: a standardized, ultrasound-anchored framework for candidate selection, procedural consistency, and post-treatment monitoring could transform sclerotherapy from a niche technique practiced unevenly across centers into a rigorously defined option within the endometriosis treatment arsenal. For the estimated ten percent of reproductive-age women living with endometriosis, many of whom face the double threat of pain and infertility, that framework could mean the difference between an ovary sacrificed and an ovary saved, decided not by a surgeon’s judgment alone but by the quiet, real-time evidence of a probe held against the pelvic wall.

Subject of Research: Ultrasound-guided decision-making for minimally invasive sclerotherapy of ovarian endometrioma

Article Title: Ultrasound-based decision-making for minimally invasive sclerotherapy of ovarian endometrioma

Article References: Zhu, Y., Mo, Y., Zhang, J., Yang, W., Li, Y., Liu, C., & Jia, S. (2026). Ultrasound-based decision-making for minimally invasive sclerotherapy of ovarian endometrioma. Journal of Ovarian Research. https://doi.org/10.1186/s13048-026-02257-w

Image Credits: AI Generated

DOI: 10.1186/s13048-026-02257-w

Keywords: ovarian endometrioma, endometriosis, transvaginal ultrasound, sclerotherapy, ethanol sclerotherapy, ovarian reserve, infertility, assisted reproduction, minimally invasive treatment, ovarian cysts, fertility preservation, gynecology

FAP is a membrane protein expressed by activated fibroblasts, the stromal cells that remodel tissue in fibrotic and inflammatory environments. In oncology, FAP has become one of the most successful molecular imaging targets of the past decade, because fibroblast activation protein is largely absent from normal adult tissues but abundant in the cancer-associated stroma of many epithelial tumors. Radiolabeled FAP inhibitors, commonly referred to as FAPI tracers, allow positron emission tomography to light up tumors with striking contrast. More recently, clinicians have reported incidental FAPI uptake in endometriosis lesions and even suggested that FAP-targeted PET could offer diagnostic value beyond MRI in selected patients. What remained unclear, however, was the biological foundation for those observations: how strongly do endometriotic lesions actually express FAP, and does the level of expression depend on whether a lesion is visible on the imaging tests women typically receive?

The Mayo Clinic team, led by corresponding author Hiroaki Takahashi, set out to answer precisely that question. Because no one had previously linked FAP expression in endometriosis to lesion-by-lesion visibility on MRI and transvaginal ultrasound, the investigators designed a retrospective study that combined pathology, immunohistochemistry, and blinded imaging review. They analyzed surgical specimens from patients with histologically confirmed deep endometriosis and superficial endometriosis, all of whom had undergone MRI, transvaginal ultrasound, or both before surgery. The final cohort included thirteen patients with deep endometriosis and nine with superficial disease, providing a matched basis for comparing the two phenotypes at the tissue level.

To quantify FAP expression, the researchers used immunohistochemical staining of the resected specimens and calculated H-scores, a standard pathology metric that incorporates both the intensity of staining and the proportion of positive cells. H-scores range from zero to 300, allowing semi-quantitative comparison across samples. As a benchmark, the team also stained colorectal adenocarcinoma controls, since colorectal cancer is known to be a FAP-expressing malignancy and therefore provides a reference point for interpreting stromal signal intensity. The comparison showed that endometriosis, across both deep and superficial forms, exhibited substantial FAP expression in its fibroinflammatory stroma, although the H-scores were significantly lower than those of the colorectal cancer controls.

A key finding was that FAP expression did not differ significantly between deep and superficial endometriosis. Median H-scores were 170 for deep lesions and 200 for superficial lesions, a difference that was statistically indistinguishable. This is a notable result because superficial endometriosis is precisely the subtype that most often escapes detection on standard imaging. If superficial implants carry FAP expression comparable to deep lesions, then a whole-body molecular imaging technique targeting FAP should, in principle, be able to detect superficial disease that MRI and ultrasound routinely miss. The study thereby provides a histopathological rationale for extending FAP-targeted PET imaging from oncology into benign inflammatory and fibrotic gynecological disease.

The second half of the study addressed the visibility question directly. Two abdominal radiologists independently reviewed the MRI and transvaginal ultrasound studies and graded the visibility of each pathology-confirmed lesion on a study-specific scale from zero to three, with scores of zero and one classified as low visibility and scores of two and three as high visibility. When a lesion’s location fell outside the available field of view, it was assigned a designation of not applicable and excluded from the visibility comparison. This blinded, reader-based design ensured that the imaging assessments were independent of the pathological FAP results, allowing an unbiased test of whether molecular expression tracks with detectability.

For MRI, no lesions were graded as outside the field of view by either reader, and the low- versus high-visibility split was uneven but workable: Reader 1 classified 5 lesions as low visibility and 16 as high visibility, while Reader 2 classified 3 as low and 18 as high. Median H-scores for the low- and high-visibility groups were 220 and 170 for both readers. Although the low-visibility lesions trended toward higher FAP expression, the differences were not statistically significant. In practical terms, MRI-visible and MRI-invisible endometriosis lesions expressed FAP at broadly similar levels, suggesting that poor visibility on MRI reflects the limitations of anatomical imaging rather than any fundamental difference in the biology of the lesion.

The transvaginal ultrasound results told a more complicated story. Because ultrasound has a limited field of view in the pelvis, one lesion for Reader 1 and two lesions for Reader 2 fell outside the imaging field and were designated not applicable. Among the evaluable lesions, the low-visibility groups were small, containing just two lesions for Reader 1 and one for Reader 2, compared with ten high-visibility lesions for each reader. Median H-scores in the low-visibility groups were 48 and 20, markedly lower than the 165 and 160 observed in the high-visibility groups. The authors are careful to note that these small sample sizes preclude firm conclusions. The apparent association between low ultrasound visibility and lower FAP expression may reflect the small number of evaluable lesions rather than a genuine biological pattern, and larger studies will be needed to determine whether FAP expression correlates with sonographic detectability.

Even with those caveats, the overall conclusion of the study is clear and clinically important: both deep and superficial endometriosis show substantial stromal FAP expression, and critically, superficial lesions that are poorly seen on conventional imaging still express the target. The findings arrive amid a growing literature on FAPI PET beyond cancer. FAP-targeted imaging has been explored in Crohn’s disease, rheumatoid arthritis, and other fibroinflammatory conditions, and several recent case reports and small series have documented FAPI uptake in endometriotic implants, including focal uptake at the rectouterine pouch and subtype-specific uptake patterns that added diagnostic information beyond MRI. Earlier laboratory work had already shown that FAP-positive activated fibroblasts are detectable in the endometriotic microenvironment, where they correlate with stroma composition and with infiltrating CD8-positive and CD68-positive immune cells. The new Mayo Clinic study adds the missing translational link between that biology and the day-to-day imaging visibility of the disease.

The implications extend to diagnosis, surgical planning, and potentially therapy. Delayed diagnosis of endometriosis remains a global problem, with patients commonly waiting years from symptom onset to confirmation, partly because superficial implants are difficult to detect with anatomical imaging and often require laparoscopy for diagnosis. A molecular imaging approach that targets the fibroinflammatory stroma shared by deep and superficial lesions could complement MRI and ultrasound, particularly in mapping disease extent before surgery and in identifying active, fibrotically active lesions among otherwise inconspicuous findings. FAP is also being investigated as a therapeutic target, so confirming its expression in endometriotic tissue opens a second avenue beyond diagnosis. The authors note that their study is retrospective and modest in size, with only twenty-two patients, and that the ultrasound visibility analysis was limited by small numbers. Prospective studies with larger cohorts will be needed to establish how FAPI PET performs against MRI and transvaginal ultrasound in head-to-head diagnostic comparisons. Nevertheless, by demonstrating that even imaging-invisible superficial endometriosis carries the molecular signature that FAP-targeted tracers exploit, the study lays the histopathological groundwork for what could become the first molecular imaging strategy purpose-built for the full phenotypic spectrum of endometriosis.

Subject of Research: Fibroblast activation protein expression in deep and superficial endometriosis and its relationship to MRI and transvaginal ultrasound visibility

Article Title: FAP expression in deep and superficial endometriosis: Association with MRI and transvaginal ultrasound visibility

Article References: FAP expression in deep and superficial endometriosis: Association with MRI and transvaginal ultrasound visibility. (n.d.). https://doi.org/10.1007/s00259-026-08189-3

Image Credits: AI Generated

DOI: 10.1007/s00259-026-08189-3

Keywords: endometriosis, fibroblast activation protein, FAPI PET, molecular imaging, deep endometriosis, superficial endometriosis, MRI, transvaginal ultrasound, immunohistochemistry, H-score, radiology, diagnostic imaging