Challenging prior assumptions: coexistence of polycystic ovarian morphology and endometriosis on transvaginal ultrasound.

OBJECTIVE: To investigate, using transvaginal ultrasound imaging, the overlap between polycystic ovarian morphology (PCOM) and endometriosis, and to explore demographic and clinical factors associated with their coexistence across endometriosis phenotypes.

METHODS: This was a retrospective cohort study of consecutive patients undergoing advanced transvaginal ultrasound examination for suspected or previously diagnosed endometriosis at a tertiary gynecological ultrasound clinic between February 2023 and June 2023. Ultrasound was performed following the International Deep Endometriosis Analysis consensus and the International Ovarian Tumor Analysis framework guided lesion characterization, with PCOM defined as per the 2018 and the modified 2023 International Polycystic Ovary Syndrome Guideline (≥ 20 follicles measuring 2-9 mm in diameter and/or ovarian volume > 10 mL in the absence of a dominant follicle, cyst or corpus luteum). Endometriosis phenotypes were classified sonographically as superficial (SE), ovarian (OE) or deep (DE) endometriosis. Demographic and clinical variables were compared between participants with endometriosis alone and those with concurrent endometriosis and PCOM. Logistic regression analysis was performed within the endometriosis-positive subgroup using PCOM as the dependent variable in a univariable model including age and a multivariable model including age and body mass index (BMI). An age-restricted (25-35 years) sensitivity analysis compared the frequencies of any endometriosis and of individual endometriosis phenotypes between participants with and those without PCOM. A secondary analysis within this subgroup compared clinical and demographic characteristics between endometriosis participants with and those without concurrent PCOM.

RESULTS: Among 165 included patients, 62.4% (n = 103) were diagnosed with endometriosis, 37.0% (n = 61) demonstrated PCOM and 35.0% (36/103) of those with endometriosis had concurrent PCOM. In the whole cohort, the frequency of any endometriosis did not differ significantly between participants with and those without PCOM. DE was less frequent among those with PCOM, whereas differences in the frequency of OE and SE between participants with and those without PCOM were not statistically significant. Compared to individuals with endometriosis alone, those with concurrent PCOM were significantly younger and had lower body weight. The proportions of nulligravidae and of nulliparae were also higher. In age-restricted analyses limited to participants aged 25-35 years, no significant differences were observed between those with and those without PCOM for the presence of any endometriosis or for any individual endometriosis phenotype. However, among endometriosis-positive participants, increasing age was associated with lower odds of concurrent PCOM in both the univariable model including age (odds ratio (OR), 0.83 (95% CI, 0.77-0.90) per 1-year increase; P < 0.001) and the multivariable model including age and BMI (OR, 0.84 (95% CI, 0.77-0.92) per 1-year increase; P < 0.001), whereas BMI was not independently associated with PCOM (OR, 0.99 (95% CI, 0.91-1.09) per 1 kg/m2 increase; P = 0.874). In the sensitivity analysis restricted to participants aged 25-35 years, the differences observed previously in age, weight, gravidity and parity were no longer statistically significant.

CONCLUSIONS: Endometriosis and PCOM can coexist on ultrasound in a tertiary referral cohort. However, the observed between-group differences were strongly influenced by age, and our findings should be interpreted as exploratory and hypothesis-generating rather than confirmatory. Prospective studies incorporating endocrine characterization, standardized cycle-phase assessment and side-specific ovarian assessment are needed to clarify the clinical and biological significance of this coexistence. © 2026 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.