O-RADS for assessment of adnexal lesions: current status, challenges and future directions

A high-priority item for the ACR O-RADS US committee is the addition of management recommendations following O-RADS MRI evaluation. The role of imaging surveillance as a management strategy for O-RADS MRI 3 (low-risk) lesions will be addressed given recent evidence showed absence of malignancy in a cohort of 4061 patients with low-risk morphology lesions on US demonstrating stability at 12 months, [ 52 ]. An O-RADS MRI management subcommittee is nearing completion of an updated version with management recommendations, expected to be released in 2026. To ensure harmonization and cohesive messaging between the MRI and US arms of O-RADS, updates to O-RADS US will be required with plans to release O-RADS US and MRI v2026 simultaneously. Committee projects include translation of O-RADS tables into multiple languages and creation of a comprehensive O-RADS manual bringing educational and supporting materials together in one document. To additionally encourage widespread use, O-RADS leadership is committed to exploring avenues to simplify the system, maintain user-friendly smartphone app and web-based calculators, and conduct research to clarify rules for system use and refine risk stratification. Image repositories for US and MRI are being created to identify key lesional features to predict benignity and malignancy. The integration of fat distribution or quantification of enhancing solid tissue to differentiate benign and malignant teratomas [ 44 ], the feasibility of replacing highly operator-dependent features such as color score with a binary option, and an abbreviated O-RADS MRI protocol with associated PPV modifications to promote use at facilities with limited MRI capabilities are of particular interest. Contrast-enhanced ultrasound (CEUS) utilizing intravenous injection of microbubble contrast agents, has shown promise in assessing ovarian/adnexal lesions with recent publications highlighting the technique, a lexicon and efforts to integrate with O-RADS US [ 53 – 55 ]. CEUS offers subjective dynamic real-time assessment of tissue vascularity using subtraction techniques to reflect microvascular perfusion patterns (Fig. 12 ). Time-intensity curves provide quantitative analysis by plotting signal intensity against time and may allow CEUS to play a role in O-RADS risk stratification, either as an adjunct tool or alternate to MRI. This may be particularly useful in regions where MRI is inaccessible, and CEUS workflow is established. Fig. 12 31-year-old patient with history of stage 4 endometriosis, previous left oophorectomy for seromucinous borderline tumor and right ovarian cystectomy for endometrioma, who presented with new 21 cm right ovarian mass. Grayscale image of the right adnexa ( a ) shows a multilocular cystic mass with sizable solid components/papillary projections (asterisks), and moderate vascularity (color score 3) on color Doppler US ( b ); lesion was scored as O-RADS US 5 (high risk). Patient subsequently underwent contrast-enhanced US evaluation. During the arterial phase ( c ), peak enhancement within the papillary projection (asterisk) is not brighter than the tissue surrounding the lesion (arrows) or the myometrium (not shown). In late phase ( d ), papillary projection (asterisk) shows washout by 2 min post injection. Quantitative analysis shows raw linear format display ( e ) with slow rise time, low peak enhancement, and low area under the curve considered a low-risk time intensity curve. Despite concerning grayscale features, low-risk quantification parameters favor a low-grade neoplasm. Pathology showed recurrent seromucinous borderline tumor with associated endometriosis. (Case courtesy of Dr. Stephanie R. Wilson, MD, University of Calgary) 31-year-old patient with history of stage 4 endometriosis, previous left oophorectomy for seromucinous borderline tumor and right ovarian cystectomy for endometrioma, who presented with new 21 cm right ovarian mass. Grayscale image of the right adnexa ( a ) shows a multilocular cystic mass with sizable solid components/papillary projections (asterisks), and moderate vascularity (color score 3) on color Doppler US ( b ); lesion was scored as O-RADS US 5 (high risk). Patient subsequently underwent contrast-enhanced US evaluation. During the arterial phase ( c ), peak enhancement within the papillary projection (asterisk) is not brighter than the tissue surrounding the lesion (arrows) or the myometrium (not shown). In late phase ( d ), papillary projection (asterisk) shows washout by 2 min post injection. Quantitative analysis shows raw linear format display ( e ) with slow rise time, low peak enhancement, and low area under the curve considered a low-risk time intensity curve. Despite concerning grayscale features, low-risk quantification parameters favor a low-grade neoplasm. Pathology showed recurrent seromucinous borderline tumor with associated endometriosis. (Case courtesy of Dr. Stephanie R. Wilson, MD, University of Calgary) Emerging developments in technologies, such as functional imaging, AI tools, and radiomics, are poised to further enhance O-RADS-based risk stratification [ 56 ]. Machine learning models applied to MRI and combined US-MRI datasets are being explored to improve lesion characterization [ 57 – 59 ]. Technique-related adjuncts, such as ADC thresholds, are being investigated to potentially increase specificity which may allow better differentiation between low-intermediate and high-risk lesions, without compromising sensitivity [ 43 ]. Furthermore, continued refinement of both O-RADS US and MRI lexicons, informed by large multicenter datasets, may further optimize risk prediction and better direct clinical management strategies.

The ACR O-RADS MRI risk stratification system was released in 2020, in collaboration with the European Society of Urogenital Radiology (ESUR) [ 25 ], to provide a standardized, evidence-based framework for evaluation of adnexal lesions characterized on US as carrying an elevated risk of malignancy. MRI provides superior soft tissue contrast, accurate detection of lipid content or fibrous tissue commonly associated with benign lesions, and functional capabilities through the use of dynamic contrast enhancement (DCE) and diffusion weighted imaging (DWI) sequences, which allow improved malignancy risk stratification. O-RADS MRI plays an important role as a secondary or problem-solving modality to complement US. Similar to the US arm, O-RADS MRI consists of governing concepts (Table 2 ) and stratifies adnexal lesions into five risk categories based on standardized lexicon terms and definitions using an algorithmic approach (Fig. 4 ) [ 6 , 26 ]. When an exam is technically inadequate, an O-RADS MRI score 0 is assigned. O-RADS MRI score 1 indicates normal ovaries and O-RADS MRI scores of 2 to 5 correspond to almost certainly benign to high-risk lesions with increasing positive predictive values (PPV) for malignancy (Fig. 5 ) [ 27 ]. It is worth noting that while the nomenclature of the US and MRI arms of O-RADS is the same, the values depicting percent risk associated with scores 2 to 5 are distinct, reflecting the higher specificity afforded by O-RADS MRI, specifically due to DCE and DWI lesional characteristics. For example, lower risk lesions with scores of 2 and 3 have lower values in O-RADS MRI (PPV for malignancy < 0.5% and ~ 5%, respectively), than in O-RADS US (ROM < 1% and 1-<10%, respectively). For lesions at higher risk for malignancy with scores of 4 and 5, values are higher in O-RADS MRI (PPV for malignancy ~ 50% and ~ 90%, respectively), compared to O-RADS US (ROM 10-<50% and ≥ 50%, respectively). Table 2 Most important governing concepts in O-RADS MRI • Assumes an average risk patient with no acute symptoms; clinical management supersedes findings based on MRI imaging alone • Score characteristic benign mature teratomas containing fat (± septations or Rokitansky nodules ± minimal enhancement) as category 2; O-RADS MRI 4 if fatty lesion contains large amount of enhancing solid tissue • Some characteristic lesion may be diagnosed regardless of score category; in such cases, report diagnosis (e.g., peritoneal inclusion cyst, dysgerminoma, etc.) • In order to obtain listed PPVs for malignancy, use technical minimum requirements including DCE with time resolution ≤15 s, TICs and recommended slice thickness O-RADS = ovarian/adnexal reporting and data system; MRI = magnetic resonance imaging; PPV s= positive predictive values; DCE = dynamic contrast enhancement; TICs = time-intensity curves Most important governing concepts in O-RADS MRI O-RADS = ovarian/adnexal reporting and data system; MRI = magnetic resonance imaging; PPV s= positive predictive values; DCE = dynamic contrast enhancement; TICs = time-intensity curves Fig. 4 O-RADS MRI algorithm for assessment categories O-RADS MRI algorithm for assessment categories Fig. 5 O-RADS MRI assessment categories O-RADS MRI assessment categories O-RADS MRI yields excellent diagnostic performance in multiple validation studies. In the initial multicenter, retrospective study of 1194 patients and 1502 pelvic masses validating O-RADS MRI, the system demonstrated a sensitivity of 93%, specificity of 91%, and overall accuracy of 96% with good interreader agreement (κ = 0.784) [ 25 ]. Subsequent validation studies have confirmed these results, with sensitivities of 91–96%, specificities of 79–95%, PPVs for malignancy of 73–89%, negative predictive values (NPV) of 95–98%, and overall accuracies of 85–95% [ 28 – 33 ]. Meta-analyses demonstrated similar excellent performance of O-RADS MRI with pooled sensitivities and specificities of 92–97% and 77–91%, respectively [ 34 – 36 ]. Both experienced and inexperienced radiologists have excellent diagnostic performance using O-RADS MRI highlighting its role as a robust tool in clinical practice [ 37 ]. Although pediatric patients were not included in the original supporting O-RADS MRI database, in a single center, retrospective study of 109 pediatric patients (median age 13 years; 7 with malignant lesions) malignancy rates were on target with 0% for O-RADS MRI 1–3, 50% for O-RADS MRI 4, and 75% for O-RADS MRI 5 [ 38 ]. Additional studies evaluate specific aspects of O-RADS MRI. In a single center, retrospective study of 137 fat-containing adnexal lesions, O-RADS MRI correctly identified all 14 malignant teratomas but categorized 15% (18/123) benign teratomas as O-RADS MRI 4, illustrating a limitation of MRI specificity [ 39 ]. Use of time-intensity curves improves the overall accuracy of O-RADS MRI risk stratification [ 40 ], although O-RADS MRI in a two-center, retrospective study of 496 patients using non-DCE MRI still achieved excellent performance [ 31 ]. Inclusion of apparent diffusion coefficient (ADC) values has also shown value in improving O-RADS MRI performance [ 41 – 43 ]. Importantly, O-RADS MRI has higher specificity than O-RADS US and can confidently downgrade the malignancy risk of some solid lesions and cystic lesions with solid components in the O-RADS US 3, 4 or 5 categories with the potential to significantly reduce the number of asymptomatic patients undergoing surgery for benign lesions [ 44 , 45 ].

Ovarian cancer is the second most common gynecologic malignancy and remains a leading cause of gynecologic cancer-related death worldwide. The estimated number of new cases in 2025 is 20,890, while the estimated number deaths is 12,730 in the United States [ 1 ]. According to the American Cancer Society, localized ovarian cancer carries a favorable 5-year survival of approximately 92%, yet more than half of patients present with advanced disease, where 5-year survival drops to 31% when distant metastases are present [ 1 ]. On the other hand, because the incidence of ovarian cancer is low and many women have benign adnexal lesions, employing a highly specific diagnostic pathway reduces unnecessary morbidity from over-treatment. Therefore, an effective approach to detect ovarian cancer with both adequate sensitivity and specificity in the general population remains an important clinical need. The Ovarian-Adnexal Reporting and Data System (O-RADS) is a standardized risk stratification and reporting framework developed to improve the evaluation and management of ovarian and adnexal lesions [ 2 – 4 ], by providing a common language for describing imaging findings and to estimate the likelihood of malignancy in a clear, reproducible manner [ 5 , 6 ]. By categorizing lesions based on malignancy risk, O-RADS aims to reduce unnecessary surgical intervention for benign lesions while prompting appropriate referral of patients with suspected malignancy to a gynecologic oncologist in a timely manner. This structured triage not only supports more accurate clinical decision-making but improves inter-reader concordance with the ultimate goal of improved patient outcomes. Over the past several decades, evidence has highlighted the role of ultrasound (US) and magnetic resonance imaging (MRI) in the evaluation of adnexal lesions which comprise the two arms of the O-RADS system [ 7 ]. O-RADS US serves as the primary imaging modality for lesion detection and characterization. Ultrasound is widely available, has real-time capability, and demonstrates strong diagnostic performance in identifying the morphologic features associated with malignant ovarian/adnexal lesions. US-based assessment forms the foundation of O-RADS risk stratification and guides next steps in management. O-RADS MRI serves as a secondary, problem-solving modality when the US exam is technically inadequate or when further lesion characterization has potential value. MRI offers superior soft tissue contrast and multiparametric evaluation, enabling higher specificity and diagnostic confidence for many ovarian and adnexal lesions. Within the O-RADS framework, the use of O-RADS US followed by the addition of O-RADS MRI in certain scenarios moves management of ovarian and adnexal lesions towards the goal of optimizing ovarian cancer outcomes and minimizing unnecessary surgery in patients at low risk of malignancy [ 7 , 8 ]. The objective of this manuscript is to review the current evidence validating the US and MRI arms of the O-RADS system and their evolving complementary roles, to discuss the challenges and barriers to user adoption, and to present the future directions of this dual-modality system to further improve adnexal lesion characterization and optimize management strategies.

Implementation of O-RADS US and MRI has been supported by validation studies and by multiple professional societies, either through development, collaboration, or guideline integration. O-RADS also aligns with the Centers for Medicare and Medicaid Services (CMS) quality and standardization goals of structured reporting, evidence-based risk stratification and appropriate referral to subspecialty care. Nevertheless, several conceptual, technical, and workflow-related barriers exist that may affect consistent adoption across facilities and institutions. In addition, barriers to clinical implementation exist on an institutional level, including multidisciplinary buy-in and training. Differences in lexicon terms, definitions and recommendations for appropriate usage between the O-RADS US and MRI arms of the system exist. For example, the small hemorrhagic cyst ≤ 3 cm is in the O-RADS MRI 1 category but O-RADS US 2 category. Dermoid contents and blood products are specifically excluded as solid ‘components’ in O-RADS US yet considered solid ‘components’ not representing solid ‘tissue’ in O-RADS MRI. ROM is used for O-RADS US while PPV for malignancy is used in O-RADS MRI. O-RADS US scoring may be used in high-risk patients, but O-RADS MRI scoring assumes a patient is not at high-risk. While some inconsistencies were resolved in O-RADS US v2022 and others are inherent in modality differences, further harmonization is needed as this has been reported by users as a limitation; the committee is dedicated to better aligning the two arms in future versions. The supporting database used to justify the five risk stratification categories in O-RADS US and MRI did not include pregnant or pediatric populations, and emerging studies will need to be referenced for generalizability. In addition, ROM and PPV for malignancy ranges were based on an underlying cancer prevalence of approximately 20%, which is higher than the general population (approximately 1.2%). While a study confirmed O-RADS US performance to be within range in a non-selected population of 913 consecutive patients undergoing pelvic US for various indications, the underlying cancer prevalence was still 8.4% [ 52 ]. As risk of disease is dependent on underlying disease prevalence, some believe O-RADS is not applicable to the general population [ 51 ]. However, such validation would require a large study of asymptomatic average-risk patients, which is highly improbable. More importantly, some users and patients may confuse “risk of malignancy” with “risk of neoplasia”; a lesion which proves to be a benign ovarian neoplasm is categorized as a “negative” outcome in O-RADS. Framing counseling around both malignancy risk and likelihood of benignity is important, especially when setting patients’ expectations. Although interobserver reliability is strong, the operator-dependent nature of US and evolving US technology introduce complexity. Spatial compounding can diminish posterior shadowing, and advanced microvascular techniques may detect previously unappreciated flow, potentially altering categorization due to difference in color score (4-point scoring system of subjective internal vascularity on color Doppler). Ongoing training is needed to improve consistent descriptor application. Workflow considerations also present challenges. Some O-RADS US 4 and 5 lesions are downgraded after specialist review or O-RADS MRI assessment. In settings when referral to gynecologic oncology occurs before additional imaging, unnecessary consultations may result. Structured pathways encouraging expert reassessment or MRI prior to referral may improve efficiency. The O-RADS MRI technique protocol requires very specific parameters to attain the PPVs for malignancy listed in the assessment categories table. Deviation from this protocol including the minimum slice thickness of acquired MRI images to detect small papillary projections, and DCE time–intensity curves may give rise to varying results. However, many practices may not routinely acquire or analyze these sequences or meet the minimum technical requirements due to limited resources or limited available MRI scanning time. In addition, applying O-RADS MRI scores to studies performed for other indications using nonstandard (non-O-RADS) protocols may not reproduce published PPV ranges, potentially undermining confidence in risk estimates. The lack of management recommendations following O-RADS MRI assessment is also perceived to be a system limitation. While it is undeniable that management is ultimately the domain of the referring provider who is most familiar with patient clinical factors such as risk status, user feedback from healthcare providers and radiologists alike suggests a desire for general management guidance, including when referral to a gynecologic oncologist should be considered.

O-RADS US and MRI constitute a complementary, evidence-based imaging framework for the evaluation of ovarian and adnexal lesions. Ultrasound remains the primary modality for risk stratification, offering high sensitivity, real-time assessment, and widespread accessibility. MRI serves as a secondary, problem-solving tool, providing high-resolution soft-tissue characterization and improved specificity when needed in lesions with higher risk features, if subjective assessment by an ultrasound specialist is not available. Validation studies for both modalities have demonstrated their excellent diagnostic accuracy, reproducibility, and alignment with expected risk of malignancy. Shortcomings of the O-RADS system include the lack of management recommendations following O-RADS MRI assessment. Inconsistencies in terminology and definitions between the US and MRI arms have only partially been addressed in O-RADS US v2022 and continued alignment is required in future modifications. Barriers to adoption stem from conceptual misunderstandings, multidisciplinary buy-in and variability in imaging protocols and workflow. Protocol standardization and provider education remain essential for optimizing implementation and consistent risk stratification. In summary, the integrated use of O-RADS US and MRI can improve diagnostic confidence, reduce unnecessary surgery, and promptly refer patients with suspected malignancy to a gynecologic oncologist, establishing a robust and clinically actionable standard for contemporary gynecologic imaging.

The US and MRI arms of the O-RADS system play complementary roles and together offer a dual-modality approach to achieve both high sensitivity and specificity in adnexal lesion risk stratification. As previously discussed, O-RADS US v2022 provides a high sensitivity up to 95.0% for identifying malignancy [ 46 ] consistent with its goal of not missing cancer. O-RADS US is very well suited for initial lesion characterization; since the vast majority of adnexal lesions are physiologic or benign, US is also suitable when imaging surveillance is needed. O-RADS MRI can improve specificity of selected lesions, especially those with solid components or incompletely evaluated on US [ 47 ]. Clinical integration depends on institutional expertise, MRI availability, and patient-specific factors. Occasionally, O-RADS US is enough and in other scenarios, the value of O-RADS MRI warrants it use. In many settings, high-quality transvaginal ultrasound (TVUS) with Doppler capabilities provides sufficient morphologic and vascular characterization to confidently assign an O-RADS US score. MRI is unnecessary when a technically adequate US shows typical features of a physiologic or classic benign lesion in the O-RADS US 1–2 categories, such as the follicle or corpus luteum, simple or hemorrhagic cyst, endometrioma, dermoid cyst, hydrosalpinx and simple paraovarian cyst (Fig.  6 ). In these cases, routine clinical management or US follow-up is sufficient. Fig. 6 45-year-old premenopausal patient presenting for IUD assessment was found to have an incidental left ovarian lesion on ultrasound. Transvaginal grayscale image ( a ) shows a 4.8 cm unilocular cyst with reticular pattern in the left ovary and no internal vascularity on color Doppler ( b ), a typical appearance of a hemorrhagic cyst, O-RADS US 2. Ultrasound was enough to characterize this lesion. No follow up imaging was needed given its size (< 5 cm) 45-year-old premenopausal patient presenting for IUD assessment was found to have an incidental left ovarian lesion on ultrasound. Transvaginal grayscale image ( a ) shows a 4.8 cm unilocular cyst with reticular pattern in the left ovary and no internal vascularity on color Doppler ( b ), a typical appearance of a hemorrhagic cyst, O-RADS US 2. Ultrasound was enough to characterize this lesion. No follow up imaging was needed given its size (< 5 cm) Lesions without solid components in the low-risk category of O-RADS US 3 are also unlikely to benefit from MRI when thoroughly evaluated with US. When active surveillance is elected, this may be performed with US within six months although shorter intervals may be considered due to clinical factors such as patient genetic predisposition to ovarian cancer or patient/provider preference. Likewise, patients may not benefit from further MRI characterization of adnexal lesions considered clearly malignant sonographically. For example, lesions that are largely solid with an irregular contour or with very strong vascularity, particularly those associated with ascites or peritoneal nodules in a postmenopausal or high-risk patient, are cancer until proven otherwise (Fig.  7 ). In such cases, the priority shifts from characterization to extent-of-disease evaluation, and cross-sectional imaging such as CT, PET/CT, or abdominal/pelvic MRI is more appropriate than diagnostic MRI refinement. Fig. 7 82-year-old postmenopausal patient presented with abnormal vaginal bleeding. Transabdominal grayscale ultrasound image ( a ) shows a 14 cm multilocular cystic lesion with large solid components associated with moderate amount of vascularity (color score 3) on color Doppler ( b and c ). Ascites was seen ( c , arrow). This lesion was scored as O-RADS US 5, high risk for malignancy and patient was referred to a gynecologic oncologist. CT scan of the chest, abdomen and pelvis (not shown) was performed to evaluate extent of disease, which showed a corresponding lesion with trace ascites and no distant metastatic disease. Patient subsequently underwent total hysterectomy/bilateral salpingo-oophorectomy and staging for ovarian cancer. Surgical pathology confirmed mucinous cystadenocarcinoma. US was enough to characterize this lesion 82-year-old postmenopausal patient presented with abnormal vaginal bleeding. Transabdominal grayscale ultrasound image ( a ) shows a 14 cm multilocular cystic lesion with large solid components associated with moderate amount of vascularity (color score 3) on color Doppler ( b and c ). Ascites was seen ( c , arrow). This lesion was scored as O-RADS US 5, high risk for malignancy and patient was referred to a gynecologic oncologist. CT scan of the chest, abdomen and pelvis (not shown) was performed to evaluate extent of disease, which showed a corresponding lesion with trace ascites and no distant metastatic disease. Patient subsequently underwent total hysterectomy/bilateral salpingo-oophorectomy and staging for ovarian cancer. Surgical pathology confirmed mucinous cystadenocarcinoma. US was enough to characterize this lesion Additionally, assessment by physicians with experience in the sonographic appearance of adnexal pathology can decrease the benefit or need for MR characterization, especially for solid O-RADS US 3 lesions, certain classic benign lesions, and potentially confusing O-RADS US 4 and 5 lesions [ 3 , 7 , 47 ] (Fig. 8 ). In O-RADS US, such experts are termed “US specialists”, and evidence supports their role in adnexal lesion characterization [ 48 , 49 ]. While implementing qualification for such a specialist is challenging due to training and practice differences across sites, experience is emphasized as the key attribute. Specifically, the US specialist may be particularly useful in facilities without MRI access or in patients with MRI contraindications (e.g., non–MRI-compatible devices, severe claustrophobia, renal dysfunction or pregnancy limiting gadolinium use) providing an avenue for appropriate clinical triage (general gynecologist versus gynecologic oncologist) without the use of MRI. Fig. 8 27-year-old patient presented with back pain during menses. Transvaginal grayscale ultrasound image of the left ovary ( a ) shows an 11 cm unilocular cyst with numerous papillary projections (≥ 4). Power Doppler ultrasound image ( b ) shows minimal vascularity of the solid component, color score 2. No ascites or peritoneal nodularity was seen. This lesion was scored as O-RADS US 5, high risk for malignancy. Subsequent review by an US specialist and was reported as a suspected borderline tumor. Patient was referred to a gynecologic oncologist and underwent left salpingo-oophrectomy and omental biopsy, without further imaging. Pathology confirmed serous borderline tumor, no surface involvement and no peritoneal or omental disease. US assessment by a specialist was enough to characterize this lesion 27-year-old patient presented with back pain during menses. Transvaginal grayscale ultrasound image of the left ovary ( a ) shows an 11 cm unilocular cyst with numerous papillary projections (≥ 4). Power Doppler ultrasound image ( b ) shows minimal vascularity of the solid component, color score 2. No ascites or peritoneal nodularity was seen. This lesion was scored as O-RADS US 5, high risk for malignancy. Subsequent review by an US specialist and was reported as a suspected borderline tumor. Patient was referred to a gynecologic oncologist and underwent left salpingo-oophrectomy and omental biopsy, without further imaging. Pathology confirmed serous borderline tumor, no surface involvement and no peritoneal or omental disease. US assessment by a specialist was enough to characterize this lesion There are several scenarios when the value of MRI is irrefutable. MRI is particularly valuable when US evaluation is technically limited. Common challenges with US include obscuration of the adnexa by bowel gas, very large lesion size, inability to perform TVUS, suboptimal transabdominal visualization, or uncertainty regarding lesion origin (ovarian/adnexal vs. uterine or surrounding structures). In such scenarios, MRI provides a larger field of view and superior soft tissue contrast often clarifying anatomy and lesion composition (Fig.  9 ). Importantly, when assessment is uncertain following a technically adequate US evaluation, the best possible O-RADS US score or range of possible scores should be reported with an explanation of how MRI may further refine categorization and management. The report should not leave the patient and referring clinician without guidance, especially since MRI may not be performed. Fig. 9 66-year-old female was found to have a large 11 cm pelvic mass on ultrasound. Transvaginal grayscale image ( a ) and color Doppler image ( b ) show a large multilocular cystic lesion with large solid components adjacent to the uterus and moderate internal vascularity (color score 3). Separate ovaries were not visualized. It was unclear whether this large pelvic mass emanated from the uterus or represented an ovarian lesion; therefore, a score of O-RADS US 0 was assigned. Pelvic MRI was recommended and performed. Axial T2-weighted image ( c ) shows a corresponding cystic lesion with large amount of solid tissue (solid arrow), small volume ascites and small peritoneal nodule (dashed arrow). Axial T1 postcontrast subtraction image ( d ) shows enhancing solid tissue (arrows) with high-risk time intensity curve. The uterus and right ovary were normal on MRI (not shown). A normal left ovary was not seen. This lesion was reported as likely arising from the left ovary and scored as O-RADS MRI 5. Pathology confirmed high grade ovarian serous cystadenocarcinoma. MRI was helpful in determining the lesion origin and detecting early peritoneal disease 66-year-old female was found to have a large 11 cm pelvic mass on ultrasound. Transvaginal grayscale image ( a ) and color Doppler image ( b ) show a large multilocular cystic lesion with large solid components adjacent to the uterus and moderate internal vascularity (color score 3). Separate ovaries were not visualized. It was unclear whether this large pelvic mass emanated from the uterus or represented an ovarian lesion; therefore, a score of O-RADS US 0 was assigned. Pelvic MRI was recommended and performed. Axial T2-weighted image ( c ) shows a corresponding cystic lesion with large amount of solid tissue (solid arrow), small volume ascites and small peritoneal nodule (dashed arrow). Axial T1 postcontrast subtraction image ( d ) shows enhancing solid tissue (arrows) with high-risk time intensity curve. The uterus and right ovary were normal on MRI (not shown). A normal left ovary was not seen. This lesion was reported as likely arising from the left ovary and scored as O-RADS MRI 5. Pathology confirmed high grade ovarian serous cystadenocarcinoma. MRI was helpful in determining the lesion origin and detecting early peritoneal disease MRI is of particular value in evaluating lesions with suspected fibrous tissue, such as fibromas, fibrothecomas and cystadenofibromas, which are often categorized as O-RADS 3 or 4 (low or intermediate risk) (Fig. 10 ). Lesions with fibrous tissue supporting a benign etiology typically show characteristic low T2 signal intensity and low signal on high b diffusion weighted images (“T2 dark/DWI dark”) [ 50 ]. In such cases, MRI has the potential to downgrade the estimated malignancy risk to the very low range of < 0.5% (O-RADS MRI 2), from 1- <10% (O-RADS US 3) or 10 - <50% (O-RADS US 4), a substantial shift with important management implications. Fig. 10 41-year-old female was found to have a 3.1 cm left adnexal lesion on ultrasound. Transvaginal grayscale image of the left adnexa ( a ) shows a 3.1 cm solid mass with diffuse posterior shadowing (arrow) and no definite internal vascularity on power Doppler US ( b ), O-RADS US 3 (ROM 1-<10%). The patient preferred conservative management, and MRI was performed to refine cancer risk. Axial T2 weighted image ( c ) shows a corresponding solid lesion in the left adnexa, with homogeneous hypointense T2 signal (arrow). Axial high b value (b = 1000) diffusion weighted image ( d ) shows this lesion was homogeneously hypointense, a “dark T2/dark DWI” solid lesion, O-RADS MRI 2 (almost certainly benign lesion (PPV for malignancy < 0.5% PPV). This lesion remained stable at 2-year follow-up and was presumed to represent an ovarian fibroma. MRI was able to downgrade the cancer risk from 1-<10% range to < 0.5% in this case 41-year-old female was found to have a 3.1 cm left adnexal lesion on ultrasound. Transvaginal grayscale image of the left adnexa ( a ) shows a 3.1 cm solid mass with diffuse posterior shadowing (arrow) and no definite internal vascularity on power Doppler US ( b ), O-RADS US 3 (ROM 1-<10%). The patient preferred conservative management, and MRI was performed to refine cancer risk. Axial T2 weighted image ( c ) shows a corresponding solid lesion in the left adnexa, with homogeneous hypointense T2 signal (arrow). Axial high b value (b = 1000) diffusion weighted image ( d ) shows this lesion was homogeneously hypointense, a “dark T2/dark DWI” solid lesion, O-RADS MRI 2 (almost certainly benign lesion (PPV for malignancy < 0.5% PPV). This lesion remained stable at 2-year follow-up and was presumed to represent an ovarian fibroma. MRI was able to downgrade the cancer risk from 1-<10% range to < 0.5% in this case Other lesions in the O-RADS US 4 category and some in the O-RADS US 5 high-risk category may also greatly benefit from the higher specificity afforded by O-RADS MRI assessment [ 7 , 47 ]. Notably, the ROM range for these categories is broad (10-<50% and ≥ 50%, respectively) and many lesions will be downgraded following MRI affecting management and clinical triage. A single center retrospective study showed that the intermodality concordance between US and MRI in large, complex adnexal mass was only moderate [ 44 ]. For example, cystic lesions with suspected solid components, septations and inner wall irregularities on US may prove to represent clot, debris, or fibrous stroma on MRI. Presumed ovarian solid adnexal lesions with suspicious features may be revealed to represent exophytic or broad ligament myomas on MRI by demonstration of a connection to the uterus or two normal-appearing ovaries. Conversely, MRI may confirm malignant features (Fig. 11 ) or reveal additional malignant findings such as tiny peritoneal nodules prompting immediate gynecologic oncology referral [ 41 ]. Other scenarios when O-RADS MRI is invaluable include when immediate risk assessment is needed or management decisions hinge on more precise characterization. For example, patients undergoing infertility evaluation may not wish to wait several months for stability confirmation. Similarly, high-risk or highly anxious patients may benefit from prompt, definitive characterization rather than surveillance with US. A more complete risk assessment is also helpful in patients desiring fertility-sparing or limited surgery. Fig. 11 39-year-old premenopausal female presented with abdominal distention and bloating. Transvaginal ultrasound showed similar-appearing bilateral adnexal lesions. Grayscale image of the right adnexa ( a ) shows a multilocular cystic lesion with large solid components, and minimal vascularity (color score 2) on color Doppler US ( b ), O-RADS US 4 (intermediate risk lesion). Patient subsequently underwent multiphasic pelvic contrast-enhanced MRI. Axial T2 weighted image ( c ) shows a corresponding right adnexal mass with solid tissue (solid arrows). The solid tissue showed internal branching and papillary “finger-like projections”, so called “sea anemone sign”, suggestive of ovarian serous papillary borderline tumor. A similar-appearing left adnexal lesion was also seen (dashed arrows). Axial T1 postcontrast subtraction image ( d ) shows solid tissue (asterisks) that enhanced less than myometrium on the early phase, O-RADS MRI 4. Patient was referred to a gynecologic oncologist and surgical pathology confirmed serous borderline tumor. MRI was helpful in confirming and further characterizing the malignant features of this lesion to allow subtyping 39-year-old premenopausal female presented with abdominal distention and bloating. Transvaginal ultrasound showed similar-appearing bilateral adnexal lesions. Grayscale image of the right adnexa ( a ) shows a multilocular cystic lesion with large solid components, and minimal vascularity (color score 2) on color Doppler US ( b ), O-RADS US 4 (intermediate risk lesion). Patient subsequently underwent multiphasic pelvic contrast-enhanced MRI. Axial T2 weighted image ( c ) shows a corresponding right adnexal mass with solid tissue (solid arrows). The solid tissue showed internal branching and papillary “finger-like projections”, so called “sea anemone sign”, suggestive of ovarian serous papillary borderline tumor. A similar-appearing left adnexal lesion was also seen (dashed arrows). Axial T1 postcontrast subtraction image ( d ) shows solid tissue (asterisks) that enhanced less than myometrium on the early phase, O-RADS MRI 4. Patient was referred to a gynecologic oncologist and surgical pathology confirmed serous borderline tumor. MRI was helpful in confirming and further characterizing the malignant features of this lesion to allow subtyping