Ductal abnormalities as primary findings on breast ultrasonography: a literature review and proposed classification

Ken Oba; Hiroko Tsunoda; Woo Kyung Moon

doi:10.14366/usg.25048

Ultrasonography > Volume 44(4); 2025 > Article

Oba, Tsunoda, and Moon: Ductal abnormalities as primary findings on breast ultrasonography: a literature review and proposed classification

Review Article

Ultrasonography 2025; 44(4): 245-259. https://doi.org/10.14366/usg.25048

Ductal abnormalities as primary findings on breast ultrasonography: a literature review and proposed classification

Ken Oba¹

, Hiroko Tsunoda¹

, Woo Kyung Moon²

¹Department of Radiology, St. Luke’s International Hospital, Tokyo, Japan

²Department of Radiology, Seoul National University Hospital, Seoul, Korea

Correspondence to: Woo Kyung Moon, MD, PhD, Department of Radiology, Seoul National University Hospital, 101 Daehak-ro, Jongno-gu, Seoul 03080, Korea Tel. +82-2-2072-2584 Fax. +82-2-743-6385 E-mail: moonwk@snu.ac.kr

Received March 18, 2025 Revised April 29, 2025 Accepted May 6, 2025 Published online May 6, 2025

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Ductal abnormalities, such as dilated ducts with intraductal lesions, are frequently the primary ultrasound findings prompting biopsy and resulting in the early diagnosis of breast cancer or high-risk lesions. However, the Breast Imaging Reporting and Data System (BI-RADS) ultrasound lexicon provides limited guidance on these findings, categorizing them merely as associated features. To address this limitation, this review presents a critical analysis of existing literature and proposes a new classification encompassing three distinct subtypes: dilated ducts alone, dilated ducts with intraductal echoes, and intraductal masses. Additionally, an interpretation algorithm is introduced that incorporates lesion size and suspicious ultrasound features to guide BI-RADS assessment. This structured approach aims to standardize terminology, improve diagnostic accuracy, and promote consistent management of ductal abnormalities, especially in asymptomatic women.

Keywords: BI-RADS; Ductal carcinoma in situ; Breast ultrasonography; Nipple discharge; Papilloma, intraductal

Key point

This review proposes a new classification and interpretation algorithm using standardized terms to improve diagnosis and reduce variability in managing ductal abnormalities. In asymptomatic women, solitary or multiple dilated ducts without an intraductal lesion may be assessed as Breast Imaging Reporting and Data System (BI-RADS) category 2, typically requiring no further evaluation. Intraductal lesions ≥1 cm or those exhibiting suspicious ultrasound features warrant BI-RADS category 4 assessment, while smaller lesions without suspicious features may be managed as BI-RADS category 3.

Introduction

On breast ultrasonography, normal ducts appear as thin, tubular, or branching anechoic to hypoechoic structures with smooth contours radiating outward from the nipple. Ductal abnormalities are identified by changes in duct caliber, lumen characteristics, or wall morphology compared to normal ducts [1]. It is essential to distinguish these abnormalities from bilateral symmetric subareolar ductal dilatation, which is a normal variant or hormonal effect frequently observed in postmenopausal or lactating women (Fig. 1). Although ductal abnormalities are most commonly identified in women presenting with nipple discharge, incidental findings during routine screening in asymptomatic individuals also occur [2-12]. The prevalence of isolated ductal abnormalities without associated parenchymal masses is relatively low, ranging from 0.6% to 2.9% in various imaging studies [2,7]. Nonetheless, high-resolution handheld and automated ultrasound technologies have improved visualization along ductal pathways at multiple angles, enabling clearer depiction of ductal structures even in dense breast tissue [13]. This advancement has significantly improved the detection accuracy of ductal abnormalities during breast cancer screening [9]. Such abnormalities span a wide spectrum of conditions; their differential diagnoses include duct ectasia, mastitis with or without abscess, benign and atypical papillomas, usual and atypical ductal hyperplasia, ductal carcinoma in situ (DCIS), and invasive ductal carcinoma [13-16].

Ductal abnormalities, with or without associated calcifications, constitute key ultrasound findings crucial for early DCIS diagnosis [17]. A retrospective multicenter study (JABTS BC-02 study) reported that ductal abnormalities comprised 10% (78/768) of ultrasound-detected DCIS lesions [17,18]. Among women with nipple discharge, ductal lesions or suspicious ultrasound features typically necessitate prompt biopsy [15]. Nonetheless, given that most ductal abnormalities are benign, avoiding unnecessary biopsy or surgery— particularly in asymptomatic women—is important. Although evidence supports management protocols for symptomatic cases, optimal handling of asymptomatic ductal lesions remains uncertain [7,9,16]. Despite their clinical significance, ductal abnormalities are currently categorized merely as "associated features" of parenchymal masses within the Breast Imaging Reporting and Data System (BI-RADS) ultrasound lexicon [19,20]. Consequently, imaging criteria for definitive assessment and classification remain inadequately defined, contributing to substantial variability in interpretation and clinical management [9,12].

This review addresses the existing gap regarding standardized assessment and classification of ductal abnormalities as primary rather than merely associated ultrasound findings, through a critical analysis of the literature. The review explores ultrasound characteristics of benign and malignant ductal abnormalities and discusses their clinical significance in both symptomatic and asymptomatic women. Finally, a structured classification and interpretation framework is proposed that recognizes ductal abnormalities explicitly as primary findings, advocating for their standardized reporting and proper integration into clinical practice.

Definition and Current Classification

In this review, the term "ductal abnormality" is not strictly synonymous with the term "duct change" as defined in the BI-RADS ultrasound lexicon [19]. While BI-RADS classifies duct changes as associated features of a parenchymal mass, this study employs "ductal abnormality" as a broader term encompassing primary ductal findings, such as ductal dilatation, intraductal echoes, or intraductal masses, regardless of the presence of an associated parenchymal mass [1]. Asymmetric ductal dilatation, also termed asymmetric duct ectasia, is defined as unilateral dilatation of a duct or group of ducts measuring more than 2 mm in diameter or an ampullary portion exceeding 3 mm [21]. Ducts with intraductal echoes are dilated ducts containing echogenic material, which can represent debris, secretions, or genuine intraductal pathology [22]. In the literature, the terms "intraductal contents" and "intraductal echoes" are often used interchangeably when a distinct solid mass is absent. Although some studies categorize intraductal masses within the duct lumen as a subset of these findings, most differentiate clearly between intraductal masses and other intraductal echoes such as debris or secretions [20,21]. Furthermore, a dilated duct connected distally to a small mass (defined as less than 1 cm) is categorized as an intraductal mass, whereas a subareolar mass not involving the lactiferous duct is classified as a parenchymal mass [3,7,9]. The term "intraductal lesion" generally refers to abnormal findings within a dilated duct, including both non-mobile intraductal echoes and intraductal masses. In this review, "intraductal lesion" is used as a broader category that encompasses both non-mobile intraductal echoes and intraductal masses.

In the fifth edition of the BI-RADS ultrasound lexicon, abnormal duct changes are described as (1) cystic dilatation of a duct or ducts with irregular caliber and/or arborization, (2) extension of ducts to or from a malignant mass, and (3) the presence of an intraductal mass, thrombus, or debris [19]. In the BI-RADS ultrasound lexicon, associated features refer to secondary breast changes resulting from primary findings, such as masses. These features include architectural distortion, duct changes, skin changes, edema, vascularity, and elasticity.

In contrast, the Japan Association of Breast and Thyroid Sonology (JABTS) guidelines classify ductal abnormalities within the nonmass abnormality category, treating them as independent primary findings that directly influence clinical recommendations and management [22]. JABTS emphasizes understanding the progression of DCIS and its ultrasound manifestations, which range from ductal abnormalities to hypoechoic nonmass areas or small masses [17,18]. Ultrasound classification of intraductal lesions began in the early 1990s with the introduction of ductal echography [23]. The Japan Society of Ultrasonics in Medicine guidelines, updated in 2023, categorize ductal abnormalities into three types: duct dilatation, ducts with internal echoes (including solid echoes, echogenic foci, and floating echoes), and irregularity of ductal caliber [24]. JABTS provides specific interpretation guidelines based on the distribution of ductal findings and the characteristics of internal echoes [1,22]. A bilateral or multidirectional distribution (i.e., multiple ducts extending to different quadrants) suggests benignity, whereas a unilateral focal or segmental distribution raises suspicion for malignancy (Fig. 1). Benign lesions, such as intraductal papillomas, typically exhibit a narrow-based solid component forming a steep angle with the duct wall (Fig. 2A). In contrast, suspicious features include a broad-based solid component forming a gradual angle with the duct wall, continuous or multiple intraductal lesions, and calcifications within a solid component (Fig. 2B). Recognizing that most intraductal lesions identified on screening ultrasonography are benign, JABTS has established updated criteria for evaluating ductal abnormalities to minimize unnecessary diagnostic work-up and follow-up in asymptomatic women [22,25]. Recall is recommended only for intraductal lesions exhibiting suspicious sonographic features.

A comparison between the JABTS guidelines and the BI-RADS lexicon underscores the necessity for a more refined BI-RADS classification of ductal abnormalities, reflecting the increasing understanding of ductal pathology and its ultrasound manifestations.

Literature Review

The authors searched PubMed and Google for English-language original articles on ductal abnormalities in breast ultrasonography published since 2000. Of over 100 ultrasound studies identified, 11 met the inclusion criteria, which required reporting benign and malignant outcomes based on clearly defined ultrasound descriptors such as ductal dilatation, the presence of intraductal echoes, or intraductal masses (Table 1) [2-12]. Two additional studies concerning intraductal lesions detected by screening ultrasonography—one from Berg’s textbook [20] and another from the Japanese literature [26]—are also discussed below.

Malignancy Rate of Ductal Abnormalities

Across the 11 studies reviewed, the reported malignancy rates for ductal abnormalities detected using breast ultrasonography ranged from 0% to 18% (Table 1). Malignancy rates varied substantially depending on the proportion of symptomatic women included in the study populations. Higher malignancy rates (16%-18%) were observed in symptomatic women, particularly those presenting with a palpable mass or nipple discharge, whereas significantly lower rates (0%-4.2%) were reported in asymptomatic populations [5,7,9]. The lowest malignancy rates (0%-2.8%) occurred among asymptomatic women undergoing bilateral whole-breast ultrasound screening with negative mammograms [7,9]. For solitary dilated ducts specifically, malignancy rates remained consistently low (0%-3.4%), irrespective of the imaging modality used (mammography, ultrasonography, or magnetic resonance imaging [MRI]) [10-12].

In the ACRIN 6666 prospective study, which included women with dense breasts and elevated risk, an intraductal mass on screening ultrasonography was observed in 0.6% (16/2662) of cases, with no malignancies detected during follow-up [20]. A retrospective study by Guo et al. [9] found an overall incidence of retroareolar masses and intraductal lesions on screening ultrasonography of 1.3% (116/9,116). The malignancy rate was 0% (0/34) among probably benign (BI-RADS category 3) and suspicious (BI-RADS category 4) intraductal lesions. When retroareolar masses not involving the lactiferous duct were included, the malignancy rate rose slightly to 1.1% (1/87). A large retrospective screening ultrasound study from St. Luke’s International Hospital in Japan identified intraductal lesions in 1.6% (334/20,247) of women screened [26]. Among these lesions, 2.7% (9/334) were malignant, including seven cases of low-grade DCIS and two invasive ductal carcinomas.

Benign and Malignant Ultrasound Features

Studies suggest that multiple unilateral or solitary dilated subareolar ducts containing anechoic fluid or mobile intraductal echoes are typically benign ultrasound findings (Fig. 3), unless they are associated with mammographic calcifications or MRI-enhancing lesions [2,13,21]. Conversely, dilated ducts containing non-mobile intraductal echoes or intraductal masses—especially those located in the peripheral breast (defined as nonsubareolar or more than 2 cm from the nipple) [3,4,6,8]—may be considered suspicious when accompanied by additional features such as calcifications, ductal wall thickening or irregularity [5,6], increased vascularity [11,12], or complete filling of the ductal lumen [7] (Fig. 4). The likelihood of malignancy further increases when these ultrasound findings correlate with abnormalities detected through other imaging modalities, are associated with clinical symptoms, or represent new or interval changes on follow-up studies (Fig. 5) [7,8,16].

In a study of 172 biopsy cases, Hsu et al. [3] reported that intraductal echoes or an intraluminal mass had a 9% probability of malignancy, increasing to 13% when a dilated duct was connected to a mass at its distal end, and up to 43% when a parenchymal mass was adjacent to multiple dilated ducts. Multivariate analysis identified nonsubareolar location and non-circumscribed margins as significant malignancy predictors. In another study involving 163 intraductal masses, Kim et al. [7] reported an overall malignancy rate of 8%. Malignant masses were typically larger, more likely to fill the duct completely, and often extended beyond the duct or involved branch ducts. Importantly, no malignancies were identified among 37 intraductal masses that did not completely fill the duct, a finding confirmed by other studies [8,9]. Panigrahi et al. [12], examining 49 solitary dilated ducts, found that all anechoic solitary dilated ducts were benign, and none of the benign solitary dilated ducts exhibited internal vascularity. Among the clinical and imaging features evaluated, only the presence of an intraductal mass within a solitary dilated duct significantly correlated with malignant or high-risk lesions upon multivariate analysis (P<0.001).

The screening ultrasound study conducted at St. Luke’s International Hospital [26] categorized 334 intraductal lesions into four types: narrow-based lesions (n=159), broad-based lesions (n=18), lesions completely filling the duct (n=65), and small masses connected to a dilated duct (n=92). Of the nine cancers identified, five (55.6%) were broad-based lesions, two (22.2%) completely filled the duct, and two (22.2%) were small masses connected to a dilated duct. No malignancies were found among narrow-based lesions. Additionally, eight of the nine cancers (88.9%) demonstrated vascularity, and three (33.3%) had intraductal calcifications. Only 1.5% (4/260) of lesions under 1 cm were malignant, with no malignancies identified below 0.5 cm. Based on these findings, waiving further evaluation for narrow-based lesions or those smaller than 0.5 cm could potentially avoid 55.7% (186/334) of recalls; incorporating the absence of flow signal as an additional criterion could reduce unnecessary follow-up by 80.5% (269/334).

Proposed Classification of Ductal Abnormalities and BI-RADS Assessment

A wide range of terminology and classification systems have been used to describe ductal abnormalities, resulting in inconsistent interpretation and management in clinical practice. To address this issue, the authors propose a refined classification of ductal abnormalities as primary ultrasound findings in the breast, utilizing commonly recognized descriptors and their predictive value for malignancy in both symptomatic and asymptomatic women. This proposed classification comprises three subtypes with increasing malignancy risk: (1) dilated ducts alone, (2) dilated ducts with intraductal echoes, and (3) intraductal masses. Dilated ducts should be categorized as either multiple or solitary, aligning with the sixth BI-RADS mammography lexicon update. When a focal intraductal lesion is identified, its size, clock-face position, and distance from the nipple should be systematically reported [15].

Dilated Ducts Alone (Subtype 1)

This subtype refers to unilateral or asymmetric fluid-filled ductal dilatation without associated intraductal echoes or masses. Multiple dilated ducts with smooth walls in the subareolar region typically represent benign findings and should be assessed as BI-RADS category 2 (Fig. 3A). Solitary dilated ducts, whether located subareolarly or peripherally, are also common findings on screening ultrasonography and should likewise be classified as BI-RADS category 2 (Fig. 3B). However, in women presenting with pathologic nipple discharge—defined as unilateral, single-orifice, bloody, or spontaneous clear discharge—a solitary dilated duct requires careful evaluation to detect an underlying intraductal lesion [14,15,27]. Ultrasonography should target the radial location of the discharging orifice, tracing the dilated duct peripherally as far as possible to enhance lesion detection (Fig. 6). Intraductal lesions may appear subtle and require meticulous scanning techniques, including optimized gain settings. Any suspected lesion should be confirmed in two orthogonal planes, as tortuous ducts or ductal bifurcations can mimic intraductal masses when viewed in a single plane (Fig. 7). If no suspicious findings emerge from imaging, a BI-RADS category 2 assessment is appropriate. However, if clinical suspicion persists, breast MRI can be considered, as it may reveal clumped linear or segmental enhancement suggestive of DCIS [16,28–30].

Dilated Ducts with Intraductal Echoes (Subtype 2)

This subtype includes ducts containing mobile or non-mobile intraductal echoes without a distinct solid mass. These intraductal echoes typically appear as echogenic material within the lumen and often represent benign processes, such as floating debris associated with duct ectasia or mastitis (Figs. 8, 9). In some instances, however, they may indicate early intraductal pathology, including papillary lesions, usual or atypical ductal hyperplasia, or DCIS (Fig. 10). Differentiating mobile from fixed echoes is crucial to avoid unnecessary biopsies. Real-time scanning techniques, such as gentle probe compression (ballottement) or patient repositioning, help assess mobility (Fig. 3C) [27]. If non-mobile intraductal echoes are hyperechoic and avascular, they may be classified as BI-RADS category 2 or 3, as such findings often resolve upon follow-up. However, if intraductal echoes appear hypo- or isoechoic, heterogeneous, or exhibit suspicious features—such as calcifications, increased vascularity, ductal wall thickening or irregularity, or complete ductal filling—the lesion should be categorized as BI-RADS category 4A (low suspicion) or higher (Figs. 10, 11). When intraductal echoes without suspicious features are detected on screening ultrasonography in women with negative mammograms, a BI-RADS category 3 assessment with short-term follow-up may be appropriate. However, irregularly dilated ducts with intraductal echoes can represent the earliest ultrasound manifestation of DCIS (Fig. 11). Correlation with abnormalities seen on other imaging modalities or interval changes in size or appearance—including subtle alterations in shape, margin, internal echoes, or vascularity—should prompt consideration for biopsy.

Intraductal Masses (Subtype 3)

This subtype refers to solid masses located within the duct lumen or small masses (<1 cm) connected distally to a dilated duct. Occasionally, ducts may not appear dilated, but a thin rim of surrounding anechoic fluid can help confirm the intraductal location of the mass [20]. Intraductal masses most commonly represent benign papillomas (Figs. 2A, 12, 13), fibrocystic changes, or duct ectasia; however, they can also indicate DCIS (Fig. 14) or invasive ductal carcinoma (Fig. 4D), necessitating biopsy for definitive diagnosis. Although core biopsy is typically sufficient, ultrasound-guided vacuum-assisted biopsy may be preferred for suspected papillary lesions, as it provides a larger tissue sample and reduces the risk of underestimation [31]. Papillary lesions often exhibit a single vascular stalk even when small, detectable with color Doppler using optimal settings and minimal probe pressure (Fig. 13). A solitary feeding vessel generally favors a benign papilloma, whereas multiple internal vascular signals raise suspicion for malignancy (Fig. 4E) [32]. Traditionally, intraductal masses have been classified as BI-RADS category 4A regardless of imaging characteristics [7, 20]. However, if an intraductal mass is small (<1 cm), circumscribed, narrow-based, and does not completely fill the duct, it may be considered probably benign (BI-RADS category 3) in asymptomatic women and managed with short-term follow-up [7,9,26,33]. A solitary intraductal mass <0.5 cm or multiple small bilateral intraductal masses without suspicious features detected only on screening ultrasonography may be safely monitored with repeat imaging at 12 months [9,26]. Further validation is needed before clinical application of this recommendation.

The interpretation of ductal abnormalities should carefully consider symptom presence, as the predictive value for malignancy varies significantly based on clinical context and detection method. In symptomatic women—particularly those presenting with palpable masses or nipple discharge—the malignancy likelihood is considerably higher (16%-18%) [6,8], and these cases should be managed following established diagnostic guidelines, such as those from the National Comprehensive Cancer Network or the European Society of Breast Imaging [29,30]. For asymptomatic women, Fig. 15 presents an interpretation algorithm to guide management based on ultrasound findings. According to this framework, solitary or multiple dilated ducts without intraductal lesions should be assessed as BI-RADS category 2. Intraductal lesions measuring ≥1 cm or associated with any suspicious ultrasound feature should be categorized as BI-RADS category 4, whereas lesions smaller than 1 cm without suspicious features may be assessed as BI-RADS category 3. These recommendations are provisional, based on current evidence and expert consensus. When ductal abnormalities accompany suspicious parenchymal masses or nonmass lesions, the final BI-RADS category should follow the interpretive pathway applied to those primary parenchymal findings [19,20,34,35].

Clinical and Research Implications

The management of ductal abnormalities and nipple discharge has evolved significantly, with a growing emphasis on imaging surveillance and reduced surgical intervention [36-39]. Traditionally, papillary lesions without atypia diagnosed on core needle biopsy were considered high-risk, necessitating surgical excision due to a reported malignant upgrade rate of approximately 5% [40]. However, recent studies, including a multicenter prospective trial, have demonstrated significantly lower upgrade rates, below 2%, suggesting that routine excision may not be necessary when imaging findings are concordant (BI-RADS category 3 or 4A) [41,42]. The earlier estimates of upgrade risk were primarily based on retrospective analyses of symptomatic women and predated the widespread adoption of digital breast tomosynthesis and high-resolution ultrasonography. Tomosynthesis, by reducing callback rates and improving lesion visibility, has enhanced diagnostic accuracy for ductal abnormalities compared to traditional two-dimensional mammography alone [43]. Similarly, recent studies reporting malignancy rates of 0%-3.4% have prompted a shift in the management of solitary dilated ducts identified on mammography—from biopsy toward imaging follow-up in asymptomatic women [10–12]. Therefore, accurate ultrasound evaluation and appropriate BI-RADS categorization have become increasingly critical. This current trend reflects a more personalized management approach, considering factors such as the detection method, imaging characteristics, and patient preferences.

The present review proposes a new classification and interpretation algorithm with standardized terminology to facilitate the recognition of ductal abnormalities as primary findings. This framework aims to improve differentiation between benign and malignant conditions and reduce variability in clinical management. Such an approach seeks to enhance precise risk stratification and support tailored follow-up recommendations. Prior ultrasound studies have demonstrated that higher BI-RADS categories correlate strongly with an increased malignancy rate in women presenting with nipple discharge [3,44]. Furthermore, this standardized approach provides a robust foundation for consistent data collection and future research aimed at refining sonographic features predictive of malignancy in ductal abnormalities. Multimodality correlation involving mammography and MRI may further enhance the ultrasonographic characterization of subtle intraductal lesions and increase MR-directed ultrasound detection rates (Fig. 11) [45,46]. Additional research is necessary to determine whether individual breast cancer risk factors—such as age, family history, BRCA mutation status, or a personal history of breast cancer—influence malignancy risk associated with ductal findings [7,36]. Moreover, longitudinal studies may clarify whether specific ductal findings or fibroglandular tissue patterns correlate with an increased risk of breast cancer [47-49].

Conclusion

This review underscores the importance of recognizing ductal abnormalities as primary findings on breast ultrasonography and introduces a refined classification and interpretation algorithm utilizing standardized terminology to enhance clinical decision-making, facilitate data collection, and guide future research. The literature analysis indicates that malignancy rates for ductal abnormalities vary widely depending on symptom presence and specific imaging features. Given that most intraductal lesions detected on screening ultrasonography are benign—and cancers identified are predominantly low-grade DCIS—careful imaging follow-up rather than biopsy may be appropriate for asymptomatic women with negative mammography. As with any new classification scheme, validation through rigorous research is essential before broad clinical adoption. Large-scale, multicenter studies are required to evaluate its diagnostic accuracy and reproducibility. If validated, this classification could inform future updates to the BI-RADS ultrasound lexicon, supporting more consistent reporting and improved management of ductal abnormalities.

Author Contributions

Conceptualization: Oba K, Tsunoda H, Moon WK. Data acquisition: Oba K, Tsunoda H, Moon WK. Data analysis or interpretation: Oba K, Tsunoda H, Moon WK. Drafting of the manuscript: Oba K, Tsunoda H, Moon WK. Critical revision of the manuscript: Oba K, Tsunoda H, Moon WK. Approval of the final version of the manuscript: all authors.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Acknowledgments

The authors would like to thank Dr. Jung Min Chang (Seoul National University Hospital), Bo Kyoung Seo (Korea University Ansan Hospital), Boo-Kyung Han (Samsung Medical Center), Hak Hee Kim (Asan Medical Center), and Sun Mi Kim (Seoul National University Bundang Hospital) in Korea, Hongping Song (Xijing Hospital), Lingyun Bao (Hangzhou First People’s Hospital), JianQiao Zhou (Ruijin Hospital), and Qingli Zhu (Peking Union Medical College Hospital) in China, and Takayoshi Uematsu (Shizuoka Cancer Center Hospital) in Japan for their expert opinion on the proposed classification in the article.

WKM is supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2022R1A2C1091282).

Supplementary Material

Video clip 1.

Mobile intraductal echoes within a dilated subareolar duct (for Fig. 3C) (https://doi.org/10.14366/usg.25048.v001).

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Fig. 1.

Schematic representation of ductal dilatation.

A. Bilateral symmetric or multiple subareolar ductal dilatations represent normal variants or benign findings. B. Unilateral, solitary ductal dilatation with an intraductal lesion (arrow)—either non-mobile intraductal echoes or an intraductal mass—particularly in the nonsubareolar region, is considered a suspicious finding that requires further evaluation.

Fig. 2.

Key ultrasound features of intraductal lesions in the guidelines of the Japan Association of Breast and Thyroid Sonology (JABTS).

A. A narrow-based intraductal solid component (arrow) forms a steep angle with the duct wall, a feature commonly associated with benign papillomas. B. Multiple broad-based intraductal solid components (arrows) form a gradual angle relative to the duct wall, a feature often associated with ductal carcinoma in situ.

Fig. 3.

Representative ultrasound features of benign ductal abnormalities.

A. Multiple dilated subareolar ducts are filled with anechoic fluid. B. A solitary dilated subareolar duct is filled with anechoic fluid. C. Mobile intraductal echoes (arrow) are found within a dilated subareolar duct. A corresponding Video clip 1 is available in the Supplementary Material.

Fig. 4.

Representative ultrasound features of malignant ductal abnormalities.

A, B. Calcifications (arrows) are present within a dilated duct on ultrasound (A) and corresponding mammography (B) in ductal carcinoma in situ (DCIS). C. Irregularly dilated ducts are filled with non-mobile intraductal echoes and associated wall thickening (arrowheads) in DCIS. D, E. An intraductal mass (arrow) completely fills the duct with associated wall thickening (arrowheads) (D) and internal hypervascularity (E), corresponding to invasive ductal carcinoma with DCIS.

Fig. 5.

A 66-year-old woman undergoing screening, with negative findings on mammography.

A. An initial radial ultrasound image shows a 0.4 cm intraductal mass (arrow) adjacent to a dilated duct in the right subareolar area. It was assessed as Breast Imaging Reporting and Data System category 2 (benign), with a recommendation for annual follow-up. B. A followup radial ultrasound image 2 years later shows interval growth of the intraductal mass (arrow), now measuring 0.8 cm. Color Doppler ultrasound did not reveal internal vascularity (not shown). Core needle biopsy and surgical pathology confirmed a 0.3 cm low-grade ductal carcinoma in situ.

Fig. 6.

A 46-year-old woman with bloody right nipple discharge and a negative mammogram.

A. A radial ultrasound image shows an irregularly dilated duct with intraductal echoes and mild wall thickening (arrowheads) at the 9-o’clock location, 3 cm from the nipple (N). B. An antiradial ultrasound image shows an indistinct margin (arrow) and wall thickening (arrowhead) of the dilated duct. Core needle biopsy and surgical pathology confirmed microinvasive carcinoma with 2 cm intermediate-grade ductal carcinoma in situ. This case corresponds to the dilated ducts with intraductal echoes subtype in the present classification.

Fig. 7.

A 61-year-old woman who presented with a ductal abnormality at the 8-o’clock location in the left subareolar area on screening ultrasound, with a negative mammogram.

A. Targeted transverse ultrasonography shows an apparent intraductal mass (arrow) as initially described by the outside clinic. However, rotating the probe reveals it to be normal tissue at the branching points of the dilated duct. B. Radial ultrasonography demonstrates asymmetric ductal dilatation (arrow) filled with anechoic fluid. No intraductal mass was identified. The finding was assessed as Breast Imaging Reporting and Data System category 2 (benign). Despite this, the patient requested a core needle biopsy, which confirmed duct ectasia with stromal fibrosis. This case corresponds to the dilated ducts alone subtype in the present classification.

Fig. 8.

A 43-year-old woman undergoing screening, with negative findings on mammography.

A. An initial radial ultrasound image shows a cystically dilated duct with mobile intraductal echoes (arrow) in the right subareolar area. The finding suggested duct ectasia and was assessed as Breast Imaging Reporting and Data System category 2 (benign). B. One year later, a follow-up radial ultrasound image demonstrates echogenic material (arrow) within the dilated duct. Color Doppler ultrasound (not shown) revealed no internal vascularity, suggesting debris; however, the finding was misinterpreted as a newly developed suspicious lesion. Core needle biopsy confirmed duct ectasia. This case corresponds to the dilated ducts with intraductal echoes subtype in the present classification.

Fig. 9.

A 34-year-old woman with left nipple retraction and a palpable mass.

A. A targeted left subareolar ultrasound image in the radial plane shows focal ductal dilatation with mobile intraductal echoes (arrow). Increased echogenicity of the surrounding fat tissue (asterisk) is noted. B. A transverse color Doppler ultrasound image demonstrates peripheral vascularity around the intraductal echoes (arrow) and in the surrounding tissue (asterisk). Core needle biopsy revealed chronic active inflammation and non-caseating granulomas, consistent with granulomatous mastitis. This case corresponds to the dilated ducts with intraductal echoes subtype in the present classification.

Fig. 10.

A 56-year-old woman undergoing screening.

A. A craniocaudal spot magnification mammogram shows grouped pleomorphic calcifications (arrows) in the left subareolar area. Multiple groups of round calcifications are also seen in the outer breast. B. A radial ultrasound image shows irregularly dilated ducts (arrows) with intraductal echoes and calcifications at the 12-o’clock location. Ultrasound-guided biopsy and surgical pathology confirmed a 3.5 cm lowgrade ductal carcinoma in situ. This case corresponds to the dilated ducts with intraductal echoes subtype in the present classification.

Fig. 11.

A 51-year-old woman undergoing high-risk screening who had undergone right breast-conserving surgery seven years earlier and had a family history of breast cancer, with a negative mammogram.

A. Sagittal T1 contrast-enhanced magnetic resonance imaging shows a 1 cm area of linear clumped nonmass enhancement (arrow) at the 6-o’clock location in the left breast. B. Magnetic resonance-directed transverse color Doppler ultrasound image shows an irregularly dilated duct (arrows) with intraductal echoes but no internal vascularity. Ultrasound-guided biopsy and surgery confirmed a 0.6 cm high-grade ductal carcinoma in situ. This case corresponds to the dilated ducts with intraductal echoes subtype in the present classification.

Fig. 12.

A 60-year-old woman undergoing screening.

A. A mediolateral oblique digital breast tomosynthesis image shows an obscured, oval mass (arrow) with an associated dilated duct (arrowheads) in the right subareolar area. B. A radial ultrasound image shows a 0.8 cm intraductal mass (arrow). The finding was assessed as Breast Imaging Reporting and Data System category 4A (low suspicion for malignancy). Ultrasound-guided biopsy revealed usual ductal hyperplasia involving an intraductal papilloma. Excision is not required if the patient is asymptomatic. This case corresponds to the intraductal masses subtype in the present classification.

Fig. 13.

A 51-year-old woman undergoing screening, with negative findings on mammography.

A. A radial color Doppler ultrasound image shows a 0.5 cm intraductal mass (arrow) with internal vascularity (arrowhead) in a dilated right subareolar duct. B. An antiradial ultrasound image shows the intraductal mass (arrow) with posterior acoustic enhancement. The lesion was assessed as Breast Imaging Reporting and Data System category 4A (low suspicion for malignancy). Core needle biopsy and surgical pathology confirmed an intraductal papilloma. Given the subareolar location, small size, asymptomatic presentation, and presence of a single vascular stalk—a typical feature of intraductal papilloma—a Breast Imaging Reporting and Data System category 3 (probably benign) assessment could have been considered. This case corresponds to the intraductal masses subtype in the present classification.

Fig. 14.

A 44-year-old woman undergoing screening, with negative findings on mammography.

A. A radial ultrasound image shows a 1 cm oval hypoechoic mass (arrow) in the left subareolar area with partially circumscribed and partially indistinct margins. The distance between the mass and nipple base (cursors) was 1.4 cm. B. A transverse color Doppler ultrasound image shows intraductal extension (arrowheads) of the mass (arrow), a suspicious finding, although no internal vascularity was detected. The color signal in the left upper corner is an artifact. The finding was assessed as Breast Imaging Reporting and Data System category 4A (low suspicion for malignancy). Core needle biopsy and surgery confirmed a 0.8 cm intermediate-grade ductal carcinoma in situ. This case corresponds to the intraductal masses subtype in the present classification.

Fig. 15.

Flowchart illustrating the authors’ interpretation algorithm for ductal abnormalities in asymptomatic women.

When dilated ducts are observed on ultrasonography, the first step is to distinguish normal variants or typical benign findings from potential intraductal lesions based on the ductal distribution. Next, the presence of an intraductal lesion—defined as either nonmobile intraductal echoes or an intraductal mass—is assessed. If an intraductal lesion is present, the Breast Imaging Reporting and Data System (BI-RADS) category is determined based on lesion size (with a 1 cm threshold) and the presence of suspicious imaging features. Solitary or multiple dilated ducts without an intraductal lesion are assessed as BI-RADS category 2. An intraductal lesion ≥1 cm or with any suspicious features is categorized as BI-RADS category 4, while lesions <1 cm without suspicious features may be classified as BI-RADS category 3. ^a)Suspicious features include intraductal calcifications, duct wall thickening or irregularity, increased vascularity, and complete filling of the duct.

Table 1.

Summary of 11 ultrasound studies on the malignancy rate of ductal abnormalities

Study	Year published	Presentation	Modality	Target imaging findings	No. of cases^a)	No. of malignancies	Malignancy rate (%)
Tiu et al. [2]	2005	Sx+Asx	US	Abnormal dilated ducts	34	2	6
Hsu et al. [3]	2010	Sx+Asx	US	Abnormal dilated ducts	158 (172)	20	13
Kim et al. [4]	2010	Sx+Asx	US	Abnormal dilated ducts	54	8	15
Song et al. [5]	2012	Sx+Asx	US	Abnormal dilated ducts	75	7	9
AL-Tememy et al. [6]	2013	Sx	MG+US	Abnormal dilated ducts	100	16	16
Kim et al. [7]	2013	Sx+Asx	US	Intraductal mass	163	13	8^b)
El Sheikh et al. [8]	2015	Sx	MG+US	Intraductal mass	251	46	18
Guo et al. [9]	2018	Asx	US	Intraductal mass	34 (87)	0	0
Ayres et al. [10]	2020	Sx+Asx	MG+US	Solitary dilated ducts	94	0	0
Choudhery et al. [11]	2020	Sx+Asx	MG+US+MRI	Solitary dilated ducts	87	3	3
Panigrahi et al. [12]	2023	Sx+Asx	MG+US+MRI	Solitary dilated ducts	49	1	2