In the second edition of BI-RADS for MR, the internal enhancement pattern “clustered ring” has been added. This is defined as small rings of enhancement, which are clustered together (Figs. 9.2 and 9.3) [39]. A study by Tozaki et al. showed that this finding was seen in 63 % of cases of malignancy (including both invasive and non-invasive), versus only 4 % of benign cases. The specificity for malignancy of the finding of clustered ring enhancement was 96 % [40].

When DCIS presents as NME, the most common distribution pattern is a segmental distribution, seen in approximately 14–77 % of cases [36–38, 41]. This is defined as a triangular region of enhancement, apex pointing to the nipple, suggesting a duct or its branches (Fig. 9.4) [39]. It may also present less commonly in a linear, focal, regional, or diffuse enhancement pattern [36–38, 41]. The MR BI-RADS 2nd edition has removed the distribution ductal from the lexicon [39].

DCIS may also present as a mass morphology on MRI. A mass is defined as a 3D space occupying structure with convex outward contour, which may or may not displace or otherwise affect the surrounding normal breast tissue [39]. This morphology has been seen in approximately 14–41 % of cases of DCIS on MRI [36–38]. Masses are further defined by shape, margin, and internal enhancement patterns. When DCIS presents as a mass on MRI it most commonly is an irregular mass, seen in 14–83 % of cases (Fig. 9.5). Less frequently it may present as an oval or round mass [36, 37, 42]. Of note, the 2nd edition of the MR BI-RADS lexicon has removed the shape lobular for mass lesions to be consistent with the mammogram and ultrasound sections. Masses with up to 3 lobulations now simply are described as “oval” [39]. The literature describes various mass margins when DCIS presents as a mass on MRI, including irregular (14–92 % of cases) and spiculated (0–92 % of cases) (Fig. 9.5). Infrequently DCIS presenting as a mass may have smooth margins (4–8 % cases) [36, 37, 42]. DCIS manifesting as a mass on MRI, may have various internal enhancement patterns. The most common pattern is heterogeneous (9–67 %), followed by homogenous (9–25 %), and less commonly rim enhancement (0–8 %) (Fig. 9.6) [36, 37]. To our knowledge, there has not been a report of non-enhancing dark internal septa in reports of DCIS seen as a mass on MRI. Of note, the terms central enhancement and enhancing septations have been removed from the new BI-RADS lexicon [39].

The least common morphologic appearance of DCIS is a focus [36–38]. A focus is defined as a lesion <5 mm, which is too small to further characterize (Fig. 9.7) [39]. The new BI-RADS edition has removed the term foci from the lexicon [39]. Rosen et al. found that pure DCIS manifests as a focus in 12.5 % of cases while 3.0 % of invasive carcinomas manifest as a focus [38]. Van Goethem et al. found that a focus was seen in 20 % of DCIS cases versus 2.8 % invasive cancers [44]. Factors suggesting that a focus is malignant on MRI include: no T2 hyperintensity, lack of fatty hilum, washout kinetics, new or enlarging in size. Signs of benignity of a focus include: T2 hyperintensity, presence of a fatty hilum, persistent kinetics, and stability [39].

Jansen et al. found that there was no statistically significant difference between MR morphology in low, intermediate, and high nuclear grade DCIS lesions [36]. Additional studies by Chan et al., and Rahbar et al., also found no significant difference in MR morphology between high grade and non-high grade DCIS [37, 45]. At this point, no study to our knowledge has shown that MR morphology is able to predict nuclear grade of DCIS.